nf1j@juno.com wrote:

> OK, folks, this is one for the list (and I'm so glad there's a list like
> this for problems like this).
>
> We've been waiting two weeks now for the dealer to finish detailing our
> '78 31' Airstream (I forget the model name). It's not rocket science, but
> it is taking a lot longer than we would have liked...and they're not
> Airstream dealers (this was a consignment).
>
> They claim they're having a problem checking the brake system. They say
> it's a two part system, requiring a vacuum line be run from the towing
> vehicle in addition to the electric brake line; that to activate the disk
> brakes, you've got to have both.
>
> Someone, I'm sure, knows all about this stuff, and how to test it, and if
> it's true, and if so, how much of a pain it is to run this vacuum line
> from the truck.
>
> Can you pass along some details and hints/tips/tricks/techniques? Please?
> We can't get them to release it to us for the walk through until they get
> this set up.
>
> Warren & Mary Ellen
> nf1j@juno.com

Unfortunately, relative to electric brakes the Hydra Vac brake system on
your
78 is rocket science. This system uses a large vacuum source, with an
electronic brake controller operating a vacuum control solenoid which in
turn
operates a power brake booster style, vertically mounted hydraulic master
cylinder which activates what was at the time the finest trailer brake
system
ever put under a trailer. And that is being modest. Unfortunately the
system
was expensive and didn't get any cheaper. It required some basic
maintenance
which almost never got done. As a result, unless the system has been used
fairly recently and frequently it typically will not work at all. Repair
parts are still available from one source that I know of, Inland RV of
Corona, CA (800)877-7311. Because of their scarcity the cost of these parts
is pretty stout. Operation and service of it is best done with a thorough
knowledge of the service manual for that coach. These days the typical cost
of converting to electric brakes outweighs the cost of repairing and
maintaining the old system. Of course there is the cost of quality vs
adequate discussion so often had on this list serve. The Hydra Vac system
was
so strong it could safely stop tow vehicle and trailer by it's self. In
point
of fact when the 34' coaches were first introduce, those coaches with the
Hydra Vac had brakes on only two of the three axles.

Charlie