[jbsocal]

I have Eagle GX boost (dub 165 mm crank with a 28t boost oneup) on a boost Lenzsport Lunchbox 29+.

When on the 50 tooth, if I back pedal, the derailleur/chain comes off and the derailleur pulley gets stuck in the cassette.

Anyone also have this issue?

If so, were you able to resolve it?

TIA.

 

[Forest Rider]

Yep

90% of 50t bikes seem to report the chain dropping.
Mine does it sometimes.

A report on MTBR a few hours ago reported they straightened their hanger and now it's fine. Could be some merit behind it but not sure I'm falling for that as the 'fix'.

 

[jbsocal]

Yep

90% of 50t bikes seem to report the chain dropping.
Mine does it sometimes.

A report on MTBR a few hours ago reported they straightened their hanger and now it's fine. Could be some merit behind it but not sure I'm falling for that as the 'fix'.

The odd thing is that I'm running Eagle on four other bikes...only this one bike has this issue...

On my two Marin Wolf Ridge Pro's, I had an issue with the chain going into the spokes...that was a B screw adjustment fix.

 

[frdfandc]

Chain stay length can play a role since you have 3 other bikes that don't do this.

But you have to remember that there isn't anything to keep the chain on the cassette gear when backpedaling.

Sent from my SM-G930V using Tapatalk

 

[jbsocal]

Chain stay length can play a role since you have 3 other bikes that don't do this.

But you have to remember that there isn't anything to keep the chain on the cassette gear when backpedaling.

Sent from my SM-G930V using Tapatalk

I just move the pedals back when restarting...that is enough to cause the issue.

This bike does have shorter 425 mm chainstays...my other 4 bikes are around 430 mm.

 

[PoshJosh]

My non eagle 1x 11spd does this too with a 42t cassette. The chainstays are very short however on my stache.

 

[phalkon30]

Eagle can be very picky, but set up right should not do this. some common things to check :
-hanger alignment
-b screw adjustment (using the red tool from sram, super crtitcal)
-chain length (follow sram guidelines, set using proper suspension sag)
-cassette or chain damage
-high limit screw

 

[Blatant]

^^All absolutely true. It’s usually the first two bullet points.

 

[jbsocal]

Eagle can be very picky, but set up right should not do this. some common things to check :
-hanger alignment
-b screw adjustment (using the red tool from sram, super crtitcal)
-chain length (follow sram guidelines, set using proper suspension sag)
-cassette or chain damage
-high limit screw

Thanks for the replies...gonna take it to an LBS to see what they say.

The drive train is brand new GX, less than five hours on it.

We used the red tool while I was sitting on the bike...other than the back pedal, it seems to shift fine.

My suspicion is that the chain is too short.

 

[jbsocal]

Eagle can be very picky, but set up right should not do this. some common things to check :
-hanger alignment
-b screw adjustment (using the red tool from sram, super crtitcal)
-chain length (follow sram guidelines, set using proper suspension sag)
-cassette or chain damage
-high limit screw

LBS fixed it...crank was loose.

Have not had it on the trail yet, but seems much better now.

 

[phalkon30]

Interesting

 

[Shinkers]

Eagle can be very picky, but set up right should not do this. some common things to check :
-hanger alignment
-b screw adjustment (using the red tool from sram, super crtitcal)
-chain length (follow sram guidelines, set using proper suspension sag)
-cassette or chain damage
-high limit screw

What I think is interesting about this, is that when you are backpedalling, the chain is only guided onto the cog under it's own chain line from the chainring. Everything that happens below the cassette really shouldn't have an effect on the chain wanting to jump off of the cog unless the derailleur is so far off that it feeds the chain onto the next smaller cog (which would still result in the chain being on the cog above the derailleur but jammed at the pulley).

Example: try this same thing but on the chain ring. While backpedalling, try and pull the chain off from above the ring. Doesn't do much.

I'm not denying that these things you list tend to fix the problem, but I can't seem to figure out how they do. The OP's issue with the crank being loose makes sense to me. The chainring may have been wobbling or chainline may have been too far outboard (which would be my first assumption any time this happens).

YMMV.

 

[jbsocal]

What I think is interesting about this, is that when you are backpedalling, the chain is only guided onto the cog under it's own chain line from the chainring. Everything that happens below the cassette really shouldn't have an effect on the chain wanting to jump off of the cog unless the derailleur is so far off that it feeds the chain onto the next smaller cog (which would still result in the chain being on the cog above the derailleur but jammed at the pulley).

Example: try this same thing but on the chain ring. While backpedalling, try and pull the chain off from above the ring. Doesn't do much.

I'm not denying that these things you list tend to fix the problem, but I can't seem to figure out how they do. The OP's issue with the crank being loose makes sense to me. The chainring may have been wobbling or chainline may have been too far outboard (which would be my first assumption any time this happens).

YMMV.

I had 3 Eagle bikes that different LBS mechanics "adjusted" last year...they did not have/use the red tool.

My sworks was adjusted using the red tool (not under sag), it shifts perfectly.

Two of the bike's chain periodically went into the spokes when climbing (shifted fine in the cul de sac or on the bike stand).

Used the red tool (bought off amazon; someone else adjusted it while I sat on the bikes)...this fixed the shifting issues on all three bikes.

 

[phalkon30]

What I think is interesting about this, is that when you are backpedalling, the chain is only guided onto the cog under it's own chain line from the chainring. Everything that happens below the cassette really shouldn't have an effect on the chain wanting to jump off of the cog unless the derailleur is so far off that it feeds the chain onto the next smaller cog (which would still result in the chain being on the cog above the derailleur but jammed at the pulley).

Example: try this same thing but on the chain ring. While backpedalling, try and pull the chain off from above the ring. Doesn't do much.

I'm not denying that these things you list tend to fix the problem, but I can't seem to figure out how they do. The OP's issue with the crank being loose makes sense to me. The chainring may have been wobbling or chainline may have been too far outboard (which would be my first assumption any time this happens).

YMMV.

Honestly I agree with you in retrospect, I was just listing common issues with setup.

 

[jbsocal]

Well, tightening the crank still didn’t fix it.

It’s better, I didn’t have to pull the derailleur out of the cassette this time.

I was restarting on a hill and moved the pedal back around...

I might try adding 2 links to the chain to see if that helps.

This bike is a prototype...specs say the frame comes with a 12 x 157 rear but mine is a 12 x 148.

Anyone know if the 12 x 157 rear would have a better chain line?

Seems like if it shifts the cassette 4.5 mm outward, that might help the chain line.

 

[ShaneXman]

Well, tightening the crank still didn't fix it.

It's better, I didn't have to pull the derailleur out of the cassette this time.

I was restarting on a hill and moved the pedal back around...

I might try adding 2 links to the chain to see if that helps.

This bike is a prototype...specs say the frame comes with a 12 x 157 rear but mine is a 12 x 148.

Anyone know if the 12 x 157 rear would have a better chain line?

Seems like if it shifts the cassette 4.5 mm outward, that might help the chain line.

Just out of curiosity, did lengthening the chain fix this issue? I hope to hear from you soon. Cheers!

-Shane