Info needed: Bendix brake booster testing

[Alastair Thomas]

Our F60S has been suffering a loss of power so, to cut a long story short, we rebuilt another engine and fitted it. The truck is still gutless so, wiping the egg off our faces, we are now puzzling as to what the cause could be.

Having been through the petrol/carb side and the ignition setting and timing we thought we would see if there was a leak in the inlet side.
This lead to our taking the Bendix brake booster off and examining it.
I removed the can from the front casting and could see nothing wrong with the spring, piston or leather diaphragm.
I do not know how to test these things on the bench.
I reasoned that since the principal of operation is to have equal pressures on either side of the piston when not operating (normally 4 to 5psi but normal air pressure in my test) and then introducing a higher air pressure to the front connection. Operating the brake linkage, the piston should move against the spring. (See picture).
Nothing happened except air coming out of the four holes in the actuator.

Could anyone advise me where I have gone wrong please?

Alastair
F60S LAAT
Ford Lynx I MkIII*

[Phil Waterman]

Hi Alistair

I have found that front shock/tub boots for motorcycles are an excellent replacement for the brake booster. Have them on my two bigger CMPs.

In my notes I have how much force the add. Most common problem I found on the booster w was dirt or not working vacuum check valve. Brake booster function of ours depends on cood engine vacuum.

Keep us posted on your progress.

Cheers Phil

[Alastair Thomas]

I am stuck caring for my Wife one hour away from the truck but I had a rare opportunity to visit it this week.
I stuffed a vacuum gauge into the pipe from the engine and got a reading in the "Good" region of the scale.
I re-fitted the servo and managed to persuade myself that it was working albeit not as strongly as when we rebuilt the truck. Being an optimist, I have decided that it may be due to there being no oil in the vacuum chamber. I just had time to put oil in it but then had to shoot back home. You will see on the soft skin forum that we are also chasing a lack of pull from the engine so the two problems may well be connected.
Alastair
F60S LAAT
Ford Lynx I MkIII* (which will be charging round the village on May8)