I have a '81 Ford L800, 429 gasser, single axle dumptruck. I am having problems with the brakes. This truck has hydraulic brakes with 2 vacuum boosters. Recently, I noticed a vaccuum sound inside the cab when braking, coming from the breather tube (which is routed from the vaccuum boosters into the cab behind the drivers seat). Definite loss of braking power. At a stop light, I depressed hard on the pedal and the vaccuum noise is constant, and then the motor begins to sputter. Checked all the brake lines, fluid and all is normal with no leaks.

I have a feeling it's a vaccuum leak somewhere. Is there a way I can test each booster? Any other suggestions appreciated....

 

The Bendix Hydro-Vac is the same or similar across all manufacturers for years and years.

You can wade through this:

Dave's Place - Hydro-Vac Info

for some basics, or search "hydro vac test" or similar for other methods.

It is normal to hear air from the tube in the cab when you let off the brake. Constant sound with the brakes on points to a vacuum leak, my guess is a torn diaphragm or seal.

From the above site:

http://dave78chieftain.zxq.net/Hydro...cOperation.jpg

 

After some troubleshooting, I discovered I have motor vacuum at the boosters. I tested each booster and discovered one of them is not working, perhaps a torn diaphram. A replacement unit from Napa is like $240 bones. I've heard alot of issues about getting bad ones, since they are all rebuilds. Does anyone have a good supplier for these?

 

I'd think NAPA would stand behind thier parts. I've had them turn down a return on a bad part.