NEPaNogaro

Hello. I have been working for the last 4 weeks in an attempt to get ride of a chassis vibration. It occurs at 70-75 MPH and feels exactly like a bent or out of balance rear wheel, and can be felt alittle in the steering wheel).

Today we determined that the back right (which also has a little thunk (not clink) at low speeds over small bumps) is sitting 7mm lower than the back left. Both fronts are within 1mm.

Can someone with an MTM suspension and stock wheels measure from the center of the rear fender to the RIM and let me know what you get on all 4 corners.

For those of you that like a good challange, here are details, any help is appreciated:
We had all 4 wheels trued by the Wheel Collision center, they were almost dead on, now they are. We replaced the tires with new S03's. (It did it before and after the wheel fix and tire replacement).

Skeptical, we borrowed someones new aftermarket RONAL wheels on a stock suspension S4 (unfortunately old tires, but the car rides smooth) and placed them on the wobbly S4, wobble still exists. Now, it could be that one ov my wheels is alittle out of true and his tires maybe out, and you can't feel it on the stock suspension, but I doubt it. Oh yeah, I used a dial indicator and checked the wheels and hubs for runout. Hubs are all within .0001 and wheels have a few high spots of .0010, but that's it. Pretty good.

Checked all front bushings and re-set them with the car at ride height. Checking/taking apart rear bushings tomorrow, although they all look good (and feel good with a crowbar). Maybe that back right is torn, if the car was not set with the MTM was put on, not sure. Either way, doubt it would generate a vibration in the steering wheel.

While working on it, found the diff is making a squeeking noise, so looks like that's another project for another day, either way, the input shaft doesn't have an unusual amount of play in it.

Pulled apart a rear inner CV joint, lots of good grease, probably not that. Car has 60,000 miles on it, and the vibration is independant of accel/deaccel and still happens in neutral/clutch in (so it's not engine vibration). It's a slight vibration, only a good driver, or after it's pointed out to you can you notice it. It's at wheelspeed. It seems to be slightly worse when you are slightly weighing the suspension (turning at speed), maybe alittle worse around left than right turns in the steering wheel. Looking at the passenger seat headrest on smooth road at 71, you see about 1/2 to 3/4 inch of movement/vibration. Does anyone else have this with the MTM suspension? It seems to have started when the suspension was installed, maybe it just got worse.

Front right half-shaft has alittle wobble in it up and down (maybe 3.5mm), left has around 2mm wobble, rears arouns 1.5mm. (This is up on the lift, suspension extended, speed 40 MPH, center to near wheel on half-shaft you can see it wobble. I think this is normal, not sure, can't see all 4 being hosed, but the front right is definitely worse.

Someone has to have some comment or suggestion. Maybe the drive axle is not lined up (diff or tranny was never removed), maybe bad CV joint (not likely, they usually change with accel/deaccel), maybe still a wheel/tire, maybe bushings - HELP!??

This is exactly what I expected to happen to a VW/Audi when it hit 60k, lots of annoying, but not show-stopping issues. What a PITA.

Thanks in advance, if your suggestion fixes it, you have drinks and dinner on me (PA/NJ/NY).

smallTTs

hub bearing, or possibley bent hub flange. Why?

Vibration is at 70-75 mph which is where 1/rev wheel harmonics occur, but you've eliminated tires/wheels as primary cause. They still are the exciters, however.

You feel it in steering wheel which would be unusual for rear vibration.

Hub bearing would not be very sensitive to drive torque, so it would always be there.

Left turns load right side more.

My $.02

NEPaNogaro

We replaced the right front HUB and bearing a few weeks ago, no difference. Wacked a huge pot hole a year ago, thought maybe it bent the hub/bearing.

NOW - maybe the knuckle is bent and the bearing is not pressing in "round", but doubtful. Maybe the tech installed the bearing bad. Maybe, doubtful.

Thanks again. I'm still skeptical of some bearing/hub.

Tbandido

I had a car that a weird vibration at ~50mph, could not be identified, multiple balances, etc. It was a rear-wheel drive. I had them check wheels and tires for "load" or "force" variation/not sure exactly what is was called, but very few shops had the machine. Then they did an on car spin balance. The difference was AMAZING, felt like different car. There was NO vibration when they were done. Good luck

smallTTs

be tweaked or the outer cv joint bad. If you didn't replace that...that would be my next step.

I agree with your "doubtfuls".

Keep us all informed.

NEPaNogaro

Thanks again, I'm not stopping till this gets fixed. Will keep everyone informed.

4kq

Great analysis, would also go for on-car balance.

smallTTs

truing or shaving the tread. A shop that can measure this is rare and they quite possibly shaved your tires as well as on-car balanced them.

FWIW, think of a tire as lots of little springs connecting the tread to the wheel. Because of variations in the construction of the tire, these springs are not all exactly the same rate. As the tire rolls with a constant load on it, that variation in the spring rate of the little springs causes the wheel to move up and down some amount. If it's under .005, you probably don't feel much, if it's .030 you should. If a tire has a 1000 lb/inch spring rate (not the suspension, just the tire), .030 deflection is a 30 pound change, or in effect, a 30 lb force acting vertically on the hub once per rev of the tire.

If you were to shave off some of the tread on the area where the tire spring rate is highest, the tire, while not exactly round in it's free state, would roll more evenly under load. Conversely, the non-uniform tire may wear the tread unevenly and appear to get worst with miles.

My $.02

Kevin K2

use spring compressor to unload springs, and check for too much free play in the shocks at the ride height position. Very little excition is needed for a large magnitude response near the unsprung system resonate speed, w/o damping. If koni shocks, they do have some initial displacement softness to them, mabe too much at a rear corner.

verify springs were installed correctly, and spring seats, if any, are in consistent shape. Sway bars should not be highly loaded with car static on flat surface.

rAudiman

I'll watch your progress on this one too -- I have a similar problem that I have been blaming (in my own mind) on a possible inferior balance job on my Tubolare's. Thanks.