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Old 09-18-2012, 02:21 PM   #1
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'94 Bounder Diesel vacuum pump replacement

A couple of years ago my vacuum pump died. This is a device required to run the cruise control and the vacuum operated dash comfort controls. And needed because a diesel engine has no vacuum system like a gas engine. Here's what the pump looks like: Gast Vacuum Pump, 12VDC

The chassis is an Oshkosh (now owned by Freightliner) and I have the original schematic for it. Fleetwood does not seem to have any drawings of where chassis parts are located.

The problem is that the voltage supply to the pump is dead. And the wires at the pump go up into a covered wiring bundle that is impossible to follow. According to the schematic, the supply comes from an ignition wire through a 22ga fuse link to a relay then to the pump.

I can't find the fuse link or the relay. I've checked near the alternator, in and around the BCC, and around the engine. I can't find the numbered wires and the relays I've found seem to have to many wires.

Does anyone know where the vacuum pump relay and fuse link are located? Or does someone have an old Oshkosh parts placement drawing for their '90's chassis?

Thanks!
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Old 09-18-2012, 07:15 PM   #2
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Sometimes it's much easier to just install a new circuit. Seems like that one should be pretty simple - but you've probably already considered that? -Al
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Old 09-18-2012, 10:51 PM   #3
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I'm not sure about your Bounder "vacuum pump" but the "vacuum generator" that provides the vacuum for my heater vent controls is much smaller than the item pictured.
The one you show is large enough to provide vacuum for a brake booster.

Mine is quite small and located on the cab side of the front firewall, under the dash, along with a softball size vacuum reservoir.
It has a built-in switch that causes it to start and stop depending on the vacuum in the reservoir.
The electrical connection is a single fused 12VDC wire which is powered anytime the key is turned to "run"........There is NO RELAY used in that circuit!
(I would not be surprised if you find what you need turns out to be similar to mine)
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'96 Safari Sahara
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Old 09-19-2012, 10:53 AM   #4
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I do have the schematic for the chassis and the pump does use a relay. I was hoping someone had already worked on theirs and discovered where the original parts might be located. It's a large rig and a small relay and fuseable link are tiny by comparison.

Finding the pump itself took quite awhile too, but thanks to a forum member I found it on an inside rail of the chassis on the passenger side next to the engine. It's stuffed up in there in an area where it can't be seen from below or above.Then there are several large bundles of wires covered with plastic sheath near and surrounding the area. Very difficult to work on. I moved the pump to the outside of the rail just for future access.

I went ahead and rewired the system as Al suggested and it's working now...it's been non-functional for 2-3 years so it's going to be a pleasure to have dash heat again. And a working cruise control.

I do like to tie up loose ends so I'm still hoping someone who has had to work on this setup might now where those parts are.
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Old 09-19-2012, 06:45 PM   #5
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That vacuum pump is way to big just to run the cruise and heater controls. I tried on of those on my 65 El Camino and ended up with a hydroboost.
The pump I replaced my air driven vacuum pump with:

Ford Superduty / Dodge 5.9L ELECTRIC Vacuum Pump

$107 + shipping. It works great. You might look around and find it cheaper yet.

Skip H
96 Monaco Windsor
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Old 09-20-2012, 01:01 AM   #6
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Quote:
Originally Posted by sjholt View Post
That vacuum pump is way to big just to run the cruise and heater controls. I tried on of those on my 65 El Camino and ended up with a hydroboost.
The pump I replaced my air driven vacuum pump with:

Ford Superduty / Dodge 5.9L ELECTRIC Vacuum Pump

$107 + shipping. It works great. You might look around and find it cheaper yet.

Skip H
96 Monaco Windsor
Well, thanks for that Skip, but the pump I'm using (which cost $300, yikes) is an exact replacement. I had part number from the label on the old one so...

Anyway, I don't know if a smaller pump would work or not. Only things that didn't work after it failed were the dash controls and the cruise control. I wouldn't feel comfortable adapting something different to the system since I don't know enough about it.
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Old 09-20-2012, 07:35 AM   #7
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The little one would likely have been all that was necessary for the cab heater controls, but when you factor in vacuum for the cruise control? Clueless. No idea.
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Old 09-20-2012, 07:54 AM   #8
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I have the same vacuum pump in mine. I move it inside a comparment so it not out in the weather. It run my heater and what ever else. P.S. thats a better price than what I paid.
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Old 01-14-2014, 08:34 PM   #9
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Vacuum Pump Operation

Now I know this is an old thread, but maybe someone can tell me - I have the same installation on a '93 Bounder, but mine is still working - for now. Because it is running continuously, I wonder 'for how much longer'. Where would the vacuum sensing switch be, that should be shutting off the pump?
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Old 01-15-2014, 08:40 AM   #10
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Just a guess, but generally if the pump isn't shutting off, it's either worn so badly it's not generating much vacuum, or more likely, you have a leak? All of the ones I've messed with have had the switch located internally. If you pull the line off the pump and put your finger over it (they aren't that strong) it should shut off right away? If not, you problem is the pump. If it does shut off, the problem is likely a broken line, or one that's been pulled off a fitting somehow? A little troubleshooting should identify any problem fairly quickly/easily.
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Old 01-15-2014, 11:37 PM   #11
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I agree with ahicks. Think it's so old it's leaking too much to generate enough vacuum to cause the built in switch to shut it off.
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