TeufelHei

I've trid everything I can think of to troubleshoot this thing, and it's no good; the speedo sensor on the transmission is not being tripped by the magnets in the differential wheel thingy.

This all comes after a LSD installation (by an extremely reputable shop) and where the speedo had a minor "issue" before it is now entirely dead. I've traced the problem to the pickup/tripper combination in the transmission. Having replaced the sensor with no results (yes it works, I tested it), I can only assume it's something to do with the wheel-magnet thingy in the differential.

Gut feeling...got the wrong differential cover and the sensor is too far from the wheel. Another possibility is that the magnets are weak, too weak to trip the sensor. I find it hard to believe that they all went bad though, and the sensor doesn't work at all when installed on the '85, though it does when installed on the gearbox from the '81 (RIP).

Any help here?? Are there any part numbers I need to look at right away?

Larry928GTS

Generally speaking, I'm pretty pessimistic when it comes to shops working on stuff that then doesn't work correctly. I'd be checking to make sure that they put the ring with the magnets in when they installed the LSD.

FlyingDog

All (non-PSD) 5-speed diff covers are interchangable. The 90+ PSD ones may be also, but I'm not sure.

TeufelHei

I've had the cover off already. The ring is there.

You sure about that Matt? I'll be willing to test a that theory by swapping the covers from my '81 and '85 to find out. They are definitely different. Bear in mind, the 928 got a Borg-Warner transmission in '85.

FlyingDog

When I had to replace mine (it developed a hole in itself... all by itself) I was told they're all the same. The one I installed looks like it's from a 78 with the studs to hold the battery box, but I don't have an 85+ tranny.

jpitman2

Is the ring bolted on correct way around? ie could fitting face A to the ring gear instead of face B move the magnet line sideways enough that the reed relay doesnt see the magnets?
jp 83 Euro S AT 50k LSD

TeufelHei

Hmmm...it's a thought. I'll take a look and see if that's a possibility.

Jim bailey - 928 International

The rear covers are NOT the same ! the location of the sensor is DIFFERENT ...

TeufelHei

Yeah, I noticed. Is there a difference in the later model diff covers? Mine says 'automat' with an arrow pointing to a blank spot right above the plug. Any chance I got the wrong cover back?

Jim bailey - 928 International

Sure there was more than one 928 trans at that shop...

cambria

Tim, Have you solved your speedo problem yet? I just put my transaxle cover back on after inspecting the disk and I am still not getting a signal to the sender.
Terry

jpitman2

You could have tested the reed relay with the cover off.....remove relay from rear cover, move past a magnet on the wheel (with a dvm connected to leads to show open/closed) and see IF it does trigger, and if so at what distance. If it doesnt trigger at all there's your culprit. If it does, the cause is elsewhere....too far away, wiring etc.
jp 83 Euro S AT 50k

TeufelHei

Ok...done all that. It's too far away, but the question remains...why? The next question is....what's the fix?

jpitman2

What was the max distance it would trigger at? ......is the excess distance lateral (sideways) or longitudinal(fore and aft)? Measure centre of sensor to nearest fixing bolt line to the right in the cover, then centre line of magnet disc same way with cover off. If these measurements are off by more than a mm or two I would suspect its the wrong cover.
jp

cambria

Tim,
The rear cover P/N for a 1985 5 Speed is 928 301 305 09. As Jim Bailey said the covers are different.