Quantcast

Sram GX 7spd derailleur doing something weird

ChrisRobin

Turbo Monkey
Jan 30, 2002
3,217
124
Vancouver
I have the DH-specific 7spd GX shifter, derailleur and the fancy one-piece cassette.

This happens sometimes after a rough descent:

Picture the chain wrapping around the cassette, and then instead of the chain wrapping around the top pulley of the derailleur, it appears to sit 'on top' of the teeth of the pulley. It just takes a little bit of shifting and more riding to get the chain/pulley back to normal. It's not the end of the world; it just makes some clicking and clacking noises and I was wondering if anyone else had that issue. I tried messing with the B-screw but I don't think it has much affect with this configuration of drivetrain.
 

velocipedist

Monkey
Jul 11, 2006
512
607
Cloudland Georgia
My sram 11sp does that due to pulley tooth wear. Ordered a new mech in November, yet to arrive and too lazy to care.

The behavior you describe happens frequently when removing and reattaching the rear wheel.

Otherwise, something seems out of line or slightly bent?
 

ChrisRobin

Turbo Monkey
Jan 30, 2002
3,217
124
Vancouver
Maybe. I also think it has something to do with the upper pulley not being close to the cassette like on a normal drivetrain. When things start flopping around on rough trails, it gives the pulley too much space to move slightly while the chain is bouncing around. I dunno...
 

6thElement

Schrodinger's Immigrant
Jul 29, 2008
9,122
5,971
I haven't bothered to try and work out if I can fix it/what's causing it, but on my DH bike that top pulley on my GX-7 will sometimes go a tooth out of sync on the top pulley. I have to stop and rotate it back a tooth to keep it quiet/working correctly.
 

6thElement

Schrodinger's Immigrant
Jul 29, 2008
9,122
5,971
Mine is a brand new bike/derailleur, narrow wide upper jockey is a dumb idea. I've always thought that with my 11 speed stuff, but that only gets the top jockey out of sync very rarely.
 

Lelandjt

Turbo Monkey
Apr 4, 2008
2,022
406
Breckenridge, CO/Lahaina,HI
Maybe. I also think it has something to do with the upper pulley not being close to the cassette like on a normal drivetrain. When things start flopping around on rough trails, it gives the pulley too much space to move slightly while the chain is bouncing around. I dunno...
I have the XO version of the same stuff and have the pulley pretty close to the cog in first gear. Same distance I’d set 8, 9, or 10 speed. Without the big jump between 1st and 2nd that 11&12spd have you don’t need to have the pulley far away from the cog.
 

jonKranked

Detective Dookie
Nov 10, 2005
70,924
13,422
media blackout
try cleaning and greasing the upper pulley.

is your chain the correct length? and does it happen in all gears, or just certain gears?
 

ChrisRobin

Turbo Monkey
Jan 30, 2002
3,217
124
Vancouver
I haven't bothered to try and work out if I can fix it/what's causing it, but on my DH bike that top pulley on my GX-7 will sometimes go a tooth out of sync on the top pulley. I have to stop and rotate it back a tooth to keep it quiet/working correctly.
You explained my issue in a clearer way. ^^^ This is what I'm trying to describe.
 

6thElement

Schrodinger's Immigrant
Jul 29, 2008
9,122
5,971
You explained my issue in a clearer way. ^^^ This is what I'm trying to describe.
Mine is on a new Commencal Supreme DH, so there's a lot of chain growth at full compression. I recall there was a small tag on the rear derailleur as I put the bike together that said it was only good up to a certain amount of chain growth. I wonder if the bike is pushing that limit?

What frame is yours on?
 

jonKranked

Detective Dookie
Nov 10, 2005
70,924
13,422
media blackout
Mine is on a new Commencal Supreme DH, so there's a lot of chain growth at full compression. I recall there was a small tag on the rear derailleur as I put the bike together that said it was only good up to a certain amount of chain growth. I wonder if the bike is pushing that limit?

What frame is yours on?
this is why i asked about chain length. i busted a link on my scott a while back, and had to shorter it by 2 links. turns out those 2 links were just enough to make it skip on the top pulley in the largest cog.
 

StiHacka

Compensating for something
that was my first thought, but its not. getting the B screw adjusted so the chain didn't skip in the largest cog caused other issues. chain is just too short after removing the 2 links.
As the cage pivot is offset from the jockey wheel's axle, shortening/lengthening a chain directly impacts how close the jockey wheel gets to the cassette, so I still think that is the major factor in your experience.
 

jonKranked

Detective Dookie
Nov 10, 2005
70,924
13,422
media blackout
As the cage pivot is offset from the jockey wheel's axle, shortening/lengthening a chain directly impacts how close the jockey wheel gets to the cassette, so I still think that is the major factor in your experience.
never had the issue before the chain got shortened (due to a break, not by choice).
 

6thElement

Schrodinger's Immigrant
Jul 29, 2008
9,122
5,971
Wife's brand new complete build bike also had this happen a couple of times on her first day out yesterday. I might just investigate getting non-narrow-wide upper jockey wheels...
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,057
637
La Verne
Mine is on a new Commencal Supreme DH, so there's a lot of chain growth at full compression. I recall there was a small tag on the rear derailleur as I put the bike together that said it was only good up to a certain amount of chain growth. I wonder if the bike is pushing that limit?

What frame is yours on?

Are you not using a lower chain guide