Rear of car vibrates (Page 1/2)
cajunfiero JUN 07, 12:25 PM
Hi everyone!

I have a 85 coupe with a 4 cylinder 5 speed. I pulled the motor and installed a new clutch, pressure plate and throw out bearing. When I put the car together and took it for a test drive I noticed a pulsating vibration in the rear of the car when I get about 45 mph. While driving at that speed if I push in the clutch and hold it down the vibration goes away. I since replaced the transmission mounts and engine mounts but the problem still persist? After further testing the vibration seems to also go away when I give it more gas while in gear.
I didn't check tires or suspension but thought it may be because of the clutch I installed? I never drove the car prior to the clutch so I don't know if the problem was there before.
armos JUN 13, 05:53 PM
Did you use poly bushings?
Back when I installed a polyurethane top mount on a 4cyl automatic, I noticed a lot of vibration but it was mostly at idle. It settled down eventually.

edit: just noticed you had the vibration *before* replacing the bushings. Sorry, don't know what else to suggest.

[This message has been edited by armos (edited 06-13-2022).]

cajunfiero JUN 13, 06:12 PM
no worries. i was acutaly planning to look at the cradle bushings. there were rubber ones on the car that appeared fine but i wish i had changed them when i had the motor out. i am not sure if that would cause the vibrations but i am running out of ideas and quick

cajunfiero SEP 10, 11:54 AM
well unfortunately i still have the same problem. i just balanced all the tires, replaced both dive axels and checked the wheel bearings. all look good. i do have a worn bushings on the rear right lower control arm? do you think that would cause it? its more of a shaking than a vibration comming from the rear.
Patrick SEP 10, 04:23 PM

quote
Originally posted by cajunfiero:

...I noticed a pulsating vibration in the rear of the car when I get about 45 mph.



Is it a RPM or a MPH issue? In other words, if you go 45 MPH in a different gear, is the pulsating vibration still there... and/or is there vibration at any RPM when the transmission is out of gear?
cajunfiero SEP 10, 04:29 PM
it only appears at certain MPH ranges and in any gear. If i speed up and/or slow down or push in the clutch it goes away. seems like its tied to the wheel spinning under a load at a certain MPH. the steering wheel doesnt vibrate at all so that it why i am looking at the rear.
Spoon SEP 10, 07:07 PM
I'm grabbing at straws now but what are the odds of a slightly warped flywheel only noticeable when drive train is engaged?

Are all the flywheel bolts the same grade & size. No odd-balls... Same goes for pressure plate bolts.

Think of it like tire balancing.

Decades ago a co-worker of mine bought a new 1959 Pontiac that had a vibration from day one. Numerous trips back to the dealer until someone noticed that the driveshaft had been undercoated exactly 1/2 of it's circumference.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

theogre SEP 11, 09:54 AM
Don't assume whatever is really coming from rear.
While Often can feel front problems thru Steering wheel... is not always true.

F'ed bushings etc can effect 1 speed but most times all speeds or when you accelerate stop or both. Because just 1 bad bushing can effect wheel alignment when you drive even if passes on an alignment machine. Most "alignment shops" now don't look for suspension problems before doing an alignment.

Don't install polly on CA's.
See my Cave, Bushings and rest of section.


quote
Originally posted by Spoon:
Decades ago a co-worker of mine bought a new 1959 Pontiac that had a vibration from day one. Numerous trips back to the dealer until someone noticed that the driveshaft had been undercoated exactly 1/2 of it's circumference.

Ziebart and other undercoating services were famous for doing that. Also spayed that crap on P-brake cables and other parts making binding and worse problems. Ziebart is still around but like in 60-80's w/ Ads nearly everywhere. Ziebart and franchisees got sued a lot for bogus claims, never honer warranty and more problems.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

edfiero SEP 22, 12:09 PM
Put the rear of the car up on jack stands and run the car up to 45 or where ever you normally feel it.
Can you feel it NOW? That would isolate it to the rear, and perhaps with a helper you might even be able to determine if it is coming from one side of the car or the other.
Gall757 SEP 22, 06:05 PM

quote
Originally posted by cajunfiero:

seems like its tied to the wheel spinning under a load at a certain MPH.



Grab the axle and 'push-pull' near the transmission. If it moves more than an eighth of an inch or so the output bearings in the transmission are worn and the axle is vibrating under load and at speed. The good news is they don't fail quickly.....but it's not a cheap fix.