Rear mech not springing back to cassette

[CyberKnight]

It shifts across the gear range ok but it does not spring back when changing from big to small on the front , feels stiff around the pivot that screws into the mech hanger.

[Brucey]

sounds like your upper (B tension) spring pivot (as fitted to most shimano rear mechs in the last 20 years) is binding. I'd suggest penetrating lubricant/working it back and forth, and checking that the spring itself isn't broken.

cheers

[CREPELLO]

Just tonight I've discovered the same problem myself. It looks like it manifests through sloppy gear change as the B-tension adjustment goes to pot, along with the mech's ability to track (approximately) the profile of the cassette.

I'll give the the mech a good drenching with oil and agitate a bit.

[gregoryoftours]

If flushing it out with lube doesn't work well enough, it's worth dismantling the b-tension pivot by removing the circlip and giving the bushing a good clean with fine wire wool. It can sometimes be a little tricky to get it back together with the spring in place.

[ChrisButch]

It can sometimes be a little tricky to get it back together with the spring in place.

Understatement of the day, in my never-to-be-repeated experience!

[Brucey]

it is a stinky job, that. There are a couple of ways that work OK IME;

1) the 'easy way'. Start with the mech bolt through the assembly, and use a small screwdriver braced between the 'B' tab and the bolt. Twist, push down, and voila the B tab is in position. Next hold the B tab in place whilst the bolt is pushed into position, and start the 'E' clip into the groove PDQ. Use pliers to squeeze the E clip home. If this doesn't work then...

2) Use something else (a large screwdriver, an axle or something, ideally with a shoulder on it so that you can push) as a guide for the B tab instead. The snag with this one is that you need to hold the B tab in place whilst the guide is removed and the correct bolt is installed. I have improvised tools for doing this using flat spanners, lengths of studding etc, over a bench vice.

Tip; if you get part-way through with the bolt in place and want to pause, if you have an M10 x 1 nut (eg from a qr rear axle) you can secure the assembly using this. If you allow ~1.5mm clearance you can pry a gap using a screwdriver and then insert the E clip to finish the job. You can sometimes use this technique to assemble the thing on the dropout, in fact.

hth

cheers

[bikerwaser]

i always try the easy stuff first and in this case i'd make sure the cable was lubed up and free, then go to the mech.

[Audax67]

i always try the easy stuff first and in this case i'd make sure the cable was lubed up and free, then go to the mech.

+1

[Brucey]

yeah, but it doesn't matter what state the cable is in, it won't affect the mech's ability to tension the chain as the OP describes...

cheers

[CyberKnight]

I will admit it now , as its a claris mech for the commuter i have just ordered a new mech for £16 and a new chain as well as its due and i can then take the old one of and clean it as a spare .

[reohn2]

As a preventive measure I always give mechs and pivots a good squirt of GT85 after a wet/mucky ride or after washing it's something I've always done as a matter of course,I rarely have such problems as a result.

[CyberKnight]

As a preventive measure I always give mechs and pivots a good squirt of GT85 after a wet/mucky ride or after washing it's something I've always done as a matter of course,I rarely have such problems as a result.

This weather i would have to wash it 10 times a week

[reohn2]

As a preventive measure I always give mechs and pivots a good squirt of GT85 after a wet/mucky ride or after washing it's something I've always done as a matter of course,I rarely have such problems as a result.

This weather i would have to wash it 10 times a week

Not necessarily,just give it a good squirting daily

[CREPELLO]

Well, I cleaned out and greased the B pivot of my RX mech last night and it wasn't too difficult at all. The B pivot bolt looked like chromed steel to me which must be susceptable to rust when the lube dries out. All my more modern Shimano mech's use SS B-bolts. They'll all still benefit from occasional lube though. The bolt fits into a simple bushing, which is a good tight fit, which would explain why these pivots can seize up when the lube dries out. Fortunately, there was no wear apart from a little rust (or was it dried up lube, which does go a dark orange?)

Putting it back together required that I locate the spring tang into the B-tension screw plate. That bit is easy. But the plate needs winding up a few degrees, so that a tab on the plate slides over and butts up to the alu lug on the mech body. Fortunately, the spring readily stays in the plate as it is eased over the lug. This simply requires holding the mech body in one hand, whilst grabbing the plate at the B-tenson screw tab (screw removed) with a parir of pliers - and twist. Then re-insert the circlip. Even the circlip was easy on this mech.