L18_B110, the master on my sedan is brand spanking new

i had the same problem that Freak said, had to grind the button away on the rod. because my new master was to suit a booster, (which use a rod to press the master, not a button head) the button head it doesn't let the master fully depress. mine as a 13/16 sunny master, i removed the residue valve out the rear because i'm running 4 discs

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Original 1200 & 120Y calipers are twin piston units & yes, they do sometimes get stuck in the slides.
When I reconditioned mine the slides were all but siezed & the pistons were also stuck pretty tight.

I've seen the problem happen twice. Maybe once they're worn they don't actually hold pressure and you don't get the problem. they certainly can cause this exact problem.

being single piston calipers, i would say try lubricating the slides in the calipers...

i've had a few cars (not neccesserilly 1200s) that have had these slides sieze and their brakes stayed on, pads worn unevenly etc etc.

thats just my 2 bobs

im running front discs on my ute with a stock single circuit drum master and the brakes dont stay on

im also running 4 wheel discs on the sedan with a disc/drum master and the rears dont stay on

ive also pulled apart a disc drum master and they both ran the same pressure valve rubbers front and rear....apparently the disc rubber is supposed to have an extra groove in it, but they both had grooves

so im doubting the pressure valve is the cause of the problem

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unless you ordered, or were supplied, a master cyl for a drum/drum configuration, which you would have if you ordered one for a 1200 wagon.

Quote:There is no need to shorten the pushrod, you need only to do what the factory did, ...... move the master cylinder away from the firewall.
The master cylinder is spaced outward by shims that are a stock part. If someone has replaced the m/cylinder, or just removed it for any reason, then replaced it without refitting the original shims, then the pushrod will 'appear' to be too long. If absolutely necessary, get some additional shims from a junk 1000, 1200 or 120Y.

As for the front brake problem, my call is with the residual pressure check valve. All non coupes in Australia came with the drum brakes, so this wagon has had the brakes upgraded, but nobody knows if the m/cylinder was altered to the coupe spec. [disc brake] or replaced with a coupe one.

It has now been replaced, but no mention if it was replaced with a coupe one or if it was altered to coupe spec. [remove front circuit residual pressure check valve]

I would venture to suggest that Cheaters m/cylinder had/has either a faulty RPCV or it's been removed or a coupe m/cylinder has been fitted in the past. Whatever the reason, the RPCV is non operational. If it was, there would be a problem with the disc brakes.

Not being aware of this situation is the most commonly seen mistake that unqualified people make when messing with brakes, but the one not readily seen is the lack of replacement of the rear wheel cylinders.

The discs require a higher line pressure [harder pedal push] to make them work & this means that the rears have a greater tendancy to lock up, so the factory fitted wheel cylinders with a smaller bore size to balance the brakes out.
If you fit stock 1200 type disc brakes, then modify or change the master cylinder & replace the rear wheel cylinders with coupe/disc brake model ones. Even new, these are cheap at somewhere near $20 a piece.

I had the exact same problem with brand new brakes/master cyl/brake lines ect. Had to take the push rod out and keep grinding it down until the was enough clearance to release the pressure. Master cyl's nowdays dont seem to have the correct push rod clearance to suit a 1200 pedal.

one thing to try before u get too invovled with removing and testing other things, lubricate the brake pedal pivot point where the pin goes through. we recently had the exact same problem on our race car and we ended up replaceing the mastercylinder and rechecking the pushrod adjustment a few times and it all turned out to be a seazing pivot point.