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I've just recently replaced the brakes on my MTB with a pair of Shimano XT hydraulics. The rear brake line was extremely long for my frame's routing, so I had to cut it and subsequently bleed the system. For the most part, everything seems to have gone well; the rear brake lever is now very firm and responsive, slightly more so than the front (which I did not shorten or bleed). However, I've noticed that the rear brake lever no longer returns instantaneously. If I had to guess, I'd say it takes around 0.2 seconds to return from the fully depressed position. By contrast, the front lever returns so quickly that it makes a slight "snap" sound when it hits its limit.

I replaced both the olive and needle insert when reinstalling the brake line. I noticed that both of these parts had a thick grease generously applied to them from the factory. I'm unsure if this is typical for Shimano brakes, though I've never seen pre-applied grease on the spares for Avid or Tektro brakes. I have a sneaking suspicion that this may be the culprit, but I'm not sure how to validate that without disassembling the brakes again and swapping in new connector spares.

This doesn't seem to affect the brake's function right now, since the pads don't noticeably drag against the rotor during the return interval. But it does concern me that I may have done something wrong while reinstalling the brake line, and that this might be a precursor to more serious problems in the future. Any ideas what I might have done wrong, or how to further troubleshoot this issue?

Some more details:

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1 Answer 1

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There are three possible things that could be causing this:

  1. Too little mineral oil remaining in the system, did you top up the brakes after shortening them?. This would create a vacuum in the system and would prevent the lever from returning fully. *--EDIT on reflection I think this is unlikely with a Shimano brake as after oil falls below a certain level air would enter the system and the lever wouldn't work.
  2. A blockage caused by grease in the needle creating a slow vacuum.
  3. A broken spring in the lever. There isn't enough negative pressure in the system to force the lever to return so this is aided by a spring in the lever which also creates suction at the piston. Did you check the brakes prior to shortening the hose? This is a known failure for Shimano brakes.

My trouble shooting would be:

  1. Check mineral oil level
  2. Check the needle for a blockage
  3. Take it to a LBS for some professional help
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Thanks for the suggestions, I'll run through 1 and 2 ASAP. I should probably clarify that the lever does return fully; it just takes longer to do so than I'd expect. –  TinKorcim Jul 15 at 21:19
    
Looks like it was blockage in the needle after all. Now that I replaced the connector parts again, everything works as expected. This just leaves me to wonder why the spare parts that shipped with my brakes were contaminated with grease! –  TinKorcim Jul 18 at 18:14

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