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?