This is a how-to guide to repair minor damage to stripped lug nut threads on the wheel hub of a 1998 Mercedes S500, aka body style "140". This article is of my own making, and from my own research. If you use any of the material within then, like me, you're on you're own. You can't hold me or anyone else responsible for whatever, so if you don't feel comfortable doing this sort of mechanical work, then take your car to an authorized mechanic.
I wasn't going to write this little DIY, for a couple of embarrassing reasons. Firstly, I was foolish to allow it to happen - I attempted to put the lugnut in with the air ratchet WITHOUT first hand starting the threads and promptly cross threaded the female threads. Secondly, my solution is utterly boring in its simplicity by using an old lugnut as a cheap tap/thread.
But this is important - just the first 1 mm or so of threads were messed up. In my case (and I hope if this happened to you then yours too) I figured this was repairable. But how?
The dealer quickly quoted me their fastest fix - and entire new hub. And as long as they had it off, how about new bearings too? After due griping, they called back with a helicoil idea. After taking off the hub so they could get to it, they would drill out the existing hole to 14mm, insert the helicoil, bond it, rethread it and viola. they quoted 5 hours of labor. I've seen helicoils stand up to some severe pressures, but after it's all said and done I didn't feel easy with this whole idea. There had to be a better way.
Now Snap-On makes a handy tool that works the threads from the back to the front. Just a great gizmo for stripped spark plug threads. I think Craftsman may make a similar tool. The Snap-on reverse thread tool is about $200.00 I was told.
But I sat there, beer (and head) in hand, just looking at this hub. I noticed there was a good gap between then hub flange where the bolts screw down, and the back of the wheel/hub/bearing. Look at the pics and you'll see what I mean. But - what if I could get in there behind it and reverse thread it myself? The big problem was an entire lugnut was too long, and would not fit around the back of the flange.
So I went over to the MB dealer and purchased a new lugnut - they are $0.97c/ea. I took it home, and got out the air saw and sawed the lugnut in half. I worked it in from behind and slowly but surely my threads were pushed back to normal. The story below shows how I did it.
My apologies in advance for posting such a simple, stupid idea. I mean, it was so dumb that I'm actually embarrassed at its simplicity. But it works, so see what you think. Total parts cost: $1.04 after tax. Dealer estimate #1 : $487.00. #2: $320.00. BTW - I'm sure this is not original, as it may been done by many in the past. I just didn't see reference to it. Good luck!
Ok, here we go. You've got to take off 1) the wheel/tire 2) the calipers and 3) the rotor. As seen above, I've just taken off the wheel. Notice the rotor and calipers are still on. First to come off is the calipers, THEN the rotor. These two are surprisingly easy to get off. If you want to, replace the rotor and brake pads while you're in there then you can tell all your neighbors you've done a brake job too, thus explaining all the noise you'll make. If you do replace the pads, remember to use brake paste on the back of the pads (only). They will definitely squeal without it! See the DIY on brake replacement for the full story.
Before the rotors can come off, you've got to pull the calipers off first. I wanted to show you where the two bolts are that hold on the calipers. You can see the other one right below the wrench at about 7 o'clock. As soon as you pull those two bolts the calipers will fall free. Simple as that. Remember to support the calipers with a coat hanger or something - just don't let them dangle by the brake lines (seen at the top of the pic). Supposedly putting pressure on the lines like that will stress them, either causing an immediate failure or worse - it'll wait until you're on a long trip somewhere and squirt your brake fluid out on the road and strand you. Or worse. Not to mention the brake lines themselves are awfully expensive.
Here's the hub with the rotor still on. This is just a picture I had in stock, so pay no attention to the missing bearing cap. I think I was fooling with the wheel bearings (another DIY), so thankfully we don't need to mess with the bearings on this job just to get the rotors and calipers off.
Notice the brake rotor sits ON TOP and around the hub - <strong>the hub</strong> is actually where the threads are.
If you look carefully, you can see my fine stripping job on the threads @ 11 o'clock. See that little hex bolt at 1 o'clock? There's only one - and that's a handily little non-load bearing screw that just holds the rotor in place while you fool around with the wheel off. Remember, that little guy torques back on at 15 ft.lbs, with Blue Locktite. So all you have to do to take off the rotor is unscrew that little bolt, give it a good whack with a hammer to unfreeze it, and off comes the rotor.
BTW - I lightly whack the rotor around the thread holes - NOT the rotor itself around the outside. Sometimes the rotors even pops off by itself - it won't give you any trouble coming off so go easy.
I've got to start out with some apologies. I had actually taken pics of this bolt head in the process of being sawed off to show how easy it was to do. But take my word for it - it was easy. I put it in a vise (not on the threads) and zipped it right off. Use a hacksaw, a metal saw, whatever.
Here's what the whole deal is about - this little bolt snub with good threads. It's ugly for sure, but it's simplicity. Now it's short enough to fit between the hub housing and the hub itself...
Now that you've got the wheel, calipers and rotors off, and the bolt sawed off, thread our little sawed off lugnut through the back of the hub like so.
I screwed it in until it snugged up on my cross threads. Not shown, but I then took a large pair of channel locks (vice grips would do nicely) and grabbed the back of the bolt. I worked it very GENTLY, back and forth until it <strong>slowly</strong> made its way through. I took my time with this, probably 10 mins or so. Be patient - work it with small torques until it pushes out the new [or old] threads. I didn't use any lubricants, maybe someone could advise if that would be better.
If you tear up one bolt, you can always saw off another one and do it again. Supposedly, the bolts are harder than the hub (anyone got any Rockwell hardness #'s on these?). So the hub will strip first. Why it's not the other way around I don't know. Gently test a lugnut from the front of our new threads to see if we've succeeded. Still a bit stiff, but the new bolt made it's way correctly all the way in.
Remember, you've got to torque these calipers back on - 85 ft.lbs to be exact. Also, these big caliper bolts [when new] are "self locking" - they actually have some plastic around the tip to hold it in. But after pulling them on/off a few times that stuff wears off. To achieve the same effect, use a dab of BLUE locktite around the bolt. You can get a little tube of it at any auto store. Blue locktite is great stuff, as it'll hold the bolt snugly, yet it's still easy to take off even years later.
BTW - wheel lug nuts are torqued at 115 ft .lbs. when you put the wheel/tire back on. If you let the "tire guys" do it at the local tire store, they'll use an air hammer to put the lugnuts back on. I tested some of their work at 250 ft.lbs + one time - and that was the limit of my torque wrench. I can see myself now trying to get a lugnut off that's been torqued to 250 ft.lbs while standing on the side of the interstate. So if you get bored you may want to go out to the garage and loosen/retorque your wheel lugnuts one at a time, if anything to keep your wheels from warping.
My apologies for the simplicity of this whole thing, certainly no insult was meant. My neighbor joked and said he was expecting some super high-tech solution and pictorial on this matter - and was sort of let down by the boring nature that this method ultimately revealed. But it's just the way I did it and it worked for me. Hope it helps!
As I always mention, please take the time to check out Jim F's site. - a lot of good info on S class Mercs on his site.