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My lads mtb bike (2019 GT Zaskar Caron elite) has a 12speed SRAM cassette on a Shimano HG freehub on a Formula hub. The chain, rear mech, chainring and cassette are replacements and barely used. When he is pushing hard on the pedals there is a slip in the drive (like if the mech is not quite set right) or as if the chain is slipping over a few teeth.
I have stripped and carefully reset the whole drivetrain numerous times but the problem remains.
Is this likely to be the freehub, if this is the case, are the Formula hubs straigtforward to work on and are parts easy to identify and source or would it make more sense to buy a replacement wheel(set)?
Do you have another wheel you could use temporarily? That would allow you to identify if he freehub is the issue.
I might have a spare Formula hg freehub as needed to sort some wheels for a mate recently and had to swap one out off a set of Whyte wheels which are rebadged formulas iirc
I'd start by riding alongside him while he tries to make it skip.
You may be able to see what's happening.
Is it doing it in all gears or just a couple?
Have you set the B gap correctly?
Checked the hanger alignment?
Nixie, fair point though I believe all options have been eliminated with only the freehub still in the frame, I'll try the rear wheel from my big bike.
Singlespeedstu, the effect can be induced in every gear, easier to do in higher gears as more torque is being applied (possibly not technically correct but you get my drift), all other settings appear normal (but will check b screw again as I know 12 speed are very sensitive).
Timbur, is the Whyte freehub removed by holding the 12mm Allen head at the non-driveside fast, then undoing (left-handed thread) the cap at the drive side?
Are the axle caps done up tight? Even a slightly lose one will cause the freehub to skip, normally a 17mm cone spanner to nip them up.
Formula freehubs are a doddle to service. I assume through axel. Sounds like the pawls are sticky.
Swapped the wheel for one from my bike and it worked fine. Stripped and cleaned freehub,pawls and spring, @fossy the pawls were a bit sticky but still slipped after cleaning and refitting. Now suspect new pawls are required or a replacement freehub.
Anyone know where Spares can be had? Pawls have groove through them where the spring locates but it is asymmetric, one side being 3.1mm the other 3.9mm.
Formula is controlled by whoever is bringing in Specialised these days. You can ring spesh warranty or tech support to get advise on spares.
From the fact its a pull out and sealed bearing job with the steel spring retaining 3 steels pawls, you've got a higher end one. Formula's brand website you can scroll through the catalogue and match up which one matchs your hub by looks alone, lots of subtle differences but you can work them out.
The cheaper hubs and freehubs where the freehub bearings and pawls are buried deep under a cheaply formed bearing race with a grove in it, are basically trash and not even worth your time bothering, spares are ONLY available via spesh warranty/tech department and a hand full of online retailers with part numbers like 'prsa0025' 026, 027 stuff like that. THey are often made with teh wrong number of bearings fitted in the race, no lubricant, junk cheap white grease which washs out the second ride in the rain, or the metals used are closer to cookie dough that actual metal. As you can tell i'm on a rant, but it should be more common knowledge this junk exists and many bikes up to around the £3000 price point utilise such junk (mostly specialised tbh), as you'll be buying a new rear wheel to replace your new bikes rear wheel within as little as 7 weeks of regular UK use. Source. Mechanic of 20 years, seen way too many folks being denied warranty by every brand with extremely premature failures and then having to turf out more money when they already have.