[checkmate1996]

Ok, while in the process of trouble shooting vibrations in the drive train and other issues - the rabbit trail ended up leading me down the remove the fuel tank trail. ( it had excessive dirt and junk floating around along with a broken in tank filter). But the fun really began after the tank was dropped and I had a good look at the transmission. Can anyone reasonably explain why someone would do this?

[The Fat Man]

Jesus wept...they are triggering the speedometer pickup with magnets bonded to the CV hub.
Did the speedo read really high?

I recall reading something a couple of years ago on TSTSNBM about how the aluminum magnet carrier can come loose from the differential. Possibly something like that here.

You are in this far, pop the differential cover for a look-see.

[SeanR]

I don't even know what to say about this.

[worf]

I don't even know what to say about this.

Oh... I do: “Glad it’s not in my shop”

[worf]

Can anyone reasonably explain why someone would do this?

They lost the little steel loop that helps retain it to the cover.
Drain Bamage
What tFM -^ wrote.

[checkmate1996]

Seth - yes the Speedo read about 10 mph higher than gps. I do know the he put a rebuilt LSD in the transmission. Could they have broken the magnets? is this fixable? Would this also impact the odometer reading as well?

Sean - doesn't this fall into one of your famous quotes??

[checkmate1996]

Can anyone reasonably explain why someone would do this?

They lost the little steel loop that helps retain it to the cover.
Drain Bamage
What tFM -^ wrote.

Dave - the 10mm bolt with the steel spring where its suppose to go is there....that's why I'm leaning toward something like seth mentioned...

[checkmate1996]

Quality content only found on Open Road!!

[checkmate1996]

Here’s a picture of a transmission and where the speed sensor sits. Doesn’t look like there is much magic there ...

[checkmate1996]

Ok some more details on the this one-

After replacing the open differential with an LSD the problem materialized. Multiple speed sensors didn’t fix the problem. So any ideas what could have happened?

[SeanR]

Are you getting a signal at all from the speed sensor? Car in the air, put a jack under one wheel to hold it solid, multimeter set on beep/continuity function and then rotate the other wheel by hand. You should be getting some beeps. If not and you know the sensor is good, then something is not right on the magnetic ring on the diff.

[Majestic Moose]

If they forgot to install the large circlip that holds the magnet wheel against the differential then the single roll pin holding it in place will back out within a few hundred miles. Loosen a drain plug and see if the oil looks like liquid aluminium.




Inside diameter worn away and enlarged.


What it should look like with circlip installed.

[checkmate1996]

Looks like it’s tine to pull the rear cover off...

The speed sensor was working because the “bandaid” was sending signal to the speedo albeit about 10 mph off.

Is this fixable with tranny in car ?

[Majestic Moose]

Yes it is, you have to disconnect the axles and remove the stuff circled from both sides to release the differential.

[worf]

Note that #13 is a shim. There will N of them on the left and M of them on the right. They are what ‘sets’ backlash. So, don’t mix’em up. And their edges can catch the bolt threads when #14 is installed. Got in a 928 with a transaxle from a local(-ish) rebuilder that managed to catch shims with bolt threads, fold them over and didn’t notice. Needless to say: bad juju that.

[checkmate1996]

For the curious ...

[checkmate1996]

F9BF3BED-F9DA-4A42-9BDE-42E0254D69B1.jpeg

[checkmate1996]

Ok- here’s some pics of my tranny with the differential cover off. The fluid was mostly dark In color with a tinge of silver looking “stuff”. Some broken “rubbery” bits were in the bottom. Other than that- no metals bits found. The Reed switch is functional as I tested against bandaid solution and the back of the diff plate. Worked with the visible magnets on the cv axle with the switch facing in either direction. No joy from diff plate.
Also - With differential plate off, the speed sensor would pick up the signal from the magnet carrier only if it was positioned closely to it.
Here are some pics. There was “black stuff” as seen in pictures coming from the magnets.

[maddog2020]

there are also different rear diff covers, for different years, and some of them don't line up with the magnet wheel from other year trans. If you have the wrong cover, the sensor will never be in the right place.

[checkmate1996]

Well just for kicks ... I did try a differential plate from an 81 transmission. No difference ... does anyone know the exact part number for a g28/10 transmission?

EDIT: I looked up for model years 82 and 86 in ROW PET database, which I have both covers and neither seem to make a difference...

Here’s a closeup pic of the circlip - it looks to be in place ...

[checkmate1996]

OK - After some additional troubleshooting, I am fairly confident that the root cause is due to misalignment of the aluminum magnet carrier and the sensor. Using my spare transmission and hooking it up to the speed sensor, it read right away no problem - even with both differential rear plates. Check out the pictures to see the problem. It looks like a spacer or possibly something went in backwards...I am not a transmission guy so I have no idea...

[checkmate1996]

Quick update: I purchased an 87-91 differential cover plate which shifted the sensor over 1 CM to the left. The sensor now works! That's the good news. Now I'm trying to figure out why is 20MPH off! Any thoughts would be appreciated!

[maddog2020]

Quick update: I purchased an 87-91 differential cover plate which shifted the sensor over 1 CM to the left. The sensor now works! That's the good news. Now I'm trying to figure out why is 20MPH off! Any thoughts would be appreciated!

Glad that solved it. BTDT. Missing magnet in the wheel?