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Discussion Starter · #1 ·
I have been battleing this problem for quite a while, here is my story...

When I crank hard over bumpy ground especialy if the back end rails on a log or rock compressing the suspension at the same time as I crank real hard the chain middle chain ring will spin under the chain. This sounded like a classic case of worn chain ring, but it wasnt that old, so stretched chain? anyway I replaced the cassette, chain, and middle chain ring. I had a TON of recomendations to mess with the rear derailur and shifter cable and I didnt think that was the problem but messed with it anyway and developed a bigger problem in the process. So after I created the shifting problem in the rear I got new shift cables and the back now shifts better than a new bike. With the elimination of the shifting issue in the back my old friend in the front raised his ugly head again and under HIGH tork especialy over bumpy ground the chain ring can spin a half turn under the chain on ocassion. Any thoughts? recomendations? here is the setup...

RF prodigy cranks, new 4 arm RF chainrings.
SRAM PC59 chain - new
SRAM 990 cassette - new
cables avid flack jacket - new
XT rear derailur - a year old.

I did hear about Giant passing out new frames in another thread for NRS bikes with shifting problems, anyone know who to contact for that?
 

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I called giant the other day because of my never ending ghost shifting problems on my p.o.s. NRS and the tech department is well aware of this drive train problem. They told me to run the full housing to the rear and drill out the cable stops or use zip ties to hold the cable on. If this didn't work, I was supposed to send the bike in for an alignment check. Which is kind of tuff since I am in the middle of a race season. I don't think they are just giving out frames- at least not anymore.
 

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Fragile - must be Italian
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Chain too long?

BobbyWilliams said:
I have been battleing this problem for quite a while, here is my story...

When I crank hard over bumpy ground especialy if the back end rails on a log or rock compressing the suspension at the same time as I crank real hard the chain middle chain ring will spin under the chain. This sounded like a classic case of worn chain ring, but it wasnt that old, so stretched chain? anyway I replaced the cassette, chain, and middle chain ring. I had a TON of recomendations to mess with the rear derailur and shifter cable and I didnt think that was the problem but messed with it anyway and developed a bigger problem in the process. So after I created the shifting problem in the rear I got new shift cables and the back now shifts better than a new bike. With the elimination of the shifting issue in the back my old friend in the front raised his ugly head again and under HIGH tork especialy over bumpy ground the chain ring can spin a half turn under the chain on ocassion. Any thoughts? recomendations? here is the setup...

RF prodigy cranks, new 4 arm RF chainrings.
SRAM PC59 chain - new
SRAM 990 cassette - new
cables avid flack jacket - new
XT rear derailur - a year old.

I did hear about Giant passing out new frames in another thread for NRS bikes with shifting problems, anyone know who to contact for that?
I have never heard of that problem. I was having a "skipping" problem with my middle chainring on my 2003 NRS, but after close inspection I discovered that my middle chainring was bent!! I straigthened it out and -- voila -- no more skipping.

It sounds like you might have too much slack in your chain. Are you sure the chain isn't too long? Verify the length of your chain by putting your front derailleur in the highest gear ratio (smallest chainring) and the back in the lowest gear (smallest cog). When I performed this exercise I was shocked at how loose my chain was -- it had enough slack to rest on the chainstay! You might discover that you can lose a few links and still be OK. Just don't shorten up your chain too much or you could risk ripping off the derailler in the opposite scenario (biggest chainring + biggest cog).

I would also tighten up the tension adjustment in your rear derailleur as that might help keep out any slack in the chain. When you are banging the bike around, your chain bangs around as well. If the derailleur is letting too much slack in the chain, it could translate into something nasty up front. I've seen people have their chains fall off the front chainrings under severe bumps/ruts...all caused by too much slack in the chain.

Good luck.

Thx...Doug
 

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Im getting chain skipping whenever I put the chain under high loads (ie standing up to peadal on steep hill) It also happens when I peadal over rough spots. IM not really worried since my bike is already a year old and im pretty sure its the chainrings or chain. Odd that you replaced everything and your still getting skipping.
 

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Discussion Starter · #5 ·
the chain is the proper length, in the small small combination the derailur is not all the way in, and in the big big combination there is only a slight bend in the chain and derailur, so that should be good. Tightening the derailur screw could help though, perhaps get a bit more tention on the chain. I think that screw can go in quite a bit further.
 

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Fragile - must be Italian
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Rear der

BobbyWilliams said:
the chain is the proper length, in the small small combination the derailur is not all the way in, and in the big big combination there is only a slight bend in the chain and derailur, so that should be good. Tightening the derailur screw could help though, perhaps get a bit more tention on the chain. I think that screw can go in quite a bit further.
What kind of rear derailleur do you have? Your description of the chain length and the position of the rear derailleur cage doesn't make sense to me. If the chain is tight in the small-small combination, then in the big-big combination the rear derailleur cage should be wayyyyy forward (about perpendicular to the ground) and the chain should be taut.

I am using an XTR 952 (pre-rapid rise) rear derailleur on my bike. I also have a SRAM PC99 Hollow Pin chain, so it should behave similar to your PC59 chain.

Thx...Doug
 

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My guess would be that the combo of the RaceFace chainrings and PC-59 chain is the problem. I also had problems with a PC-59. Try switching to a different type of chain. It's a cheap way to troubleshoot.

I bought a PC-99 (they are thinner) and had absolutely no problems after that.

Also, RaceFace middle rings wear out quickly, even with regular maintainence. I get about 500 miles out of them They are fine while they aren't worn, but after they start to wear, they let go of the chain easily under torque (standing).
 

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check the chain, might have a tight link in there somewhere. experiment w/another chain.

dirt diggler
 

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openwound
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b-screw is not for chain tension

If you're referring to the screw that is adjacent to the derailleur mounting bolt, that's for adjusting the upper guide roller in relation to the cogs, not for chain tension.

To check proper for *proper/correct* chain length, with the bike level, put the chain in the big ring, big cog. The derailleur cage should be at about a 45-degree angle. If it's at a lesser angle the chain is likely too long; greater angle and it's on the short side; and if it rips the derailleur off of the frame...um, way too short. :eek:

I've been battling ghost-shifting issues on my nrs for a time and have only just gotten it -- basically replaced all the drivetrain components and bought one of John's bearing kits. Rides like a new bike now.

cheers
 

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I agree...

dirt diggler said:
check the chain, might have a tight link in there somewhere. experiment w/another chain.

dirt diggler
Replacing just the chain is an easy and cheap diagnoses. If it STILL skips, and you have made sure there are NO bent middle ring teeth, you may have to pony up for a new chainring and perhaps new cassette. Cassettes should last a VERY long time though. I'm into mine (xt 11-34) for about 1500miles now. I just hose off any mud, wipe the chain of major gunk, and relube.

Also, are you positive it is NOT a spent/worn rear hub? If those little teeth in the ratchet mechanism wear down, you will start experiencing slipping when torque pedaling.
 

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openwound
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--Cassettes should last a VERY long time though. I'm into mine (xt 11-34) for about 1500miles now. I just hose off any mud, wipe the chain of major gunk, and relube--

Agreed. I had about as many miles on my last. I'm a firm believer in changing chains fairly frequently which also helps to extend the life of the cogest.

--Also, are you positive it is NOT a spent/worn rear hub? If those little teeth in the ratchet mechanism wear down, you will start experiencing slipping when torque pedaling--

Yup, positive. This is typically preceeded by some pretty nasty sounds -- been there, done that.

Mine was due to worn components, and unfortunately without a cog wear tool it was just too difficult to call so I replaced it. That was the last item and that did it. I am kinda bummed to hear about rf chain rings wearing out. Mine "looks" fine but phaps I should be looking into replacing it soon.

Of course, after blabbing so long, I should also add that I installed a set of the *long travel* arms when I did the bearing r&r. That could be (could have been) contributing to or exacerbating the issues, too... But like i said, now it seems to be working like the nrs I'd come to know and love.
 

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Raised from the dead!

I have 2002 NRS2 and am experiencing the same problem....particulary when climbing or torquing the chain.

Here is the weird part - it only skips in the rear when the chain is on ANY cog BUT the largest one and the smallest one. Is that a derailure issue or simply an out of tune derailure issue? Any thoughts?
 
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