Elusive vibration starting 55 and continuing to highway speeds
 

Hey guys! I've got a driveline vibration that I'm really getting annoyed with. I thought it was the wheels/ old tires that came on the car, but then I switched to the summer 19's I got for the vehicle and what do you know, the vibration remains COMPLETELY the same.
If it makes any difference, I've got a base model 35D with NON air/SLS suspension in the rear.

A few things about this vibration:

1) It seems to lessen with more throttle, but when I let off at highway speeds, I believe it gets a bit worse. I will double check today on the way home.

2) I know it's not my wheels and tires. It's been the same with 2 sets of wheels and tires, completely different sets at that. 18's, then 19's, first with Michelin latitude snows and next with continental DWS.

3) The vibration changes base on what's in the car. If I have a decent load in the trunk, like 200-400 lbs, the vibration is lessened to a decent extent.

4) While towing, which normally puts 500-600lbs on my hitch, the vibratino is still present with just as much "amplitude"(felt vibration shake) but with a different frequency. It'll be smooth for about a second, then vibrate 3 time within a second, and oscillate like that.

My thoughts kind of lead me to a center support bearing, mostly because I'm not quite sure what the heck else it could be. It's clearly something that's rotating, and the slight change while in compression in the CV joints from a load/ squatting with the trailer makes sense to my engineer/track car mechanic mind. The vibration vibrated my passenger seat visibly, the back of the seat moving probably an inch front to back with vibration. I also commute 100 miles a day, 80% of which is on the highway, and I'd love to get this beast into smooth sailing mode. Any suggestions?

does light braking trigger (at 55) it or make it worse?

It’s your axle CV joints. Time get new/rebuilt front axles. You can double check by grabbing the shaft between the two boots, and wiggling it in every direction. Especially side to side. Any movement or even a clanking noise, yup axles. Just hunted same problem a few months back.

I'll definitely jack it up and check the axles, but I'd be very surprised if it was them. The only thing that DOESN'T vibrate is the steering wheel!

I will check, but I'm fairly certain that braking doesn't change it at all, other than it going away with the lowering speed. At 55 is is VERY light, almost unnoticeable. 70-75 seems to be the sweet spot for it, which is where I spend all my time for the mpg's.

on older BMW models speed specific shimmy tends to be the control arm bushings going out. Give your control arms a once over "while you are there".

This was why I asked. Light braking will load the tension strut (aka llower control arm) and exacerbate the shimmy


OP, if you have never replaced these and you are over 100k, should be a no-brainer. $90 for Lemforder part. ton of DIYs.

If it's more noticeable while making sweeping turns on the highway, braking, or transient events that load / unload the front suspension, I'd also guess front torsion arms, and / or balljoints on the front control arms.

If it's when driving straight, comes & goes at certain speeds, changes with throttle input, changes with rear height / load in the trunk, then I'd put more money on U joints on the rear drive shaft (which can also damage the CSB & Guibo if left to where the car becomes undriveable)...

Car has 220k and likely that the tension struts need doing regardless....

The shimmy definitely gets a bit worse on lift, with the weight shift forwards I guess. It kind of comes and goes all the time, some drives i'll be pretty smooth and some drives it'll be a vibrating mess. When on heavy throttle, it does pretty reliably go away though. Turns don't seem to affect it whatsoever. Especially not making it worse.

There doesn't seem to be any weird wear on the front tires though, so it does come as a little odd to me. I need to do my front springs/ shocks anyway, because they're chattering recently over hard bumps. Maybe I'll pop new tension struts in there when I'm there anyway sometime this summer.

I'll get under the car before that, and give all 4 axles some good wiggling and see if anything moves at all. Maybe I'll Bend some heat shielding out of the way and check how the rear driveshaft and CSB looks. I can't see the joint with the heat shielding in the way. I've never seen a bad U joint but I'd imagine it would have a bit of noticeable play in it, right? The CSB would be obviously cracked/ shot rubber,

If the U joint on the driveshaft is bad, is a new driveshaft the fix? Or can they be rebuilt?

Bet you an e-beer its the tension strut bushing. AT 220k I would do the whole arm, not just the bushing.


I'll bet the silicone filling on yours ruptured 100k ago...