Perplexing steering problem on my R129 98 SL500

[alabbasi]

All, maybe you can help me with my problem. I've owned my 98 SL500 for about 12 years but in the last couple of years, I've barely driven it because i have a very harsh steering vibration. I rebuilt the suspension not too many miles ago and used quality parts. It has 18" AMG mono blocks on it and even though it's had 3 different sets, the problem persists. I but the car on the lift and everything is tight. Ball joints, bushings, transmission mount is good, flex discs are good. I'm at my wits end. The shake is so bad that I hate driving the car now.

I may switch back to the original 16" wheels as a last resort.

 

[195910]

Wheels if balanced properly and with good tires would not cause this issue. You already tried 3 different sets.
Check the driveshaft center bearing.

 

[emerydc8]

Did the suspension rebuild include a new steering damper? Assuming the SL500 has one.

 

[R129 UK]

Is it affected by vehicle or engine speed?

Have you knocked it into Neutral to see if anything changes?

 

[gsxr]

I'm not yet convinced it isn't wheels/tires. Take a set of front wheels from another car that has ZERO vibration. Install them on the R129, see if the problem changes or goes away. If the shake remains and is the same intensity, you've eliminated wheels/tires as the problem. If the shakes goes away (or is significantly reduced), get those wheels/tires Road Forced to single digits per Jlaa's excellent writeup. You may also have a bent wheel (need to check via dial gauge, not eyeballs).

Assuming it's not wheels / tires: Check the steering damper that Jon mentioned above, along with shifting in to neutral for grins as R129UK noted. Next up - check the toe setting. If the toe is way out of spec, this can cause hellacious front wheel vibration... don't ask how I know. Also wouldn't hurt to look at the driveshaft center bearing, but those vibes shouldn't make the steering wheel shake.

 

[alabbasi]

@gsxr - Initially I thought the wheels were bent so I took the set of my 00 E55 and put them. I still had the vibration on my R129 and the E55 behaved flawlessly. The next set of wheels were from my 02 E55. I'm considering going back to the originals because 1) These are all heavy monoblock 18" wheels which could be a problem and 2) I will throw new tires on the car wheels a the same time.

I'm not yet convinced it isn't wheels/tires. Take a set of front wheels from another car that has ZERO vibration.

I'm 99% sure I did but it's been a while (in terms of time and not miles). I'll pull the damper off.

Did the suspension rebuild include a new steering damper? Assuming the SL500 has one.

Yes, I tried this and still got the shake. I was convinced that it was the driveline for a while and bought all the parts. I took it to a friend who's a mechanic to have him do the work as I was planning a trip and my lift is tied up. He inspected the driveline and said that everything was good. He also inspected the steering which is why we're back at the wheels. I'm not convinced it's the wheels given that I had a violent shake between 40-80 that went away when i put the same wheels on another car.

Is it affected by vehicle or engine speed?

Have you knocked it into Neutral to see if anything changes?

 

[doolar]

Discs, pads and brake calipers I would have checked next. Seized caliper, disc worn or out of true, pads least likely, if they’re toast you’d probably have the warning light. Caliper also a long shot, I would start with the discs.

I once chased a stubborn vibration on a W201, and in the end after checking everything, rebalancing wheels etc etc it turned out the new front discs were warped out of the box.

It was quite a vibration that, more prominent than just 10 grams incorrect balance in a tyre.

 

[gsxr]

Check toe with a tape measure, make sure it's slightly toe-in (not toe-out).

Doolar has a good idea with the brake as well - worth checking runout.

 

[alabbasi]

I'll check the alignment. It's not brakes as the issue in the steering or driveshaft. The brakes are smooth and the pedal does pulse. It's been so long since I've driven this car that I should take refresher. I might do a video.