Brake Master cylinder seals

[Disco]

Hello all 

I am trying to bleed the brake system and find I can get a hard pedal which when released air rushes back into the reservoir. The seals between the reservoir and cylinder are leaking so this where I think the air leak is . I have fitted a seal shaped like cylinder and pushed the plastic reservoir pipes into the holes but is doesn’t seem very sealed . Do I need a different seal which has a thick top to it to seal between the cylinder and the bottom of the reservoir?
or do I fit a remote reservoir as supplied by kitspares ( the seals don’t seem to be part of the kit 

thanks in anticipation 

Chris D

[Darren Knowles]

Evening 

i had leak on my master cylinder ended up replacing in end as I couldn’t get it to seal kit spares do a sierra replacement off shelf 

hope you get sorted 

dazza

[RallyChris]

5 hours ago, Disco said:

Hello all 

I am trying to bleed the brake system and find I can get a hard pedal which when released air rushes back into the reservoir. The seals between the reservoir and cylinder are leaking so this where I think the air leak is . I have fitted a seal shaped like cylinder and pushed the plastic reservoir pipes into the holes but is doesn’t seem very sealed . Do I need a different seal which has a thick top to it to seal between the cylinder and the bottom of the reservoir?
or do I fit a remote reservoir as supplied by kitspares ( the seals don’t seem to be part of the kit 

thanks in anticipation 

Chris D

I can’t really understand the symptoms you have reported - when you release the brake pedal this should allow fluid to pass back from the pressure side of the master cylinder piston(s) into the reservoir; there shouldn’t be anything causing a vacuum in the reservoir that can pull air in from outside.

One thing to check might be if the same symptoms occur if you remove or at least loosen the cap of the reservoir. If the cap is not vented correctly (I.e vent hole blocked) then you could be pulling a vacuum in the reservoir when you apply the brakes and this is then relieved when you come off the pedal and this is somehow causing bubbles to appear in the fluid. If this does make a difference then it reminds me of the process used to bleed hydraulic bike brakes using syringes at either end of the system, where pulling a vacuum causes air bubbles to be pulled out of the fluid.

Chris

[Daveo]

Hi Disco   

                 As far as seals go for master cylinder I found some on e-bay and also a a company that does all manner of brake stuff 

hope it helps. Dave

 

https://www.ebay.co.uk/itm/224348977315  1988>93

 

https://www.ebay.co.uk/itm/143893693240 1982>88

 

https://www.ebay.co.uk/itm/284066302989 1982>87

 

https://brakeparts.co.uk/shop/Ford/Sierra

 

PS  remember to  disconnect the vacuum pipe from the servo or inlet manifold before you start to bleed them.

 

 

 

Edited February 17, 2023 by Daveo