S_Johnson

Ok, so I've been chasing this problem for like, a year, and I'm absolutely at my wits end with this car.

It has a nasty vibration in the rear end, it fades in and out, and goes from barely noticeable (relatively speaking) to so bad the dash moves up and down, and the seats are vibrating back and forth! It's only at freeway speeds, from about 58MPH and up.

I have brand new Greg Weld Aluminum wheels, and mickey thompson radials in the back (15x10).

I just replaced the axles and bearings, and had the wheels balanced a couple of months ago, and neither had any effect.

I just finally took it into a auto shop. Who said that my axle's have "end play," and that ALL of my bushings are stiff and old, and so any vibration is transmitted to the frame, instead of being dampened.

But here's my question. I've had someone follow me on the freeway, and he said that it LOOKED wierd. He said it almost looked like my tires were jumping up and down, that he could actually SEE the vibration!

Would "end play" be causing that???? and if so, how do I adjust it?

Any thoughts? I'm about to shove the car off a cliff I'm so fed-up with this issue...

Thanks guys...

camaronewbie

If it did not so it until after the new wheels/rims, I'd blame those first.

8t2 z-chev

jack the rear end up so wheels are off the ground,
support the axle on stands,run car and observe the
wheels for any runout-sounds like they are not locating
properly on the hub and have runout.
A friend once had this exact problem with a '73 mustang
-he had to make little rings so the wheels would center
properly on the hubs;problem all fixed
It is common for 10 bolts to have some axle end play,
mine has some and has no vibration problems....

S_Johnson

What exactly do you mean by "runout?"

This car vibrated before with different wheels and tires I believe.

Also, these rims are the "unilug" type, they use centered washers for 5x4.75 lugs.

Thanks

red rock

iTrader: (2)

Have you checked the obvious first? Driveshaft, U-joints, Shocks, Broken bolts on rear suspension, bent axle hubs.

S_Johnson

The shocks are new-ish, I replaced them about a year and a half ago.

There are no broken bolts that I'm aware of,

The axles are new (to me anyways),

I haven't checked the driveshaft or u-joints, however,
The vibration seems to slow for the driveshaft though,

Thanks

matthufham

iTrader: (5)

dont think you're crazy, my friend said the same thing about my rear wheels hopping, and i have the same vibration on some new american racing wheels and a few sets of tires. happened on 2 rear ends, 2 sets on control arms, and 2 different driveshafts.i've replaced the tranny crossmember and the mount. i'm really lost

S_Johnson

No kiddding, I feel your pain man. Literally...

You can hold your hand up against the passenger seat headrest, and HEAR a rythmic slapping sound as the seat vibrates back and forth... the top of the seat moves like, 3/8 of an inch!


sigh...

JamesC

iTrader: (5)

Just throwing a brick in the dark: What kind of trans mount are you running? In some cars, a poly mount can induce incredible vibration.

JamesC

S_Johnson

everything else is stock to my knowledge, I stated pretty much all relevant stuff in the first post, Thanks for trying though...

jmd

iTrader: (4)

What is "I believe" ? Did you never run the car on different wheels and tyres? At this point, your best option is to trade wheels with a local person with an S10 or G-body or F-body and drive the car.

Based on the other driver seeing the car vibrate, it is extremely likely that the wheel / tyre assemblies are the problem.

This. But also, tyres can be potentially out-of-round as well. Goodyears are horrible at this in my experience.

naf

iTrader: (7)

Don't feel like the Lone Ranger, ALL of these cars want to vibrate at 55-65 mph. Some things to check:

Same vibration with different wheels/tires on the back?

Drum rear? The drums may need to be balanced. Stick with aluminum if you can.

New bushings in the rear control arms and tranny may help dampen vibration back there. Combined with new motor mounts they may also restore original driveline alignment.

I've had good success with an aluminum driveshaft in my 85 TA but it only had slight vibration prior to installing the shaft. About the same level of vibration brought about by tires that are past due for rotation. If your vibration is in the rear end, past the shaft, don't expect much improvement.

My 87 transmits a fair amount of motor/driveline vibration to the body but I'm running poly motor/trans mounts and lakewood lcas in back with poly bushings. That vibration (more of a hum) will change pitch depending on load/rpm.

S_Johnson

Well, I ran the car with a different set of wheels and tires before, but they were bias-ply tires, that had noticeable flat spots, however, the vibration feels very similar to what I remember (9 months ago), so maybe the tires weren't the problem.

The problem, is that the vibration tends to come and go, one day it's REALLY bad, another, it's not bad AT ALL, so you never know if it's what you did, the road, or what.

I mean, maybe the bias ply's didn't have a problem, maybe it was only a "good" vibration day when I changed to my new radials...

It's nearly impossible to gather empirical evidence, because it ALREADY fluctuates hugely...

naf

iTrader: (7)

Vibration will often vary with temperature as bushings and soft parts (tires too) expand and contract. Road surface smoothness can vary as well throughout the day.

However if it's varying that much I'd take a little time to get under there with a impact wrench and loosen then re-tighten all of my big bolts-with the suspension loaded.

Is the vibration at all dependent upon track? turning/straight?

My TA will develop a slight vibe after a few thousand miles. Means it's time to rotate the tires.

S_Johnson

Ok, so, Here's my conclusion, I've driven it a lot the last couple of days, and I've been paying VERY close attention to the vibration.

It seems like a harmonics problem, the way it comes and goes does NOT seem like a tire/wheel problem.

The auto shop mentioned that my frame is bent+cracked up by the steering box mount, and that my whole frame flexes really bad.

He actually refered to the car as "a giant tuning fork..." I think I'm getting road vibrations transmitted to the frame because the old "stale" bushings, and I'm getting a harmonic vibration set up because of the way the frame/subframe flexes.

The only problem is, I can really deal with THAT until the front end is fixed... (got dinged up in a fender-bender...)

The whole nose is pushed over slightly to the drivers side, and NOTHING lines up right in the front. So I need to take it in, have the nose pushed back over, then that crack welded up.

And I think I need to have some SFC's, but my exhaust rides in the same place, so that will require some doing...

And then of course, the bushings... and maybe an aluminum ls1 driveline.

Any thoughts?

naf

iTrader: (7)

Get the crack fixed and pick up a wonderbar for the front end.

New Moog (rubber) front control arm bushings in my TA helped a bit, but that's probably because they're transmitting less tire/road surface issues to the chassis.

S_Johnson

Ok, here's the skinny.

I had all the wheels balanced at a shop here, and they said the fronts were out about 1.5 ounces, and the rears were 4.5 out, and 2.5 out, each.

He mentioned however, that the tires had alot of "runout." I don't get it, I mean, the tires AND wheels are basically brand new! argh...

Anyways, I'll check this evening to see if the vibration is still there/better/worse, and go from there.

But what do you do about "excessive runout" exactly? he said the only way to check for a bent rim is to take the tires off, and check the rim alone on the balancer, but I didn't have the time/money to have him do it then... They were EXPENSIVE...

Oh, and they replaced the lower ball-joint on the drivers side as well, they said it was bad.

naf

iTrader: (7)

Most tires have some run-out. Very few are close to perfectly round. When they put it on the balancer they can see how much it's out of round as it spins. "Excessive" is probably a judgment call. What brand of tires?

Rotation and balance runs around $50 here. They usually knock the weights off before they put it on the balancer though. Were the weights they gave you for the tire free of the previous weights? Not excessive either way.

S_Johnson

My rears HAD no weights no them, they had spun off, I checked before I took them in.

Also, although it appears to have helped (the vibration doesn't seem to get as bad), this didn't solve the problem, it still has the same vibration, it just doesn't get as extreme.

The tires are Mickey Thompson Sportsman S/R Radials, 26x12R15LT's to be exact.

The wheels are Welds' I think DragLites, but I'm not sure, I don't remember, they are 15x10, with 5.5" backspacing, and unilug, for 5x5.5/5x5.75 lug patterns...


The runout MUST be the problem, as I can't find anything ELSE wrong, and he said it WAS enough to be causing vibration.

I guess I need a thirdgen owner here in the triad to come over and go for a ride with me with THEIR tires+wheels

Any volunteers? I have new 4th gen leather seats, very comfy...

knight123

iTrader: (4)

Wow - have the exact issue going on with mine. Right at 65mph the car will start to vibrate and depending on the day / time it will be worse or better. Since it keeps changing it hard to pin down if anything is making it better.

I had the rear tires balanced a few times, replaced the u joints and made sure everything was tight.

Yesterday I ran the car on jack stands to 80mph - the car was smooth until 80 and then started to shake. I leaned out the river door and watched the drivers rear tire and it seemed to rotate smooth but when the vibration started that tire started to shake / wobble, not bounce type movement but side to side like it was a bent axle but only at that speed. looking at the tire end on you would think it was a orbital sander it moved so much.

now I could not see the passenger tire and the rear has a lot of play between the pinion and the tire - I can rotate a tire about 3 inches in it's arc before the pion starts to turn, had the cover off and all looks ok without taking stuff apart. This is a 10 bolt auburn posi axle with 135k on it as far as I can tell.

This is the first time I got the car on the road since I owned it so I don't know if this was there before etc it was sitting for 2 years before I got it and not running (ebay junker rescued!)

So I plan to replace the rear with a disk unit or the one from my parts car and see if that helps. Everyone who looked at the car local (garages) said it was the driveshaft - I have the aluminum shaft and I might believe them if it was not smooth on the stands, would have thought it would vibrate either on the floor or on the stands. Don't know if this helps you but your not alone.

squatingeagle

knight 123 most likely it the rear wheel bearing. that gm service manual says vibration in the axle is caused by a rough rear wheel bearing