The proportioning valve is located just behind the trans crossmember on the drivers side in the open section of your rails,it may be a drum setup the you may have to remove the valve all together or there may be just a line joiner insted of the valve.

Matty,

I had a similar problem with my HQ Statesman when I first got it - deceased estate too, car had been sitting for years. Turned out that the brake hose on top of the diff was swollen. The master cylinder had enough pressure to push fluid through this hose, but the much lower return pressure meant that the fluid couldn't pass back through the tiny ID, hence keeping the rear brakes locked on. It would be worth keeping this in mind along with the other suggestions. You could also start by flushing out the old brake fluid.

Rhys

Thanks for your replies, guys. Something funky going on with reply notification emails, I only got the first one.

Rhys, good suggestion. I've thrown the gauntlet at it (brakes aren't dear) with machined drums, new shoes and wheel cylinders. Road Worthy guy said I have to replace all brake lines to the rear (excluding the hose above the diff), but may as well replace that as well.

ABS guy said proportioning valve (in the location you said, Dr Terry) is not likely to be the problem, but that he could rebuild it (not longer available new).

There's another reply not shown below now for some reason, regarding swapping of the front/rear chamber connections on some replacement master cylinders - has anyone heard of that?

Small resevoir at the front and threaded holes where the lines go in the same place as the originals, meaning the front resevoir that is now meant to be connected to the rear circuit is operating the fronts. To put one of these master cylinders into an early car you have to bend the brake lines to suit. The cylinders done properly have the threaded holes moved with the resevoirs BUT the couple I have seen have been not moved.

Dr Terry

The only effect I could see it having, if I am correct, is that the rear uses a non-return valve seated in the connection point to the Master, whereas the front doesn't, correct? If so, probably a mute point, as if they were reversed, it would make the front lock on (as opposed to lock up), not the rear.

One more thing, the brake lines (pipes) that go from the master to rear cylinders have been targeted for replacement by Mr Roadworthy due to rust. I'm told these cannot be purchased new - does anyone know someone who makes them up in Melbourne area (I'm in Brunswick).

Thanks Gents.

also if the lines are reversed the front brakes would stay locked on as the non return fitting would keep the pressure to the disks. when i fitted disks to front of my eh i did not realise the non return valve in the master cylinder had to be taken out and as soon as the engine started the booster locked the rear brakes on. maybe your master cylinder still has the non return valve installed.

What you are all saying is correct, but for one thing. It's not actually a 'non-return' valve. it's a residual pressure valve.

It's purpose is to hold a small residual pressure (5-7 psi) against the seals in the drum brake wheel cylinders to make them seal better when the brakes are not being used.

If the 2 master cylinder outlet pipes are reversed the likely outcome is the possible weeping of the rear cylinders over the long term & increased front disc pad wear because the calipers are never fully released.

As I mentioned earlier, reversing the 2 pipes won't cause any operational dramas with the rear brakes.

One other possible cause of the rear lock-up is the condition of the tyres. You mention it is a deceased estate, are the tyres very old? These model cars were prone to rear lock-up under heavy braking anyway, if the tyres are old & hard the rear lock-up will be cronic.

Dr Terry