in my 1990 GXL,

the car vibrates a little whenever I go faster than 100MPH, but only if I'm in 5th gear (overdrive). I can go the same speed (or faster) in 4th gear without getting any vibration.

why does only 5th gear vibrate? is this normal for all transmission? normal for old transmissions?

thanks

 

Are you saying the shift lever is buzzing?
There are two issues with shift lever buzzing.
The first is the bushings.
The second is ths the spring over the selector rod pocket.

Try adding just enough shim under the lower pivot ball bushing to take out the slack without stiffening the action.

Also the selector rod pocket bushing could be bad or missing.

 

no, it's not the shift lever itself, it's the whole car (I can feel it through the seat, steering wheel, pedals [mostly the seat] )... but only if I'm in 5th gear.

thanks for that diagram though! it could come in handy soon.

 

i have that problem to and im not sure what it is either

 

nice diagram

 

One possibility is the U-joints.
As a U-joint starts to fail, it first looses it's grease, then the needle bearings start to wear and make slack & excess clearance. The extra wear allows the shaft to wobble off center giving the vibration.
The vibration can vary with speed, or with the random position of the joint as you apply power.
Then the needles start to rub & bind on each other.
As they bind & pop free from binding, you can hear a "tink" sound that rings the tubular shaft.
This can usually be heard just as you start moving.

Here is a shot of a bad U-joint next to the used shaft I got to replace it.