Posted by Rob Steller on March 01, 2000 at 00:13:21:
In Reply to: Brake Leak thru Booster? posted by Bill Nasby on February 28, 2000 at 16:09:27:
Bill,
Sound like you have a separate brake booster, probably bolted to the chassis somewhere beneath the cab. I have seen two general designs of these. The newer is much larger in diameter than it is long (two pie tins stuck together) The older, which I have on my 58 and 63 W-300, is more like a coffee can in shape. This is the old Bendix hydrovac, and sports a huge leather piston seal inside. The newer style has a rubber diaphram, I believe. The hydrovac can leak brake fluid into the vacuum side of the piston (ususally to the front) where it will rest until you go down a hill, and/or stomp on the brakes, forcing the stored fluid up the vacuum line into the intake. In this configuration I'd say that you have a hydrovac problem and no master cylinder problem. I have cleaned and lubed my hydrovacs, but I think you have to send them back to Bendix for rebuild (big bucks?) You could try disconnecting the vac line and try a hill to see if the smoke goes away. Make sure you can stop it without the booster first! Good luck! Rob