I have a 1990 F350 Crewcab 5 speed with the 7.3L diesel and gale banks turbocharged. Recently the brakes started acting strange. The pedal feels very hard but doesn't have any assist 99% of the time. The consensus to date is either the vacuum pump or the canister are not working properly. I would like to know how to determine which one and what is required to fix?

For example how is the vacuum pump lubricated so that it seals and creates vacuum?

There appears to be some vaccum being created but I don't know how to tell if it is enough to operate the canister correctly or if the canister has failed somehow? No rust on the canister that I can see. I don't hear any vacuum leaks.

When running above 2,000 rpm. the brake light goes off and the power assist works initially but then goes away within about a second. Is the pump not up to the task or is the canister defective and bleeding down?

Thanks in advance for any help offered.

Doug

 

good question! my 92 350 has similiar probs! I can hear vacuum from around the pedal and my brake lights dont come on until the pedal is depressed about half way. sometimes my e brake makes a clicking sound too. maybe your thread will help me too!

 

to check the pump, put a vacuum gauge on it. you should have at least 19 inches of vacuum. under 17 is bad, over 20 is preferred. to check the booster if the pump is good, shut off the engine, and pull the hose out of the grommet on the booster. if you hear it suck in, the booster is good usually. if you do not hear anything, the booster is bad.

 

I have a 91 F350. My canister started leaking, so I just unhooked it. Booster works fine without it. It may become a problem if I pumped the brakes alot.

My pump is creating around 20 vacuum

 

What should a vacuum pump read when it's new ?

 

at least 21 inches of vacuum.
i really cant tell you what a new pump should read, cause i have never tested one.

 

My truck's vacuum pump is pulling 18lbs.

Does it need replaced ?

 

well, it all depends on the trans. if you have a stick, you should be able to get a year or two more out of it.
if you have an C-6, i would not replace it till it starts to give you problems shifting.

if you are already having problems with the C-6 shifting, than a new vacuum pump should fix the shift problems.



i have had vacuum pumps pull as little as 13 inches of vacuum on manual trans trucks and the power brakes still worked fine.


but on the same token, i have seen some that would screw up with as much as 17 inches.

 

F350 goatee,
If you hear air leaking near the brake pedal when applying the brakes, you need a new brake booster.

 

The vacuum pump can continue to pull up to 21HG at a standstill idling.....but when operation of the brakes happens it does not have the recoverey speed it should. This is when braking problems arise.

 

My truck does have a C6. It did have shifting issues until I had the VRV adjusted.

It now shifts "firm". Not super hard, but firm. Just like it has a shift kit.