Main.TrailIndexPage | Suspension | Front End

Front End

This component is part of Suspension.

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I had a complete front-end rebuild a few months ago after catastrophic failure of a lower control arm. The rebuild cost around $2500 for parts and labor and included shocks, springs, swaybar bushings, king pins, and a lot of rubber.

I took my car in to have it aligned about 2 years ago as I had a slight wandering at high speed. My alignment man said that short wheelbase vehicles must have tight front ends and stated that I had some kingpin wear on the right front. Never having worked on a Mercedes before he really didn't want to do it, so I ordered the parts and did it myself. It wasn't too bad a job. The parts cost were only about $150, which I thought was reasonable.

I replaced the upper and lower outer arm kits (contains special bolts and seals) and the kingpin kit (kingpin, seals bushings and washers). The inner (upper and lower A- frame) bushings were still tight. The kingpin assembly is unique (typically Mercedes) even if you've done front-end work on kingpin vehicles before; you must have a good manual.

The upper kit contains a thread-type bushing that threads into the upper part of the kingpin. The most difficult part of the job was reaming the new bushings to fit the kingpin. I cut groves in my old kingpin to act as a reamer and finally honed it until I got a good slip fit. Also fitting the upper assembly back into the upper a-frame was a bit of a challenge, compressing the seals in forceing it in.

Pete Lesler says: be wary of the shop that wants to rebuild your entire front end. The kingpins and bushings used on this front suspension if lubed regularly will last for a very long time. When did you last have the front end lubed? Did all of the fittings take lube? Is there an audible squeek when pushing down on the front fenders? If there is a squeek, that means one of the fittings is dry and the bushing is dry. If all fittings take grease and no squeeks, I would look elsewhere.

A good way to check out the wear on the kingpins is to jack up the car and let the front tires suspend. Grip the top and bottom of the wheel. Then atempt to rotate the wheel towards you and away from you in a vertical plane. If there is significant play, you will feel it. Then to check the idler arm bushing, check the right (passenger) wheel by gripping the wheel at 3 and 9 o'clock and try to rotate in a horizontal plane. If there is play you will feel it as well.

The problem you describe could be attributed to worn idler arm bushings, worn steering shock, worn road shocks, and poor alignment. Any or all of these in concert could exacerbate your condition. They would probably need to be replaced in a front end rebuild anyway, so start here first. I would have these all checked before plunking down the money for a complete front end rebuild.

After having checked the steering shock and aligning the wheels, I've concluded that my left kingpin needs work, as I can definitely wobble the wheel. In comparison, the right side is very tight. So in the near future I expect to overhaul at least the left side kingpin.

Does that involve only replacing the bushings in the steering knuckle, or should I go ahead and order a replacement king pin (which runs about $500 at MB)?

Do you also have experience removing the spring? The MB manual says a "special adaptor" (see 32-5) is to be used to assist in this task. Of course they do not suggest how sneaky the removal and installation of the spring might be. While I'm "in there" I also expect to replace the submount(s), and many other rubber and metal bushings. I'll be sure to also take a close look at the idler arm.

The kingpins are usually not the problem. You may want to check the lower/outer control arm bolt and fixture. These are common wear items and there is a repair kit for both the upper and lower units. They hold the kingpin ends and can fool one into thinking bad kingpin bushings. Worth checking first.

Will Samples says: I do the kingpins regularly. The kit is about $70 for one side. You will need a method to hold the upper and lower A frames in place against the coil spring pressure. Turnbuckles with hooks on the end do well. Once the kingpin is out, you will install new bushings and have to ream or hone them to fit the new kingpin. A local machineshop can do this. I always replace the upper and lower outer control arm kits. They are the main wear points and critical to the front end. I sell the kits and related parts, if that helps.

I am trying to replace my king-pin bushings, and have removed the stub-axle/kingpin assembly from the car. The Haynes manual says to simply loosen the lower nut, and then " rap it sharply with a hammer" to loosen the lower knuckle support. I tried that, but wasn't successful. I don’t want to go too crazy on it because I would like to re-use the king-pin if possible. Any other ideas to get the lower knuckle support off the king-pin?

If you're going to the trouble of pulling out the king pin you might as well replace it while you're at it. Would not recommend just doing the bushings. By the time these things go, the top end of the king pin is usually gone as well. This is where that hollow pin with the eccentric fits so they can do the caster/camber adjustments. They usually go because the grease fitting is often overlooked when doing a chassis lube.

You can find the king pin kits at some very cheap prices if you shop around. Some places are asking outrageous prices, though. I saw a complete set (both sides) of these at Carlisle this spring for about $100 for the set and that included the bushings. When you replace the bushings you will have to have a machine shop line bore them to final size.

Ok, probably a good idea to replace the king-pins as well - what would be the easiest way to get the lower knuckle off without damaging the stub axle? I bought one of those "Tiger torches" that attach to a propane bottle – do you think heating the lower knuckle would do it? – then, a day or so later: Just to follow up on my previous post - the heat worked wonders to remove the lower knuckle support. For the majority of us that don't have access to an oxy-acetalene torch, this tiger-torch is a worthwhile investment. It costs about US$20.00 and comes with a 6' hose that simply screws onto a regular 20lb. propane BBQ tank. It puts out serious heat!

Once I had the king-pin removed, i noticed that the majority of the wear was actually on the king-pin itself, especially in the lower bushing area, and not the bushings themselves. When i slipped the new king-pin in, it felt nice and solid, and just for a split second i considered taking the easy way out....but i guess i better just have the new bushings put in after all this work. It was a bit of a challenge disconnecting the tie-rod from the knuckle arm. Both my pickle-forks were too big, and checking a local tool store showed nothing smaller than 21/32" available, same as my smallest.

The tie-rod is about 3/8" dia. I modified a large washer to act as pickle fork, but it was not rigid enough. I then inserted the pickle-fork between the still-inserted washer and the tie-rod, and then it finally popped loose. The slotted nut on the bottom knuckle bolt is very tight (130lb/ft), so have a breaker bar handy. The bolt came out easy enough, but as soon as I removed it, there was residual road spring tension that spread the A-arms another 2.5" or so. The manuals (Haynes and Chilton) did not mention doing anything with the road spring at all.

When the time comes to put it all back together, I will get a heavy friend to sit on the fender to compress the spring. Hints: Do NOT ask your wife for help, nor your brother ('cause he ain't heavy, remember? :-)).

If you need them, spring compressors would work, or you could follow the manuals: to remove the spring, they say to have a jack under the A-arm, then disconnect the lower A-arm mounting bolts, then slowly lower the jack (car frame of course supported as well). I had disconnected the shock absorber according to the manual, but it never would have been in the way, and might even keep the A-arms from spreading. Try leaving it connected.

Next, the upper cam-bolt had rusted to the hollow threaded bolt, so I had to use a power recip. saw to cut through the cam bolt in the space between the suspension arm and the king-pin. Now to find a machine shop to do the new bushings!

Joe Alexander: that is a tapered fit and they can be difficult. Try loosening the nut up then use a floor jack to lift the car at that nut. You can use a large socket between the jack and the nut. Now rap it sharply. The weight of the car and the sudden jolt should pop it loose! I hate to tell you this, The king pins usually account for 95% or more of the wear, while the bushings actually wear very, very little. You will feel the wear ridge at the top of the kingpin.

I just took my king-pin/bushings in to the machine shop to be re-bushed. The mechanic mentioned that it is possible to re-surface the old king-pin in a lathe, and then custom-size new bushings for it, for probably a lot less than buying all new parts. Just another option.

Is there any easy way to check/adjust camber after refurbishing king pin bushes etc.??

Dan Caron: Yes, the upper pivot has adjustment for camber.

Front end adjustments are not something you should do. I had my complete front end adjusted recently for $35.00, but this was added to all of the front end work after my recent encounter with a exit sign post; (after hydroplaining on wet payment). Complete front end alignment includes Tow-in, Caster and Camber. This takes special tools, and experience.

Improper adjustment will mess up your car's handeling and ruin a set of tires. Take it to a well known shop. Expect $35 to $100.00, more for four wheel alignment. Ask if they've ever aligned one if these vintage Mercedes. The first time I had my car aligned locally, I took my book and explained to the technition where the adjustments were.

Polyurethane bushings

I have a 1987 Ford Thunderbird Turbo Coupe that I run constantly on the German Autobahns at 100+ MPH. At about 150K miles even with the shocks electronicly on firm the car was beginning to float at those speeds. I rebuilt the whole suspension, springs, rollbars, shocks and poly-graphite inplace of rubber throughout. This was all FMOC parts except the shocks (Tokiko) and the poly-graphite. Now it rides like a truck at low speed not like the luxury car I bought. It is OK at 100+ miles per hour but not at low speed. I don't think I would do the poly-graphite again.
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