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Discussion Starter · #1 ·
Completely new here, and completely new to disc brakes! I've just retrofitted a second hand Avid Juicy 3 rear disc brake to a very good steel frame bike using an A2Z MTB disc brake frame adaptor. It's completely solid and works well - no leaks, pistons are smooth and braking is good.
When compressing the lever, there's a good solid point where the pads connect with the disc. This works fine in terms of braking when riding. If I keep the lever compressed it very slowly travels to the fully closed position against the handlebar. It is really slow, and the brake really is solid, but is this right? I bled it really carefully, de-gassed the fluid and got rid of all bubbles, and like I say there's no leaks. What's likely to be the cause of this?
 

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Sounds like there is still some air in system. Of all the hyd brakes I've used, Avids were at the bottom. I lived with Avid 3's on my Heckler for a couple of years...they were needy and a pain to deal with. Everything was more of a hassle with them...pad changes, bleeding, etc. I finally tossed them for Shimano Deore's which have always been great for me.
 

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I don't see how air in the system would explain this lever behaviour. If you had air in there, the lever would feel spongy first, but once the air got compressed and the pistons and pads in the caliper still managed to grab the rotor, lever should stay put. To me this indicates a very slow leak somewhere. Either external, or internal. By internal I mean fluid is getting past the primary cup seal on the master cylinder piston and slowly migrating into the cavity behind it. So I would try replacing that seal first.

Page 17-20:

https://www.sram.com/sites/default/files/techdocs/2010_avid_technical_manual_english_final.pdf
 

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Discussion Starter · #5 ·
Looking at the pdf I reckon that's it, if the primary seal was leaking that would cause exactly the issue I have, a slow movement of fluid from in front of the piston to behind into the reservoir, so good solid braking but with a slow movement of the lever when compressed. Looks like a fiddly job but do'able, and worth it as I took the bike out last night and the braking was in a different universe to the previous V -brakes! Just got to find a seal from somewhere.
 
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