Early ABS sensor fix by Committee/928 Community
 

Background - 84 to 85 ROW 16v & USA 32v 85 to 86 early cars with the optional ABS system have a different sensor setup to the later style.
The early sensors have been NLA for a few years now ( I have searched the World to find them with no success) and the issue is becoming critical in that many of these cars do not have working ABS systems.

We have a plethora of experts in the 928 community with the required skills to overcome this problem. I am willing to inject time, resources and money to this project in an effort to overcome the problem.

The early ABS system seems to be reliable but the Achilles heal is the sensors. They degrade, wires, connectors and sensors suffer failure.

John Madden did an excellent write up on how to repaire an existing sensor --

https://rennlist.com/forums/928-foru...d-sensors.html

How do we find a cost effective alternative to fit the current system?

I have a set of front and rear hubs/axles from an 85 ROW car along with the ABS brain.

Alan, Doc Mirror - what do we need to do to make this work. Is it all about the fit of the sensor or?

I would be a customer for these if available. '85 Euro S2 16v 4.7.

Bump - anyone??

if a mount adapter is fabricated and the newer sensors are mounted & connected do they work? I noticed that the newer sensors are longer. What is the diameter of both? How far away are both from the spinning teeth on the hub?

what is the impedance of the factory ones available vs the NLA ones?

From what I have been told so far the sensors of the same era are the same apart from fit. If we can define the dimensions of the port for the early v the size of the later sensor that could be a good starting point.
One of my initial concerns is to source a readily available sensor to move forward. No point in going to all the trouble to accommodate a sensor that also goes NLA in a couple of years.
Someone on FB suggested a BMW sensor which certainly looks like to original and may work but I could only find one available from all the wholesalers.
I will work on the port dimensions as a starter.

Thanks for your interest in the project Sterling.

Does this mean we should also be looking at other sensors that are the same as the early and late versions?

Last night I ordered a Bosch replacement (part #92860640201) that said on numerous supplier sites would work. I will let you guys know how it goes. There was also another manufacturer of the same part, Standard Engine Performance.

Last night I ordered a Bosch replacement (part #92860640201) that said on numerous supplier sites would work. I will let you guys know how it goes. There was also another manufacturer of the same part, Standard Engine Performance.

928 606 402 01 is the sensor you already bought and as we have all told you is for USA 86.5 to 95 cars and fits the rear. If your car is really an early 86 then this sensor WILL not fit.
Good luck.

Yes and it does not work on the early cars. It is the same one you bought from Pelican and showed on FB.
Are you sure you have an early 86?

I am looking at early sensors for all cars in the 80's to see if I can find something that is a closer potential fit - but equally has a good supply and can sustain the need of the 928 for a few years.

As Bosch seem to stop making many components after 20 years or so (e.g. the 968 MAF) then a replacement ABS sensor from a modern car seems a good strategy.

Roger,
Can we get somebody to post some up close pictures of the correct ABS sensors? I've got no dog in this hunt, but I don't mind helping look. :)

I am in this boat. Will be willing to measure/test/hit with hammer on my car as needed.
Very frustrated with ABS at this point.

Not sure if this one for a Volvo would work, but the sensor end looks pretty similar, looks to have plenty of cable length, but would require the connector to be replaced.

the center extension may or may not be the same dimensionally and would probably be the critical aspect.

Wiring and connectors are trivial IMHO. Length, diameter and mounting are more critical. Then comes impedance and if it actually generates the correct pulse as the toothed wheels passes by.
I am hoping that whether it uses a simple coil or uses a Hall Effect sensor, all the Bosch stuff generates a similar pulse.

If we can trust the 924/244 guys ( Snarky dig ):
https://rennlist.com/forums/924-931-...cal-specs.html

"I'm not sure that the ABS sensors require any excitation to operate; I believe they're just passive hall effect sensors like the engine speed and reference sensors."

"Right you are. George Beuselinck confirmed this fact for me over on Pelican:
Quote:
Originally Posted by 944 Ecology
The S2 wheel speed sensor will generate a sine wave without other inputs. From peak to trough, it's probably 1.5 volts.

You should probably hook one up to an oscilloscope and see if it meets your needs.
Thanks!"

"If the dash unit needs a square wave of 5 or 12V, the stock sensors wont work without extra circuitry.

If you want some links to hall sensors (that will make the signal you need) let me know."

Thanks Simon - I have ordered a couple front and rear from a 940 Volvo.
Compiling dimensions this weekend.

Had time to look at this further.
Dealing with the rear sensors first.
I have found an alternative that seems in good supply. However a few questions.
Diameter is the same - bolt location is the same - the top plastc round section with the O ring is smaller but fits. A larger O ring should solve this issue.
Two wire - black and brown so that should make connection easy.


So the problem is length. The small section of metal at the bottom is about 10 mm too long. This is the magnetic part.
Seems solid material. Can this be cut down in length by 10 mm and still work?




https://cimg1.ibsrv.net/gimg/rennlis...316f35307b.jpg

Definitely worth a try. But i think the point on the end will be important for them to work.

It' only a guess, but I speculate the magnet is actually up inside the sensor and the extension if just ferituc steel. I would guess it can be freely machined to the desired shape. The point will give increased resolution as the tooth appoach and departure will give a steeper rise and fall signal since it is acting on a narrower sensor profile.

It's worth a try to shorten it by machining. Although it might disturb the magnetic field of the ferrous material

Hi Roger, I also have the same problem on my 1985 S2, Just wondering if you had any luck with the Volvo option. As an aside the picture does look a lot like the front ABS Sensor.
I did follow the process outlined for repair and managed the repair. Unfortunately now 6 months on the abs light has come on again so without checking yet have assumed the repair didnt last.
Thank you for your efforts here and that Volvo one certainly looks a close fit. Regards Wayne

Any news on this? I may be in the market for ABS sensors for my '85 Euro.

Thanks,

I don't have an answer on effect of trimming down the piece Roger found, but would be willing to test it. Interesting that his looks more like the front sensor, which does have a long probe. My measurements show the rear as being slightly wider than the fronts, at ~18.23mm vs ~17.98mm, so Roger's find may be a good fit for the front with a thin shim/sleeve, or just a thick O-ring

Here are some measurements I took to help in the search for a replacement:

Fronts:https://cimg0.ibsrv.net/gimg/rennlis...ef6d8b6856.jpg

Front Body Length
https://cimg1.ibsrv.net/gimg/rennlis...6739efd795.jpg

Front Body Diameter
https://cimg3.ibsrv.net/gimg/rennlis...396e76d597.jpg

Front Base Diameter
https://cimg5.ibsrv.net/gimg/rennlis...47d0211bdc.jpg

Front Bosch Part Number

Here are my measurements for the rears:

https://cimg5.ibsrv.net/gimg/rennlis...fdf9a23065.jpg

Rear Base Diameter
https://cimg6.ibsrv.net/gimg/rennlis...65ec1a943a.jpg

Rear Diameter
https://cimg7.ibsrv.net/gimg/rennlis...a098569fd5.jpg

Rear Length
https://cimg1.ibsrv.net/gimg/rennlis...8ef2cbc2ed.jpg

Rear Bosch Part Number

Additionally, the 911 Speed sensor 996.606.406.00 also may have some potential as a rear, if somebody had one to take measurements:

https://cimg0.ibsrv.net/gimg/rennlis...4dafb1e5d2.jpg
https://cimg1.ibsrv.net/gimg/rennlis...1856e0781f.jpg

I also looked at the AIM sensor, but it appear too narrow, based on the drawing ( Diameter looks to be 15mm). However, appears to be made by Honeywell, so that may be another lead for sensors.:
https://cimg3.ibsrv.net/gimg/rennlis...54f9c814ff.png

The Bosch Catalog tells us nothing we don't already know, it is unavailable and they do not spec an alternate:

https://cimg0.ibsrv.net/gimg/rennlis...07171c3eb8.png

It looks like that drawing says the diameter is 17.90 mm, which looks pretty darn close.

I haven't had a finger on the pulse of this thread, buts just read through it. Instant thought: Beware trying to "machine" the center pin. They tend to be sintered rather than a cast, extruded or forged part, and need a lot of care especially if you decide to adjust the shape. The risk is that there will be a fracture up higher inside the plastic shell. You won't see it, and the piece will will no longer function. The coil will still show correct Ohms so no apparent reason for not working. Impact damage seems to be a primary killer of the sensors. It used to be from accidental contact/impact with the toothed ring, but maybe that's better these days. Cable and connector damage is similarly popular.

Still too short though. OE Rear ABS Length is about 46.75mm. AIM Length 31.8 mm.
For an induction sensor, I think that is way too much of a difference.

Coming back to this option, couldn't you just shim it 10 mm instead of machining it down (with all the problems that entails)? There isn't unlimited space in that area, but 10 mm doesn't seem like that much.

Thoughts?

In the picture above -- is the tip broken off the lower sensor? translated: Is the bottom picture a damaged version of the new top one?

Dr. Bob,
The bottom sensor is what the 928 sensor looks like. The upper sensor is from another car.

My question would be: could the new sensor be taken apart to machine or swap the tip to the shorter version and decrease the opportunity to damage any other part of the sensor?

No, that is the way it is supposed to look. That's the rear sensor. The front looks a lot closer to the "new" part in the picture.

Also, does anybody have a pin out diagram for the ABS controller unit and connector? The wiring diagram in the WSM doesn't exactly achieve what I need - which is to identify the 2 pins that correspond to each of the 4 wheel sensors and measure resistance and voltage.

A bonus question: there doesn't appear to be a steering wheel input to the system. Is that correct? I think most modern cars use that to determine the differential in wheel slip due to turning.

Thanks in advance.

OK, found it myself if anybody needs it.https://cimg0.ibsrv.net/gimg/rennlis...8338132a2f.jpg

Leveraging the miracle of Amazon Prime's liberal return policies and huge inventory, I ordered several ABS sensors that looked like they _might_ be useful in our search. I will test and report back.
https://cimg9.ibsrv.net/gimg/rennlis...a2cbd208bb.jpg

Excellent, I'm excited to see the results. It looks like I am in need of 2 rear replacement sensors.

I has some positive, but not conclusive results. The sensor I got that looks the sames as Roger had for a Volvo:
https://cimg9.ibsrv.net/gimg/rennlis...ccc496ddf7.jpg

Looks to be very, very close dimensional to the FRONT ABS sensor:

https://cimg0.ibsrv.net/gimg/rennlis...aa966b0c98.jpg
https://cimg2.ibsrv.net/gimg/rennlis...1545fd1b8e.jpg
https://cimg4.ibsrv.net/gimg/rennlis...a8cfcc40e5.jpg
https://cimg5.ibsrv.net/gimg/rennlis...0d3f4cff8a.jpg


I did not get a change to do any actual installation, as I had to get everything buttoned up for track event next weekend and did not want to start anything I could not finish, or that would be an unknown variable on the track.

So, no actual testing until next week, but will post results as I gather them.

Related note: since the original connectors are crumbling, I have been using connectors like these as replacements. Good enough, or is there a better alternative?:
https://cimg8.ibsrv.net/gimg/rennlis...065fe2d607.jpg

I have good news. The Volvo style sensor :Manufacturer Part NumberABS193 3515092
ALS554Found here on Amazon:
Work as front sensors, with the following caveats (none of which are a shock):
1. You need to replace the connectors
2. The grommets don't match up perfectly
3. They do not have the "barrell grommets" that clip into the OE wire holder clips. Barrell Grommits is my term, don't know what they are really called. If somebody can tell me the right term, I can search for a source.

But the head fits perfectly in the spindle, and it delivers the required signal pulse. Testing show no errors, and thanks to heavy rains today, I was able to confirm that ABS worked as expected when the brake pedal is mashed .
https://cimg6.ibsrv.net/gimg/rennlis...40f9fdcdfb.jpg
https://cimg2.ibsrv.net/gimg/rennlis...39e1662206.jpg
https://cimg3.ibsrv.net/gimg/rennlis...73825c9ab0.jpg

If this was going to be offered as kit, I would expect:
1. The connector already installed on the sensor and, plus one to replace the harness end. Challenge is that crimping these is done best with the correct style crimper, something many will not have. Alternative to pre-assembly is to include a correct style crimper in kit ( or as option) and detailed instructions.
2. A nice grommet for the pass through of this wiring, the brake fluid line and the brake pad sensors. Mine is a bit of a hack job, and I DEFINITELY did not want to disconnect the brake line for this. I basically have three grommets that sort of fit, held in place with black silicone. Functional, but ugly.
3. "Barrell Grommets" on the wire that allow use of existing OE wire clips. I used wire ties, which are functional, but ugly.

The bad news: This still did not solve my issue, in that firm bump puts the system into fail mode. I have replaced:
1. All four sensors
2. All relays
3. ABS ECU
Only things not swapped so far:
1. ABS Pump
2. ABS Harness
:mad:

Back to more good news:
I may have a sensor that DOES fit rear perfectly ( except for electrical connector, as expected). Since I don't think I am having issues with my rears, this is a lower priority for me.

Great progress, Ken- thanks for taking on this project!

Hey Ken, question about the front connectors...how are you getting to those? I have early '86 and those things are way down there! Just curious did you go through the wheel/fender, or down from the top in some way?

Thanks!

This is awesome Ken thanks so much...so basically I fish the wire upwards so we can make the connector change ..you're basically behind the shock tower but in front of the brake master cylinder...a tough fit but if you can make it so can others. I'll be so glad not to have to hit the trouble light dismissal button every time I start out!.

Amazon Link for what I am going to try:

Doesn't take a sharp eye to note the above does not look like the OE. Comparison:
https://cimg2.ibsrv.net/gimg/rennlis...738935c37c.jpg
https://cimg3.ibsrv.net/gimg/rennlis...4f58ebb4a9.jpg

But, it looks to have all the same critical physical dimensions: Length, Diameter and mounting hole placement.
Electrically, it shows about 1,000 Ohms resistance, which is in the range we want.
So, assuming it does fit, all it needs to do is generate a pulse that the ABS ECU recognizes, which I am 75% certain it will do.

BONUS: Comes with two sensors, cheap. I would recommend you replace both

I will probably test out this weekend, but if you get a jump on it, please post results.

I did not get a chance to test the rear this weekend. Spent MUCH more time than planned on replacing ABS pump unit.
1. Porsche, once again, made removal/replacement much harder than required. A few minor changes to the bracket, 928.355.041.02, and it would have been easy to slide unit out of the wheel well. But, because they are spiteful jerks, it was a complicated puzzle box dance that required a lot of extra removal under the hood.
2. Then getting it back connected, the below brake line was a HUGE PITA to get reconnected:
https://cimg6.ibsrv.net/gimg/rennlis...92f1b5c6b9.jpg

Ken,
Do you have the "barrel grommet" off an old sensor you could send me? I may be able to cast a new one out of rubber you could slip over the new wire (before attaching the new connector) or if you have the new connector installed already you could just split it lengthwise and put it on the new wire.

Matt

I'll see what I can do. PM me your address.

Hi gang...any updates on these? Attempting to do both fronts and was just wondering how everything came out?

Matt.

have a car in the shop with ABS LIGHT on, bad rear sensor.....for now, we split the signal from the known good sensor in the rear to feed the signal for both rear sensors to the control unit and that worked....looks like you can modify the rear sensor from a later 928....cut the metal upper piece off and seems to be equal to the length of the old sensor....the oring was even on it.....car had to leave so we did the wire trick and light stayed off ....

Guys just finished test driving new front sensors in the early '86 using the part Ken does above...I have ABS for first time in honestly 3 or 4 years??

Its dry outside right now so the testing I've done has been limited...but it's definitely working again.

I used a butt splice connector from old to new sensor and loads of vaseline and pulled the new wire up so it traces the same path....I use junior timer type terminals into Molex connectors..not as good looking as Mr. Rudd...I was a little paranoid about dust / etc getting to the terminals from the back so used friction tape around the whole thing and the nice thing there is it makes a nice grippy surface and the connection slides right into the same clip :)
I took my time...did it over a few days...don't try to do the first one all at once and don't do it when you're tired...the process to pull the wire takes a little patience and maybe a couple back and forth trips from the top of the engine to where the sensor wire goes into the wheel well but they work.

Ken thanks for the hard work! So glad to have ABS again!

Okay, finally got around to installing testing the rears. It's a bad news/ more bad news scenario. If you recall, I am testing " " for the rears, which look like this compared to OE rears:
https://cimg8.ibsrv.net/gimg/rennlis...de6bbd8996.jpg


First bad news, which was kind of minor, was that I had to Dremel out the mounting hole to allow the mounting screw to align with its hole in the hub:

Holes not aligned:
https://cimg5.ibsrv.net/gimg/rennlis...09db0987d0.jpg

Holes not aligned

Out of Box:

https://cimg0.ibsrv.net/gimg/rennlis...9e41fd29f6.jpg

After some Dremel magic:
https://cimg5.ibsrv.net/gimg/rennlis...31aff75f51.jpg

Successfully mounted:
https://cimg8.ibsrv.net/gimg/rennlis...1ed8fcff11.jpg

The worse news. It simply did not work, ABS warning light came on after a few feet.

Testing at ABS controller connector showed about 1,200 ohms across each sensor, so I knew I had good connectivity.

I hooked up the Oscilloscope across the rear sensor pins in the connector and went for a drive:
-rear, left between term. 8 and 9
-rear, right between term. 24 and 26

Flat line, no measurable signal:
https://cimg5.ibsrv.net/gimg/rennlis...d1224a3d7f.jpg


For comparison, the fronts ( Pins 4+6 and 21+23 ) return this:
https://cimg2.ibsrv.net/gimg/rennlis...0a1270dbcd.jpg


A live trace of Front Right looks like this:

My theory is that the Volvo sensor I an using for the rear is set up to sense a pulse/signal along the "edge" of the bar, like the front sensor, not across the tip of the sensor, which is where it would be on the rear.

The search continues, and I welcome input, suggestions, theories.

I agree with Ken that the Volvo part ABS264 does not work on the rear. Fitted it last weekend after filing the screw hole out with a chainsaw chain file. ABS light comes on after the vehicle starts moving.
Resorted to repairing the ABS sender using the John Madden method described. ABS back to working. I suspect there is a good possibility that the Volvo front ABS unit may work once cut down to the right length. Next time the rear fails will try the Volvo front cut down.

I used the same part and got the same result, minus the oscilloscope results. Thanks for confirming what I suspected.

Looking at some other candidates on the web, something straight from Bosch may be the best bet.

The sensor that looks like it may have the best chance of fitting is off a mid-80's Mercedes 380SL. Problem is that, while I might pay the price if it actually worked, they are WAY too expensive for me to hack up as test subjects that may not work. Seem to go for between $300 and $450 each.

Airtex 5S11004 , or WELLS SU12457

https://cimg9.ibsrv.net/gimg/rennlis...5b71d59aef.jpg

Ouch..yes def. too expensive to Frankenstein just to find out if works or not...looks close though from the pic...

Try finding a used one. I'm sure there are many out there.

I've got a search configured on EBAY for a used version, but so far, no joy.
If there are better sites for used MB parts, post links.

https://www.google.com/search?source...92.WHqyMwkCgj0

Maybe here is something!

https://www.pkwteile.de/autoteile/me...138/abs-sensor

hinten = rear

https://www.ebay.de/p/Bosch-02650040...9128230&chn=ps

Hope it helps!

bump....any info?

Ken and the rest of you - Kudos.
Working with Sean @ 928Docs to make a kit for the fronts that we can sell complete to customers.
They will fit S2 84/85, S3 85 ROW, S3 85/86 USA (not 86.5) when ABS was fitted to the car.

How much? I am going to try and get my oldest 1985 928S2 Strosek out on the road again. ABS has never been working since I bought the car in 1986.
Åke

The rears are still a problem AFAIK. So far no luck in finding an easy/affordable fit.

Working that out now.* Had to order some new wiring bits and we are going to try a couple of sensors to test.* Give it a couple weeks and Roger will know more.

Any plans for Rears as well?

Have not found a sensor that is compatible yet. Still searching.

I do need to know what the exact length the wire is from sensor end to connector end on the fronts. We got this figured out after that.

I tried one set of sensors recommended on here, but they didn't work. I'm assuming that the inductive characteristics were not matched, continuity was good back to the controller. Unfortunately, inductive characteristics are not published, and I don't think anybody knows the same for the original sensors. It will have to be pure trial and error.

Just curious, which ones work at the front? Can they be adapted to the rears? I think the difference is they need to be about 10 mm shorter. Can a spacer be created to achieve that difference? I will give it a try if I know which front sensors to buy.

Thanks,

928 Wolf It would be useful to note which sensor you tried as there are multiple examples discussed in the thread. Two owners have reported success with the 3515092, ABS Speed Sensor for the fronts.
They were both S3 cars USA. Yours is a Euro and could be 16v or 32v. Putting your car details in your signature would be really helpful.
AFAIK all cars from 84 to 85 (86.5 USA) had the same ABS system when fitted.

I tried the rear sensor:

It didn't work. My car is a 1985 Euro, 16V engine.

This is the sensor I tried, with no success.

Thanks for your help. I'll get the front sensor that was proven to work, and will try to make it work.

If anyone needs a set of early front or rear sensor's PM me. I upgraded my 928 to S4 suspension front and rear. The ABS worked perfectly before the upgrade.

I could use the set as a template to build new ones for the fronts.

Bump....any news on rear sensors? My fronts I put on (see earlier posts ) in this thread are still running perfect but I know it's only a matter of time before the rear ones need attention...

Bump. Was wondering if anything was cooking somewhere for rear sensors....

I need to read the whole post which I havent but just noticed the title as I am about to pull my rear suspension.

How do the ABS sensors differ from the crank speed sensor I wonder?

Does not look feasible as they are NLA - any other ideas Ken??

I've got nothing, except I keep an eye on Ebay and Craigslist etc for old sensors that may pop up. Unfortunately "Hope is not a strategy"

I removed an ABS sensor from the rear of my 85 S2 today as I am refurbishing the hub and it needs to go in the oven. Unfortunatly the plastic housing is rather brittle and snapped in the process. As these ar NLA does anyone know if this is repairable as the main body of the sensor appears intact? Thanks

https://cimg0.ibsrv.net/gimg/rennlis...e18197a5ca.jpg
https://cimg1.ibsrv.net/gimg/rennlis...c34f62efd8.jpg

We are testing an alternative for the rear as we speak. Hopefully it works - fingers crossed.

Excellent please do let me know!

Any success will be posted on here.

Some progress. I spoke with Roger late last week and he brought up some good points and had some ideas that needed testing. Apparently, he had spoken to Bosch directly, and while they did not have a viable solution, it got his gears going.
Data Points:
- The front sensor is very similar to the rear sensor in all dimensions, except the front sensor has longer probe that is designed to lay "across" the ABS ring teeth, as it is inserted from the side. The rear sensor comes in from the top, so has a much shorter tip.
- While the front OE sensor is also NLA, it _might_ be possible to build a spacer/adapter that allows the "new" front solution to also work in the rear, since the new solution is very close in dimension to the OE solution ( obviously)
- The big question is whether once in place, would this generate a usable pulse from the moving magnetic field at the tip, instead of along the edge where it had been designed to do so.

So, I took one of my old front sensors ( #PartsHoarder) and ground a tip on it ( In the past I was VERY hesitant to try to modify the tips, because the part was unobtanium, but now I care less):
https://cimg0.ibsrv.net/gimg/rennlis...199879e1aa.jpg

Then did some careful measurement, and JB Welded a stack of 3/4" washers together to make a spacer:
https://cimg5.ibsrv.net/gimg/rennlis...c8a4ebdc00.jpg

Put it in place:
https://cimg5.ibsrv.net/gimg/rennlis...1124ff0bae.jpg


And, with this very crude mock-up, was able to generate what appears to be a reasonable sensor pulse by spinning the hub by hand.

So this strongly demonstrated that with a little cleverness, the fronts _might_ be usable in the rear.

But wait, there's more. ( and yes, I know my parking brake is shot)

Well done and thank you for your efforts. I read through the thread and, having tried unsuccessfully to track down down a rear sensor in Europe I came to the same conclusion i.e if the Volvo one works on the front can it be made to fit the back, so was planning in experimenting although not for a while as I am completely rebuilding the rear axle. Incidently I also wrote to Bosch and got a similar reply today (note the spelling errors are not mine!)
__________________________________________________________
Hello,
Thank you for your email.

Part number 0 265 001 053 (Porsche sensor) has been discounted, no repair possible or spare parts available and no longer available in the Bosch aftermarket. Please contact your vehicle manufacture for a replacement or an equivalent.

Best regards
Zain
Robert Bosch UK Holdings Ltd
Broadwater Park
North Orbital Road
Denham, Uxbridge
UB8 9UX

following.......

So, now that I had crossed the mental Rubicon of hacking up an un-replaceable part ( which, BTW is essentially what Roger suggested way back in post ), I decided to see if I could just shorten the Front OE sensor, grind a tip onto it and get a decent signal pulse. So I sacrificed another OE Front sensor out of my part hoard.

I used a Dremel cutting wheel to trim the tip down, and then ground out a point to match the OE Sensor:
https://cimg5.ibsrv.net/gimg/rennlis...a1cc4b85ab.jpg

This also created a nice strong signal pulse in my mock up scenario when spinning the hub by hand.

So, now I have two similar paths;
1. Sensor with minimal grinding, but requires fabrication of a spacer/adapter ( which, in production would be much nicer than my JB welded washers)
2. Sensor with more cutting and grinding, but no spacer.

Next step is to get two of the actual "new" style front sensors, make the necessary adaptations and see which works best in practice.

Possible pitfalls:
-The "new" sensor may not take kindly to being cut and machined. The heat or vibration of the cutting and grinding may cause damage;
-The "new" sensor way work differently and not generate a pulse when excited from the tip ( *Phrasing)
-The "new" sensor tip may be of a magnetic material that does not cut/grind well;
-etc

Happy to send you new front sensors so you can grind away. Will be in the mail today.
Well done Ken.

As Ive now destroyed both rear sensors while removing them from very corroded carriers I'm going to have to experiment with one of the proposed solutions above. Roger mentions volvo 3515092 as a potential so I ordered two and here is how they look once fitted. I have no way of testing them for some months as the car is still in bits but at least they are rather cheap here in the UK. The main issue I assume is that they are designed to pick up the surface variation from the reluctor teeth on the side (like the fronts as per the second photo) rather than the tip so I'll need to make sure the reluctor is rust free and the sensor is as close as possible to the teeth.
I was hoping to splice in the old connector however the old cable is completely perished under the sheathing so will replace both male and female connectors with superseal plugs.

https://cimg3.ibsrv.net/gimg/rennlis...f813aeaa55.jpg
https://cimg1.ibsrv.net/gimg/rennlis...5f4db058d4.jpg

Any news Ken?

By the way Ken/Roger if you are looking for material to use as a spacer I highly recommend the disc that Constantine supplies with his super bearings to aid installation. Not sure what kind of plastic it is but it is both strong and easy to shape. It's also close to the correct thickness just needs a bit shaved off

I hope to have some "postable" progress tonight or tomorrow.

I was hoping to have more progress to report this morning, but things always take longer than expected.

As hinted at earlier, I am following the path of trimming off the long probe of the “Volvo” ABS sensor, versus the alternative of spacing it out. Based on my testing of a modified OE 928 front ABS sensor, this route seems to make sense, i.e. that scenario works.

To that end, the length to be trimmed is fairly critical. Leave too much on, and you risk grinding into the hub teeth, or getting contaminated with all the schmutz that can build up around the magnetic tip. Take too much off and you degrade sensor signal. The math to figure out how much signal loss you suffer per 0.1 mm increased distance is beyond me, so I am going to trust the original engineers and just get the length as close as possible.

To that end I have been working on a jig that will allow length to be matched as closely as possible to original. First, I realize this is a lot of extra work since I will likely only be doing two sensors, but I feel it is important. Secondly, I know my fabrication skills are not up to Greg Brown levels, but I gave this some long thought, and I think the threaded bolt solution with jam nuts should give fairly precise and repeatable results, despite the crude construction. So, here is where I am with the length jig:
https://cimg0.ibsrv.net/gimg/rennlis...6ec6b2c9f3.jpg
https://cimg2.ibsrv.net/gimg/rennlis...0bd0285d7e.jpg
https://cimg8.ibsrv.net/gimg/rennlis...1f4509aaf8.jpg

1. I am crafting a similar jig that will allow me more accurately grind the tip at the end to match OE sensor;
2. While doing this, I was reminded of something I had noted earlier, the "Volvo" plastic base is ~1.5mm more narrow than the OE base. So I think a fatter O-ring is needed, to help seal up the mounting hole and center the sensor as originally designed.

Hi ken
If it helps, the reduction in magnetic field is directly proportional to the distance. That should apply in this case. So hopefully distance shouldn't be too critical.

John-
Thanks! If I read this correctly, lets assume the correct gap is 1mm +/-. That means if I am off by an additional 1mm, I could lose half my signal. I have seen the O-scope trace. The signal is pretty noisy with the car running, and I suspect the ABS brain may have marginal filters at best. So, I'll get it as close as I can with the tools and skills I have.

If I had more time, it would be fun to add successive shims and see how far out we could go and still get a usable S/N ratio.

But I can and will run O-Scope traces of current setup vs when the new setup is in place. Vmax, Vmin and Vpp at a constant speed should give a good snapshot of how the replacement does compared to the existing.

I completed the reshaping of the “Volvo” sensors to match the length and shape of the OE sensor as closely as my skills and toolset would allow. Should be able to install and test in the next few days
https://cimg0.ibsrv.net/gimg/rennlis...f3f14c607.jpeg

I remembered to test resistance before installation!
https://cimg1.ibsrv.net/gimg/rennlis...d69cf20f4.jpeg

https://cimg5.ibsrv.net/gimg/rennlis...7021e422a.jpeg
I talked earlier about the new sensor having a slightly smaller diameter than OE. I Compensated with an R-11 o-ring. R-11 is ID 16mm x 2.5. Ideal fit may be more like 15mm x 3.5, but I did not have one. Not sure how critical a perfect deal is, but the R-11 is not bad.

Sensors installed:
https://cimg3.ibsrv.net/gimg/rennlis...2727ea5e9.jpeg
https://cimg6.ibsrv.net/gimg/rennlis...9187781bf.jpeg

The good news: No warning lights on start up and no clicking of the sensor hitting the teeth.
I also replaced my parking brake shoes.

The bad news, about a half mile down the road, ABS warning. This typically indicates a signal error. A short or open circuit would alert immediately on start up.
Means I have to connect up the diagnostics and see what if any signal we are seeing. :(

https://cimg9.ibsrv.net/gimg/rennlis...f3fc04e53.jpeg

I hooked up my ABS tester. I was hoping to find that only one or the other new rear sensors was failing, which would indicate that my plan was sound, but that I had made some kind of mistake in the construction. Unfortunately, both rear sensors were showing poor signals. Below is a video of what the testing looks like, comparing a good signal with a poor signal:

Next steps?

I am going to try to clean up and tweak my sensor tip shape.
If that fails, going to pursue using a spacer and an unmodified tip.

I wanted to confirm what was going on before I starting making any new changes, so I hooked up my handy o-scope.

First, here is what the current working front sensor traces look like. As a reminder, these are the same Volvo based sensors, but they have not had their probe/tip machined in any way. Pro-Tip: If you ever want to do this, get help. Driving, managing the o-scope and trying to take pictures by yourself is a recipe for trouble. The RF and LF sensors read fairly clean wave forms of between 0.43v and 0.87v:
https://cimg3.ibsrv.net/gimg/rennlis...1446b6dd54.jpg
https://cimg5.ibsrv.net/gimg/rennlis...8f2d7bb747.jpg

However, the RR and LR traces don't get above 0.19v and seem very noisy. I don't know if its the low voltage or the noise or the combination, but the signal is not good enough for the ABS control:

https://cimg7.ibsrv.net/gimg/rennlis...671f2f1b10.jpg
https://cimg8.ibsrv.net/gimg/rennlis...a28c36f62e.jpg

So my current POA is still to pull the sensors and clean up the tip and see if that improves the signal. I may also pull a hub to see if I can get a clear view of the actual tooth to probe tip clearance. Despite my care in machining, I may still have created too much of a gap.

If it doesnt work out Ill have a look here in Europe at other cars fitted with sensors that measure the signal vertically (unlike the volvo sensor). here is an example that looks the same but not sure about the dimensions yet.

https://www.aliexpress.com/item/1238...AbTest=ae803_4

I clean up the tip to give a more refined point. Did this with a Dremel wheel, vs. the coarser bench grinder I used initially:


https://cimg8.ibsrv.net/gimg/rennlis...e2a9caa10e.jpg

Initial results were good. I got about .10V higher signal, an I was optimistic when a several mile test drive showed no alerts.However, did get an ABS alert on the way to work this AM ( about a 15 mile commute). So made progress, but still not ready for prime time. For comparison, the front sensors generate between 0.50V and 0.90V:

https://cimg6.ibsrv.net/gimg/rennlis...da5277026e.jpg

You're the man, Ken! With an 86 this is something I'll be needing.

I'm wondering (and this ain't me asking you to work harder than you already have/are) if you were able to get eyes on the actual distance between the sensor and teeth? I know the requiresa whole nuther level O effort...

As it is now I have NO sensor in place, a mess O wires, and a carrier that strangely doesn't even support a sensor - the rear passenger side. A carrier from an earlier car? A mess. Long ways to go,,, and time to get there - I guess.

Keep up the amazing work Ken.... Cheering you on and appreciating you efforts, over here!!!

That was actually my plan. I had my gap gauge ready and even broke out my HD Air Wrench and had the big nut off. Then I remembered what a pain it was to actually get the hub off from there and the real probability of destroying the bearing IIRC. So I altered my plan. But yes, I would very much like to get an eyeball on that gap. I think the gap distance is critical. "Magnetic force obeys an inverse square law with distance. ... If the distance between two magnets is doubled, the magneticforce between them will fall to a quarter of the initial value." So if I can close the gap by 1/2, I should get 4x the signal.

Unless there is a real limitation in the equipment/parts/supplies you have (the sensor design itself),,,, I know you're going to figure it out. I also think the gap is critical...

Truly admire you insight, determination and willingness to do all this for all of us out here. No isht! It's a big deal! Thank you.

Okay, much progress.
I re-machined the tips to make the point more defined. I did this with a small grinding wheel on a Dremel tool. See post #130 on 6/10. This fixed the signal strength.

However, the new intermittent issue after bumps was frustrating me. If you recall, that symptom was what was driving me crazy way back in the beginning. I found the new cause, and although the symptom was the same, the root cause was different.

Apparently either the stress/vibration of the machining or the heat of the machining, or both, broke the magnetic probe free in its housing, allowing it to rotate somewhat freely:


So I get a fresh Volvo sensor and machined another one. This trick this time, to improve the process, was:
1. To be more careful
2. Use needle-nose vise grips ( same as in the video) to hold the base of the probe. This both kept it in place mechanically, as well as acted like a heat sink to keep the probe from getting too hot at its base.

Testing shows all is good. Good signal and no errors.

This is great work, hopefully the results are good enough to eventually have a part available to buy from Roger.

Thanks for the hard work on this, great job.

Very promising, and thanks, Ken, for all this work- potential big benefit to our community.

Some summary tips:
1. Tip shape is important. Not a pyramid and not a fine point. Think "big screwdriver".
2. Apparently, the sensor does not mount perpendicular to the teeth in a Volvo, so it has a slight twist, say 15 degrees. You will have to machine that out, as you want the tip to be as close as possible to parallel to the teeth.
3. Tip to Tooth distance is important. If in doubt, machine it a bit too long, loosely test fit, gently spin the wheel and feel/listen for the vibration of contact. If you get some, grind of a hair more until no contact.
4. Be careful and use some type of a heat sink/ mechanical brace to keep the tip from getting too hot or breaking loose while you are grinding.

Wow! I'm just now seeing this thread. There has been a lot of great work done over the last 2 years. Ken, it looks like you've gotten real close with the rear sensor shape grinding. I agree with what you've discovered: It's very important for the flat on the sensor to be parallel to the teeth on the spindle. Also, I have an old ABS Service Book which states that the clearance between sensor and spindle needs should be .35mm. This seems like it would be difficult to hit with a grinding operation.

https://cimg9.ibsrv.net/gimg/rennlis...acb660aded.jpg

https://cimg6.ibsrv.net/gimg/rennlis...8f60ca8de4.jpg

https://cimg8.ibsrv.net/gimg/rennlis...372ba99e3d.jpg

Other note: The ABS control unit pin assignments in Post 43 are incorrect. At least for my 86.0. Pin 11 is not connected to the front right speed sensor. I had the correct pin assignment 2 years ago, but I can't find it now.

The front and rear sensors that I refurbished 2 years ago are still working, so it seems like the repair is robust. I also had a friend create a tool to reform the rolled edge on the sensor metal shell (the last step in my documentation that I didn't complete originally--linked in Post #1). I'd like to help out the 928 community by repairing some of the broken sensors out there. After doing this repair a few times, I can report that it is not too difficult if you have a steady hand with a dremel and soldering iron.

Bringing this back to the top.
I would love to hear more about refurbishing the existing sensors. Hitting a gap in a blind hole at exactly 0.35 mm (to what tolerance?) would be difficult. Any help with this would be greatly appreciated.

With the refurbishing procedure, there is no need to change the length of the sensor, so the .35mm gap is maintained by the original parts. The refurbishing steps are in post #4 here:
https://rennlist.com/forums/928-foru...d-sensors.html

Bump. Was wondering if we had any more news on rear '86 / S3 ABS sensors? Looks like from re-reading this thread we can use a dremel or similar tool on a Volvo unit or fix the existing one by unrolling the outer case and re-soldering the sensor wire where it broke. I looked around online today and it still looks like retailers are grouping the S3 rear sensors with the S4 units.

Thanks
Matt

My ABS was working fine until yesterday (84 Euro S with optional ABS). Suddenly the antilock warning came on and apparently, my rear right sensor is dead. I measured the resistance and I get nothing. The sensor wiring looks ok and measuring at the plug in the wheel well, same reading.

Is there any progress on commercializing the rear sensor replacement? Or is it a DIY job to tweak the volvo sensor? Does someone offer the repair of the existing sensors as a service, preferably in Europe, to keep shipping costs down?

We have the rear sensors being tested as we speak. Should be available in January.

That sounds like good news! Any idea on pricing yet?

Hi, I might be able to help you out, I'm in Belgium too. Just send me a PM.

You sir, are THE MAN. Thank You!!!

Hi Roger... did you end up managing to find a solution for the early rear ABS sensors?

Yes - A little bit more involved than the fronts but we have a solution.
Working on bringing it to market soon.