Disc brake mounting bolts – size help? Think I ruined my forks :-(

I see!

Hmm, makes it a bit murky then. You could try talking to them but I don’t know how far you’d get with a complaint – they might say something along the lines of “you should have done a trial fit etc before tightening etc / or you should have got a bike shop to fit them etc….”

I agree though – it’s pretty confusing why shimano have now reverted to using those conical washers.

And also – you don’t have this problem with 203 discs as due to the offset the mount bolts to the fork then the caliper to the mount, and with 160 it’s direct mount – it’s only 180 mounts that act as a spacer and the bolts pass through the mount into the fork leg.

I don’t know the inside depth of a post mount bolt hole so it wasn’t common sense to me.

I just thought the bolts would be the same length and engage at different points.

I’ll just run them till they/I die. I just hope it’s not mid ride.

PS, where you’ve broken through the end of the thread wont have much effect at all on strength of either the brake mounting or the fork. That is so long as there are no internal cracks you can’t see. It’d be worth a couple of steady road rides with gentle braking after you put it back together just to make sure the existing puncture hole doesn’t get worse or other cracks form.

Hmm, makes it a bit murky then. You could try talking to them but I don’t know how far you’d get with a complaint – they might say something along the lines of “you should have done a trial fit etc before tightening etc / or you should have got a bike shop to fit them etc….”

Really? Did you actually suggest that? And when they have finished laughing, I imagine they will politely remind you to apply a ‘little bit’ of common sense & check first.

I’m sure the lowers will be fine. As others have said, just use some old, shorter bolts & ride the bike.

I’m sure you will laugh about it in days to come. It’s not the end of the world.

I know and I totally accept I should have thought to check first.

I won’t make the mistake again.

So is the advice to use shorter bolts with the 160 disc or get a 180mm disc and use the bolts and adapter that came with the brakes .

Hmm, makes it a bit murky then. You could try talking to them but I don’t know how far you’d get with a complaint – they might say something along the lines of “you should have done a trial fit etc before tightening etc / or you should have got a bike shop to fit them etc….”
Really? Did you actually suggest that? And when they have finished laughing, I imagine they will politely remind you to apply a ‘little bit’ of common sense & check first.

I’m sure the lowers will be fine. As others have said, just use some old, shorter bolts & ride the bike.

I’m sure you will laugh about it in days to come. It’s not the end of the world.

POSTED 32 SECONDS AGO #
Yes – I did suggest that. That’s why in my post I said you “could” and “I’m not sure how far you’d get” and that they may say about a trial fit (ie common sense – not wanging it all together straight away etc without checking the bolt length etc – which is what I do be it at work or at home when building something new)
It was in answer to the OP saying he might speak to ribble about it. I wasn’t suggesting they would go “sure, you’ve knackered your bike by fitting them without checking etc but hey, it’s ok – we’ll see you right……”

Seriously – the OP asked for some advice. People have given it. If it were me (or you by the sounds of it) you would have checked first, and put it down to experience that it was damaged post your efforts to fit it and not gone back to the shop to complain – as a lot of other posters suggested that the shop had got it wrong- etc but the OP didn’t and came on here asking for an opinion.

Shorter bolts would be fine.

Unless you fancy this as an excuse for a bigger disk on the front 🙂

I’d be scared the bigger disc would exert more pressure and snap the forks lol.

Do I have to use the cone washers?

Oh and can anyone measure the bolts on their 160mm shimano calipers please. 🙂

Assuming you haven’t stripped the threads in the fork, then either get shorter bolts or a 180 mm rotor and you will be fine.

No the threads are fine. Don’t think there is any damage internally.

I guess it’s just if the bottom mount cracks and snaps off.

So what exactly is the damage to the forks? Looking at the flaked paint, to me it looks like you’ve only just slightly deformed / bulged the (threaded?) ends of the mount where it meets the outer.

The mounts are on the outside of the outers, nowhere near the internals – as the threads aren’t damaged I’d really not worry about it. TBH lots of RS forks have paint that peels off in large flakes, if it was thicker you wouldn’t even have noticed.

Like you said at the very very worst the mounts (yes, then the caliper too) would come off, but the fork itself would remain structurally safe.

It looks like it’s bulged the magnesium there is what looks like a hairline crack going round the bottom of the mount.

Think I’ll send them to loco and see what he says.

Ok, fair enough on loco’ing them if you suspect a crack.

This is the underside I’ve just noticed:-

So the bolt bottomed out and deformed the mount itself? How big an Allen key were you using?!

Looking at that I’d be VERY wary of using the forks now.

Bear in mind a cast structure isn’t the strongest structure, and there is now a fault in the casting, which will get worse. The lower mount is continually being cyclically loaded in tension (think about how the brake works – lower mount being pulled in tension under braking, upper mount being compressed) I’d be looking for some new lowers.

Sorry mate – don’t want to scare monger but I’m sure you like your face as it is. The forks won’t collapse but I’d bet the mount coming off at some point with the brake attached.

There are certain things that folk who are lacking in common sense shouldn’t be allowed to do, and this is one…

FFS did it not even occur to you that by removing the adaptor you’d probably have a bolt 10mm longer than you’d need.

And they’re bollox’d, ebay ’em 🙂

Well if it was me I’d use them and not worry about it, but it’s obviously up to you.

<unhelpful>At least you won’t do that again though 🙂 </unhelpful>

So the bolt bottomed out and deformed the mount itself? How big an Allen key were you using?!

I would be asking how big a drill the allen key bit was attached to…

That must have taken some ooomph to do that?

are you sure its not a sticker?

Personally I’d be inclined to use them but check them properly before and after every ride.

lower mount being pulled in tension under braking, upper mount being compressed

Both are in compression – unless the wheel is rotating around the brake pad not the axle, and if it’s doing that you’ve got bigger problems 😉

There are certain things that folk who are lacking in common sense shouldn’t be allowed to do, and this is one…
FFS did it not even occur to you that by removing the adaptor you’d probably have a bolt 10mm longer than you’d need.
And they’re bollox’d, ebay ’em

Ok thanks.

I assure you I didn’t use any force at all.

I’ve built lots of bikes and never had an issue. Today I made a mistake.

The resistance was no more than the usual resistance from the blue stuff on threads.

Like I said I have no idea how deep a mount bolt hole is so had no idea 10mm would make such a difference.

It’s a tough call, the casting is obviously damaged but to what extent and to what effect this will have will be virtually impossible to determine without X-ray equipment ect.

Personally I would ride them but keep checking the lower mount after every ride. It’s unlikely you would have a catastrophic failure without getting warning signs fist of the disc rubbing so just bear this in mind during a ride.

Ditch those long bolts and the washers and just use a pair of standard m5 caliper bolts with the fixed washer

Mosey, that sucks. The crack in your bottom mount does look worrying. The course of action I suggest for you would be as follows (similar to that already suggested but with a couple of important distinctions)

Run a 5.2mm drill all the way through the mount. It looks in the last photo like you should be able to drill right out the other side of the mount, which I would do if possible but your aim should be to get atleast 4 or 5mm past where the crack has occurred. Don’t use a 5.5mm drill, this would be good if you were using a fine pitch thread but the threads are standard pitch and a 5.5 will result in a very weak thread.

Run an M6 tap into the hole you have just made deeper.

Get a bolt is exactly the correct length, leaving around 1mm clearance at the bottom of your new deeper hole (or ideally you have been able to drill right through the mount in which case just get a bolt that just protrudes).

If you do this you will be bolting into at least 4/5mm of good thread, beyond where the crack has started which should reduce the stress on the crack and with luck, your fork will hold together just fine.

Obviously, then check the forks every time you ride. Good luck whatever you choose to do.

Cheers winch. I think I’m gonna find out about new lowers or just sell them as spares and repairs.

I will see how much new lowers are. If it looks expensive I may as well buy new.

I think I’ll get a second opinion in person from the LBS.

What a muppet I am.

Bolts aside – if they are M6, just run a 5.5mm drill through there CAEREFULLY to clear the back out then run an M6 tap in to clean the rest of the thread up.
If there was that little material left at the base of the hole than I wouldn’t worry about strength.
I’d clean the back with a countersink too just to make it look nice.

Don’t use a 5.5mm drill. The correct size is 5.1mm. 5.5mm will only leave 0.25 of material each side of the bolt.

What a muppet I am.

I wouldn’t beat yourself up about it. It’s not as if you drove a petrol tanker into the local orphanage while throwing kittens out the window.

Well Jamie, you don’t know where I’ve been this evening yet 😉

Well Jamie, you don’t know where I’ve been this evening yet

Not again! 🙁

funny new post to post 180disc ones, two bolts instead of four, probly to save a couple of grams, that’s pretty poo…

They’ve been around for 3 years or more. Much neater mounts imo.
Sorry tho mosey, no help there I know. Sucky situation, most of us have popped threads or filed a bit too much off something etc along the way.

I’d be scared the bigger disc would exert more pressure and snap the forks lol.

less force from a 180mm rotor, so it’s ok. If you need a new mount and bolts just PM me, I have a box full and don’t use PM forks these days, got spares I can send you foc.

Cheers mate, I appreciate the offer.

Think I’m gonna need new lowers minimum. The crack doesn’t look safe at all.

Ill see what happens next week.

Me…I’d pop a 5mm drill in, go about 10mm deeper & run a tap down. Take the bolt down past the kinked bit. I would have thought the threads would strip before it did too much damage.

Ben Cooper is right, both the mounts are in compression so the crack may not be the end of the world. I’d try a bodge before forking out for new lowers.

Anyone Manchester/Stockport way wiling to give a bodge a go? I’ve not got a drill or the knowledge to do that.

I can bring you beer in return 🙂

Anyone any idea how much lowers are?

I’ll do it for you if you can’t find anyone local, you just pay the postage. Obviously no guarantees provided what so ever etc etc!

Lowers are about two hundred quid, but that’s ready to roll with decals and axle and everything inside like bushes and seals, you just do a lowers service and slide em on instead of the old ones..
You’d have a spare axle and hose guide in the end as well if that’s any consolation..

See I can get new forks for that. Would I be better selling mine as spares or at least the moco unit and buying new?

Lowers are silly expensive. If you’re going to write off the forks then I’d say yes, strip them for what ever bits you can sell and buy some new ones.

They are the RL Gold model. No idea how much to sell the csu, damper etc.

I’ll ring loco see what he says and go from there.