Hi there. Many thanks for your message. Yes I have been slowly adjusting the rear brake adjusters as they are manual and not self adjusting type. They have seemed too improved a bit. I will do more this weekend. But very interesting your comments on the overheating brake fluid. That may just be the problem.
I will kept you know how I get on.

Hi all. Well I have done all I can now to this dam Mazda. I have replace nearly the whole system now and it still looks up. Now the front is doing it. So what I have done is back off all the adjusters so that the bakes will only work when the pedal is almost on the floor. I drove to work (2.5Km) and back again. and yes you guessed it by the time I got back the brake pedal was all the way to the top with very little movement will operate the brakes and then they get hot. very hot.
The car is now standing on the edge of the cliff but as the brakes have jammed on I can't move it. I have changed the no return valve between the engine and the servo.
I just do not what to do now. I will have to try and take it into a garage but trying to get them to understand what I have done will not be easy as my Thai is far from good.
I will let you all know what happens!!!!!!!!!!!!!!!!!!!

Maybe the problem starts at the front. They are disk brakes, right? The calipers must be able to move sideways. So take the wheels off and grab the calipers and push/pull on them. They must move with ease. If they don't move the sliders are likely all caked up with rust and corrosion. Sandpaper and light cover with high temp grease should make them go again.
I had to use sandpaper wrapped around a wooden dowel to open up the holes for the sliders inside the caliper.
There are rubber pieces that supposed to keep dirt and water out of the sliders. They can jam the sliders if there is rust behind them.

Of course you could also use another vehicle and push that thing forward by 5 feet or so!

Hi there. Yes the problem is still there with or without the servo/boster unit connected

Hello to you. I have replaced all but two front slave cylinders and most of the brake lines now. The two front slaves seem to be working fine so I have left them.
My observations are that as the brakes are used all the slave cylinders move out them return under spring pressure. But after a very short time the all stop doing that and will not return at all so the brake pedal gets higher and higher until there is no more movement to be had then all the brakes start to bind up and get very hot.
One thing I have noted is the gas regulator has been mounted just in front of the master unit and get hot as a result. Maybe this is what the problem is over heating the master unit and the fluid and expanding it making the brake come on and not letting the fluid return??????

Slave cylinder in the front? That means you have drum brakes in the front. They are usually called "wheel cylinders".

Gas regulator? Are you referring to a fuel pressure regulator? Nothing related to the fuel delivery system should get hot anywhere.
Or are you referring to a catalytic converter? These suckers get very hot and they normally have heat shields around them.

Whatever it is you could put a heat reflector between the parts in question to see if it makes a difference.

Could you take a picture of the area and post it here?

Yes the car has drum brakes all round. I have put some heat reflecting material between the Gas regulator and the master cylinder. This has made a difference but to problem is still going on.
One thing I have noted. Is that yesterday we had a big rain storm and lots of water all over the road. The engine cooled down and so did the wheels. The brakes where hard but when I got to where I was going only some 8 km the brakes came back to normal and stayed there. Then all the way home again. This problem is therefore defiantly heat related and not something jamming in one of the drums.

Now we are getting somewhere.
Please, clear up for me what a "gas regulator" is. I believe you mean " catalytic converter". Do an image search for the two terms then you will be able to tell.

It is likely that your truck has lost the original heat shield. Try to find an original one or at least some pictures of an original one so you can fabricate a replacement.

Keep in mind that gases expand more than liquids under heat. Either the liquid starts to boil or there is still air in the area that gets heated while operating the vehicle. I would flush the fluid. It is not that expensive.

Hi Again. Yes I’m beginning to think that there may still be some air in the system and that's what is getting hot making the fluid push the wheel cylinders out.
The gas regulator is directly in front of the master cylinder. The car is only running on gas at the moment as I have not got a working petrol pump. I will be looking into that this week as I need to sort it out. It has been this way since I got it. Running on gas that is. the brake problems have only started since I had new rubber pipes fitted as they what a bit on the bad side. Like splitting. It has gone downhill since then.

Swifty: you really could have helped us by telling us how the truck is set up. I had no idea that it is capable of running on 2 fuels.
Explain to me why should the gas regulator should get hot? Which kind of gas it using?
I really have no idea about gas as fuel.