Hydrovac, air-pac, air-hydraulic cylinder...

From: Bjorn Brandstedt (super_deuce@hotmail.com)
Date: Thu Sep 19 2002 - 05:02:21 PDT


Ken,
Don't trust the LO when it comes to lubing the air-pac. I have one dated
1965 that suggests using GAA (bearing grease!), "Fill to plug level with
GAA" it says. That's just wrong.

OHT refers to hydraulic oil. Considering the type of equipment it is, use a
good quality pneumatic oil, like you use for your air tools.
The lube port in the back of the unit leads to the large air chamber, which
is filled with compressed air each time the brake pedal is applied. It
pushes a large piston against the hydraulic brake fluid in the slave
cylinder and produces the boost.

When the brake pedal is released, the air is exhausted via the valves, which
now become lubricated. The exhaust must have a clear path to the outside
world and if clogged will not permit the brake pads to return. The brakes
lock up. If the valves stick (=not lubricated) the brakes will not release.
The brakes can be manually released, if this happens by openeing the service
connection (on the driver's side) at the rear of the vehicle. This is a
direct line to the large air chamber of the air-pac.It must be closed for
the brakes to work, of course.

The exhaust, or vent, is routed and joined with the vents from the fuel tank
and master cylinder and are finally connected to the engine crankcase
breather tube.

I have separated the air-pac vent on my vehicle and it enjoys its own path
to the outside through a 3/8" copper tubing, which is terminated high up on
the inside of the firewall in the engine compartment.
There are rebuild kits (Memphis Equipment, about $50.00)if you need to
rebuild the air-pac.
I think that covers it.

By the way, the check valve between the two air resevoir tanks is part of
the deep water fording kit and all vehicles may not have that factory
installation. When fording, the bellhousing is pressurized and if the engine
stalls out, one tank is saved for whatever needs, brakes etc.

Bjorn

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