Series 3 new brakes binding - master cylinder problem?

Hi - my first question on Landyzone.

I've had a 1975 88" Series 3 for five years. Recently the brakes failed (peddle hit the floor). The resevoir was below minimum (mea culpa) but as there was no sign of leaks anywhere I went to refill and bleed the system. However, the bleed nipples on both rear wheels sheered off. So I stripped everything down and fitted new Delphi cylinders, Mintex shoes, springs and pipes going back to the T connector on top of the rear axle. I then set the snail adjusters to minimum and, with the hubs fitted, bled the system again.

Everything seemed fine, and the pedal was hard, but the rear wheels/hubs were seized after the pedal was released. If I released some pressure via the bleed nipple the brakes would free up and the hub would spin again. I took the hub off, applied brake pressure and saw that both sides of the wheel cylinder expand but that the trailing shoe side does not contract when the brake pedal is released. All springs etc are properly fitted (I've tripple checked).

I haven't been able to find any answer to the non-returning brake on the internet. A friend suggested that it is possibly to be expected, given that the springs are quite weak, and it could just be a matter of driving around for a bit to free things up! I wondered if my bleeding wasn't up to scratch - but that would result in spongy brakes which I don't have. So I wondered if the master cylinder is at fault (should it be actively releasing the pressure in the system when the brake peddle is released?) - but again I can't find anything on the internet to suggest it is or it isn't. I'm a bit loathed to start fiddling with the master cylinder on the off-chance.

Does anyone have any ideas? Advice, suggestions etc very welcome.

if the master cylinder push rod is over adjusted the fluid cannot return from the system into the reservoir. check pushrod adjustment

Also return spring on the pedal should be in place [ under the dash ] but the most likely cause is the above.

Thanks for suggestions.
Minecab: The pushrod seems to have the recommended 1.5mm of freeplay.
Tottot: The spring is there and attached to the pedal.
I'm going to have to replace the front cylinders as well (bleed nipple stripped its thread) so maybe that will miraculously cure the problem, but for the moment it remains frustrating.

Old seals breaking up in the master can give your symptoms [ little bits floating around the system blocking flow ways ] Is the fluid dirty to look at ?

tottot said:

Old seals breaking up in the master can give your symptoms [ little bits floating around the system blocking flow ways ] Is the fluid dirty to look at ?

Click to expand...

Thanks for that idea. When I first bled the fluid it was filthy - but it had been in there for years and years. Looking at the jar of old fluid I can't see any actual bits floating around. If I push the cylinder pushrod in it comes back out quickly and positively - if that means anything. Am I right in thinking the only way of really knowing is to take the cylinder apart and replace all the seals regardless (or replace the entire cylinder - pic of current one attached)? And then flush the system with clean fluid?

As had been said, could well be adjustment in the master cylinder. Apply pedal so wheels are stuck, then undo the adjuster on the matter cylinder completely, then see if your wheels are free

kermit_rr said:

As had been said, could well be adjustment in the master cylinder. Apply pedal so wheels are stuck, then undo the adjuster on the matter cylinder completely, then see if your wheels are free

Click to expand...

Thanks Kermit_rr - I'll give that a go. So just to be sure: Apply brakes and with pressure stil on, undo the adjuster completely and check if wheels are free OR apply brakes, release brakes (at which point wheels will still be locked) and then undo adjuster?

A collapsed hose can also cause your symptons fluid can enter but not return.

If when the brakes are stuck on you then un do the brake pipe union on the master [ the one in the pic ] and the brakes release then you will know the problem is with the master.