Brake issues AB180 International Tipper

Gents, just recently my old AB180 brakes started acting up, the pedal goes hard and no real brakes. They do sort of work. I checked the vacuum hose from the pump and found it partly collapsing so cut it short and refitted it. I bled the brakes, found some air in a rear cylinder. I noticed when my mate pumped the foot pedal that a small column of brake fluid rose up form the open top of the master cylinder, almost like air was being displaced. I am wondering if my master cylinder needs a kit. There are no obvious leaks and there is a canister that the vacuum hose leads to which I gather must be some form air filter, I un clipped it and cleaned the oil bath element, looks like a suport spring may be missing so made a coiled spring out of fencing wire to hold it in place then replaced the outer canister with new oil to a level on the side.
This truck would be from about 1972 or there about. Normally the breaks are pretty good. I checked out the booster under the passenger side, no hoses broken no obvious leaks, opened the bleed screw on the I assume assisted brake master cylinder and clean fluid came through.
I wonder if there is a valve somewhere that needs cleaning, gents over to you.

Cheers

Heelerau

Possibly the slave piston in the booster frozen.,or maybe the diaphragm is torn,listen to the booster air inlet,see if the booster is valving vacuum and air.An AB would be from early to late 1960s.If you have a Perk,its possible the vanes in the pump are worn completely away,so no vacuum.Booster should be a VH90,dunno if you can still get repair kits.

Certainly seems like the vacuum booster is not working.

To check the booster, pump the brake peddle without the engine running till hard. Then keeping your foot on the peddle with pressure, start the engine and see if the peddle drops further towards the floor. If it dose, Indicates the boosters working.
If it dosen't, the problems ether lack of vacuum or in the master cylinder.

If the master cylinder is worn,either the pedal will go down to the floor,or slowly leak down.It will likely have fluid leaking under the boot.......Having driven Inters with hydraulic brakes some, its my opinion that the single line boosted system is dangerous.....it works well..until you get a fluid leak and there are NO brakes.....IMHO any hydraulic system should be separate front and rear.....I saw an unusual VH90 booster failure once where a pin came out of the internal pushrod and completely failed the brakes,causing a rear ender into a line of cars. It was caused by an el cheapo repair kit sold by PBR and made in Bangla Desh.

Somewhat off topic. I have always been a bit edgy with the brakes on thec1600. Was thinking about retrofitting another booster and dual master cylinder off the acco. Anyone else contemplated this?

Checked the vacuum with my calibrated trigger finger, vacuum pump is working, checked under neath, I undid the bleed plug on the vacuum inlet line to the diaphragm vacuum there, then replace it. Lo I have brakes. I did do as above post suggested and go no movement when I started the truck. Makes me wonder when I released the vacuum whether it allowed the piston part of the booster to release ? The truck does stand for long periods. I will change the brake fluid in due course. Time will tell if there is still a problem, as it is a paddock toy and rarely goes out on the road I can make sure all is well thanks again gentlemen .
Cheers all Heelerau

here s an important tip...........if you rebuild the master cylinder on ANY boosted system,...do not.....include any retained pressure valve in the master cylinder....It will cause the brakes to lock on and stay on as long as there is vacuum in the system......This applies to any inter with a booster,air or vacuum.......or any other vehicle with a booster ,even a car.

I just started the truck with the brake pedal pumped hard, when the engine started and ran for a while nothing happened, pedal stayed hard, then later slowly went to the floor. I noted the other day when I had someone helping me to bleed the system when the pedal went down a fountain of fluid went up an inch or so from the open top of the master cylinder.

Looks like I can get Perth Brake Parts in Welshpool to rebuild the booster. Did some more messing about with it this arvo, and it looks like it is definatley a holed diaphragm. Had the same thing happen with my old 1976 F250 and had to get its power booster and master cylinder done. up. Pig of a job getting it off the fire wall, not so bad refitting it. Came up nicely.