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By checkmate1996
#81498
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?
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By The Fat Man
#81509
Jesus wept...they are triggering the speedometer pickup with magnets bonded to the CV hub. :eek:
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.
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By worf
#81531
SeanR wrote: Thu May 20, 2021 9:03 am I don't even know what to say about this.
Oh... I do: “Glad it’s not in my shop” :roflmao:
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By worf
#81532
checkmate1996 wrote: Wed May 19, 2021 11:16 pm 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.
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By checkmate1996
#81533
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?? :roflmao: :biggrin:
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By checkmate1996
#81534
worf wrote: Thu May 20, 2021 9:39 am
checkmate1996 wrote: Wed May 19, 2021 11:16 pm 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...
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By checkmate1996
#81535
Quality content only found on Open Road!! :roflmao: :roflmao: :roflmao: :biggrin: :biggrin: :biggrin:
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By checkmate1996
#81628
Here’s a picture of a transmission and where the speed sensor sits. Doesn’t look like there is much magic there ...
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By checkmate1996
#81745
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?
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By SeanR
#81792
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.
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By Majestic Moose
#81793
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.
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Inside diameter worn away and enlarged.
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What it should look like with circlip installed.
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By checkmate1996
#81811
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 ?
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By Majestic Moose
#81812
Yes it is, you have to disconnect the axles and remove the stuff circled from both sides to release the differential.
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By worf
#81814
Majestic Moose wrote: Sat May 22, 2021 1:08 pm Image
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.
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By checkmate1996
#81874
For the curious ...
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By checkmate1996
#81875
F9BF3BED-F9DA-4A42-9BDE-42E0254D69B1.jpeg
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By checkmate1996
#81923
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.
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988224F2-61BE-4AC3-AA75-F8A484069240.jpeg
F1A5FB68-8503-4144-8BE5-5956F34A94F3.jpeg
40BFA488-49A3-44AA-ABAE-0FF6419717BD.jpeg
2EB041EF-2BC5-44A4-97CF-EAE8056ED3EC.jpeg
C0E7D241-881A-4794-8DD6-09F5337F4224.jpeg
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By maddog2020
#81939
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.
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By checkmate1996
#81946
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 ...
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By checkmate1996
#82045
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...

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85 Transmission LSD
85 Transmission LSD
85 Transmission Rear Differential Cover
85 Transmission Rear Differential Cover
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By checkmate1996
#84784
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!
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By maddog2020
#84800
checkmate1996 wrote: Thu Jun 10, 2021 10:18 am 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?

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