Bubbles in brake master cylinder
Discussion
Hi all,have rebuilt rear calipers new Pistons,seals etc and refitted to car.Was having problems bleeding so bought easy bleed kit.When I press brake pedal to the floor I can see bubbles rising in master cylinder after bleeding all calipers and the pedal is spongy. rear of the car is up in the air.Brakes functioned fine before strip but one rear calipers was weeping.How can I get the air out of the master cylinder? Or anything else it could be? Thanks dave
I use easi-bleed all the time on all my cars for bleeding the brakes and clutch and take pressure off the nearest tyre so 23 psi, and have never had an issue. The air connection is on to the top of the master cylinder so the air will not mitgrate into the brake fluid like a fizzy drink. If air is still there then it must be getting in somewhere, or the reservoir got too low and air was drawn into the pipes? Make sure there is a good air gap within the master cylinder but also ensure the easi-bleed container doesn't run out. I always bleed the furthest caliper first and then work my way to the one nearest the master cylinder. I also let it have a few shots of "full flow" to try and push the air out. If the bleed flow is too slow then trapped air in the pipe high spots may not be forced out.
Hi ,thanks for the inputs.Tried easi bleed again,bled the rear calipers -got some air out oil running clear.With easi bleed still pressurised bleed nipple shut brake pedal feels good and rear wheels lock.When pressure released from tyre for easi bleed there's a gurgle of bubbles in the master cylinder! With kit removed pedal goes soft and I get bubbles each time on the upstroke of the pedal.Its Sunday and I've run out of clean brake fluid -so will have to come back to it.I have only undone three connections on the rear calipers,nothing else .Oil level in master cylinder after calipers strip was very low?Am I looking at master cylinder reseal kit?servo problem? Any other ideas greatly appreciated. Dave
Unless there is a problem with a bleed nipple there is every chance that the master cylinder is playing up
The servo is only an assist and can't cause this problem
If this happened to me I would be asking myself "why is there a problem now when it was ok before I touched anything". I'm assuming the brake system didn't have a problem with air in it until you got to work
The servo is only an assist and can't cause this problem
If this happened to me I would be asking myself "why is there a problem now when it was ok before I touched anything". I'm assuming the brake system didn't have a problem with air in it until you got to work
french dave said:
Hi,could the piston be stuck in the fwd position and not returning inside master cylinder? Might re pressurise using easi- bleed and tap side of master cylinder.Or could I leave all connected and remove from front face of servo and see if piston fully back?dave
Yes you can split the servo from the master cylinder to check the piston is backHi,split master cylinder - piston fully back -operated with screwdriver and returned ok each time.re-attached and push brake pedal to floor -same as before - little resistance and bubbles seen when pedal rising.Me thinks new master cylinder reqd.I take it with a new master cyl you fit then fill and then bleed -you carnt pre bleed it? Thanks Dave
There are two pistons in the master so you were only seeing one of them when the master was removed.
I would suspect the master.
In answer to the 'way has this happened when all was well before' question the answer is in normal operation the master only works in the first few millimetres of travel. When you bleed the brakes the master goes full travel which can trap the piston in the end of the cylinder which may be rusted or gunged.
Back to easybleed. Keep pressure as low as possible. Higher pressure compresses the air bubbles making them smaller and more difficult to shift.
Steve
I would suspect the master.
In answer to the 'way has this happened when all was well before' question the answer is in normal operation the master only works in the first few millimetres of travel. When you bleed the brakes the master goes full travel which can trap the piston in the end of the cylinder which may be rusted or gunged.
Back to easybleed. Keep pressure as low as possible. Higher pressure compresses the air bubbles making them smaller and more difficult to shift.
Steve
Steve_D said:
There are two pistons in the master so you were only seeing one of them when the master was removed.
I would suspect the master.
In answer to the 'way has this happened when all was well before' question the answer is in normal operation the master only works in the first few millimetres of travel. When you bleed the brakes the master goes full travel which can trap the piston in the end of the cylinder which may be rusted or gunged.
Back to easybleed. Keep pressure as low as possible. Higher pressure compresses the air bubbles making them smaller and more difficult to shift.
Steve
Thanks for the explanationI would suspect the master.
In answer to the 'way has this happened when all was well before' question the answer is in normal operation the master only works in the first few millimetres of travel. When you bleed the brakes the master goes full travel which can trap the piston in the end of the cylinder which may be rusted or gunged.
Back to easybleed. Keep pressure as low as possible. Higher pressure compresses the air bubbles making them smaller and more difficult to shift.
Steve
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