1988 560sel termbles at 80 mph
 

My compliments to the members in this community. It is a pleasure to read the post with technical information and humors in between.

I bought my '88 560sel, July 01, at 97K mile. Now it is 103K mile.
The car has the following done:
1. Engine mount, starter. (before I got).
2. Timing chain, rail, tensioner. (preventive works, thanks to the recommendation from the members of the Forum and my Indy.)
3. Flex disc. There was a crack in it.
4. Climate contol blower. Soon after I got it, it would stop working intermittently. A good knock under the glove compartment helped it to start.

The car runs and rides very well. That really calms down my wife's fear about the luxury car. I don't think you can find other cars would even come close when comparing performance/price.

I think I got the car shake-down pretty well at this point. The future maintenance items are projected by my Indy according to their experience. That makes me more comfortful with the decision to go for an well-aged used luxury car first time. I'm glad to find an Indy right in town and they do have good reputation for their work.

The only problem I have not been able to resolve is that the car starts a high frequency minor tremble in the front, you can feel in the front seats not just the steering wheel, when it comes close to 80 mph. At 80mph, it is very consistent trembling. It is not that I drive at that speed all the time. The combination of passing and trembling makes you wonder if any misfortune is waiting to happen down the road.

The tires are Pirelli 6000. They came with the car. They are still in good shape according to all the experts (Indies, tire stores). They are balanced and re-balanced, rotated and re-rotated. I know if it is not balanced well, the trembling starts at lower speed.

The only theory other than the tire that I heard is from my Indy.
It sounds like he has a long experience with W126. He, another owner of 420sel, was a mechanic at the MB dealer. I was told that this is a well-known ideosyncracy of W126 suspension system. He said that his 420sel does the same thing. This happen arond 80-85 mph. No trembling below and above this speed range. The only time he did stop the trembling is after a set of new tires installed. But it came back after 12k mi.

I kinda disagree with him on this subject. I played with the tire pressure and found that it can influence trembling happen at different speed. My friend has a '87 420sel and has no such problem.

My theory is that the suspension system does not have tolerance with slightly out-of round tire.

Can someone shed a light here?

Thanks.

Sr. Tango

You are correct about the tolerance for out of round or other tire problems. Both of my cars exhibit the same sensitivity to tires. However on my 91 I had what I thought was tire imbalance. But I also needed to turn the front rotors since there was some pulsing when I applied the brakes. I tried tire balance a number of times with no luck. Even new tires did not solve the problem. Then I turned the front rotors to fix the braking surging problem and low and behold the tire vibration went away. Thats a first in my book. I can only assume that the pulsing brakes must have been rubbing ever so slightly and caused what felt to be tire imbalance. I never would have guessed that turning the rotors would solve a vibration problem.

Dave,

Will put it on the checklist for the next visit.

Thanks.

Sr. Tango

Some Porsche 911's had the same problem. We always balanced the front tires on the car.

Replacing the rotors on my Infiniti G20 solved a nagging vibration problem that I thought was a tire balance problem.

I started a thread a week or so ago titled "bad tires or bad balance".

Got some great input and links to check out.

I recommend getting your tires balanced at a shop that uses the Hunter GSP 9700 balance machine.

I think checking the brake rotors for rot is a good idea, but on the other hand tires can cause a lot of wierd vibration problems. If your tires are old, I would go ahead and replace them before you drive yourself crazy chasing this vibration down - start with the obvious first! Secondly, I have read that it is very common for certain model BMWs to vibrate and highway speeds, and the ONLY way to eleminate the problem was to use a special balancing machine that balances the wheels while they are on the car. Ask around for a shop that can do this.

Hope you solve the problem.

Greg
'84 300D

I was told before, as Greg suggested, to find a place can do high speed, wheel on car balancing. I haven't been able to locate one around here yet.

Really appreciate all the input.

Thanks to all of you.

Sr. Tango

dave-

my mechanic told me that MB rotors are not to be turned.
when i replaced my rotors two years ago, i remember we
have gone through 3 rotors before we found a perfect one.
any minor deviation resulted in pulsating brakes and flapping
sound when brakes are applied.

Yea, I hear that all the time. I dont buy it. What is different about MB rotors that they cant be turned? I have turned half a dozen without any problems. What do you have to loose?

I pretty much feel as Dave does as long as you do not go below minimum on the rotor.

The DO NOT TURN MB ROTORS things is about as ridiculous as the coolant issue. Check out what M.B.DOC had to say about it in this thread.

http://www.peachparts.com/shopforum/diesel-discussion/12589-warped-rotors.html

I'm glad in a way to read of others with the same mysterious front end vibration at 80 mph in an W126 SEL. I have had new tires, new shocks, balanced & rotated a dozen times....very frustrating since most of my driving is on the interstate. Have also had new rotors, despite never having the pulsating brake problem. Am getting to the point of selling the car, and swearing off all S-class, as I understand the W140 has the same problem, esp early W140s. The vibration occurs right at the speed you want to travel. :-(

JoeB

Have you checked out your suspension components?

Check your tie rod ends. They are cheap to replace and can cause exactly this kind of vibration.

Have you considered you may have a wheel force variation problem with your tires?

If you do, the Hunter GSP9700 is the only machine that can balance your tires. It will also tell you if they can't be balanced.

I just replaced my Pirelli P6000s with a set of Bridgestone Potenzas on my W124. They were the Veloce Sport versions. I had been unhappy with those tires anyway, and felt they wore prematurely.

I had tried to get a shimmy corrected when I got the Pirellis...after four tries at getting them balanced, re-balanced, etc., I gave up and lived with the shimmy.

The shimmy disappeared once I switched to the Bridgestones.

I say...LOSE THE PIRELLIS!!!

Simple question:

How are the front rotors turned? Speciaifically?

Thanks.