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  #1  
Old 02-01-2012, 12:01 AM
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1987 300SDL front wheels vibrate when braking

Hi all,
As the title says I'm having some issues with the front wheels (appears to be both but could be just one) wobbling or shaking when I slow from highway speed to make a turn. This doesn't always happen every time I brake. When I try and bleed off speed or slow in a straight line prior to turning things seem ok. It's when I'm slowing quickly from 55-60 MPH and then turn.

I'm not very experienced with suspension issues and frankly haven't done much with the suspension on this car other than change shocks, tires, rotors, pads and wheel bearings. All of which were done roughly 5K miles prior to my current vibration issues. Tires are relatively new Michelins and I don't find obvious signs of bulging or other issues.

Can someone perhaps give me some pointers on what to look for in the suspension that would cause the symptoms I'm having. Of course, if you'd like to give a primer on what the various parts do that would be a plus and much appreciated. As I said, I'm weak on suspensions and would love to know more.

Regards and thanks in advance,

P
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Old 02-01-2012, 12:25 AM
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Unlikely to be a problem with the suspension if that's the only symptom. Sounds more like warped brake rotors, but I had a similar experience with crappy Uro brand idler arm bushings.

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  #3  
Old 02-01-2012, 12:25 AM
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There is a video at mercedes source com that talks about the front suspension inspection of a 300SDL; check it out. From your description, it sounds like you may have worn guide rod bushings. They help stabilize the front control arms under braking.
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Old 02-01-2012, 07:59 AM
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Quote:
Originally Posted by foolio View Post
There is a video at mercedes source com that talks about the front suspension inspection of a 300SDL; check it out. From your description, it sounds like you may have worn guide rod bushings. They help stabilize the front control arms under braking.
I agree...
on the 126 they are fairly easy to replace too. you will need to be able to lift and support the car of course. level concrete is pretty important here.

to see if it's the bushings, walk beside the car while some one else is rolling forward, and have them pump the brakes while you watch the rods. odds are good you are going to see them pop in and out. you can also look at the rods where they enter the bushing, and see rust and torn seals, that's a good sign they are toast.
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Old 02-01-2012, 06:02 PM
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I 2nd the wrapped rotor(s). It's when your going highway speeds and slow down fast that you notice. I had it happen on my Nissan Titan. Got worse over time.
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Old 02-01-2012, 06:05 PM
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My 420 was vibrating badly at random when braking, bushings all in good shape. Found the culprit quickly: Ball Joints. They were extremely shot. Inspect them closely!!! Replaced mine and its smooooth now.
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Old 02-01-2012, 10:44 PM
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Thank you all for the suggestions (and the video on suspension!).

I know that I'll be doing some suspension parts inspecting this weekend.
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Old 02-05-2012, 12:40 PM
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Suggestion: consider the rear brakes in the process. If you have bad worn pads or frozen cylinders you can be putting too much work on the fronts. I had the same problem and changed the front rotors and pads only to reap very little. My mercedes suggested the rears and there I got the most benefit. Good luck.
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Old 02-05-2012, 02:02 PM
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My mercedes suggested the rears and there I got the most benefit.
Just curious, were the suggestions made in German or English?
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Old 02-05-2012, 02:15 PM
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I would expect both English and German from mine. She's been here 25 years, so she should know the language by now...
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Old 02-18-2012, 10:34 PM
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And now for closure of this thread:

I spent some time looking at the suspension components and following the advice here, on the Mercedes Source videos and tidbits found elsewhere on the web. Didn't find any issues in the steering or suspension with the exception of the steering dampner. Took the car to a local guy who has worked on MB and other imports for about 20 years or so. He couldn't find any run out in the rotors and agreed that suspension looked good.

Did find that the drive shaft bearing was shot. Replaced that and it cleared up about 80% of the shimmying/shaking when coming to a stop. Still had issues though.

I decided to replace the pads and rotors anyway since, in looking through my paperwork, I could not determine where I'd bought the rotors last time I did this job - around 9000 miles ago. I began to suspect that I had shot myself in the foot and purchased eBay rotors because I am an idiot at times evidently.

Spent today changing the rotors and pads. Along the way I noticed that there was a great deal of play in the left front bearing. Way more than the .02 mm or whatever it is that's allowed. No matter, changed the rotor and readjusted the bearing play to proper. rotated tires and changed out the dampner.

End result; smooth stops, no shimmies shakes or vibration. Balo rotors and Pagid pads. Hope this fixes things under there for a while, at least until I can build the garage and dig out the work pit so I don't have to lay in the dirt to do all this stuff.

Thanks for the input all!
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Old 02-18-2012, 11:21 PM
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20 year veteran didn't notice bearings out of spec?

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  #13  
Old 02-19-2012, 12:08 AM
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I guess not.

Of course, coulda been the combination of new rotors/pads and not the bearing at all. Just felt too wiggly to me when I got in there to poke around.

This probably means that in a few weeks I'll be re-doing bearings cause mine are too tight...
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Old 02-19-2012, 03:23 AM
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I just did the rod bushings, did one side first and had the alignment done, I have a 83 300sd, after the alignment it drove better but when I pressed on the brake it would shoot to the right. I was doing the right rod bushing and found the bushing connecting the rod and the lower control arm together was bad. The mechanic couldn't see it was bad during the alignment but noted that he had a heck of time with that side.
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