DaveT.D.

I'm trying to confirm the info contained in FCP Euro's video on front pad and rotor replacement for my 2017 X166 GLS 550. The video says that the torque should be 85 NM plus 45 degrees rotation.

Time: 8:20.

This if for the two 21 mm hex bolts that mount the caliper carrier. The 85 NM is straight forward, but then adding 45 degrees doesn't seem correct. I can get about 5 degrees using an 18 inch breaker bar pulling harder than the torque which was required to break the bolts free. Are these torque-yield bolts which can't be reused? I'm able to pull with 150 lbs which would be 225 ft lbs or 305 NM, but I'm not sure even that would get me 45 degrees.. Before I cause serious damage to the hub, I need confirmation of the correct spec.

Help would be greatly appreciated.
(P.S. Why did Mercedes go with 11 mm hex bit for the caliper slider bolts - total nonstandard size. Bit isn't available in my local NAPA, and they can't even order it because Carlisle says "out of stock". )

John CC

WIS says they must be replaced. Torque is 80NM (60 ft-lb) plus 45 degrees.

5 degrees is pretty small and hard to measure. Are you sure you're measuring it correctly? One full flat of a hex bolt head is 60 degrees.

BTW, resist the urge to call them 21mm bolts. They are 14mm (M14) bolts. The torque for a 21mm bolt would probably be about 500 ft-lbs.

DaveT.D.

John CC,

Now I understand my problem; trying to reuse already stretched bolts. Unfortunate (and potentially dangerous) that the YouTube did not say the bolts must be replaced. I'll pick up a new set of 14mm bolts

Follow-up question: Are the rear bolts also single use torque-angle bolts? What is the rear carrier bolt tightening spec - the same 80 nm + 45 degrees?

Dave

John CC

60NM plus 45 degrees. These are M12 (12mm) bolts. It does not specifically call for replacement. There are notes that are somewhat ambiguous. They say generally bolts tightened using the "angle controlled torque method" are permanently deformed and must be replaced. They also list exceptions, one of which is "stretch bolts". Since the fronts specifically call for replacement and the rears don't, I'd say no.

John CC

I'm in the process of replacing the front brakes on my GLK and the front caliper carrier bolts are also M14 bolts. The torque spec is 180NM (133 ft-lbs). Replacement is not called for.

chassis

All German brands specify single use caliper bolts.

If you can’t achieve torque or angle you have the wrong wrench (too small).

John CC

Where is this information hidden? I've found it in some manual pages and not in others. So I figure I find it where it's "required" and don't where it's not.

chassis

MB WIS (ebay)
BMW newTIS when it was available now TIS from BMW for a $32/day subscription
Porsche PCSS available on an hourly subscription basis if you have an LLC

John CC

That's where I'm getting my info from. It calls for replacement on the GLS but not on the GLK.

John CC

Took the back brakes apart today. The carrier bolts clearly had locking compound on them when new. I suspect that's what they're calling "self locking". That's probably why they recommend replacement. (It's probably buried in a note somewhere.) Nothing that can't be fixed with a drop of Loctite, though.