half-shifts after hitting bumps?

[Mize]

Started in yesterday's races. Repeated today.

Basically if I hit a good sized bump, my rear derailleur will go slightly between gears - like I tried to shift but the cable wasn't tight enough.
Here's the strange part...I can shift up and down on the cassette and the problem persists with the "between gears" sound...the only thing that stops it is a quick shift to my smaller chainring and back to the big one...a "re-shift" of the FD if you will.

So on the one hand it seems like a FD alignment problem since "re-shifting" the FD fixes the problem. On the other hand there is zero FD rub with this problem, only RD noise...almost like the bump slightly rotates the RD and the "re-shift" straightens it out again.

Any ideas?

This is SRAM Red 22, standard cranks, 11-28 cassette. Hanger was checked just three weeks ago and wheel is seated and tight.

Thanks.

[Twinning]

I had this exact problem. Mine was due to a bent hanger but you said you check yours already so not sure. Is this your ar1? I've seen you on the ar forum


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[maxxevv]

So, it doesn't happen when its in the BIG chainring ?

Try adjusting the tension on your RD B-screw. Might be a little loose/low in chain tension and also your cables might be a little dirty/dry, check those too.

[Mize]

Twinning, yes this is my AR1. I may re-check the hangar but it was good 3 weeks ago.

Maxxevv: it has always happened when in the big ring. Hit a bump, noise starts. Only way to get rid of it is to shift to the small ring then quickly back to the big ring.

[kode54]

check cable. could be frayed and ready to snap.

[Mize]

I'll have it in the stand tonight to go over every inch. Did a quick check Saturday night between race days and couldn't see anything obvious.

[kode54]

before my shift cable snapped...a few rides before...my shifting was erratic. couldn't get it in the right gear. but shifting up or down and back to original gear seemed to help...until it finally snapped. mine snapped near the shift levers and this was on an older DA7900...not the DA9000 that some say have problematic shift cables. your case could be something else like friction in the shift housing...but if you ride in the rain and such, you never know.

[Twinning]

before my shift cable snapped...a few rides before...my shifting was erratic. couldn't get it in the right gear. but shifting up or down and back to original gear seemed to help...until it finally snapped. mine snapped near the shift levers and this was on an older DA7900...not the DA9000 that some say have problematic shift cables. your case could be something else like friction in the shift housing...but if you ride in the rain and such, you never know.

I had the same problem as the OP but I was riding a brand new frame with brand new cables. Fixed by straightening the hanger and I also remember taking out one link of my chain to create more tension. That could also possibly help. Not the cables because I have been riding the same cables since I fixed it and nothing is wrong


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[drider85]

I have seen a number of Felts in the shop with internal cable resistance causing erratic shifting concerns. I would try cleaning/lubing the cable. Now for the long shot/crazy idea...if your frame was cracked and flexing that could cause ghost/erratic shift concerns.

[bombertodd]

+1 checking the hanger. I have the same issue a while back and the hanger was slightly tweaked. It looked straight to the eye but the alignment tool said otherwise.

[Mize]

Well one of the few tools I don't have is a hangar checker. $90 for a precision piece of extruded aluminum guess I'll be swinging by the LBS tomorrow...

[bombertodd]

I paid $60 for mine. I wrench on about 8-10 bike regularly (family/friends) so it was a no brainer purchase. After owning it for the last two years I don't know how I lived so long without it. A perfectly aligned hanger makes derailleur tuning a breeze. It has solved many headaches for friends too. I'd say more than 90% of shifting problems that cannot be fixed with cable/barrel adjustments result in hanger issues. Often I've found hangers bent that could not be seen with the eye, even brand new hangers! If you like working on bikes I would highly recommend buying one.

[ajh]

I had the same issue and it was the soft pulleys that had worn

I bet if you take the derail off and then take the cage apart you will find that the lower front part of the inside cage will have wear marks

The chain jumps off the lower pulley and will allow the chain to rub against the cage

Switching gears fixes this like you found but to fix you need new pulleys

That aero soft durometer on the pulleys to quiet them also wears pretty fast

[Mize]

I had the same issue and it was the soft pulleys that had worn

I bet if you take the derail off and then take the cage apart you will find that the lower front part of the inside cage will have wear marks

The chain jumps off the lower pulley and will allow the chain to rub against the cage

Switching gears fixes this like you found but to fix you need new pulleys

That aero soft durometer on the pulleys to quiet them also wears pretty fast

Seriously? This bike only has like 1700 miles.

Remember it's only by switching chain rings, not rear gears, that it goes away.

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[ajh]

My bike only had 3000 miles on it when I had this issue. It can also be compounded by a rear derail hanger that is not perfect. if your derail is clean then just check the lower front of the inside cage for a little wear by flipping your bike upside down and checking with a flashlight. Thinking back I also used going to a different large ring to fix. It was over 6 months ago so it is no completely fresh in my memory.