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Discussion Starter #1
hey guys, well yesterday my speedo started going nuts, it will drop 10-20 MPH and back to norm fast, well after some research i figured the place to start is the VSS on the rear diff. I replaced the sensor and the truck is doing the same thing. Its a 97 PSD auto trans. i have found that most people also had issues with the trans shifting when the sensor was bad, well mine shifts great as if there was no problem at all. Now there is one other issue though about 50% of the time i go to hit the breaks its activating the RABS system (not pulsating but just stiffens the pedal) I stopped by 2 dealerships to ask them and they both said the VSS, after explaining that i replaced it and checked the wiring they stated that i would have to schedule a diagnosis..... no thanks!

So is there any other ideas as to where to look? im gettin agravated
 

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Two more possibilities.

1. The rear ABS sensor reads off of the speed sensor ring in the rear end. The ring isn't really attached very well to the ring gear. Occasionally you will find one that is a little loose and wobbles as it turns. This can cause your problem.

2. The speedometer is controlled by the GEM, under the dash. Windshield leaks seem to happen in this area. When this happens, weird things can happen including erratic speedometer problems. Watch to see if rain has any effect on the speedometer.
 

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Its a 97... could be the vacumn pump... I doubt it, but it could be. At least for the brake issue...
 

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Discussion Starter #4
thanks guys will check on it, Its not the vacuume pump, that has been replaced but it has something to do with the speedo they started the exact same time
 

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Discussion Starter #5
ok so heres what i found...
Pulled the diff cover and found that there were some small bits of metal in the bottom of the pumpkin (dunno whats normal after 224k) i cleaned everything up and found that the "sprocket on the rear end ring gear that looks like a bicycle sproket had 2 teeth that were slightly messed up, so i took a file to it and cleaned them up a bit, cleaned everything and replaced fluid with synthetic and resealed rear cover, the speedo still acts up.
Even though there is a very minor bit of dammage i have a feeling the chipped teeth are a part of the problem, whats involved in replacing the sprocket? and whats it actually called? thanks!
 

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I believe you are referring to the speen sensor ring. You have to pull the center section out of the differential to replace it. It isn't all that tough. Just make sure you pay close attention to where each crush ring (I think that is the term) goes to that you get it all back exactly the same way.
 

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Two more possibilities.


2. The speedometer is controlled by the GEM, under the dash. Windshield leaks seem to happen in this area. When this happens, weird things can happen including erratic speedometer problems. Watch to see if rain has any effect on the speedometer.
Its not the GEM that is getting water on it, it is the fuse panel assembly. I had mine out to inspect both the GEM and the fuse box. The internals of the fuse box was all covered with green and blue corrosion. The GEM is fine. My speedo was going crazy to because of this, also the blower motor would be affect as well as the wipers and interior light.
 

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Discussion Starter #8
so you guys think its the ring? anyone know of a how-to on replacing it?
 
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