Bicycle Mechanics - What is wrong w/ this stupid bike? HELP!

When climbing a hill, or when an abrupt load is put on the crank, it will sometimes slip about 90 degrees. So if you are standing up, climbing a hill, sometimes the pedal will just drop out from under you. The chain alignment is fine, and the chain rings have plenty of life left in them. I don't know what to do about this because I can't trust it on a hill. I am afraid that at any moment, it is going to let go and dump me. This is a Giant XTC 2 hardtail w/ a Raceface evolve xc crank. Can someone give me an idea here, because my local bike shop has no idea. It is only 2 months old. Thanks a lot!

How radically angled is your chainline when this happens? Are you in a big-big combo? Assuming you aren't getting rub and the derailleur isn't misaligned, maybe your chainline is too sharply angled, pulling the chain off the ring. Perhaps an adjustable BB might help? Other possible explanations might be a crooked or broken chainring tooth or sticking link on the chain.

Check the rear hub. The prawls inside or the teeth they engage with or both may have worn out.

If you are not familiar with taking a hub apart then have your LBS take a look at it.

Also, if you are a larger rider such as my self and use a lot of torque you will round out the prawls very easily. If it is some what of a new bike it may be covered under warenty.

:beer:

p.s. Welcome to the forum.

What wheels/hubs are on your bike?

Originally posted by dirtbikedude
Check the rear hub. The prawls inside or the teeth they engage with or both may have worn out.

Erf... I misread. I thought the original poster was saying that the chain was getting dumped after 90 degrees of rotation.

I forgot to add that this problem has gotten steadily worse over the past few weeks.

Here are the bike specs:
frame Supersized ALUXX SL double butted aluminum frame, integrated forged headtube, double integrated gussets
fork Manitou Skareb Comp, 3" travel
derailleur Front: Shimano Deore, Rear: Shimano Deore XT
derailleurshifters Shimano Deore, 9-speed
cranks RaceFace Prodigy Ride,ISIS Splined, 22/32/44T
pedals Shimano M505 Clipless
handlebar Titec Enduro XC, 6061 butted
stem Titec Fast Al
headset FSA Integrated, Cartridge bearings
levers Avid AD3
brakes Avid SD3 direct pull
saddle WTB Rocket V
seatpost Titec X-Wing 27.2
rims Mavic X221, 32H
hubs Shimano, 32H, QR, casset
tires Hutchinson Python Air Light, 26x2.0
cassette Shimano HG-50 11-34T, 9-speed
spokes Stainless Steel 15G


My friend has almost the same bike except 2 years older. He had almost exactly the same problem and it turned out to be the bottom bracket failing. Is that a possibility here? Thanks again everyone!

They might be Deore hubs.

Originally posted by jchristena
My friend has almost the same bike except 2 years older. He had almost exactly the same problem and it turned out to be the bottom bracket failing. Is that a possibility here?
Maybe -- I had something similar happen with my Trek MTB. Sometimes when I would stand on the pedals I would get a 'pop' from the drivetrain. I checked the chain and it seemed fine and the LBS checked the hub and it was fine, as were the chainrings and cassette. Finally the guy at the shop noticed that the BB had a LOT of slop in it -- you could grab a crank arm and move it like 5 mm in & out. What was happening was that under load the loose BB allowed the chainrings to deflect sideways enough that the chain was riding up on the tops of the upcoming chainring teeth instead of meshing properly and that was the 'pop' I was feeling. Haven't had a problem since the BB was replaced.

Well I am thinking it COULD be the freehub body, the b.b, or the cassette slipping on the freehub body itself. I would check all three, or since it is so new take it back to your LBS and have them check these things out.

They had a problem with the Formula hubs but since it doesn't have them, that's out. Have you ever tried removing the rear wheel and reseating it? Probably have but it's just a thought. Might be in a little cockeyed. Other than that, do like Hunter said and have the lbs check the cassette, bb and the freehub. It also might help to have someone ride close to you on a hill and watch to see if the chain is jumping cogs or not. If it's not, it almost has to be the cassette or freehub.

This is going to sound really left field but...

A work colleague recently had problems with his chain jumping on the 11T cog (MTB chainrings, etc). He had just fitted up a Wipperman chain with Powerlink during a process that saw him replace the cogset as well. Well, the problem just refused to be sorted. New freehub, all sorts of dismantlment and readjustment by a mate (not me). It caused a fair degree of mirth and merriment among other bikers in the office. Then he mentioned the problem to his LBS.

"Wipperman chain?"
"Yes."
"The 11-tooth cog?"
"Yes."
"Have you got the Powerlink the right way round?"
"WTF!!!!!" Blank look and dropped jaw.

So, check your chain and see if it has a Powerlink. Apparently the link has a "fat end" and a "skinny end" on each half. The skinny end is supposed to be in front on the inboard side of the chain (ie, the side that faces the hub). With the Powerlink the wrong way around, the cog next inside the 11T was picking up the fat bit and causing the chain to jump. Maybe to do with the shape of the teeth and the ramping. But don't ask me any more about the technicalities because I don't know. He swapped the link around, and the problem was solved.

Just a thought from someone else's recent experience (and Jaimie65 and I are still chuckling over it).

R

*sigh*

First of all, powerlink's would belong on SRAM chains, and they are omnidirectional. Only one way they can go.

Secondly, slippage is caused, usually, from maladjustment of the derailuer. 90% of the time that this happens on a new bike is because of cable stretch. Under load, the chain tries to torque up or down. The stretch allows the derailuer to slightly pull down, enough for the chain to hop, but stay on the cog.

If you've had this checked, we move on.

The chain. If it is a new chain, on an old cassette, it'll happen. The cassette wears with the chain. a new chain is not stretched out, and the cassette is worn to a chain that is. Slippage ensues.

NEXT

The cassette. Looks like lots of life, but are the teeth "shark fin" shaped? If so, new cassette time (along with a new chain, and sometimes, new chainrings). This can happen in as little as 3 months.

if the bike is stock, chainline is not an issue.

A side from chainwear/cog wear/chainring wear and cable stretch, not much else can go wrong on a new bike.

The pawl's wouldn't be rounded out. The Deore hubs are cheap, but they aren't total ****. They will last a few months. My old Joytech lasted more than 2 years.

It might be a tight spot in the chain. Check that also.

From what you've described, it has to be one of 2 things: Either your chain/cogs are worn out (easy for a bike shop to check), or the pawl is gone. Neither should happen in a 2-month old bike, unless you ride 200 miles a week. Go back to the shop you bought it from, and make them fix it. Then don't ever go back there again, because they are jerking you around hoping to avoid a warranty repair.

That is definatey a problem shop if they are jerkin you around like this. Never go back.

The pawl? I'm sorry, is there another term for that that I may be more familiar with? Pardon my ignorance... I had a couple of shops check the teeth on the chainring and both said that they are perfect... The bike probably gets about 40-50 miles a week on it at most. I appreciate all the help!!

the pawls are what engage the free-hub body.

They could have been rounded off or damaged.

Derailuer maladjustment is my guess for the problem.

i have the same problem. switched out the bb cranks cassette and freehub from one frame to another. under load something slips, although i don't notice what. thought it was the rings/cog/chain but after i came upon this thread, i figure it might be the bb or freehub that's worn (probably the bb). i knew it had to be something other than the chain and ring and cog because it's a singlespeed. will double check the bb but what can i do to fix it? should i just replace it?