300SE 126

while removing the front brake caliper the upper retaining bolt snapped .Need advise on a replacement bolt and removing the broken stub in the carrier .the stub is flush ,no protusion to get a grip.
Thanks
mak

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mark

There are several ways you might rescue this. For all, suggest using lots of PB-Blaster or Kroil to chemically allow some loosening. Also, some heat on the carrier may be helpful. Note that, not being immediately familiar with your exact solution, my suggestions are somewhat generic and apply to any bolt that has broken off inside something.

First, drill it and use an easy-out. Be very careful about the easy-out, they are extremely hard but also very brittle. You have to have a straight shot at the easy-out, or it may bust off in the bolt and they yer screwed 2x.

Second, it's a through hole, drill the bolt and the heat and vibration may be enough to loosen the grip and it will spin right through with the drill bit.

Third, and if the hole isn't through, many of us nowadays have reversing drills. If not, a cheapo at WalMart may be enough... _IF_ you can find a reverse drill bit. The bit should be a little less than the diameter of the bolt so you don't cut the threads, but often if you can find such a thing, the heat and vibration of drilling will be sufficient to back out the busted bolt.

Once in a while you can weld "something" to the bolt that will be sufficient to turn it out.

There is also, rarely, a machine shop service that uses some kind of high voltage magic to remove bolts frozen in. You'd have to contact a machine shop for this to see if they have it, and take the part to them. The likely means disabling your car for a while, but you're at that place already.

As for another bolt, the dealer is the place to go for mission-critical parts. You may be able to read the hash marks on the bolt head and determine the grade of the bolt and get it at a hardware store, but BE SURE that you get at least the same grade. DO NOT substitute any common galvanized or coated bolt simply because "it fits". DO NOT use anti-sieze upon reinstallation unless MBz does it that way.

Mark, best to buy a replacement bolt at your local MB dealer. Call ahead so you're sure they have that specific caliper bolt in stock. You want to use only high grade parts in the braking system.

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Fred Hoelzle

Thanks most helpful advise . now to get all the required items for the operation and have a go at it.
Regards
mak

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mark

took quite a effort and eventually it came out.replacement installed.
mak

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mark

You're supposed to replace them all EVERY time you remove them. Just check WIS.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

since which year onwards is this applicable.?
mak

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mark

I'd just drill it out from the front side.. outward side which will back off the bolt(generate a loosening force as you drill). start with something like 3/16, 1/4 and try your best to center punch the bolt and get close to the actual center. If it doesn't come out by the time you get close to the threads.. use an easy out. I would soak it for a day with Kroil before drilling too.

For the replacement, dealer works if you have one close. Heads on all metric hex bolts are marked the strengths in Mega pascals or maybe it's kilo. 8.8 , 10.9, 12.9 etc.
So get the right length(measure the other one) and they are just course thread bolts- 10.9 would be my guess. Fastenal, acehardware etc.. should run you a couple bucks for a pair. I'd replace all of them both sides. Install with blue loctite to prevent corrosion in the threads and failure that you just experienced.

Good luck!
Michael

Thanks : the caliper bolts are indeed 10 9 course, . I cant figure out why it sheared off while opening .When reinstalling i put medium loctite on the new bolts and torqued .the ABS system did not like the pushing back of caliper pistons i think needs pressure re-bleeding
Theory behind replacement at every opening .?

regards
mak

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mark