'94 Camry V6 transmission vibration

My 94 Camry XLE with V6 automatic exhibits a drivetrain vibration upon braking in Drive around 20mph and 750rpm. No vibration at idle or acceleration or any other operating condition.
Since it happened right after new tires, I went back to the tire shop. They blamed worn CV joints and replaced both half shafts. Problem persisted and they were stumped. They said they replaced the front rotors and pads. My brake shop verified no brake problem and suspected motor mounts. Another independent shop found no mount damage and suspected transmission. I had also had a tranny shop do a fluid change, but they could not diagnose.
Brake shop noticed that there is no vibration if I brake in neutral. So I now have the habit of shifting to neutral just before reaching low speed and rpm, and so avoid the problem altogether.
Any ideas? I am going back to the tranny shop for more extensive testing, with the suspicion that downshifting is not occuring at the right speed and engine rpm is too low???
Razi

I had the same problem with my 94 camry too but only happens for like 3 sec. and then goes to normal. Another problem that happend at the same time is when i touch the break pedal the reverse (R) light comes on in the dash and i have a rear light warning on. All the lights work except that the taillights go off and then brake lights go on. Even though this all happend at the same time i still think they are not related...but not sure because it was the weirdest thing thats ever happend to me. ANY ideas let me know! Thanks

I'd take it back to the tire shop and have them rotated front to back...presuming you have all four new tires that are the same type and size. If after rotating the problem persists then the tires are not to blame. But if the symptoms change...reduced vibration or now the vibration seems to come from the rear, then you probably have a defective or improperly mounted tire.

Tires are usually marked with a small dot to indicate the "light" side which should be aligned with the wheel's valve stem (the wheel's "heavy" point), in hopes of minimizing balance issues of the tire-wheel combo. Many tire shops just slap them on and then rely on weights to balance it out. Let us know how it goes.

MYSTERY SOLVED!

cmanderyota, do not delete your post on this thread, because you were right on. I was having that same symptom of the reverse indicator coming on when I touched the brake pedal, but I had dismissed it as an unrelated problem.

I went back to the tranny shop today and they fixed both problems, in fact it was one problem, that a wire harness in the trunk was damaged and a particular wire was grounding out or something. This was causing the torque converter to be on when the brake was on, and I guess not allowing trannny to downshift. The vibration was just like a lugging an engine in a manual shift when you dont downshift when slowing down.

I dont know if this is a common Toyota problem with wiring, but it is weird and could not be diagnosed by my tire shop, brake shop, and even the tranny shop the first time, until my independent repair shop pointed me back to them.

Thanks all for your comments.
Razi

This is the strangest issue I have ever read in this forum! :) You win! It's also amazing cmanderyota had an identical problem. I can't understand how a short in the trunk could lead to this sort of issue. That is bizzare.

dave mc

Razi, so i was wondering how much did this cost you and what part it might be exactly...your post was so helpfull and a real piece of mind for me. I thought it was really something majorly wrong with my car!!! Thank you. I just can't afford another car right now.