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I have bled my brakes numerous times with both methods pumping out through non return valve and pushing in from each corner.There are no leaks in the system,back brakes fully adjusted.All components are new.I can pump a 3/4 pedal and hold with no reduction.However if I leave the pedal for a few seconds the pedal goes almost to the floor.When holding a firm pedal all wheels are hard on and no leaks.Its a new master cylinder so what can be the problem All help welcome Alan.

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Hi Alan,

have you got new.refurbished calipers?  If you have it could be the caliper piston seals drawing the piston back into the calipers too far.

So you can pump them but if you leave them for a short period then will feel airy.

This will eventually relieve itself but to speed things on Depress the brake pedal and wedge it down for 24/48 hours 

 

Roger

Edited by RogerH
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On most cars this symptom is caused by rear brake shoe travel: the springs slowly pull back the rear shoes creating the long pedal on next application.

Any easy way to prove this is to apply handbrake, if the long pedal problem goes away it proves its pull-back of the shoes... in that case check for worn drums (they are cheap), worn shoes or wonky adjusters. My early 70's BMWs have a residual pressure valve in the rear brake line to stop this pullback and extend service interval on the brakes.

If thats ruled-out then switch to master cylinder as suspect - especially the little rubber seal on the end of the piston assembly (or it's seat)...if that leaks then pressure bleeds back into the Mcyl reservoir...symptom of this is 'swirl' in the reservoir as the brake pedal is pressed. 

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13 hours ago, Alan Hawley said:

I have bled my brakes numerous times with both methods pumping out through non return valve and pushing in from each corner.There are no leaks in the system,back brakes fully adjusted.All components are new.I can pump a 3/4 pedal and hold with no reduction.However if I leave the pedal for a few seconds the pedal goes almost to the floor.When holding a firm pedal all wheels are hard on and no leaks.Its a new master cylinder so what can be the problem All help welcome Alan.

Check the length of the new push rod with the old, they are often too short. Failing that pump the brakes up hard and jam the pedal down with a piece of wood between it and the seat and leave for 24 hrs.

Stuart.

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