corvette90

hi all

my car discovered some rear vibrations on higher speeds, above 70mph
Vibration did not change with clutch in-out, speed up, speed down, trans in neutral or in gear..was only dependent from speed

balancing and rotating tires front to rear didnt change anything, finally i decide to change u-joints

...and i found this..(pic below)



my Question, can this type of wear cause this vibration? didnt have had a chance for a test drive yet, but your opinions would be very welcome

thank you

Midnight 85

Your pic is too small for my old eyes to be able to really tell but any time a u joint has the kind of wear ridges in it like that it means there is enough material worn away to cause excess clearance. It does not take much of an offset to cause a vibration, especially at the speeds you described.

ch@0s

What he said

corvette90

hi and sorry for the small pic, i tried several ways to make it bigger, dont know how to do

anyway, thank you for your statement, confirms my thoughts

Midnight 85

I got your pm but accidently deleted it. If the dark ridges on the u joint are grooves worn into the steel, it needs replacing. If it is just dark grease then you probably have another issue causing the vibes.

corvette90

Hi

the dark ridges are feelable with the fingernail, the other u joint has severe scuffing, there are some spots where the hardened surface is worn through, about .02" deep in the material...

greetings

Midnight 85

Yep, they're done for, you did not say if the pics were of the ones in the driveshaft or the halfshafts but if it were me, I would change all 6 of them. It's not that bad of a job but it is one you only want to do once every few years.

corvette90

was on highway today, vibrations started again, always at around 80mph and get worse with speeding up...

things done so far..

Rotated tires (front-rear)
Changed all 6 u-joints
driveshaft was balanced..
slip yoke is new
tailshaft bearing is new
tires were balanced..
shocks are new..

im getting out if ideas, next thing is to change the driveshaft to a custom made one..

my driveshaft have been professionally balanced, but i know, that it have a bit of runout, GM driveshafts are not famous for beeing very high grade...

im also run 3.73 gears which give me around 4000rpm on the driveshaft with 80mph..maybe thats simply too much for a stock drivehaft?

any other opinions out there?

thank you

DanielRicany

Did you lubricate the U joints before driving it?

Midnight 85

It's possible your driveshaft is not quite straight. I would take it to a machine shop & have them put it in a lathe & spin it up to see if it is true or not. Most good shops can straighten a bent shaft with great results. I seriously doubt the stock driveshaft is inadequate for your car. Even with the 3:73 gears, if you have to run it all the way to 80 mph to get the vibration I can guarantee you whatever it is, is small.
I would also raise the car & spin the wheels & watch for a very slight bit of runout from a bent rim. Just keep in mind, it is going to be slight so watch real close. Did you have the driveshaft balanced or was it a PO that had it done? If it was done before you owned the car then I would venture to say it was a problem the PO was trying to cure also.
Can you borrow another driveshaft from someone? If you can't find any runout on the shaft or the wheels then I guess a 4 wheel alignment would be a good idea but I'm not sure being out of alignment would cause a vibration.

corvette90

hi Midnight85 (and all others)

i had the driveshaft balanced, with balance sheet and everything...
will check for wheel runout also..

i doubt that misalignment will give vibrations, normally just bad driving manners...and the car was aligned , not too long ago..

anyways, i will kepp you updated...

gerardvg

I agree with Midnight 85
Wheel alignment is your next step, note have had reputable mechanics balance the wheels and encountered horrible vibrations went back and had them balanced again ...same. Tried another tire retailer and it was perfect not even the slightest vibration.

There are some places that can balance the wheels on the car..

Also check your rear suspension bushes, make sure there is no movement.

Warped disc rotors can give a vibration however that is usually felt thru the brake pedal when braking.

Good luck, nothing worse than a rattle or vibration

Midnight 85

[QUOTE=gerardvg; Wheel alignment is your next step, note have had reputable mechanics balance the wheels and encountered horrible vibrations went back and had them balanced again ...same. Tried another tire retailer and it was perfect not even the slightest vibration.[/QUOTE]

This is what you must keep in mind, just because work was done, does not mean it was done right. Good luck.

Rob31

I would check all the wheel bearings . Get it off the ground , grab a wheel at 10 & 5 and see if it has some play .
Any chance it in the front ? ball joints

Midnight 85

Just had a thought, have you checked the c-beam bolts to be sure they are tight?

Ziggy91

I just replaced the u-joints in my rear because I've had the same problem as the OP. Vibration at +70mph and hard accleration. I had the same ridges/marks in the joints aswell and found that one of my dogbone nuts wasn't secured all the way down, causing the poly bushing stick out enough to rub on my rear shock. Definitely solved something there, but where are the c-beam bolts and what else should I look at to tighten? I still have my 85's rear end on stands so this is a perfect time to check everything.

Midnight 85

There are two vertical bolts through the center section and the C beam at the differential and the same through the tailshaft of the trans. Maybe someone has some pics of them they can post.

Midnight 85

The two holes you can see just behind the driveshaft yoke is the location of the c beam bolts, there are loose nuts on top so you will have to put a wrench up there to hold the nut while tightening. Once you find these you will know what to look for on the trans.


[IMG][/IMG]

Ziggy91

/\ Thanks for the visual, Midnight.

Ziggy91

Finished replacing the u-joints earlier. Filled them with marine grease and took it for a slow spin. Drove around town and back home without any vibration and very smooth driving... much better throttle response to the wheels. Also no vibration at +70mph. Still have a ping... need to look into this.