taz777

I've managed to strip the thread inside my rear brake caliper. It's a hydraulic brake and one of the bolts isn't tightening properly. When I removed the bolt, a thin spiral of aluminium was wound around it. The other bolt tightens fine.

Due to it being a brake, I cannot take risks. It's a flat-mount caliper with a 140mm rotor.

As it's a custom brake system (Specialized/Tektro/TRP), would I need to replace it with an identical caliper or could I get a more widely available third-party flat-mount caliper and possibly take the opportunity to upgrade the rear rotor to 160mm?

If this could be possible, then what would be the procedure to replace the caliper? I'd need to drain the mineral oil and would probably just drain it using gravity at the caliper. After that, is it a simple job to replace the caliper whilst keeping the lever and hose?

dsbrantjr

Repair via insertion of a Heli-Coil is a possibility and will result in threads stronger than the original. Could you drill the hole through and use a longer bolt with a nut on the far side? Should be at least as stong/safe as tapped threads in aluminum.

fietsbob

Sight unseen ?, Just replace it with new , and don't over tighten it next time..

taz777

I cannot drill through as it's a very compact flat-mount caliper.

taz777

I've been using a torque wrench at the lower end of the torque setting for the caliper bolts. I was trying to centre the pads after conditioning the brake pads.

When I got the bike new 10 months ago I noticed that I needed all of my strength to remove the pedals as they had already been overtightened. I'm just wondering if the caliper bolt had been overtightened at the factory or during the workshop prep?

The bike is still under warranty but I doubt the shop will replace the caliper for free.

What's worse is that it's a non-standard OEM caliper so I'm pretty much resigned to having the shop replace it.

This happened at a very bad time as I had got the bike working perfectly and was looking forward to riding it regularly.

taz777

To bring some closure to this, I booked my bike in at my local Specialized store. Just prior to that I had noticed that only one piston was moving, and this may have been the cause of all of my headaches with the rear brake on my bike since I got it.

Anyway, whilst the bike was still under warranty, and the fact that I had stripped the thread on the caliper, I fully expected to pay for a new caliper. I also asked the shop to bleed the front and rear brakes.

Much to my surprise, the bike was ready yesterday with a new rear caliper and a front and rear brake bleed. When I went to collect it, the store only charged me for the brake bleed and the replacement of the caliper was done as a gesture of goodwill.

So kudos to Specialized as I've had several issues regarding the custom brake systems on my bike and the lack of information on those parts and lack of availability.

Asi

The best upgrade for post mount threads on forks and frames:

If thread is somewhat functional insert M6 threaded rod/stud with threadlocker (or epoxy if it's more flimsy) and tighten the caliper by nuts and washers.

If threads are badly damaged, tap to M7 hole and now you either can use M7 bolts (might need some enlargement of holes in the caliper), or make use of M7 threaded rod.
For convenience clamp the M7 threaded rod in a vice and make M6 threads on the end of it with a die. This way you would have nice new strong M7 threads in the frame/fork solid mounted with threadlocker and normal M6 stud to mount the caliper with no mods to it. Clamping with nuts and studs instead of a bolt is much better as threads are no longer wearing inside the frame/fork but on the stud.. if that gets stripped.. just replace the stud.