Will electrical problem affect transmission

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ruswin

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I will try to keep this short. I have a transmission that is about 90% functional, slow 1-2 shifts, been doing it for a while now. That's not the problem.
A few weeks back, my 94 M8 started downshifting on the highway from 4 to 3. I parked it for a while. In that time I installed a new radio. (Yeah new tunes) After installing the new head unit, I took it out for a ride and the trany was working fine again. I disconnected the battery terminals during the radio install and also was into the power distribution block So I attributed the trany problem to a bad electrical connection? (The battery terminals were a little dirty.) The car ran great for about 700 miles / 2 weeks before the downshifting started happening again. Is it possible that the battery, the alternator or something else in the electrical system affecting the trans like that? I had the battery tested, they said it was OK. I read 14.1 volts to the battery while the car is idling.
Is the trany just gone or what? I don't understand why it drove perfectly for 700 miles before the problem re-occurred. I still think it is electrical. I had installed a new MLPS sensor a few months back and it seemed to still be adjusted correctly. Could an intermittent short cause the 4-3 downshift? I really need to solve this before I drive my car 800 miles from home on a business trip. Any help is always appreciated. :)
 
Doing some more research, could the TSS transmission speed sensor or any other sensors trigger this problem?
 
I have recently tried a new MLPS, TSS and VSS.
The downshifting problem started only recently, long after the first MLPS was installed. I drove the car for about 1500 miles on a used trans that I installed, it seemed to be OK, but not perfect either.
I am on my second MLPS, I don't think it is the problem. Being so intermittent of a problem, I was hoping something electrical or sensor related was causing the problem. Now I am thinking the trans is just shot or failing little by little? Would anything else cause such an intermittent problem? When it is working fine, it will drive perfect @ 75 on the highway for miles, then out of the blue starts downshifting. If I take it out of OD, when it happens again, the OD light turns off as though it gets selected again.
 
Wouldn't be the O/D wires / switch acting up, by any chance?
 
I'd also check to make sure the wire for the OD button on the shifter isn't frayed.
 
I've got to piggy back on this. I'm new to the forum and have a related problem. My ODO button is NOGO. I'm told by the dealer it's due to broken wires INSIDE the shifter that can't be replaced outside the factory. The only fix I'm told is to replace the shifter. I'm finding plenty of shifters for 97s on ebay, but my Mark VIII is a 95. Bottom line question: Can I install a shifter from a 97 in my 95?
 
The wires inside the shifter CAN be replaced - dunno who told you that. On a gen 1, the 2 O/D wires are attached to a plastic rail with metal contacts which slots into a groove inside the shifter. The wires go out from the shifter, under the center console and terminate at a black 2 pin plug near rear of console.

Also, if you use a small screwdriver with care, you can just pry out the O/D switch.

Edit: Here's a pic of the contact rail with O/D wires I removed from my shifter:

contactrail.jpg


AND, here's a tech article:

http://www.lincolnvscadillac.com/tech/lincoln-mark-viii/overdrive-switch/index.htm
 
THANKYOU SO MUCH. I can't wait to get that button working again. The thing is geared s'darn HIGH, especially when the tranny gets warmed up. Thanks again! Hope you don't mind if I PM you later asking a couple more add questions about the project. Cheers!
 
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