w108 Kingpin question and clarification

[dmtinker]

I've read the few posts here that discuss (in passing) king pins. Some of them quite good but still a bit lacking. But still some of it is a bit vague. So since I have "excessive play" in my kingpin, I have to correct it before I can register my car. So....a few questions:

1. I read that the kingpin has both bushing and washers that have to be adjusted. i.e the washers have to be the right thickness and the bushings have to be "honed". What I don't have is the standards or specifications for the thickness of the washers. I also don't understand why the bushing have to be honed i.e. why they aren't produced to the necessary tolerances. I assume it's so that they can adjust to a specific car?

2. Is the kingpin a part that is static or is it adjustable to alter the ride of the car? I would seem to me that it would be a static part.

3. I bought a kingpin kit that includes the bushings and washers. Are there any tips, tricks or insights anyone could give?

4. Is there anything I should ask that didn't?

Any help would be appreciated. I think I'll probably do a write up for this since I didn't see one. I'll probably do the same for a few other things I have to do on my 67 w108. I think it would be very beneficial to the community. The DIY articles we have are a bit spotty.

That being said, any help I could get would really help me along.

[ggenovez]

If you look right above, there is a buy parts tab, put in your info and you should find this king pin repair kit.

here's a quick link

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1X30XYA9A26U10C0NI&year=1966&make=MB&model=250-S-001&category=All&part=King+Pin+Repair+Kit

[dmtinker]

I already have the kit with pin and bushings, although I haven't opened it up yet.

[daidnik]

This is not the easiest job. You have to drop the lower control arms to remove the springs, then you can remove the whole hub assy from the control arms with the kingpins in and deal with the removal of the kingpins off the car if you're not lucky as to be able to get the bottom caps loosened from the kingpin tapers with the coil spring pressure (doubtful).

You need to have the front end pretty high off the ground to drop the control arm. You'll need a good 6 inches of clearance under the tires with the car up on jackstands in the front.

Disconnect the brake caliper from the hub assy w/out breaking the hydraulics and hang the caliper assy from something in that wheel well with a piece of wire to get it out of the way.

Disconnect the shock & remove the anti-sway bar link assy. You might want to remove the anti-sway bar link assy before getting it all jacked it, it will be easier.

You'll need some support under the lower control arm when disconnecting the shock as it holds the lower control arm back a bit from full extension. It's very unsettling to have something go "pop" under the ~1000 lb force of the coil spring!

You can disconnect the kingpin lower joint from the lower control arm by removing the lower pivot bolt that goes thru the cast iron piece on the kingpin taper at the bottom. You have to compress the spring with a floor jack under the lower control arm right near the kingpin to get that lower pivot bolt out.

This matter of controlling the compression and restraining of the springs shows the art of this whole process. One MUST be careful when dealing with these springs.

After disconnecting the lower pivot and dropping the lower control arm and removing the spring, you just remove the upper pivot eccentric adjusting bolt to get the hub assy off.

Once the hub assys are off, you can then deal with getting those cast iron pieces off the tapers on the kingpins using a hydraulic press. On mine I also had to use an air hammer to get them to crack loose even with the force of the press so be prepared. There is also the chance that you might get lucky and the force of the coil spring with some rapping might get it off, but don't count on it. Just give it a try before taking out the lower pivot bolt. Loosen, but DON"T remove the bolt on the cap & give it some stiff raps without any support on the lower control arm. It will either come loose or it won't. Either way, you then proceed to drop the control arm.

Once you get the bottom caps off the kingpin taper, then the kingpins can be removed.

Then the old bushings have to be driven out. Then the new bushings have to be driven in. You have to be careful with the new ones as you don't want any accidents on those new surfaces. You also have to be careful not to get them 'cockeyed'. They should be driven in to about the same positions as the old ones, and take note of which is the upper vs the lower bushings; they are different lengths.

After installation, the bushings must be honed to fit. In the old days, they used reamers to do this. Don't do that. Honing is literally a hundred times more accurate and doesn't cost much. I think I paid $40 to have them done and they fit absolutely perfectly. Honing can size a hole to the millionths of an inch.

Since you feel play in the vertical axis of the wheel, don't be surprised if you also need the upper pivots, which is usually the case. Those will set you back another ~$40 per side at 'super deal' internet pricing. You will also certainly want to get the grease seals for the upper & lower pivots (4 pcs ea side) they are a dealer part (I believe), but they shouldn't cost too much.

While you have it all apart, clean & inspect the control arms, especially the lower ones. Once in a while, they develop cracks near that outer pivot hole.

You might also feel for play at the inner pivots upper & lower. A little play here doesn't hurt you too much. Inspect the rubber ring grease seals on the inner pivots. If these are shot, now's the time to replace them. It's usually the failure of these seals that allow corrosion and create play in the inner pivots. The seals are cheap; they're a dealer item.

As you see, it's not an easy job. It's involved, but it's not rocket science.

Be careful with the springs, and be careful of the sharp edge of the ring in the kingpin grease seal at the bottom of the hub assy when driving out the old bushings. Don't ask why I make note of this.

[dmtinker]

Just a couple of questions for clarification:

What exactly does "honing" involve? In which dimension is it honed? Does it have to be fitted and marked?

What if I can get the kingpin bottom caps loosened from the tapers? Does that mean I can do this in the car?

What are the upper pivots that I may need to replace?

I've heard a lot about watching the spring. I've removed hubs and springs frequently without a problem. I've always used a screw spring compressor. Doesn't anyone use these anymore? They compress the spring and keep it that way until you are ready to release the tension.

Thanks for your input. It's a great write up so far.

[MunichTaxi]

One of the members wrote about his repair process. DieselDog?

Since he's 'been there, done that', try using the Search feature for 'Kingpin'.

Not to blow you off, but very few members have done this repair.
Just removing the coil spring can be fatal, without using the Mercedes Coil Spring Compressor.

[dmtinker]

Originally Posted by MunichTaxi

One of the members wrote about his repair process. DieselDog?

Since he's 'been there, done that', try using the Search feature for 'Kingpin'.

Not to blow you off, but very few members have done this repair.
Just removing the coil spring can be fatal, without using the Mercedes Coil Spring Compressor.

I've actually read it. I'm just looking for insight from people who have done this as you said.

[daidnik]

Since you want to replace the kingpins, replacing them "in/on the car" doesn't apply. The kingpins must come off, therefore the hub assy/steering knuckle must come off.

The upper pivot threads thru the top of the kingpin. Look at your replacement parts. The upper end of the kingpin has a threaded hole running crosswise thru the squareish top. The upper pivot goes thru that and has a couple of pieces; a threaded piece that threads into the aforementioned hole that is a fine tweak for caster, and an eccentric that goes thru a thru hole in the caster adjustment piece. This is a camber adjustment.

Go to http://www.diypartscatalog.com and supply make/year info for the car. I used a 1968 250S since this is what I had, but this setup was the same on all the W111 & W108 cars. Look in 'front axle/suspension' and you'll see pictures on the upper & lower , inner & outer pivots. This site has great pictures of the parts and their prices are pretty good. If you buy from there, try to stick to Febi & Lemforder for suspension parts. Meyle is NOT as good.

Regarding your question of using a spring compressor, these are generally used on 'strut' suspensions, which are totally different. There is just plainly no room to use any of these except the kind that have plates that slide in thru the side and then key into a screw with special 'dogs' to engage in the plates. The screw then goes thru the hole in the bottom of the lower control arm. Such a tool is necessary in some cases, and Mercedes makes available such a tool. It's something of a pain to use. It is used mostly for rear axle coil springs on the rear axle designs subsequent to the W108.

In the 108 front axle it is far easier and safer to drop those control arms and allow the springs to extend.

Study the parts pictures at diyautoparts along with your kingpin kit.

Might as well add new spring pads while your in there. These are quite cheap, and you'd be amazed how much difference replacing these old rubber parts makes in damping shock/vibration and you can't tell if the old ones are bad by feel. It's not like they crumble/crack in your hand, but what's important is that the shock damping quality has CHANGED over time. In the suspension, if it's old and it's rubber, replace it if it's not terribly expensive.

[dmtinker]

Regarding this picture, I assume the bushings that need to be honed are the cylindrical ones? In what dimension are they honed and how is that process accomplished?


I also wanted to say thank you for all your info. I will take a lot of photo's and write up a procedure so no one else has to go through hunting down all this info.

[daidnik]

The bronze bushings are what is to be pressed into the steering knuckle and then honed to fit. You will take the steering knuckles and the kingpins in and the machine shop will hone them to fit. With a good hone job, the kingpins, lubed with a light coat of light weight oil will just drop right into the holes like there's no resistance at all, yet hard side loading on the kingpin will not show any play. Totally sweet!

In the picture, the washers on the bottom are the ones that go in that bottom joint. The one with the slots goes in with the slots facing the other washer (the stack sizing washer). The slots allow the grease to get into that joint and lube the washer interface.

The big thin-walled ring is the 'sharp-edged' one I cited earlier. This one is press-fit on to the steering knuckle at the lower joint. It's part of the grease seal around that washer stack.

The kit comes with three sizing washers of different thicknesses. After you get the new bushings honed to fit, you can do a test assembly of the stack to find the right sizing washer, just don't crank the nut down on that bottom piece, you'll want to get that bottom piece off the taper without trouble. As the iron piece starts to get pinned on to the taper, the contact force starts to go up very steeply as a function of position on the taper. This means that the tightness of the washer stack is not going to very different when the cap nut is cranked down in the assy on the car than it is in your 'test assy' sizing when the nut is snugged. I think the difference in the sizing washers is ~0.005" between each of the three, so this is the "resolution" that you are grappling with. You want the thickest washer that will allow the cap to be pressed on to the taper, so in the sizing, start thickest first and see if the kingpin binds before the nut gets snug. If so, then remove the cap; go the next smaller and try again.

[dmtinker]

Thanks again. I will be doing this in the next day or two and will distill all this down so that it's available to all.

[daidnik]

I looked at the book of exploded views on these parts and see that I may have misstated the positions of some of these things in the stackup.

It looks like the thin-walled collar ring and the sizing washers are on the TOP side instead of the bottom.

When you take it apart lay the parts out in order and make some notes about the stack.

It will help to have some calipers or a micrometer handy to measure the thickness of the washers, etc

[Tony H]

Hi,
I have done all this quite recently on my 3.5 coupe. First-removing the springs is not for the faint of heart. There is no practical way to use a spring compressor. The manual says to remove the lower inner pivot bolts and lower the lower control arm. Make sure the car is raised fairly high as the spring will be much longer than you expect and make sure your jack is stationary as the force of the spring will want to push it off to the side-even a heavy floor jack.
Also-when you install the upper carrier to the kingpin you must fully torque the nut to measure the play. The play changes dramitacally as the nut is tightened. Also insure the tapered surface of the kingpin and carrier are totally free of oil or grease as that will totally mess up the free play. When you do the final assembly of the kingpin it must be in a jig to insure the upper carrier is aligned to the kingpin. The factory manual outlines all this.
I could not obtain the correct play with any of the included compensating washers and ended up having the machine shop machine 2 of my old thrust washers to the correct thickness. When the correct play is achived there will be a slight drag when turning the kingpin. I would highly reccomend having a good machine shop install and setup the kingpins.
Tony

[dmtinker]

What is the correct play? What should be nuts be torqued to?

[bimmer630]

Does anybody know if the bronze bushings are available anywhere seperate of the kingpin kit?

I damaged one pressing it in