# Disc brake post-mount stripped on fork lowers



## derockus (Mar 27, 2009)

So the threads inside one of the post-mounts on my crappy Dart3 are stripped. Not sure how it happened (didn't ham fist it). My plan was to buy a self tapping bolt (don't know if I can get an allen-head kind) that is slightly larger than the current bolt and remount that way. Does anybody have any better ideas? (No, I'm not going to buy a new fork, bike is just a goof-off project anyway.)


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## gmcttr (Oct 7, 2006)

Google Heli-Coil. Do it yourself if you are good at that sort of thing or have a machine shop do it for you.

A self tapping bolt sounds like a bad idea.


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## nov0798 (Nov 27, 2005)

Are you sure the threads are messed up? try installing a new bolt with new threads first. If you dont have a tap set to chase the threads, then try to slowly insert a new bolt, and see if it cleans them out. put the bolt in a little, then back out, then in a little, then back out, and so on. Use a lubricating fluid while doing it to help with any friction. 

If that doesnt work, then heli-coil is a better option as the GMCTTR noted.


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## derockus (Mar 27, 2009)

I am sure the threads are toast. The bolt itself is in fine condition and when it was removed there were pieces of threading that came out with it.

Why do you think the self-tapping bolt is a bad idea? All I can think is that they are not designed for frequently removal... true?


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## mitzikatzi (Sep 9, 2008)

gmcttr said:


> Google Heli-Coil. Do it yourself if you are good at that sort of thing or have a machine shop do it for you.
> 
> A self tapping bolt sounds like a bad idea.


I once needed a Heli Coil installed. The cheapest place around town that would do it turned out to be the Lawn Mower shop.


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## IcecreamLtDan (Aug 1, 2010)

A self taping bolt would probably crack or break the post is why. If you can't get the original bolt back in using some lubricant then the heli-coil idea is your best bet by far.


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## bad mechanic (Jun 21, 2006)

Yeah, pass on the self tapping bolt. There are just too many ways for that to go wrong.

They're right that you need a helicoil, or even better, a timesert:
http://www.timesert.com/


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## customfab (Jun 8, 2008)

This is why I hate post mount.

What bike is this fork on? Felt had made an error and speced bolts that were too short on a couple of models of bikes and they were replacing the lowers for people. This pretty much always happened out of the box but if the original bolt is too short I would contact the manufacture and see if they are doing anything about it. If all else fails a helicoil is a perfectly good solution.


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## derockus (Mar 27, 2009)

customfab said:


> This is why I hate post mount.
> 
> What bike is this fork on? Felt had made an error and speced bolts that were too short on a couple of models of bikes and they were replacing the lowers for people. This pretty much always happened out of the box but if the original bolt is too short I would contact the manufacture and see if they are doing anything about it. If all else fails a helicoil is a perfectly good solution.


The bike is a cannondale F5, my first mtb from a few years ago. They may have made the same mistake as Felt because the bolt that stripped the post was 10mm long and the the other (unstripped one) was 20mm. This ended being the way I fixed it too because theres was about 5-8mm more of threads inside the post. I just soaked a new 20mm bolt in loctite and tried not to over torque it.

This solution should be enough, I'm just screwing around trying to put together a snow bike to dork around on. The fork innards are basically toast anyway, not to mention i bought the thing off craigslist.


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## wv_bob (Sep 12, 2005)

customfab said:


> This is why I hate post mount..


+1 My Salsa has them on the back too.

I wish Avid at least made an adapter that bolted to the PMs, and then the brake to the adapter, so if I need to re-align the caliper the threads on the PMs are not involved. The less I have to run the bolt in and out of the PM threads, the happier I'll be.


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## wv_bob (Sep 12, 2005)

derockus said:


> They may have made the same mistake as Felt because the bolt that stripped the post was 10mm long and the the other (unstripped one) was 20mm.


The bolts should be two different lengths. I don't remember which goes where off the top of my head, but you can tell which is which by looking at the fork. Good thinking of trying the longer bolt in the stripped hole, I'd forgotten about that trick but I've used it plenty before on car repairs.


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## mtnbiker4life (Sep 19, 2005)

derockus said:


> So the threads inside one of the post-mounts on my crappy Dart3 are stripped. Not sure how it happened (didn't ham fist it). My plan was to buy a self tapping bolt (don't know if I can get an allen-head kind) that is slightly larger than the current bolt and remount that way. Does anybody have any better ideas? (No, I'm not going to buy a new fork, bike is just a goof-off project anyway.)


I would get a tap to chase/clean up the threads. Then use Loctite Form-A-Thread compound.

http://www.midwayusa.com/viewproduct/?productnumber=986916


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## Stupidjeep (Mar 19, 2009)

I was in desperate need of a tap to chase threads once, and I dremeled lines down a bolt of the same size. I think I made 4 cut lines down the bolt lengthwise and it worked perfectly for me. I think I remember going slow and using WD40 or something. Good luck


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## TwoHeadsBrewing (Aug 28, 2009)

Just wanted to say a big THANKS to the contributors of this thread! I had the same problem with the stripped threads on my Float 140. I called 3 bike shops locally, and they all either wouldn't work on it for warranty/liability reasons or didn't know how to fix it. Google led me here, I picked up a 6mm HeliCoil kit at the auto parts store for $30 and I'm back in business. Just a quick run down of the process in case anyone else needs the info:

1. Pull the fork off the bike. This will make drilling, tapping, and setting the helicoil easier.
2. Put the fork on a workbench or a firm solid surface.
3. Put a punch or small screwdriver in the hole and mark the depth with a sharpie. Make the same mark on your tapping tool.
4. Make a mark on your drill bit so that you do not exceed the depth of the hole and destroy your fork lowers.
5. Using the required drill bit, drill out the stripped post mount hole. Take care to go straight up and down, and straight left and right, so the threads will line up properly when mounting the caliper.
6. Blow out all shavings.
7. Using the provided tap, carefully tap the threads and pay attention to go straight in. You can start this by hand, then use pliers or vice grips to complete tapping the threads. Make sure to stop when you reach the mark you made.
8. Blow out all shavings.
9. With the supplied tool, thread the coil insert into the newly tapped threads. Don't force it, it can take a bit to find where the threads start.
10. Screw in the coil until the top is below the surface of the fork.
11. With a punch or small screwdriver, break off the coil insert tab. Remove tab from the hole.
12. Thread in a new bolt just hand tight to clean up the threads(not previously used screw, which is most likely damaged). Remove the bolt.
13. Reassemble fork onto the bike.
14. Bolt on the caliper and don't forget to use thread locker and tighten bolts to spec.


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## Doughnut Spaghetti (Jul 21, 2011)

I would definitely go the Heli coil route, my friend it just did it on the crank case (these are aluminum and notorious for stripping if you over torque your bolts) of his motorcycle it worked perfect, it that doesn't work you may be able to drill it out and re tap it to a larger diameter bolt. Maybe one mm up. Do you have any pics?


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## TwoHeadsBrewing (Aug 28, 2009)

Doughnut Spaghetti said:


> I would definitely go the Heli coil route, my friend it just did it on the crank case (these are aluminum and notorious for stripping if you over torque your bolts) of his motorcycle it worked perfect, it that doesn't work you may be able to drill it out and re tap it to a larger diameter bolt. Maybe one mm up. Do you have any pics?


Unfortunately, I don't have any pictures. I was way too stressed while drilling into a $500 fork :eekster:! I should have relaxed though, it was a piece of cake. It's a pretty easy task, just make sure you select the correct size HeliCoil for your bolt (usually 6mm), drill straight in and mark that drill bit. If you drill too far, those lowers are toast!


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## Doughnut Spaghetti (Jul 21, 2011)

Did you put a little piece of tape on the bit, so you don't drill to deep?


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## TwoHeadsBrewing (Aug 28, 2009)

Doughnut Spaghetti said:


> Did you put a little piece of tape on the bit, so you don't drill to deep?


Yes, exactly. You can also use a small hose clamp that will guarantee you won't drill to deep.


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