Hope Mono Mini - Stripped Bolt Thread on Rear Caliper

blaina76

I have a set of Mono Mini's from 2005 (the ones with the gold cap on the caliper). Whilst riding this weekend I noticed a rattling noise and on closer inspection found that the rear caliper had worked loose from the frame. It would appear that whilst servicing my bike, the bike shop (and I'm not sure which one as it's had a few services by different bike shops in the last couple of years) had over-tightened one of the bolts and wrecked the thread on the lower of the two bolt holes in the caliper. The upper bolt is fine but obviously it is taking all the strain. Do I need to relace the rear caliper or is it possible to re-thread the bolt hole or find an alternative solution? If I do need a new caliper, is it possible to get hold of the same kind of caliper as I have now? If not, is the new mono-mini caliper compatible with the rest of the 2005 system that I have, or would I need to buy a whole new rear disc brake?

nicklouse

you may be able to get it helicoiled. Talk to an engineers shop or trusted LBS.

Splasher

As Nick says, a helicoil should rescue it but otherwise a new Mono Mini caliper is compatible.

nicklouse

Splasher
my only concern is if there is enough metal on the caliper?

there should be but...

Splasher

Nick,

I've had a look and I think it should be OK. There's a fair bit of meat around the hole:



and an M6 helicoil uses a 6.3mm drill and even after thread cutting is only 7.35mm at the widest.



Nothing to lose in trying it, because the caliper's no good without threads anyway?

nicklouse

or as like in the above picture the bolt will clear the disc fit a longer bolt and put a nut on it....

Splasher

nicklouse wrote:

or as like in the above picture the bolt will clear the disc fit a longer bolt and put a nut on it....

Ah, just thought, it may not clear the rotor. It only clears on this arrangement I think because it's a 140mm IS rotor with a +20 adapter. If you look at the hole in the adapter (which is where the hole would be in a 160 IS caliper) it doesn't clear.

Certainly worth a look though. Any chance of a pic blaina76?

nicklouse

but i feel that the photo shows the top bolt where in the OP it says it is OK..

Splasher

A fair point, but the bottom bolt is more likely to foul the rotor I reckon. Obviously the position of the frame mount could have an effect, and this pic is complicated by the +20mm adapter, but it looks unlikely. OP pic would be best though.

blaina76

Thanks for the replies guys. I've had a loook at the caliper and I don't think there is any scope to use a nut on a longer bolt as it wouldn't clear the rotor (160mm). I think the helicoil is the only option - excuse my ignorance though, but what is a helicoil??

Thanks again for your comments. I was in Afan at the weekend and noticed the caliper had come loose on the climb at the start of the Whites Level. Having tightend up the top bolt (being very careful not to overtighten and shag that thread too) I managed to ride for the rest of the weekend with only one bolt actually holding the caliper in place - albiet with regular checks to make sure the bolt was still secure. It actually held fast all weekend. However, I'm off to Colorado and Moab in a few weeks and don't really want to rely on only one bolt holding the caliper in place as I suspect I will need my brakes to be 100% reliable!!

A mate of mine suggested using threadlock in the lower bolt and said that the braking forces are perpendicaulr to the bolt so there is no force on the bolt as such and that threadlock and a secure top bolt would suffice. I'm, not so sure!

Splasher

See piccie above. A helicoil is the thing in the jaws of the calipers. It is a coil of specially shaped wire that screws into a new larger thread (created with a tap that comes with the helicoil) such that once in place, the inside of the helicoil provides a thread of the same size as the original.