Outer Limits 4x4 Board

Gday all,
Another problem arising from my weekend away...

The brakes are not working well. After continued use into the camping location, the brake light came on on the dash and the brake pedal went hard and the brakes barely worked.
After putting up with it throughout the weekend, i figured it was vacuum because they work fine if i use them sparingly, but if i pump the pedal etc, they fail. Also, as i start the car, the light comes on and then slowly fades as though it slowly builds vac...

Is this right?

I bought a vac meter to measure the pressure, but cant find out what it should be... anyone know that numbers for the vac pump, reservoir etc?

Any help appreciated, thanks

A VAC leak sounds probably, I am assuming the fluid level is ok? Yours have a vacuum clutch booster? Hows the clutch feel? Maybe try blocking off the clutch incase you are loosing vac through the clutch

What car/engine?

sorry, BJ74, 13BT engine

Tanks for that, the clutch feels the same as normal.
Ill start isolating the problem by removing vacuum components

Check out the blades in your vacuum pump. The ones on the 80 series diesel are bakelite and when worn/damaged will reduce its ability to create vacuum.

What vacuum reading did you get with your gauge? I haven't played with diesels much but I assume the vac pump would need to generate similar vacuum pressure to what a petrol motor creates to provide optimal brake assist. Healthy petrol vacuum is about 20in/Hg so you should be getting this. If not then you have problems in the vac pump.

Hopefully someone who has more experience with diesel vac pumps can confirm or correct what I've suggested.

Thanks.

I pulled a vac line off the pump and straight away got around 25in/Hg. So i think it's fine

Then i pulled off the vac line to the booster and heard the 'psst' of the vac and plugged my meter in. It SLOWLY rose to the same level as the pump. (or just under)

I also found that there is a sensor on the vac reservoir going to the brake booster, so the problem could be arising from there.

I might unplug the clutch reservoir and plug that into the brakes and see if that fixes it, if so, i might need a new reservoir......$$$$