MERCEDES-BENZ: ALIGNMENT/CHASSIS DIAGNOSTICS

By Steve Brotherton,
Import Specialist

April 2002

Although I really enjoy driveability diagnostics and "Check Engine" light troubleshooting, half of my job every day is wheel alignment. I do this because I like it, and I like it because it is the last area of the car that can be "tuned" - the last area where I can evaluate and then make adjustments to improve the condition. As it turns out, Mercedes-Benz creates one of the most adjustable cars going (at least up to the more recent versions).

I almost exclusively diagnose M-B cars, but I align everything from Chevy pickups to Ferraris. And no car has more ability for correction, nor is any easier to adjust, than Mercedes-Benz. Because of the range of adjustments, the ability to make proper adjustments has much more importance than it would on systems that give poor response to adjustment, or have none at all. In other words, if one is confused about where to correct to fit the actual performance to the range of possible accepted measurements, then one will likely have trouble with M-B. Within the tolerances is the ability for large performance corrections. This also is compounded by the fact that as with most European cars, tires and alignment affect ride and driveability more so than on domestics.

Probably the most important reason for a misconception about M-B alignments came from the very high caster values of most cars built since 1973. That year, M-B came out with its 116 chassis "S" Class, which had about 10 degrees of caster. At that time, many alignment machines only went to 5 degrees caster.

Not only did the equipment cause a problem, but those not familiar with such suspensions (about everyone at that time) had a very hard time getting both the camber angle and caster angle at the same time. Changes in the adjustments made such a difference to toe that if the toe of the adjusted wheel wasn’t kept at zero, the camber was read wrong.

In cars with less than 3 degrees caster, camber remains basically the same throughout most of the small changes in toe settings. Because things moved so fast and the camber changed so much with toe, many chased their corrections back and forth across the spectrum.

The real clincher with M-B alignments is the use of the spreader bar. The factory-recommended tool made by Beissbarth (part # 860 000 883) is undoubtedly not used by most alignment techs. I personally do not use it, but I might be a special case as I easily can test the spread characteristics with my 6'4" 280-lb. frame. I never align a car that has more than the min.-max. tolerance given in the alignment specs when spread and compressed. The spreader bar has always been an issue with me, but I have always had consistent, good results the way I adjust toe-in. Because this issue bothered me, I recently bought the bar from Beissbarth (it came with the M-B# 900 589 01 27 00 on it) and have now used it on two cars. The toe change on one was 1.4 mm and on the other it was 0.9 mm. Since the tolerance of accepted toe is larger than this amount, I assume that is one reason I have had good results without the bar. I also tend to qualify my anticipated toe correction by the tire wear present. This is probably the most important factor in alignment success.

I probably have gotten good results with some non-conventional techniques using the tools and experience acquired over 30 years. But it’s probably not good to try and discuss them in a short article. Of more benefit would be a list of some facts that affect getting the proper performance results.

One further area that lacks tooling is that of adjusting ride height. Since this is not readily adjustable, it is not of high priority unless one is diagnosing a problem.

Most alignment machines will not have specs for rear camber because M-B would have you calculate proper camber from a chart of ride height vs. camber. The height is only changeable on normal sedans (without load leveling or hydraulic suspension) by changing springs or spring shims. All that matters about rear camber is that it is the same side to side and that the tires aren’t wearing on the inside. The charts are available on your vehicle repair information system software for those who want to verify that they are in some sort of range.

The rear end has never had camber adjustments and did not have ready toe adjustments until the 201 (190) car came out in 1984 with the first multi-link rear suspension that is now used on all models.

The swing axle rear of the earlier cars had a correction for toe through the replacement of the control arm bushings, which had their centers drilled slightly off center (part #123 352 07 65). Correction up to 10 minutes can be gained per wheel. To do the correction, alignment had to be measured and the necessary direction of movement decided. Then the whole suspension had to be disassembled and the bushings set to the anticipated position. Then they could not be changed. If you made a mistake, the whole thing had to come back apart with hopes that the bushing could be removed and reused in the right position.

From years of making adjustments, I can tell that if the vehicle has a non-tire-related drift/pull, the caster bias side to side will need to be changed at least a degree along with a stacking of camber to the opposite side by at least a half degree. This becomes especially important on the new suspensions that are used on 202/210/208 and other models. These cars have no on-car correcting mechanisms (i.e., cams, shims and turn buckles).

To make a correction, the bolt kit (part #210 330 00 18) is required on as much as all four corners of the two lower control arms (see Fig. 1). This kit contains special bolts and washers that allow a 3 mm movement of the bolt to either side of its original centered position. An outward movement at the rear and inward movement at the front will change the caster about 0.60 degrees.

If I am trying to fix a drift to the right (if non-tire-related, I recommend swapping tires side to side to be sure before the bolt replacement), I will want to do this 0.60 caster on the right side (caster increase 0.60) and probably also put both bolt kits to the inside on the left control arm to keep caster while moving camber about 0 degree 40" more positive.

It is possible to get the same effect by reducing camber on the right side and reducing caster on the left. It depends where you started, but the amounts and direction of movement stays the same.

For a right-hand drift, increase caster side to side by a up to 1 degree (the actual side-to-side caster difference should be only 0.5 degrees, but a degree can be had if the left side is 6 degrees and the right 5.5 by reversing the measurements to left 5.5 and right 6 degrees). The same applies to camber: with a right drift the camber should be moved to a 0.5 degree higher positive setting on the left vs. the right.

The replacement of these control arm bolts are not particularly easy with the car on the alignment machine. I have been using the large U-shaped puller (see Fig. 2) designed for late-model Camaro/Firebird caster and camber adjustments. It fits in a hole in the control arm and the frame, and tightening the turnbuckle will pull the control arm to the center against the action of the spring. I use my swing air jack to push up on the control arm at the bolt. The arm doesn’t want to be in position to insert the bolt without some heavy persuasion. I also place another bolt into the hole as I drive the old bolt out so the bushing cannot totally leave the hole.

SUBFRAME MOUNTS

One part that is often overlooked when doing suspension diagnostics on M-Bs is the subframe mounts, which are not used on all models. If a vehicle is so equipped, they can cause various symptoms. In Fig. 3, the subframe mounts appear at four corners of a suspension that was removed from a 107 chassis (380SL) so that the pan could be removed during a timing chain update (yes, they are still out there). On this suspension, the rear mounts always collapse first causing caster to be reduced beyond the minimum.

On rear subframes, movement can cause both noises and driveability problems. The most common problem I am seeing with the later multi-link rear suspensions is wear on the bushings of a fairly cheap link that goes at about 45 degrees to the direction of travel. When this occurs there is a large change in toe between acceleration and deceleration, causing the car to act like it is steering itself in accordance with load. This link is currently M-B #210 350 33 06, costing about $27.

This would be an easy, profitable repair except that this part number is for a redesigned part that uses a larger bushing on the end that wore out. In order for the bushing to be increased, the attaching bolt diameter was reduced. This also then requires a sleeve where the new smaller bolt passes through the bearing carrier. Many aftermarket suppliers are still supplying the link as originally installed (with the larger bolt hole), which can be a blessing or really mess up a day (if you get the old link sold as the new one and need the new one).

Most suppliers will sell the link under at least the new number. The original, #201 350 56 06, has the larger hole and will not work on the 210 chassis, which originally came with the small bolt. This change occurred by chassis number around 1998. To use the new link in the updated form, bolt kit M-B #210 350 45 06 and sleeve M-B #210 352 00 43 also must be used.

FRONT-END WORK

Since we still work on a significant number of 10-year-old M-Bs, the most common front-end repair we do is the ball joints of the lower control arm on 123 and 126 cars, with 124 cars catching up. We affectionately call the rear lower ball joint the caster joint because it is part of the turnbuckle that quantitatively adjusts caster on these cars (see Fig. 4).

The prime purpose of this joint is to take the longitudinal loading of the front suspension. They can get so bad that the front wheels can be felt moving forward and backward during braking. It’s rather unusual to get that bad because, before that, a clunking sound is usually the complaint with actual diagnosis often quite difficult. Once familiar with the symptom, one can condemn the joint when the boot is broken and the clunk is evident.

Another common complaint due to this mount/ball joint is brake pulsations and/or shimmy at a resonant speed around 60 mph. Weakness in this direction seems to be a European favorite as both BMWs and Volvos also have these problems.

The other M-B with this problem is the 140 chassis "S" Class car. In this case, the rear bushing of the front lower control arm is hydraulically filled and has gone through redesign for lack of stiffness (see Fig. 5). I believe that this bushing should be stiffer than what M-B uses every time a larger tire/wheel combination is used. The hydraulic bushing doesn’t stand up to these abusive tires.

I have corrected the stiffness problem in a couple cases with the hard polyurethane bushings like those used by many BMW suspension tuners. The proper repair is the factory bushing (to be sure of the latest compounds) and good tires of the proper size. For the 18 and 20 inchers, something else is needed.

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