Disc brake fitting

[Phil Fouracre]

Not sure if this is the right place for this, ''tis query on mtb fitting, but, only used on the road
Just doing a bit of cleaning and maintenance on my Giant Stance, bought purely for comfort, not performance. Thought I'd check pads and clean everything. My query is, when reassembling, and gently tightening the bolts fixing the disc brake housing to the base of the forks I managed to strip the thread!! First time it has been taken apart, and, I was retightening hex key only between thumb and finger, not exactly forcefully, now, really pissed off!
Worse, when I removed the bolt again, there was alloy on only the last two threads! So not exactly well fitted at factory. Don't know if it would be a Giant fault, or Rock Shox?
Also, wondered about the washers used, why would cap and dome washers, normally used on rim brakes, be used on this, as there is no adjustment for the disc housing to move this way?
Should I have a moan? Or just get some longer bolts? Anyone know how much thread there would be in the base of the shock?
Suggestions appreciated.

[gloomyandy]

What make model of brake is it? Seem to remember that Avid/Sram use cup and dome washers to provide adjustment/alignment of the caliper.

[Gattonero]

You ought to have about 10mm of thread engaging the PM mounts.
If you say there is only two threads, then a short bolt was used and is manufacturer's fault.

Are they the original bolts? Easy to spot because they often have a knurled/ribbed surface on the head plus the blue patch of threadlock.

But why would you remove the calipers? There's no need for that even for the deepest cleaning, just remove the pads from the caliper.

[tim-b]

Hi
Does this brake have a longer mounting bolt and a shorter one?
I think that the washer order is recessed threaded on to the bolt first, followed by the domed (flat faces to bolt head and caliper )
Regards
tim-b

[Brucey]

is it like this?



if so the curvy washers are fitted in this case not for adjustment as in Avid calipers but to allow for the fact that the bolts would otherwise be bearing down at an angle on the back of the caliper, once the caliper spacer is fitted. This need for this sort of thing (plus the fact that you have easily stripped threads in the fork itself) is a weakness in the post-mount design. The fact that the bolts appear to be too short is probably a fault in production.

I would suggest that you could clean the threads in the fork (with a tap M6x1), and fit longer bolts. Better yet, studs could be fitted to the fork with threadlock, and nuts used to secure the caliper. This way the remaining threads in the fork can all be utilised and will also see the least load/wear in future. Do check, but IIRC the usual bolts are 10.9 grade. It is best if you replace any hardware with a similar strength grade, and to use threadlock of some kind. The usual bolts have a smear of blue threadlocking paste on them.

BTW do check what the correct torque setting is for these bolts; the fork lower may well be a Magnesium casting, and the torque setting may be lower than you expect; threads are very easily stripped in Mg castings.

Although I would probably have take the thing apart and (hopefully) might have noticed that the bolts were too short, I would be hopping mad if this had happened to me with a new bike BTW. If there are not enough threads left in the fork now, the cure is either fitting thread inserts (helicoils) to the fork, or replacing the fork. If the bolts were too short it ought to be the retailer's responsibility to sort this out for you.

cheers

[Phil Fouracre]

Brucey - fantastic, many thanks for all that. Yes, exactly as your picture. Was wondering about washers, as flat face of disc mech was against flat face on forks, wasn't thinking of bolt head not sitting flat. Think I will go for your stud option, as 'belt and braces', maximise whole depth of thread and lock it in position. Was even thinking of drilling and tapping for larger bolt! I would guess that as shocks are on a basic bike they would not be particularly high spec, so would that mean lower quality alloy? Even though I'm 'a little fed up'!! and, assume it's within warranty, I really don't want to be into returning the forks and being bike less. Having not had good experiences with bike problems/repairs from dealers in the past I'd rather sort/hopefully improve it myself. Thanks for info on bolt spec, have a very helpful local firm, Western Bolt, who have been great, over the years, with all sorts of weird requests! Now intend to remove and check all bolts, as we bought two identical bikes, assuming all wrong!!!

[Brucey]

the bolt grade is usually marked on the heads of the old bolts, but some OEM caliper bolts have a special manufacturer's mark that identifies them instead. In such cases you can only work out what the strength grade is by reference to the manufacturer's data.

cheers

[bobc]

Be very thankful you found this in safe circumstances. Potentially lethal manufacturing error by the sound of it.
Hopping mad is well understated....

[Gattonero]

...Was even thinking of drilling and tapping for larger bolt! I would guess that as shocks are on a basic bike they would not be particularly high spec, so would that mean lower quality alloy?...

You could use an Helicoil, though works in a situation where you have more material around. In such case, the problem is that you won't have enough strength supporting the Helicoil, it's likely to fatigue and crack in the long term.

I would advise to have it sorted for good with a warranty, before doing the job yourself: ain't your fault and you've paid money to have something working right in the very first place!

[tim-b]

Hi
If your Stance has a 180mm disc then it will need a post mount adaptor (160mm doesn't). The adaptor may have a "thin" end and a "thick" end as Brucey's photo.

Does this brake have a longer mounting bolt and a shorter one...

...to accommodate that difference and are they in their correct mount holes?

I'd be surprised if the fault that you describe made it through assembly without stripping, and QA and pre-delivery at the retailer

Regards
tim-b

[Phil Fouracre]

tim-b, thanks for that, exactly right! Decided to investigate further yesterday, after bruceys help, and yes, removed both bolts, and one longer - fitted wrong way round! Have checked depth of thread in tapping, and, even with the bolts fitted correctly, they do not utilise it fully. Am now going to go for new bolts long enough to use all of the thread, or, thread lock stud to full depth!

[NATURAL ANKLING]

Hi,
If tapping hole in soft non ferrous metal always use some cutting fluid, if non available then some gear / engine oil on tap.
Soft metal is notorious for ripping if tapped dry.

If using a stud then do not over tighten into thread, be careful there, let the threadlock (medium strength) dry first before tightening the nut.
Studs fitted at factory in this type of application normally only have threads on the stud on the portion into the base metal, then a plain shank then the nut threads, so its like a double ended bolt (manifold studs) the short thread binds into hole when thread runs out, also the thread may well be tapered to lock the thread in hole.

But care is needed to make sure that the application will with stand this force expanding hole, when using manifold studs.
You will need to use plain studding / headless bolt at correct spec to be safer.
BUT if tapping hole deeper make sure that the drilled tapping hole (either you drilling deeper, not too deep! / existing depth) is deeper that the threaded hole so the plain stud will jam on unthreaded portion and NOT bottom of blind tapped hole, using a taper tap (2ND taper) will make sure that the stud jams in the taper threaded part for sure.

More likely that the stud bottoming in hole will crack the threaded mounting boss than a manifold stud if my points above are not followed.
Good luck, take your time.

[reohn2]

tim-b, thanks for that, exactly right! Decided to investigate further yesterday, after bruceys help, and yes, removed both bolts, and one longer - fitted wrong way round! Have checked depth of thread in tapping, and, even with the bolts fitted correctly, they do not utilise it fully. Am now going to go for new bolts long enough to use all of the thread, or, thread lock stud to full depth!

Just to add,the top bolt is almost wholly in compression under braking so utilising almost the full depth of the tapped hole with a bolt long enough even though a two or three threads are goosed shouldn't be detrimental to performance.

[Phil Fouracre]

Many thanks to everyone for their help, it always amazes me what a mine of useful info this forum is, and how happy members are to offer help and advice. Just fitted new, longer, bolts with the cap and dome washers, spec as per bruceys suggestion, and added blue thread lock. Will keep a careful eye on everything from now on!