KenRudd

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 #22, so all credit to him), 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:


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

KenRudd

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

ROG100

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

SRaouf

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.

ROG100

Any news Ken?

SRaouf

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

KenRudd

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

KenRudd

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:

KenRudd

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.

John Speake

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.

KenRudd

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.

KenRudd

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.

KenRudd

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

KenRudd

I remembered to test resistance before installation!

KenRudd

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.