Brake lever not "springing back"

[cheadle hulme]

Shimano 105 rear brake and STI on Jamis Quest, only 1000 miles or so.

The rear brake has been "sticking" and therefore not returning fully when released. This means the lever is not tensioned and has c10mm of play. This makes it rattle.

I thought the caliper was gummed up, so today stripped it down and full regrease. Remounted caliper and returns fully open no problems (without cable).

Lubed the cable inners and checked cable was freely moving - all fine.

Reconnected cable expecting it to be fine, but still it sticks. I can pull the blocks out by another 5 mm either side after releasing the brake.

Shimano tech documents aren't much use.

Anyone got any ideas?

 

[Mr Pig]

It's a very simple system. Something must be sticking somewhere, you just haven't found it yet.

 

[simoncc]

Almost certainly friction in the cable. The little bit sheathed by an outer casing that runs from the top of the frame down to the brake is a good place to investigate.

 

[LLB]

Almost certainly friction in the cable. The little bit sheathed by an outer casing that runs from the top of the frame down to the brake is a good place to investigate.

I'd say this is the case as well. Is the pin in the brake lever greased as these can stiffen also.

 

[mickle]

I will wager my avatar that the cause of the problem is that your brake blocks have worn down enough to catch under the rim. Apply and release the brake then turn the wheel and they'll spring back. New blocks time, or just file or otherwise carefully trim of the step.

 

[Ashtrayhead]

Almost certainly friction in the cable. The little bit sheathed by an outer casing that runs from the top of the frame down to the brake is a good place to investigate.

Seconded.....it's where all the crap builds up. The cable might just need cleaning and lubing. That happened to mine a couple of weeks ago!

 

[cheadle hulme]

Right, its doing my nut now. Thanks for the replies btw.

I've isolated it down to the shifter. If I pull the cable through tight by hand, the shifter returns to closed with no play. If I then pull the shifter, and pull the cable through normally, it moves to closed but there is still play (5 - 10mm).

If I then pull the cable TIGHT, another 5 mm comes through - but with a kind of click motion. Theres no noise, perhaps a step would be a better way to describe it.

If you look at item 12, where the nipple goes, its not sitting in its housing correctly and lifts up when the lever returns.

Pulling through the extra 5 mm by hand seats it correctly, but the caliper itself won't.

Should the barrel be attached so it doesn't ride up or does it just sit in the holder (item 8)? I can't tell from looking at it.

http://techdocs.shimano.com/media/t.../ST/EV-ST-5510-2171_v1_m56577569830611828.pdf

 

[mickle]

There is a kink, a tight spot or corrosion in the cable which is causing more drag than the spring in the brake can overcome.

 

[LLB]

I will wager my avatar that the cause of the problem is that your brake blocks have worn down enough to catch under the rim. Apply and release the brake then turn the wheel and they'll spring back. New blocks time, or just file or otherwise carefully trim of the step.

You can use mine if you want

 

[mickle]

You can use mine if you want

Awa and bile yer heed.

 

[LLB]

Awa and bile yer heed.

In all fairness, I have a great deal of respect for your expertise on all cycle component issues Mickle

 

[mickle]

Thank you very much, very nice of you to say so Linford.

Have you been drinking?

 

[LLB]

Thank you very much, very nice of you to say so Linford.

Have you been drinking?

Stone cold sober - it must be the cough medicine

Apart from some major mud slinging in P&L over some well trodden ground (well it is P&L) I can get on with anyone (nearly )

 

[Dave5N]

Awa and bile yer heed.

I know where Magnatom's spellchecker is now. You've got it.

 

[cheadle hulme]

Enough of your bickering now. The barrel that the nipple goes into rotates in its little cradle with 2 very tiny plastic washers. They weren't quite enough to hold the nipple in and when the lever was returned, it "sprung" the nipple barrel out of its cradle.

The tension in the caliper wasn't enough to pull it back into the cradle and it sat a few mm above where it was supposed to.

I've fashioned a slightly wider washer for one side and it now stays put.

All reassembled and working fine.