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Discussion Starter · #1 ·
Hi Guys...this aluminum frame Epic Comp has been solid for 3 years, only the consumables had to be replaced.

Suddenly the rear through axle is getting loose all the time. After 1hr ride, axle worked itself completely out. Lucky, it came out when I stopped.

Nothing on Utube on this. Anyone run into that? The axle does not have lock mechanism. Bike shops are busy and I want to keep riding.

Question along same lines: how tight should that black locking nut against bearing should be? Pictures show axle in place, the 2 nuts on rotor side and nuts removed - bearing showing.

Thanks!
 

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Regarding the axle, you can try to clean it and apply one or two drops of blue loctite, or equivalent product.
Never had a axle come undone, but I would be freaking out if it would happen to me :/.
If those are the formula hub that usually come on specialized bikes, that black lockring should be tight enough to prevent any axle play, but not tight to the point where it's forcing the inner race to much, because the axle don't have shoulders to support the inner race. If I have to quantify, I would go with stronger than finger tight but not much more. Tighten in small increments until you feel the bearings no longer run free and smooth, than back the lockring and check if runs free and smooth, repeat until you don't have play and the bearings run free and smooth, it can take a couple of tries :).
 

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Discussion Starter · #3 ·
Thanks Aglo for the hints! TMK Loctite will only work on clean metal. The through axle has grease on it - not sure it's needed? Should I clean the whole axle?

I will adjust the lockring per your suggestion.

Still very puzzled what's causing the axle to unscrew itself.
 

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If I'm not mistaken, all my thru-axles came dry and with a drop of loctite from factory.
But I always apply a thin coat of grease on the threads because I don't want them seized. But if your thru axle is coming undone, you have the opposite problem.
Just clean the threads on the thru axle and nut, and apply some thread locker, the tread locker also prevents corrosion so you don't need to worry about getting the thru-axle seized.
Don't forget to let the thread locker cure, usually around 24h is enough.
I have seen some people complaining about the thru-axle coming undone, but I don't remember anyone reaching a consensus as to why it happens.
 

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Thanks Aglo for the hints! TMK Loctite will only work on clean metal. The through axle has grease on it - not sure it's needed? Should I clean the whole axle?

I will adjust the lockring per your suggestion.

Still very puzzled what's causing the axle to unscrew itself.
Try to get Loctite #243... it is a little more tolerant of oil/grease contamination
 

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The black and silver nuts should be tightened very firmly against each other. It's somewhat like adjusting a cone type hub. The black nut is only very slightly tight against the bearing, but very tight against the silver nut. You hold the black nut with a cone wrench and tighten the silver nut firmly against it. The trick here is not getting the black nut too tight against the bearing when the silver nut is firmly tightened.

Some hubs have the same setup on the drive side with left hand threads.

In general, loctite isn't used in this application.
 

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Discussion Starter · #7 ·
My problem was (is) I did not have a proper 19mm cone wrench to hold the black nut and get it real tight against silver one. Made one this morning, but not very good (short handle) and waiting for proper one to come in.

For now cleaned the grease from axle and threads. Will test ride tonight. As it is, the axle was loose every ride. Will report progress.
 

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Discussion Starter · #8 ·
Hi All...anyone one know if cartridge bearings are pressed into hub against some stop lip? Or does friction hold them in place?

I got the black lock nut set by bike shop and tightened, but after 15 miles the wheel wobble is back. It appears the bearing is drifting towards the center of hub.

Can't think of anything else. Have not looked at the other end - the cassette end, if anything that presses against the other bearing is loose.
 

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I don't know for sure what hubs you have, but as I said before they probably are some Formula hub.
In this hubs the outer bearings races sits against a lip on the hub shell, and the bearings are held on place by an interference fit. The axle goes in thru the drive side and has a lip that sits against the inner race of the rights side bearing. On the non drive side the axle is held in place by the lock nuts. So, if the bearings are pressed in correctly, if they aren't shot, and the lock nuts are tightened correctly there shouldn't be any play/float.
But it's a bad design that causes premature bearing wear and the lock nuts need to be set correctly so it doesn't exacerbate the already premature wear.
 

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Discussion Starter · #10 ·
Hi Aglo...I do not know who made the hubs - they are listed as Specialized hubs in the data. Appreciate your guidance on this. I'm going after the bearings, as that's most likely suspect at this point and all that expensive. I have approx 2K miles on these bearing on clean trails. I avoid mud and water. I'll let LBS do the bearings. Unfortunately it's a long wait for shop time, so I'll be riding lame bike until then.

I hope to report on results, once new bearings are in.

Thanks.
 

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Discussion Starter · #11 ·
I had drive side bearing replaced and for now situation is stable. The rear wheel does not wobble and axle does not move. Perhaps worn bearing caused the movement and other things got loose.

I noticed front axle is larger OD, than rear. Felt there's more load on rear wheel. Maybe the heavier axle is to add stiffness to fork.

Specialized Epic Comp 2017 - anyone know what part number wheel bearings this bike takes? Front & rear, but especially rear. Specialized does not list them, or I can't find them. Their TS is closed.

Thanks.
 

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you read the part numbers off the seal. 6809 i think.

now i have rebuilt these hubs thrice.

look up sram 746 hubs to see an exploded view.

you need three wrenches to set the preload.

remove the brake rotor
take the 19mm and hold the inner part firm.
use a crescent wrench or similar to back off the outer nut.

its a lock nut. designed to be tightened against the preload nut.

the axle is super soft aluminum. it stretches as you tighten down the locknut. be gentle. if you cant break it free with fingers it should be fine

now how do you tighten them against each other. insert a suitably sized allen wrench into the axle end or as i do. find a nut that fits and tighten two down against each other on a piece of threaded rod. then grip the rod with vice grips.

set the wheel on a garbage can or the garbage bin as i do.
set a finger tight preload
finger tighten down the locking nut
then insert the tool into the axle end to hold the axle from turning
force the inner preload nut against the locking nut with the 19mm and the crescent wrench.

everything will shift.

this is why you removed the rotor

hold it up vertically and grab the hub and spokes with your fingers and press your palms into the axle and see if you can make the axle shift left right. it shouldnt move

but if you hold and spin the wheel. the axle bearings shouldnt feel notchy. they should spin smooth

beacause of the way things shift and the play in the tool fitments etc. you will have to mess with this a few times before you get smooth bearings and no axle shift. it may help to have an assistant hold the axle tool


its dumb. an inner bearing spacer machined to fit would solve it all. but that part has to be dead on.


good luck
 

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upgrading to a set of angula contact bearings would make things last longer, but they require perfect bearing preload as well. usually done with a wave spring washer.

enjoy!
 

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Discussion Starter · #14 ·
Anyone know the clearance between wheel bearing inner race and axle OD? Thanks

upgrading to a set of angula contact bearings would make things last longer, but they require perfect bearing preload as well. usually done with a wave spring washer.

enjoy!
 

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Discussion Starter · #15 ·
Thanks Fuse6...if you could make a video of this procedure - it would be great. Have not seen one on YT. My axle OD is about 12mm, so 6809 is unlikely, as it has ID of 45x58x7.
 

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Discussion Starter · #16 ·
...and thanks for pointing me to SRAM 746. Found the diagram at:

https://www.veloruf.de/n/shimanoteile.html?id=50191219

...and helpful thread on mtbr

https://forums.mtbr.com/wheels-tires/sram-mth-746-hub-help-1087454.html

Seems others had similar problems. At present the wheel is not wobbling, so do not want to mess with it. Forgot to check the bearing numbers, when I had it apart.

you read the part numbers off the seal. 6809 i think.

now i have rebuilt these hubs thrice.

look up sram 746 hubs to see an exploded view.


good luck
 

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I think your problem has to do with the bearing preload and tightening of the lock nut which others have addressed. But since loctite was mentioned, a better alternative for the larger diameter axle that tends to have oil and grease migrate to the threads, is teflon tape.

Wrap a couple turns on the threads while gently pulling on it so the tape slightly stretches, in the direction a nut would tighten on them. It's good to count the turns in case it's too tight or not tight enough you have an idea what to do if a wrap needs to be added or removed. Regular teflon tape will probably only last once and have to be reapplied once the axle is removed. However, if you get the tape for use with natural gas it is thicker and may last longer. There are some premium brands that are advertised as being thicker as well. I know this is a bit of a tangent but teflon tape can be useful in certain situations that loctite might be helpful but not work well.

There is also a product called vibra-tite VC3 that gets 'tacky' but remains flexible and allows removal and repositioning unlike loctite that gets hard and fractures once the fastener turns. This is the stuff that comes on bolts that aren't installed and looks like a patch of loctite already applied and dried.

Edit: typo
 

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The hubs are made by Formula and I had the same problem with the wheels that came on my 17 Enduro comp. They're good wheels and have sense put them on my daughter's 19 stumpy comp. The wheels on her bike were stupid heavy and wouldn't take to tubeless setup to save my life. Any how, I had the same issue with the wheel becoming wobbly. Found that the preload wasn't correct and would slowly back out. I agree with what others have said about cleaning the threads and tightening and preloading those lock nuts.

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