[MikeD]

When I turn the cranks on my Big Hit backwards on the repair stand, the chain will upshift if it's in one of the larger cogs. The derailleur does not move, but the chain skips down the cassette. It takes a few hard turns of the cranks for this to happen. When riding, I seldom backpedal enough for this to be a problem, but it annoys me nonetheless. :angry:

Any ideas? I'm using Northshore cranks on a RF freeride BB...113mm spindle. It's a 68mm BB shell, with an E-type ft dr.

I tried another chain...same deal. I tried another cassette...same deal.

New rider? New mechanic? Any possibilities besides these?

MD

 

[mudpup]

Shift into the largest cog while on the stand. Look at the derailleur pulleys and see if they are really close to the cog. If the derailleur bobs up and down when you pedal forward or backward you need to adjust the rear derailleur B screw. The pulleys could be jamming upward on an extreme backpedal and forcing the chain off.

Another thing is that the chain and pulleys may not be centered up with the cog. If it is slightly outward it could cause those problems as well. That would mean you have a bit too much slack on the inner wire of the derailleur and you need to increase the tension. Hopefully you have enough adjustment to do it with your derailleur adjustment barrel down at the derailleur and/or at the shifter. If not you will need to tighten the cable by slightly loosening the pinch nut down at the derailleur and pulling the cable tighter; then retighten the nut. I usually pull the cable tight with a fourth hand while on the large cog and make sure when I do, that the chain and pulleys are centered with the cog. Also, before I do this I give myself 3 turns of use at the derailleur barrel and 2 turns worth of adjustment at the shifter barrel as well. Also when I do this, I tighten the H & L screws down so that I can maximize those adjustment capabilities as well for when the system wears.

Another thing is that you should insure that your cable is seated in the housing and shifters before you do all of the adjustments. To do that you should shift to the smallest cog and while pedaling pull the rear derailleur cable up with your hand to put the chain on the large cog and then stop pedaling. While the chain is resting on the large cog pull firmly on the derailleur cable a few times and then release it. Start pedaling to put the chain back on the small cog. Do the same with the front derailleur as well.

That's just a WAG though.

 

[MikeD]

Appreciate the advice...I'll give it a try.

MD

 

[Toshi]

Poor chainline? If so, then nothing will help.

 

[oldfart]

Its chainline. The derailleur has no affect on this symptom. My bike does it too.

 

[MikeD]

I was having probs with the chainline and just corrected them...(my rear tire was too fat, so I added spacers and a chainguide to move the chain far out enough to clear it.) Now I have the proper chainline, I'm pretty sure. I'll do the detailed check tonight if I can.

I think it's alignment of the large cog and the jockey wheels. I'm going to try a new der. hanger when I can get one, and maybe a new derailleur if that doesn't help.

Thanks all for the asssitance so far.

MD

 

[BikeGeek]

Originally posted by MikeD
I was having probs with the chainline and just corrected them...(my rear tire was too fat, so I added spacers and a chainguide to move the chain far out enough to clear it.) Now I have the proper chainline, I'm pretty sure. I'll do the detailed check tonight if I can.

Chainline, as I understand it, has nothing to do with the chain clearing the tire. It has to do with the position of the chainring relative to the position of the cassette. Symptoms include poor shifting, "ghost" shifting, or "chatter" of the chain on the cassette, as well as others. If you "corrected" your chainline to clear your tire, you may have caused the problem you're trying to fix.

 

[MikeD]

It's just that in order to clear the tire, I had to set a jacked up chainline. I've since gotten a thinner tire and brought the chainline back to normal.

 

[mudpup]

If you look at chainline in terms of the chain's contact points, there are 3 points of contact - chainring, cassette, and rear derailleur. If one is out of alignment it will cause problems. That may be considered an unconventional viewpoint of chainline, but, all of the contact points contribute to problems. It is a misaligned triangle.

 

[Montara]

I have observed this phenomena. It can be caused by the shift ramps and scallops in the cog teeth. The ramps are designed to allow and aid the chain to climb up to a larger cog under power in the forward direction. In the backward direction the narrower profile and increased clearance of the ramped teeth can actually work backwards, by failing to grab the chain and allowing it to fall off to a smaller cog. Moving the chainrings out is gonna make this worse. I would try to move your chainline back in as much as possible to reduce the angle the chain has to go through between the chainrings and cogs. I doubt it's the derailleur or pulleys, in the backwards direction they aren't influencing the top run of the chain, but hey - I could be wrong.

 

[mudpup]

Regardless of direction the derailleur pulleys affect how the chain wraps on the cassette cogs, ie, how centered the chain will be on the cassette.

 

[Yanick]

i got the same problem, and i think it was because my casette body was to dirty. I justed dismantle it, cleaned it and had solve the problem.

i know it sound weird but for my hadley hub it has work.

Yanick