Elusive vibration starting 55 and continuing to highway speeds

[spyro235]

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?

[ard]

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

[spyro235]

Originally Posted by ard

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

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.

[RDAvena]

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".

[ard]

Originally Posted by RDAvena

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.

[SlickGT1]

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.

[spyro235]

Originally Posted by SlickGT1

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!

[spyro235]

Originally Posted by spyro235

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 swapped the tension struts. Car feels more stable under braking which is nice but didn’t effect the problem at all.

[spyro235]

Originally Posted by SlickGT1

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.

Wait, axles shouldn’t move linearly to their direction? I haven’t checked the fronts, my bad, but both rears slide back and forth about an inch in the hub-diff direction.

[SPL15]

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)...