pump brakes and pedal hardens and lose braking power!

[DMH]

So something really rather dangerous on my GQ. If I pump the brakes 3 times at least, the pedal becomes very hard to press and I lose a helluva lot of braking power. The previous owner said it might be the brake hoses. The COR chap thought it might be the brake booster. Graham (pathfinder) said it could be the vacuum pump after I telephonically described it.

Brake fluid level is fine.
I did replace the alternator recently but the vacuum pumps on the back do seem the same size. The new alternator is a 50A (upgraded to 120A) and it seems likely the old one was a 70A.

Thoughts please Trollers.
Thankyou

[Tinus lotz]

Well...brake booster or vacuum pump in my opinion

[Peter Connan]

Well...brake booster or vacuum pump in my opinion

+1

[AndriesS]

Without sounding stupid here, is the engine running while you are pumping the pedal? if it is not then it is fine.

Start car, don't touch pedal. switch off . You should be able to apply the brakes a couple of times before it goes hard. If it is hard immediately then it means you have a leak that empties they brake booster very quickly and could be the brake booster or one way valve
Keep your brakes applied (should feel hard and very high) and start engine, should feel as if brake pedal is sucked in.


Brake pipes will either bulge under pressure so if someone can pump the brakes while you inspect the rubber hoses and look for pipes bulging or in my experience will keep residual pressure and you will find one of your brakes are binding/dragging and running hot.