gasmanstl

Hello all,

I have an 85 Euro (german) 928S 5-speed, and the beginning of this story is that, very infrequently, and seemingly related to perioods of disuse (parked in garage during winter), my speedo quit working completely, interspersed with periods of erratic readings. Essentially I drove the car a couple of days anyway (sans speedo) and it went away (last time, a couple months ago).

Enter other info, which I did not relate to this problem until I did some troubleshooting: the cruise control works only occasionally, and of those times, only occasionally does it truly function, and then usually not for long; it then drifts to way slower speeds, or just stops.

Having a set of honest-to-god factory manuals, I read the appropriate section and grudgingly took out the "tempostat control," as they call it, which lives under the center of the dash, and broke out the multi-meter. I completed all of the diagnostics, which were essentially normal, with the exceptions that, on some terminals where I was supposed to read "battery voltage" under certain conditions, instead, I read a half-volt or so less......AND......where it says to measure the resistance between terminals 11 and 12 and move the car slowly back or forward to test the speedometer sensor.

The "correct" observation is that the resistance alternates between infinite and zero. My actual observation was that the resistance alternated between infinite and about 27 ohms.

It would seem, then, that the sensor is, in fact, bad. (No testing procedure is delineated for the "tempostat control.") I'm curious about a few things, having read some previous posts on this subject: 1). In the opinions of those who know something about this, is this a big enough discrepancy to cause the problems with both the cruise control and the spedometer (which has been functioning normally for weeks now)? 2). The values of infinite and and zero resistance suggest a physical, electrical-contact-nature to this sensor device, and I believe I read someone referring to a rotating magnet in a previous post. What is the actual nature of the sensor device? 3). Someone said it was located upper driver's side of tranny - is this in an auto, manual, what year, etc. (believe it or not, after looking in all four volumes of the factory manual, allegedly all there is, NOWHERE does it tell me where the damned thing is - the only reference to it I saw at all was in transmission section, which terrified me that it might be an internal component. It said, at the beginning of removing tranny, to disconnect the spedometer sensor lead). 4). Pursuant to the last question, how difficult is this item to replace?

Thank you all in advance for your help.

Clay

GoldenPTL

I believe it is on the back of the transmission above the drainplug. Should be able to see looking from the rear. One small bolt holding a wire to hold the sensor in place.

The only other electrical wiring to the manual is the reverse switch towards the front and on the drivers side.

jpitman2

Usually caused by bad connection in connector in front right corner of spare wheel well, OR bad contacts where connector goes onto pod circuit card. First is easy to check and clean, latter, bit harder. There is an alloy wheel bolted to diff crown wheel with 8(9?) magnets let into it. The sensor on the diff cap is a reed switch that closes momentarily as each magnet passes by. Rarely fails.
jp 83 Euro S AT 50k

SharkSkin

The fact that the cruise circuit as well as the speedometer are acting up points to one of the connectors they have in common, either at the base of the CE panel or in the rear wheelwell as mentioned.

The connections on the bottom of the CE panel are:

Sensor: R12, R13(gnd)

Speedo/cruise: K22

Make sure that when you spin the wheels you get the same readings ar R12 & K22. If not, there is a problem internal to the panel. Make sure R13 is a good ground. Also check the connector in the tire well. The sensor itself is a reed switch, opening and closing as magnets on a disc pass by. Resistance checked directly at the sensor(or the tempomat test, or checking between R12/K22 and ground or R13) should be infinite or nearly zero, changing as you rotate the wheel. 27 ohms implies dirty contacts somewhere. That type switch usually either works or doesn't, they tend not to fail halfway in between.

gasmanstl

Thanks to all for quick help, and to Dave:

""" The connections on the bottom of the CE panel are:

Sensor: R12, R13(gnd)

Speedo/cruise: K22 """

Could you please tell me what (and where) the CE panel is, and to what the designations K22, R12 and R13 refer? I'm afraid I'm clueless...

Thx again

Clay

SharkSkin

"CE" is "Central Electric", the panel under the passenger floorboard.

The connectors along the bottom are marked A, B, C, D etc. left to right along the bottom.

The pins within those sockets are numbered by column then row, counting from the left then up. Note, this is for 85+ the designations for pre-84 panels are similar but different. See the example below:

In this example, I have shown "X" at locations B24, C13, and E25.

HTH

gasmanstl

Thanks to all for help...will try to fix & advise.

c.

gasmanstl

Hokay...I went sharkulating at some length today, and accomplished quite a bit. Got all of Mr. Wally P's "yearly electrical maintenance" done, since I felt inspired, and as far as I know, that stuff had never been done...then, feeling very, very inspired, I removed all relays from the CE panel and buffed their posts with my Dremel/wire wheel - and then, unplugged all of the big, fat connectors lettered A-W and hand sanded EACH and EVERY connector on the board, on both sides. It was pretty easy, really; I cut a tool out of a very rigid, flat piece of plastic which fits exactly into the connector slots and glued a piece of sandpaper to it. Using this tool, I was able to clean up 5 connectors at once on one side with 20 or 30 swipes of the sandpaper.

So here's how it went...terms. 11 and 12 of the tempostat controller connector varied between infinite and 27 ohms before beginning...........after cleaning the connector in Frt Rt of spare tire well, the resistance varied between infinite and 4.5 ohms..........and after sanding every connector in CE as above, I then measured infinite and about 1 ohm.

Than's the good news...bad news is that despite the clinical improvement in the performance of this sensor.....the lousy Cruise Control still doesn't work. @#$%^&%#@%

SharkSkin

OK, have you gone through the entire WSM procedure to the point where it says to replace the cruise brain? If so, you could try to disassemble it and re-solder all the connections. That's what finally worked for me. Berryman's B-12 took the coating off of the connectors, but you have to be VERY careful to keep that stuff away from plastic and paint. IIRC it didn't affect the main plastic connector on the brain, but check it to be safe and keep it off of the plastic components on the circuit board!

More info on this page.

gasmanstl

Hello Dave...

And thanks! I wouldn't have saved $$$ if you hadn't prodded a bit:

Yep, next step per WSM was to replace the brainbox. Then read your post, took box out and removed guts. Just like you said on your page: nothing looks burned or cracked or dry, all looks fine. @#$% ...no focus of injury...and I'm not too sure I want to be soldering around on this thing, I'm fair with electrical things, but I'd hate to wreck this thing even as a core and cost myself another hundred or two dollars...

Ahh well, no guts, no glory. Down to auto zone for the Berryman's. I was almost ready to spray the backside of the thing, upside down of course, when I remembered the little black foam rectangle thingie glued to the backside, which keeps the board from buzzing and vibrating. I carefully pull it off, and the adhesive stays stuck to the board and solder joints, looks pretty cheesy, and I guess it'll come off OK with the Berryman's. (After proving it was not soluble in B12) I used a toothbrush with the solvent to scrub the varnish off the board. Presently, off comes this adhesive/tape thing from backside of foam, and what do I see under there but CORROSION on the solder joints and the conductor tracks on the PCB. Looked gnarly. Only under the tape. I briskly scrubbed and sprayed and sprayed and scrubbed, until no more would come off (corrosion or varnish - mind you that not 100% of the varnish actually came off. More like 98%. No matter how long I scrubbed, some just wouldn't come off. Maybe it's actually flux or something.) Anyways...

It looked so gnarly when I started under there, and so much better when I was done, that I just thought fluck the whole thing - I'll plug it in and try it. Lo and behold...cruise works. Didn't have to solder every little durned connection after all.

Now it works as good as it *ever* did, which, IMHO, is not terribly wonderful. It will hold a speed right on the money, but it does so by mashing the gas and letting up on it alternatively at about 5 second intervals. It's never being smart and keeping a constant throttle setting, it's always speeding up and slowing down. It's maddening. Does yours do that?

Also, since you have prior experience in PCB construction, I wonder if I should spray some kind of varnish back on the backside of this thing, and it so, what?

You've been a great help, and thanks. Nice sharky. I will post some pics of mine as soon as I get her cleaned up a bit. I just sent my orig 85 phonedial wheels off to the same place in Cali to be rechromed. They're beautiful.

SharkSkin

Mine doesn't surge at all... it holds speed as if I stapled the speedo needle in place. Sounds like you still have some flakey connections in the brain. I had no evidence of corrosion, all the solder joints looked good yet re-soldering them fixed the problem. Someone posted this link a while back to some videos on soldering that you might find useful: http://radiojove.gsfc.nasa.gov/elab/soldering.htm

Be sure to re-flow each solder joint quickly so you don't heat-damage anything. If you can practice on something else you might be better off... I think it only took me a few minutes to re-solder all of the joints once I had access.

Once you have it re-soldered and behaving correctly you can get some stuff at Radio Shack or elsewhere that can be used to seal it back up, but that shouldn't be necessary unless you are in a humid climate.

gasmanstl

Hello all/Dave:

Well, after a trip out of town and thinking about how I was going to do this for awhile, I have done it with success. Some of these little solder points are pretty tight, at least for a schlock like me to attempt to solder with a rather large-tipped iron, so I couldn't see myself just sort of re-flowing the joints and maybe slathering a little more solder on some of them. I'm way to meticulous for that, I had to do it right. So I went out and bought a solder-sucker and learned to use it on a discarded board. After making too few mistakes on the discarded board, I started on the sharky cruisebrain; making a few more mistakes, I eventually got all of the connections desoldered adequately without destroying the board. (I didn't believe the components would actually fall out; only one did, and I had taken copious digital pics of both sides of the board in case I made a major screwup.)

After sucking the board, it was pretty clear what points were supposed to touch and which ones were not. Still, I referred to the pics of the backside many, many times to make sure I had not screwed up, and did actually identify a couple of areas I had to revise the work after careful inspection (little solder trails that touched something they shouldn't have, and points where I didn't put quite enough solder on the joint.) Overall, having done one, I think I could do it now, much better, in less than hald the time.

The whole project actually took me about four hours, during which I ate dinner and farted around a bit, as well. And when I was done, it was RAINING! I do not go out in the rain with my shark, given a choice. So I couldn't test it....!@#$%^&....until this morning.

Worked like a charm. Will still surge a little bit when you cruise at very low speeds, eg 30-35 mph, but the improvement is vast. On the highway, it's like a new cruise, works at least as good as the one in my camaro, and accelerates like it intends to go somewhere NOW...

Thanks for help, Dave. I would have never attempted that before reading the list here. I am sure to have many more questions - I'll try not to me a nuisance -

All should read SharkSkin's webpages about his adventures with various systems of the shark. I have already ordered my 10 ml bottle of Stabilant-22, and plan a more comprehensive revamp of the CE panel and to service all of the 900 grounds identified on (Wally's?) list...as well as to take apart the dash and clean all of those connections. My car has been plagued with electrical gremlins since the day I got it...and killing them is *fun*... :-)

Clay

SharkSkin

Wow, you really went all-out, Clay! Glad to hear you got it working, the money you saved on replacing the brain more than made up for the tool costs! I just re-heated/re-flowed the joints, adding a touch of new solder to get the new flux on the joints. And yes, killing gremlins is very satisfying.

BTW, I've updated my page with the source for the 50mL bottle of Stabilant @ $75.

Thanks for the update!

gasmanstl

Rats......50 cc's for $75?? I just paid $50 for 10 cc... :-\

gasmanstl

Wait, no...I bought 10 ml of the *concentrate* for $50...so same amt of stabilant - I just have to dilute my own. I have plenty of absolute ethanol or isopropanol...care should be taken to only use nearly anhydrous solvent, not that drugstore stuff. Anyway, I got it from:

POSTHORN RECORDINGS
142 West 26th Street
New York, NY 10001-6814
Tel: 212 242-3737
Fax: 212 924-1243