Master Cylinder problems

[mmidland]

At the weekend, I changed my servo & master cylinder for a second hand one and also renewed both brake pipes on the rear trailing arm as they were beginning to corrode. I renewed the brake fluid and bled the system using an Eazibleed system. I bled the system using the order in Haynes (NSF, OSR, OSF, NSR) and also bleeding the cylinder furthest from the master cylinder (NSR, OSR, NSF, OSF). However, without servo, the brake pedal can be pressed about 25mm, feels spongy and is a lot worse than before. This did not appear to improve whichever way I bled the system.

I have since tried bleeding the brakes over a few nights using both the Eazibleed and the usual 2 person method with little improvement. I finally resorted to isolating the rear brakes by fitting bleed nipples to the rear flexibles. Still no improvement!!!!

I am coming to the conclusion that it is the M/C that is faulty but there is no fluid leaking where the M/C is attached to the servo. Is there any way to check the M/C eg connect the M/C to sealed & bled pipework and check for pedal movement?

Any suggestions on what I can do to try and remove the pedal spongyness? Is there any benefit in starting the engine to get the servo working?

Any guidance appreciated as the car is now due for it's MOT and I am sure it will fail in this condition.

Thanks
Richard

[Chris Y]

Either the 2nd hand master cylinder you picked up is dodgy, or more likely the rear shoes are not adjusted correctly and they're taking up slack when you press the brake pedal.

Ensure that the self-adjusters on the rear shoes are not seized, and are taking up the slack correctly, and then adjust the handbrake so that when you spin the rear wheels, you can just hear a light scuffing sound. Don't adjust it so that the wheels hardly turn, or turn forever, just so they're 'about to touch'.

This should eliminate all the slack in the system, which should give you a firm pedal. If not, report back here and let us know what type of 'sponginess' you're feeling :-

1) the pedal has long travel, but is otherwise quite firm at the end of the travel
2) the pedal keeps going down, the harder it is pressed
3) the pedal is reasonably firm, but has quite a lot of 'squish' at the end of the travel

If 3), then it's generally air in the system, or a perished rubber hose ballooning. 2) indicates a leak in the system or a knackered M/C. 1) is bad adjustment in the shoes/calipers, or pads/shoes not bedded in correctly..

[mmidland]

Thanks for the suggestions.
I have fitted bleed nipples to the rear brake flexibles to isolate the rear brakes and eliminate any problem with rear slack adjusters.
I have not touched the rear brakes but the drums appear to just contact. I can reinstate the rear brakes and check slack adjuster operation if that would help.
The pedal moves about 25mm before going firm. The sponginess is compared to the firm pedal with little movement before I started messing around with the brakes!!!
This would appear to be type 3) - should i persevere with the Eazibleed or the traditional bleeding method or is there anything else I could try?
Many thanks
Richard

[Monty O]

Read somewhere ages ago that to get rid of all traces of air, remove drum and push slave cylinder piston back into its bore as far as poss, then bleed. This reduces the quantity of fluid in the cylinder, and so the likelyhood of trapping air!
And shouldn't the brakes shoes be adjusted by the adjuster, not by tightening up the handbrake cable? This adjustment is for play in the cable.

[BIGDAVE]

;) hello its my first time replying to a thread.the master cylinder may have a air lock.have you tryed to loosen the pipe unions on the master cylinder while someone depresses the pedal at the same time then lock the union at the bottom of the stroke.make surer to catch the fluid as it comes out the union.do the one nearest the pedal firstyou must do it as quickly as you can.then bleed the brakes as normal.