maxvol

iTrader: (2)

For starters:
the car is an 82 with an FC subframe swap. Rack and pinion, 13BT with a Knightsport turbo pushing about 14 PSI.(plus supporting mods... Blha Blha)

My issue is the horrid vibration I get from the rear end of the car when I go anywhere past 4,500 5,000 RPM, just when the engine is starting to make some power.

Ive talked to a few people around my area, and we came up with a dogtracking hypothesis (Twisting and off center movement of the rear diff). I looked at the 4 link bushings and they seem rather soft (like jelly), which supports my initial thought.
This is where I run into more variables, could it be the fault of the Watts linkage?(as its job is to keep the diff centered?)

I have ordered the 4 link Poly bushing kit, should I order the Watts link kit?

I have never ran into this problem before, as I never pushed such high HP numbers... The car drives like a dream, I can boost in all gears and if I baby it I dont get the vibration.

I dont have bin rot, so thats out...

If anyone has any more suggestions and/or Ideas, please chime in...

81WideMariah

iTrader: (8)

Sounds like pinion bearings to me.... has the diff/rear been rebuilt yet?

maxvol

iTrader: (2)

The diff is strong, I can launch it and spin my 265 with no issues. I can cruise and its quiet and the LSD works great, I flushed it and got nothing but clear oil from it..
But no the diff has not been rebuilt yet, did not see a need for it..

The vibration can be felt in my seat, as shaking (maybe vibration was the wrong word to use).. It is not speed dependent but rather starts when I put the power down.. I can drive the car at highway speeds and have no issues

mikexj1020

What about driveshaft u-joints? Is there any play in the shaft?

Just a thought.

-Mike

t_g_farrell

iTrader: (1)

What about your clutch?

Could be slipping. If your in 4th gear on the highway and floor it does it do this as well?

maxvol

iTrader: (2)

Just changed the 4 link bushings and found some of my problem. The upper passenger link bushing was fused with the bolt and insert. Then I noticed that one of the arms had a slight bend compared with the other, changed it with another I had laying around.
The car drives much better!!, but still have some shaking from the rear above 6,000RPM.
My course of action now is to change at least the body side bushings of the watts linkage (As the all famous argument begins about changing them all...) And I ordered new shocks...

"What about your clutch?

Could be slipping. If your in 4th gear on the highway and floor it does it do this as well?"

I tried... its not as bad in 4th and 5th.. but I now believe that the rear suspension geometry is off.. due to 29 year old bushings...

BeenJaminJames

Replace those bushings...ALL of them. A slipping clutch should not cause the low frequency vibrations you speak of, nor should a bent control arm, although if anything is bent it will worsen the effects of any play present in your bushings. Jack up your differential, grab a large prybar, and push/pull/twist/etc. each bushing in every direction. A good bushing wont go anywhere, a bad one will move a little with some firm (not rough) coaxing from a prybar.