brakes loosing pressure

[horrace]

i have been having fun and games with the brakes on the pick up. its all standard drums no servo.
i had it professionally bled and adjusted which ended up with the shoes binding when hot as the garage adjusted the rod on the m/c too much. i had to slacken this off and cant seem to get it right, its either too much and they bind or not enough and it takes a couple of pumps.
I have replaced the shoes and drums now and am not sure that the brakes are quite right..... when i push the pedal first time it has a bit too much travel and a couple of pumps later it seem about right.... when i brake again its fine, but try the brakes again 10 min later and its back to too much travel and a couple of pumps,
i guess the m/c is losing its pressure?
the m/c rod has approx 3/4" travel before it bites.
could it be the m/c is faulty? it was new a couple of years ago..

[horrace]

or could it be the brake cylinders? i guess if the seal in these go they will also lose pressure?

[horrace]

i should also add that the pedal doesnt lose pressure when i keep my foot on it

[MarkyB]

Gentle steady pressure is what you need to test the M/C easier done with your hand.
3/4" travel if this is between the rod and the end of the M/C I'd say it's too much 1/4" travel should be plenty, the main thing is that the brakes aren't under pressure from that rod all the time.
Is the fluid level going down?

[bmcecosse]

Classic symptoms of the brakes needing adjusted up! Slacken the handbrake cables - adjust up the shoes on all drums so they rub slightly - then pull up the handbrake cables to put the lever where you want it. Simples.

[Dean]

I have to pump my pedal up, although it's hardly noticable when driving.

Without pumping the pedal up, do the brakes work well enough in an emergency stop?

Proffessionally done or not are you sure the brakes were bled correctly? and why did they feel the need to mess with the M/C?

[Neil MG]

If you have to pump the pedal there is something wrong, either the pads way out of adjustment, easy to check and fix or there is an internal leak in the master cylinder. This is of course assuming there is no fluid leaking, in which case the cause will be obvious. The master cylinder internal leak is common and the usual failure mode, although not often recognised in the early stages. It's often difficult to diagnose because there is no fluid loss and the brakes will work after a second pump. They may not work in an emergency stop though! Sometimes you can feel the pedal slowly moving down under constant pressure, but if the leak is small it may not be easily discernible.

[horrace]

will check all suggestions today. thanks

[bmcecosse]

To check - clamp all the brakes up hard on the adjusters so the wheels won't turn - is the pedal right there/rock solid now ? It should be! Obviously you then have to slacken back - but do this as little as possible - a slight rub is ok.