W108 front end vibration - PeachParts Mercedes-Benz Forum

R72benz · #1 03-28-2022, 08:05 PM

For a few months now I have been trying to diagnose a front end vibration in my 1972 280 SE. Everything is fine up to 65 MPH then the steering wheel starts to vibrate. It gets worse as I continue to accelerate. This started after the subframe mounts were replaced. I have had the front end professionally aligned, the wheels balanced twice, and tires rotated. The vibration still persists.

Next steps?
Replace brake disks? Doing a parts search I find solid disk offered. My current disks are vented. Any idea which is correct?
New wheel bearings? I have the parts on hand, just procrastinating. Does this sound like a possible cause?

Any recommendations would be appreciated. I have learned much from this forum in the past.

rumb · #2 03-29-2022, 01:11 PM

Other things to look at:
tie rod ends and steering damper(shock)
king pins
motor mounts
trans mount
check the wheel bearings - use a dial indicator to set correctly to .1mm end play
..
My understanding is that a vibration at a certain speed is wheel related.

If it was brakes, that would only occur while braking.

R72benz · #3 03-29-2022, 10:10 PM

Thanks for the list rumb, I will check these items as you suggest. The steering damper has been changed. This all started with a broken support strut that sits next to the steering damper, so I replaced it along with the support strut. The only reason I mentioned brake disks is that a coworker of mine had a similar problem and it was a disk. I will only replace them as a last resort. They were replaced not that long ago by the previous owner.
Thanks again.

cth350 · #4 03-29-2022, 10:18 PM

If the wobble changes with a very slight application of the brakes, then I'd wonder about the rotors, but otherwise, I'd wonder if it's actually RPM related instead of road speed related.

What happens if you shift down a gear while at a low speed and then accelerate?
-CTH

R72benz · #5 03-30-2022, 07:23 PM

That’s a great suggestion CTH, that would tell me if it was motor mounts or transmission mount. I did check the outer wheel bearings awhile ago and they looked fine. If this test eliminates the mounts, I will go after the tie rod ends next. I would hope the person who did the front end alignment would have found any issues with the king pins, but I am not that knowledgeable regarding those parts.

twinockchef · #6 04-03-2022, 11:41 AM

Replace every piece of rubber. No matter what they look like. Fifty year old rubber will be useless. Start with the torsion bar, engine and transmission. When changing the transmission mount also replace the flex disk. Replacing this rubber should eliminate the vibration.
Then take a serious look at the kingpins and the upper and lower control arms (there could be some serious wear that should be addressed). Have the alignment shop test the condition of the king pins. The control arm wear will be difficult to detect because of the tensison from the main springs. Check the grease nipples and the rubber seals on the pivot points.
The rubber mounts on the front springs will also be hard and inflexible and should also be replaced.
I had a catastrophic front end suspension failure a few years back. I completely rebuilt everything and it blew me away how well the car handled when I was done.
Good Luck

Tony H · #7 04-03-2022, 02:14 PM

When you mention having the alignment checked did the shop follow the process of loosening the driveshaft sliding joint when they set the castor, settling in the driveline and then tightening the sliding joint? Changing castor moves the engine fore/aft putting pressure on the flex disc and driveline. I'm sure no one does it but it might matter.

R72benz · #8 04-05-2022, 06:46 PM

Thank you for the suggestions. I did try running it at the same rpm in second gear as suggested by CTH. No joy, the ride was smooth and steady at the same rpm as going above 65 in third gear. I have no idea if the alignment shop loosened the driveshaft, I will ask but I doubt it. It was the only shop in our town that would touch it. I was lucky to find them.

Looking through the repair records from the PO, he had a significant amount of work done to the front suspension including a control arm replacement. Most of the rubber has been replaced and the flex disk looks good. Will do a check of tie rod ends and have the alignment shop check the kingpins. The vibration is not severe and only starts above 65 mph. Although it tells me something is amiss, 65mph is fast enough for me with my hobby car. If I need to go faster I will drive my Lexus.

Thanks again for the replies. If I find anything I will post again.

TZ_280SEL · #9 04-13-2022, 07:59 PM

When you say the “broken strut support” are you talking about the strut rod from the subframe to the right frame? That would lead me to believe alignment. That strut is supposed to be loosened I believe when the alignment is done. Caster is set in two ways on this car. Loosen this strut, the driveshaft slip joint, and the bolts on the sway bar. Two of those are eccentric IIRC and will slide the bottom of the subframe front to back. This sets gross caster. It is then fine tuned with the threaded insert at the top of the kingpin. If the strut is too tight, I could see it causing the subframe to do some strange things…especially at speed.

It is almost impossible to find a shop that can align these front ends. It is a lost art.

R72benz · #10 04-16-2022, 10:33 PM

Thanks TZ. Impossible is more the case in our community. I have called a number of alignment shops here and they won’t touch it. They did refer me to the one shop that works on vintage cars. I have no idea if they followed all the steps you listed. I am expanding my search for an alignment shops in surrounding cities.