Diesel Pusher, Electric Vacuum Pump, Questions

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James Lerch - 21 Jan 2007 00:45 GMT

Greetings,

Long story short, my Dad purchased a '93 Damon Challenger from his
neighbor. The RV hadn't been ran for the last 11 years. Somehow I
became the repair man and I've got most everything back in working
condition, but still have a few oddball issues.

For instance, the electric vacuum pump wouldn't come one. The pump
is needed for cruise control and the front cab air conditioning. Today
I finally traced all the wires down and found a defective relay back
in the engine compartment.

However, that made a new problem. Is the silly electric vacuum pump
supposed to RUN whenever the key is on? I thought it would shut down
after it created a decent vacuum. But no it runs all the time, and
makes a decent vacuum. Everything appears to work, but I can't
believe the pump is supposed to run for hours on end :0

I traced all the vacuum lines, inspected the vacuum reservoirs, and I
don't see any leaks, but I don't see any type of vacuum cutoff switch
that might turn the vacuum pump on/off.

Any Thoughts?

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Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "

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Tom J - 21 Jan 2007 01:25 GMT

> I traced all the vacuum lines, inspected the vacuum reservoirs, and
> I
[quoted text clipped - 3 lines]
>
> Any Thoughts?

Vacuum lines in vehicles leak some even when new. I would think it
would need to run all the time to maintain vacuum, just as it does on
engines with belt driven or gear driven pumps.

Tom J

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Gazz - 22 Jan 2007 00:35 GMT

but I don't see any type of vacuum cutoff

>> switch
>> that might turn the vacuum pump on/off.
[quoted text clipped - 4 lines]
> need to run all the time to maintain vacuum, just as it does on engines
> with belt driven or gear driven pumps.

Is that an american vehicle thing :)

My motorhome has a simple mechanical engine driven vacuum pump, goes
straight ot the brake servo and a tee to a 3 litre vacuum resovoir.

Have been working on the engine for the past month and a half, (cam belt
change, fuel line re-routing for running on bio-diesel, re-making the 2nd
alternator bracket and so on.. so obviousely it hasnt been run for over a
month and a half)

Got it back together yesterday, and the first check was to press the brake
pedal to check the wiring to the new scooter rack lights worked, (i.e.
checking ih had brake lights on the rack) and the pedal went down under
vacuum assistance, it's been over a month and a half since the vacuum pump
was run, and it kept enough vacuum in the resovoir for 3 full pedal presses
with vacuum assistance.

I would have expected an electric pump to be powered only when vacuum is
needed, especialy as the one mentioned seems to only run the cruise control
and ac, so when they are off the pump shouldent need to run,

The brake buddy type things you get for working the brakes in a toad have an
electric pump that only operates when it's needed, shutting off when enough
vacuum has been created.

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James Lerch - 23 Jan 2007 18:51 GMT

>Vacuum lines in vehicles leak some even when new. I would think it
>would need to run all the time to maintain vacuum, just as it does on
>engines with belt driven or gear driven pumps.

Pulled the pump out this weekend, the manufacturer is Gast. While I
had the pump out took it apart and it seemed in serviceable condition.

While putting everything back together found one issue, but it didn't
really change anything. They had a vacuum check valve installed, but
it was on the wrong side of the vacuum accumulator. While we had
everything apart, I traced every inch of the 40 foot of vacuum lines,
no cutout switch anywhere.

Good news is I don't have any leaks, the dash vacuum pots still work
after sitting all night :)

I've had some suggestions on how to build a cutoff switch from a few
other groups (old vacuum advance from an ignition distributor), and I
might tinker with that idea.

Thanks for you time!

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tkranz - 22 Jan 2007 13:13 GMT

I have a 1993 Itasca diesel pusher on an Oshkosh Chassis. Sounds like it
might be the same chassis as yours. Same "silly electric vacuum pump".

In the four years I've had mine I have rebuilt the pump once and replaced it
once. It is powered through an engine oil pressure switch and runs all the
time the engine is running, so far as I can tell. If there is a high vacuum
cut off, as would make sense, I have not found it in four years and have not
taken the time to plumb one in. Neither have I done a test that absolutely
confirms that the pump never shuts off, since it is hard to tell if it is
running when the engine is running. But it seems that is the case.

Hope this helps confirm your observations. Check for an oil pressure switch
that might have shut the power off when engine is off at one time. Mine
does not run unless there is oil pressure.
- Tom

> Greetings,
>
[quoted text clipped - 34 lines]
> Education will not; the world is full of educated derelicts.
> Persistence and determination alone are omnipotent. "

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James Lerch - 23 Jan 2007 19:05 GMT

>I have a 1993 Itasca diesel pusher on an Oshkosh Chassis. Sounds like it
>might be the same chassis as yours. Same "silly electric vacuum pump".

Mines a Gast model # MOA-V124-JH. Seems like a decent pump, at least
I've heard of the manufacturer :)

>In the four years I've had mine I have rebuilt the pump once and replaced it
>once. It is powered through an engine oil pressure switch and runs all the
[quoted text clipped - 3 lines]
>confirms that the pump never shuts off, since it is hard to tell if it is
>running when the engine is running. But it seems that is the case.

Ours is tied directly to a relay which is energized whenever the key
is in the run position. I'm pretty confident I'm going to build a
vacuum cutoff, but I have another problem.

Do you have Cruise Controll on your oshkosh chassis? (Ours is an
Oshkosh as well). If so, dose your cruise cotrol have "FORD" and Ford
partnumbers all over it? (ours does.)

I was pretty confident the cruise control would start working once the
vacuum pump started running, but no... that would have been too simple

So, where does one go to learn about after market Ford cruise control
modules on an Oshkosh chassis?

Thanks for your time,

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tkranz - 24 Jan 2007 04:06 GMT

I have had mine (also Ford) serviced at a local shop that does heavy truck
repair. The parts are readily available, but I'm not sure where my shop
gets them.

In my opinion, it is a crappy cruise control. Mine has needed major repair
about once a year. Most frequent problem besides failure of the "silly air
pump", is separation of the control rod from the vacuum diaphragm - and this
is not readily apparent without getting a very close look or taking the
diaphragm off. Happened twice on my unit.

> >I have a 1993 Itasca diesel pusher on an Oshkosh Chassis. Sounds like it
> >might be the same chassis as yours. Same "silly electric vacuum pump".
[quoted text clipped - 40 lines]
> Education will not; the world is full of educated derelicts.
> Persistence and determination alone are omnipotent. "

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