[Disk Brakes] I Stripped a Thread in a Disk Hub. Now What?
 

Yup. It was one of those just happens to other people sort of things, but I really did it this time! I sort of don't have the budget for a new hub right now, even one of them "affordable" Aliexpress types. I put some extra blue Loctite on the bolt and stuck in in there, but will I die if I ride the bike with the other five bolts securing the front rotor?

Also, the hub's rotor mounting flange is the full type, meaning that - in theory - I could drill six new holes at 30° off of the original ones and tap them out. Question is can I - or should I - attempt this sort of repair at home? And, if I do attempt it, should I be using a 4.5mm drill bit for an M5x0.8 thread, or will a 4mm drill bit do?

Is there room for a nut behind the rotor mount?

If I can find me one of them low-profile, Nyloc type nuts, maybe! But a regular, non-Nyloc, low-profile one will likely fit with room to spare. I'll take a look and report back.

Jam nuts.

​​​​​​https://www.mcmaster.com/products/jam-locknuts/

Or Helicoil. Or tap the next size up. Or use a rivet.

Or skip it - there are 5 others.

Thought of doing that, but elected not to go that route because there isn't that much material between the hole and the edge of the flange...

+1 on Helicoil

Barry

Front or rear? What sort of riding? I'd be inclined to fit a thread insert, or just clean it up and add a drop of JB Weld.
You want a 4.2 mm drill and M5x0.8 tap.

Front. Just normal city street riding in a pretty flat urban environment - nothing extreme.

M4x0.8 is what I meant to type; no idea what happened there! I already have a set of taps in this size and a 4mm standard bit. I've also got a 4.2mm bit, but that one is the wood type.

use a nut or jam nut and some locktite, or a helicoil. you can get good helicoil kits on ebay

/markp

ummmn, some Disc Brake bike hubs used to only have 4 screws... i can see a 4 screw hub from here.....

i bet 5 screws will be fine for a while, considering 4 worked so well in the past.

I'd keep an eye on it.. check it frequently... which should be done anyway, right?

just a thought... :innocent:

Weight weenies will run just 3. I ran 5 for a long time on a rear of one of my mtn bikes after one of the holes/tabs on the hub broke.

You will probably be just fine running only 5 bolts--the most likely problem is worse disc alignment. This is unlikely to kill you.

I might consider getting a slightly larger tap--#24 is 5.48mm wide, or you can tap to 5.5mm if 6mm looks sketch. Or helicoil it back to 5mm.

Helicoils require miminal hole radius increase, equal to the depth of the original thread. (Thread depth equals approx. 0.7x pitch) So odds favor Helicoil as a practical solution.

Otherwise, you might cut a bolt down to make a threaded stud. Push it through, and superglue or Loctite a thin nut behind the flange. Once cured, use a nut on the front for the rotor. The advantsge is that you're not tightening with minimal thread engagement.

OR

Do nothing, and assume it's still fine for non-severe conditions.

I would also vote for Heli-coil as the clearest expedient method for repair. Make sure of what size fasteners you are working with, though; there seemed to be some confusion in what the actual thread spec is.
As a side note, if you have a set of number drills (1-60), there will be something much closer than half-millimeter increments for drill selection for tapping a hole. In the case of the Heli-coil, make sure to use the recommended drill size and the tap provided in the Heli-coil kit, or the correct tap for the insert however you procure the gear.

As others have noted, if the other screw connections are good, probably nothing to worry about.

I've heard of weight weenies running 3 bolts in a rotor. I ran 5 for a few months and didn't die.