Annoying Vibration....

[Ala75Vette]

I'll try to keep this as short as possible. I have what I suspect to be a drive train vibration, possibly from the drive shaft/u-joints, or possibly from the transmission. I suppose it could also be from the engine, but I'm doubtful that's the case.

I recently got rid of a lot of my vehicle vibration by tightening up the exhaust. Amazing how big a difference that made. I had the wheels balanced, still vibration. I checked the drive shaft u-joints per the Hanes (the long stretch of road, check for consistency of vibration at affected rpm in each gear, then do a 10-15 mph throttle/off throttle check for 'thumping'), and in this 'driving' test could not positively identify the u-joints as the culprit. Have not jacked the car up and visually checked u-joints/drive shaft yet, but will do that this weekend.

Had the harmonic balancer, timing chain & gears replaced recently. That also got rid of a bunch of vibration.

My (4-speed manual) transmission leaks, and is hard into 2nd and 4th when it's cold, but fine once it warms up.

The vibration isn't overwhelming, but enough to be annoying. I'm just afraid if I don't deal with it soon, it'll transition from the annoying phase to the $$$$$ phase. It occurs mainly at 1900-2000 rpm, but I have a real hard time telling if it only occurs with clutch/no clutch, only while I'm in 2nd or 4th, etc. I know that doesn't help much, but any ideas?

Thanks,
Frank

 

[DDLS3]

Ala75vette

Halfshaft U-joints are often the culprit. There is no really good way to tell short of removing the halfshafts and checking them. They could be dry, and stiff which is not at all apparent while the shafts are in place.

 

[MidShark]

;stupid
I totally agree. I couldn't see any movement on my driveshaft or halfshaftson my '81. But when I took them off, one on the driveshaft was stiff, and one on each halfshaft was thoroughly shot.

Dick

 

[Eric]

The other two are probably right but heres what stopped my vibration. You say you tightened the exhaust up but now for a question: Is the pipe running through the crossmember vibrating on the crossmember. One of mine was and I managed to get it to raise up off of the crossmember by adjusting the clamps and, viola, no more bad vibes.

Good Luck!

 

[Stallion]

The other two are probably right but heres what stopped my vibration. You say you tightened the exhaust up but now for a question: Is the pipe running through the crossmember vibrating on the crossmember. One of mine was and I managed to get it to raise up off of the crossmember by adjusting the clamps and, viola, no more bad vibes.

Good Luck!

Eric, how exactly does our exaust lay through the crossmember? I know it goes through it, but what does keep it from banging on it? Is there just a hanger for each extension maybe?

 

[69vettester]

If you dont know when anything has been replaced, heres the order of fix, from cheap to expensive!
1st..Ujoints..all of them.
2nd..Slip yoke.
3rd..Trans Bearings.
4th..Rear wheel bearings.
5th..engine crank not balanced well.

could also be drive shaft angle from rear of trans to carrier yoke.(see specs for driveshaft angle) this must be within tolerance or vibration occurs.

If you have the time, do the first two, not very expensive and is regular replacement, maintainence for a vette power train, especially the U-joints.

Hope this helps..
Tom

 

[Ala75Vette]

Thanks, Tom. I'm in the process of replacing the drive shaft u-joints, and while I'm at it, the trans output seal (it leaks). Should have it done by the end of the week. I had 3 out of 4 half-shaft u-joints replaced, along with rear bearings, both sides, a couple of months ago. The angle of the drive shaft to carrier yoke.... hmmm, didn't know that could be a problem, but actually, that may explain some of it. I also recently replaced L/F motor mount, and transmission mount, and the new tranny mount was a lot 'thicker' than the old one (by about a 1/4-1/2 inch). I thought at the time it was because the old one was compacted/bad, but maybe the new one has too much lift. In any case, once I finally get things all put back together & get the chance to test drive it, I'll update this post. Thanks for all the great advice!

Frank

 

[Bob Chadwick]

Eric, how exactly does our exaust lay through the crossmember? I know it goes through it, but what does keep it from banging on it? Is there just a hanger for each extension maybe?

Proper adjustment of the various angles and clamps on the exhaust pipe will move it away from the crossmember cutout.

 

[shivelresk]

You may want to check the the rubber hanger muffler mounts in the back of the car. I have a vibration on my car which I believe is from where one muffler is pushing the rubber portion of one of the hangers against the rear bumper cross support beam that goes across right by them. I've adjusted the muffer as much as I can but I think that I'll actually have trim a little down from the area where it connects to the rear exhaust. I don't experience the vibration on mine all the time, but when I do it's mainly when I'm going slower, especially like toward the end of an off ramp, following highway driving, and other faster to slowed driving. Hope this might help.

 

[Eric]

Eric, how exactly does our exaust lay through the crossmember? I know it goes through it, but what does keep it from banging on it? Is there just a hanger for each extension maybe?

See Bob's response above. It took some tweaking but a few twists here and there at the clamps and it moved where it needed to be.

Thanks Bob!

- Eric

 

[twald1957]

Two things to check. I dumped about two grand in my 1979 vette trying to get rid of a vibration problem (see my "Bad Vibrations" post.
First thing to check for are your rear wheel bearings clearance.
Jack up the rear end and support with jack stands. Grasp the tire with your left hand on the outer top to push, and your right hand on the inner bottom to pull and rock back and forth to check for
any noticable play.
Don't "Push" too hard for the half shaft yokes will have some noticable travel which is normal.
Secondly, if the trailing arm bushings have not been changed in some time, they could be the culprit as was my case along with an out of tolerance rear wheel bearing.
If and when you decide to replace the bushings I only reccomend using the polyurethane ones from vette brakes.
Afterwards take your car and have a complete front and rear alignment.
NTB did a great job on mine.
Good Luck!
T.G.

 

[JohnZ]

If the vibration is worse under even moderate acceleration, take a look at the rubber cushions where the diff nose bracket bolts to the frame crossmember; if the bolt loosens up or the cushions deteriorate (which loosens the attachment), the nose of the diff moves up under acceleration, changing the operating angle of the rear prop shaft U-joint, and in some cases the U-joint can even contact the underbody. This is a chronic issue with older C2/C3's, and seldom gets any attention. If necessary, replace the cushions with OEM parts - the urethane replacements are the wrong size, wrong thickness, have the wrong size washers and inserts, and are junk.

You'll get a better reading on the condition of your rear wheel bearings if you do the check with your hands at 3 and 9 o'clock instead of 12 and 6; if you do it at 12 and 6, you'll get additional compliance (movement) due to play in the camber strut bushings, half-shaft U-joints, and twist compliance from the trailing arm front bushing. With your hands at 3 and 9, there will be no compliance from other components (unless the trailing arm front bushings are loose or shims are missing) to confuse the check.

 

[Ala75Vette]

OK, here's a post u-joint replacement update. Finally got the two u-joints replaced, plus the trans output seal + refill trans with gear oil (that stuff smells bad, by the way, and when you dose yourself with it, quite the gearhead aroma to attract new friends). Replacing the u-joints got rid of some more of the vibration, but not really much.... still have that nasty vibration at 2000-2100 rpm/50 mph. I have to think it's something to do with the transmission, so I'm contemplating new bearings/seals for it in the not-too-distant future. Checked out my diff nose bracket cushions, and they don't seem too bad. So, I feel good knowing I've got new u-joints just about everywhere, but don't feel content that I've eliminated my vibrations, since I have not. Still can't completely rule out the exhaust, but when I (finally) install my sidepipes that'll rule that out, hopefully. Hmmmmph. As always, thanks for all the great advice, and I'll keep the forum posted as I sort things out further.

Frank

 

[SwaveDave]

Also check your exhaust where it goes thru the center crossover ; if it is touching the frame...it will vibrate at various rpms.