B screw on XTR RD M971
m3trackboy
Posts: 97
Adjusting the B screw seems a bit vauge, is it best to adjust either without a chain, peddling fwd / backwards.
I'm getting chain jump and think the B adjustment is out, the mech looks strait.
On the stand shifts perfectly but when rideing hard i.e. up hill chain jumps but stays on the same cog, happens in all gears.
Cassette is in good condition, hanger was bent but have straitened it, chainline looks good (by eye).
So far have changed BB bearings, middle chainring and chain.
I'm getting chain jump and think the B adjustment is out, the mech looks strait.
On the stand shifts perfectly but when rideing hard i.e. up hill chain jumps but stays on the same cog, happens in all gears.
Cassette is in good condition, hanger was bent but have straitened it, chainline looks good (by eye).
So far have changed BB bearings, middle chainring and chain.
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Comments
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B-screw has no effect on normal running, only shifting, jumping is a function of chain and cassette only, sound slike one or both are knackered.Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0
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it seems to jump progressively worse (sorry bad English!) the smaller the gear is, its as though the chain isnt being fed on the cogs from the deralier. I will try a new cassette but the one on there looks good.
The only other course of action will be to strap a GO PRO and film it
Thanks for your input0 -
Procedure I use on sram . Set high stop , set low stop . Set b tension in small ring front largest at back . Minor adjustments then at cable adjuster to get clean shifts up and down cassette . Incorrect cable tension definitely affects mine ( like you it can be fine with no load but get problematic under load ) . Make small quarter turn adjustments only and adjust one thing at a time .0
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The B tension screw affects chain wrap around the teeth of the rear cogs.
More chain wrap means faster shifts (ie chain derails from one cog onto another faster), less wrap means vague slow shifts. Check this by unscrewing and screwing in the B tension screw fully.
But, in the small-small and/or big-big combinations at zero B tension, the upper pulley wheel teeth might hit the teeth of the cogs causing the derailleur cage to judder back and forth. The meeting of teeth causes extra noise and wear on the pulley wheel, and may diminish shifting performance. The juddering cage could lead to chain drop especially when pedalling backwards.
So, the B tension screw is used to remove the juddering effect of the derailleur cage at the extreme combinations but is kept mininal for faster shifts.0 -
Chain wrap has no effect on shifting, otherwise you'd never get it to shift in the highest gears!
The jockey to sprocket gap affects shifting as the smaller the gap there less scope there is for the chain not to be 'forced' to shift by deforming between the 2.Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
The Rookie wrote:Chain wrap has no effect on shifting, otherwise you'd never get it to shift in the highest gears!
The jockey to sprocket gap affects shifting as the smaller the gap there less scope there is for the chain not to be 'forced' to shift by deforming between the 2.
Come on man, this is the basics and you're already falling at the first hurdle?
I included a way of proving it for yourself if you doubt what I stated:Check this by unscrewing and screwing in the B tension screw fully.
Go and try it on your own bike. Shift through the gears with the B tension set at zero and at max setting, and observe.
Report back what happens.0 -
When my new cassette comes tomorrow will try it, every other adjustment seems positive but this one seems very vague, there could of course be another problem like the spring is gummed up, will check and report back.
many thanks to everyone on this post and my earlier one which is connected.0 -
Try reading what I wrote, as I told you how the B-tension screw does affect shifting, your test will prove nothing......bikaholic wrote:The Rookie wrote:Chain wrap has no effect on shifting, otherwise you'd never get it to shift in the highest gears!
The jockey to sprocket gap affects shifting as the smaller the gap there less scope there is for the chain not to be 'forced' to shift by deforming between the 2.
Come on man, this is the basics and you're already falling at the first hurdle?
I included a way of proving it for yourself if you doubt what I stated:Check this by unscrewing and screwing in the B tension screw fully.
Go and try it on your own bike. Shift through the gears with the B tension set at zero and at max setting, and observe.
Report back what happens.Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
May well be that the cassette is just too worn for a new chain to mesh properly. It could be ok under normal running, but as soon as some power is applied it slips.m3trackboy wrote:Cassette is in good condition...
So far have changed... chain.
Generally best to change chain and sprockets at the same time.0 -
Defo
new cassette being fitted over the weekend.
Problem started when I broke a spoke, LBS 2 week waiting list to replace and true wheel.
Bought a new wheel and put an XTR cassette I bought SH sometime ago, "only ridden a few times"
Chain slip, replaced:
Middle ring gear
BB bearings
Chain
Hanger
Cables
My original Cass has done many miles and was SH 2 years ago, the spare on closer inspection is toast, even the chain whip slipped.
I know the new cass will cure my problems, kicking myself didnt look closer at my old cass. Everything else needed replacing so good exercise.
Thanks for the post0
