Occasional vibration, felt and heard, lasting only 1 or 2 seconds and only when

JNRTOWNCAR

MEMBER
2003 LINCOLN TOWN CAR
4.6L
V8
RWD
AUTOMATIC
112,000 MILES

I replaced the entire rearend at 104k miles, after that it made whirring sound only on decelleration at freeway speeds, I was told that was the sound of new/tight gears and it would go away after I drove a few thousand miles. It did not go away so, I took it back at approximately 110k miles and he made some kind of adjustment to the "shim" in the rearend and no more whirring on decelleration. All smooth and quiet now but, there is an occasional, brief vibration(felt and heard)only after the transmission is in overdrive and has shifted thru all 4 gears strongly and smoothly. It does not make this sound all the time, just occasionally but, it seems to happen more frequently now. The rearend mechanic inspected the entire car, found a torn lower control arm bushing and said that could cause the vibration so he replaced that another 450.00 on top of the 2100.00 for the rear end but, that did not stop these occasional vibrations at freeway sppeds. So now he tells me it must be the overdrive gear in the transmission going out and says I should take it to a transmission specialty shop for a diagnosis. Please help! Thank you john

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

Your description matches a shudder caused by the lock-up torque converter. To identify that, hold the accelerator pedal perfectly steady at highway speed, then tap the brake pedal with your left foot. You'll hear the engine speed increase by 200 rpm, the go back down a couple of seconds later. If you feel that shudder when engine speed goes back down, it's the torque converter locking up.