Vibration....at about 60mph... - PeachParts Mercedes-Benz Forum

Plantman · #1 11-17-2003, 06:42 PM

Good evening.

In search for a cure to my front end woes, I changed my front shocks today as they were sort of making this funny pinging noise when going over small bumps, nto too mention the normal clunking noise associated with bad shocks.

After lifting the car up and removing the wheels, I noticed that the screws that hold the lowere part of the shock were not completely screwed in, which explains the pinging noise. Had I known this I might have just tightened them down and not purchased the new shocks.

Anyway, I did so, and the car 's front end is nice and tight. No rattles or pinging over any kings of surface.

I also purchased the idler arm rebuild kit and was about to undertake that mission. Before doing so, I checked to see if there was any play in the idler arm and it also appeared very tight.

The dilemma is that the car still vibrates at any speed higher than 60, goes away at about 68-70 and comes and goes after that.

Could that still be the idler arm? I was running out of time and figured since it was so tight that it was not needed.

Any ideas where to look?

BTW, the tires are in good shape and were rotated and balanced last week.

Thanks

rwthomas1 · #2 11-17-2003, 06:48 PM

Hows the alignment? Are the wheel bearings adjusted correctly? Is there any play in the driveshaft or its components? How about the CV axles? I had one go and it vibrated quite badly. Check the tires VERY carefully. Maybe a belt failed on one of them and even when balanced it is still out of round? Hope this helps. RT

Plantman · #3 11-17-2003, 07:03 PM

I had to have a few compnents replaced before it was able to be aligned. The car does not pull in any direstion.

I will check the tires a bit more closely tommorow when the sun comes out.

Plantman · #4 11-17-2003, 07:06 PM

Also forgot too mention that there is a black wire, near the end of the transmission that has been severed. What might that be for?

leathermang · #5 11-17-2003, 07:20 PM

That is the antivibration wire....

psfred · #6 11-17-2003, 07:34 PM

Vibration at particular speeds has to be something rotating.

Bent wheels, out of round or misshapen tires, bad wheel bearings, bad driveshaft, bad rear half-shafts, etc.

On the front of the car, anything loose will do the same thing -- bad ball joints, bad tie rod ends, bad idler arm (if it's tight, it's OK), loose steering box, bad control arm bushings, bad track rod bushings.

Vibrations at specific speeds usually end up being tires or wheels -- at whatever speed the vibrations turns up the wheel movement and the natrual vibration harmonic of the suspension match, so it shows up at higher energy than the shocks can dampen. At other speeds, it won't reinforce the same way so it is much less.

Peter

CSchmidt · #7 11-17-2003, 07:43 PM

Folks,

My '87 SDL also vibrates starting around 50 and lasting to around 70. It is a faster vibration than a wheel ( and not as strong), so I'm guessing driveshaft / center bearing / or axle(s). So how to trouble shoot? Nothing is obvious at external glance, but I haven't pulled down the driveshaft cover yet either.

It was suggested in the past to CAREFULLY support the car and run it, but I would not feel good spinning things that fast. I did just see an ad in the paper for a local dyno shop. Anybody been on one? What if I was to mark the usual suspects with a white mark and have someone run it up to the vibration speeds on a dyno ( or a speedometer shop I would guess as well). Would they let us get close enough to shine a flashlight under to look for vibration?

Any other suggestions without just swapping parts?

Thanks,

Chuck with the well massaged bottom

Plantman · #8 11-17-2003, 07:46 PM

Leathermang, I just spit out my club soda. Very funny.

It was by coincidence that I saw that wire and no, I did not relate that to the vibration. Just bringing it up.

leathermang · #9 11-17-2003, 07:50 PM

Always turn your head to one side when spitting club soda...like when the doctor says " cough"....
It is good for getting out spills in clothes but not good for your keyboard....

240Demon · #10 11-17-2003, 09:54 PM

Leathermang: your proctologist called, they said they found your head!

jim16671836 · #11 11-17-2003, 10:37 PM

I would get the rear half of the car up on jack stands(this will be as safe as being on a dyno and if you are worried also place a couple of hydralic jacks back there also) and run it up to 70 with a couple observers checking the back half..If no vibrations then you know it is in the front half of the car...

leathermang · #12 11-18-2003, 05:34 PM

THere is a tool which might help track this down... There is such a thing as a mechanical ' tach'.... this is a spring wire deal which is held on something and the tube around it is adjusted to get the maximum swing of the wire.... then you read the occillation rate from the side... this tool could be held against the dash for instance....
You can figure the wheel turning rate from stuff... and if the vibration rate is approx 3 times the rotation rate of the tires.. then you can figure the problem is driveshaft related.
Some changes were made ( like so many other things ) in the flex discs.... some cars in the corrected mode have different ' stiffness' discs on the front than rear.... when they originally had the same ( if memory serves me ).

Plantman · #13 11-18-2003, 08:25 PM

After a somewhat frustrating day(non-mercedes related) I think my indy found the source of the vibration.

1. The power sterring box has way too much play

2. He say there is a bearing near the rear of the tranny, front of driveshaft that is apparently worn, causing vibration.

The steering box will cost me $445.00 installed for a rebuilt unit with 1 year warranty.

I will have to wait for the bearing info until he digs in.

Hopefully, this will cure the vibe and the car should handle very well, considering the front end has been practically rebuilt.

CSchmidt · #14 11-18-2003, 09:02 PM

Leathermang,

Good idea to calculate the vibration rate. I'll try to do some math and measurements tomorrow and see if that leads to axle or driveshaft. I'm guessing the 87 SDL has about a 3.X:1 rear end ratio? That should be enough difference to see. I'm at around 251Kmiles now so just about anything is fair game for replacement.

Thanks again!

Chuck

jim16671836 · #15 11-18-2003, 11:39 PM

I didn't think that you had the vibration by rpm in each gear....I thought it started at a higher speed...why would the transmission cause the vibration only in high gear...
I am just asking.....Maybe I am missing something...I would jack it up and try it out on jacks and jack stands...just the rear end to see...Jim