General questions to assist me:

1. How to determine if new springs, particularly, in the front are warranted?

2. Could a slightly bnt or out-of round rim be the culprit of an intermittent slight bouncing sensation (high in frequency) at certain speeds, lets say, between 65-75 mph?

Couple of things that will hopefully help you to find the answers to your questions.

1) Springs are designed to absorb impact and return to their original shape. In addition to this they also play a large part in ride height and quality. Personally I have never seen a factory spring require replacement due to any of it's factors having worn out over time, unless that vehicle had suffered a great deal over a very long period of time. I have seen a number of cars that have had badly modified stock suspension that have absolutely ruined the handling qualities from stock however. The easiest way to work out whether what you have is wrong or not is to go for a ride in a similar vehicle. Describing vehicle qualities always leaves room for personal interpretation.

2) At 70mph you should feel more drivetrain harmonics than you would at 30mph. My 560 certainly has more feedback than modern vehicles at 70mph but it doesn't really change all the way through to 120mph. A simple wheel balance will ascertain whether or not you have a problem with a wheel or tire, and balancing should be performed reasonably often anyway.

For what it's worth I often think that my 560 makes a lot of squeaks and rattles but my passengers just do not hear the same things I do, over time I become more sensitive to things I guess.

Cheers
Matt.

It should be obvious from inspection if the springs are broken. Despite what Matt says, springs do deform with age, usually becoming shortened. As a result the ride height will reduce. I don't know if this model has auto leveling which may make diagnosis difficult, but otherwise check the ride height at each wheel and compare with the specification.

A bent rim may well produce the syptoms you describe. So will an out of round tyre. I have known tyres to balance up OK on the machine, but become out of round at high temperatures and speeds. Oscillating suspension can also indicate worn shock absorbers.

Thanks, Neil.

Can someone advise me of the proper ride height for W126 front end, '88 420 SEL with stock 15" wheels?


Also: 2 more questions:

1. If ride height is a tad higher in the rear, will this throw off the proper suspension angle of the front end?

2. How can I check to see if one of my front rims is slightly bent, either on outside (I don't think so) or on the inside?

The spring height can have an affect on the caster angle but this could be adjusted.

To check the wheel for trueness jack up the car and spin the wheel. Use a reference device like a block of wood and watch the wheel as it turns… if you see any wobble check to see if it is coming for the tire or the wheel by moving the block next to the rim.

Also Check

The steering Linkage Tie rod ends center link and Ilder arm and bushings. The best way to do this is have someone wiggle the play in the steering wheel wile the car is on the ground watching each part. If the ball in the tie rod socket moves inside the socket it needs to be replaced. Also watch the center-linkage and make sure it going right to left not up and down.

If any of these parts are worn it can cause a pulsing in the steering wheel at certain speeds or amplify a slightly out of balanced wheel .

Neil is correct in that springs can deform however as I said in my post I would not expect to see spring sag on your 126. I would be confirming the ride height with a similararily equipped 420 before looking at replacing springs. A quality tire shop will be able to pick up most issues during balancing and a rotation at the same time will help track down the culprit wheel.

Matt.

Robert,

Ride height will give you some indication of spring wear, but there are other items like worn bushings and bent suspension pieces that can affect ride height. Specific to springs, I think worn pads contribute to the 'thump' you hear when you go over a bump that might have been more muted when the car was new. If the spring keeps the car up at all, I don't think it's worn enough to change it's natural frequency to the extent that you feel vibrations. A rule of thumb that I haven't seen on this forum is to change spring pads when you change shocks. Certainly can't hurt.

Look for a tire shop that has a wheel balancing machine that puts pressure on the wheel. It measures the effect of radial runout so you'll know whether or not the wheel is out of round enough to cause vibrations.

A specialty alignment shop, maybe one that caters to folks who do track events, should be able to sort out your steering and suspension quirks.

In my case, 90% of the wobbles, jitters, rattles and vibrations were fixed by changing from Bridgestones to Michelin MXV4+s. A bigger improvement than replacing 130K mile shocks and dead tie rod ends, IMHO. Maybe you already have Michelins...

Sixto
91 300SE
81 300SD

"For what it's worth I often think that my 560 makes a lot of squeaks and rattles but my passengers just do not hear the same things I do, over time I become more sensitive to things I guess."

Matt,

Very very well said, it echoes my sentiments exactly. I feel the same with my 280SEL too!

__________________
Mervyn

1979 W123 (200/M) Midnight Blue
1983 W126 (280SEL) Dupont Deep Black (Previously Pristine Silver)