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Today I bled an Avid Elixir 1 after it had gone soft over the winter. I followed the directions in the Park Tools Big Blue Book completely, used an Avid bleed kit and opened a new bottle of DOT 5.1. The bleed went well and the lever had good pressure afterwards.

I went out for a couple of hours and came home and thought the brakes seemed softer. I stood the bike on its rear tyre and pumped the brake 10 times and by the end the lever was against the grip.

I checked both plugs and they seemed to have a good seal.

Any ideas on what I could have done wrong or could be wrong with the brakes to allow significant air into the system?

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If the lever had good pressure initially, and you had enough fluid in the reservoir (did you check it after the ride) then the only way for air to get in would be a defective cylinder seal. Or positioning the reservoir sideways such that air is pumped in instead of fluid. If air is already in the system then pumping will make the lever stiffer, not softer. –  Daniel R Hicks Sep 29 '13 at 11:19
    
@DanielRHicks my question was a little ambiguous, I didn't go for a ride after the bleed, my bike stayed in the stand. WHen I got back out to the garage later I performed what I thought was the best test for air in the system. –  DWGKNZ Sep 29 '13 at 19:29
    
@DanielRHicks - is the a way to test the seals on a brake system? –  DWGKNZ Sep 29 '13 at 19:33
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2 Answers 2

up vote 2 down vote accepted

Your bleed was probably not perfect. It is normal. Pulling a perfect bleed is a bit hard for first timers.

Possible reasons for a not perfect bleed:

  • you did not fully reset the pistons before starting the procedure
  • you did not apply enough negative pressure and move oil from one syringe to another many times in order to remove all the air bubbles
  • you did not bleed the lever (push the lever all the way in and apply negative pressure on the syringe on the lever)
  • you introduced some air (and/or lost oil) between the time you removed the syringe and fitted the torx screw back in
  • you introduced air from the sirynge accidentaly (a bit rare)

My suggestion is to rebleed (not fully, but just enough to remove the air). Push oil from the bottom (caliper) using a 90% full syringe and pull from a 10% full syringe from above at the lever. While doing so, stop pushing from the bottom and continue pulling from above to apply negative pressure. You'll probably see 10-15 bubbles appearing at the top syringe.

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How do you "you did not fully reset the pistons before starting the procedure" –  TravisK Mar 21 at 23:08
    
Remove pads and gently push pistons back into their housing. Do it with a plastic tyre lever. –  cherouvim Mar 22 at 5:48
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If you stood the bike vertical, the hose could have been at the highest point of the reservoir. Any air in the top of the reservoir would have been introduced in to hose and caliper when you cycled the lever. I would rebleed the system and avoid cycling the lever when the bike is vertical.

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The system does need to be rebled, but I would like to have some understanding of why there is air in the reservoir first. When I bled the system I am reasonably sure I purged all of the air. Standing the bike up vertically is a test to indicate air in the system, it won't introduce it. –  DWGKNZ Sep 29 '13 at 11:15
    
@DWGKNZ - How will standing the bike on end not introduce air? In that position the port in the reservoir is no longer at the bottom of the reservoir but at the side, very likely above the fluid level. –  Daniel R Hicks Sep 29 '13 at 11:21
    
@DanielRHicks - my understanding was that the Elixir series were a 'closed' system, the brake operates in a sealed system with air only entering through a poor bleed or damaged seal. –  DWGKNZ Sep 29 '13 at 19:27
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