Vacuum Pump for the power brakes.

B

Bob Dunahugh

New member
Sep 17, 2012
2,784
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The 76 GMC that I got for our daughter last week. The PO had done everything imaginable. One added feature is a very nice vacuum pump. And about a 3-gal tank as a vacuum storage tank. I know ZERO about having this vacuum pump arrangement. And hearing that pump run every time I even touch the brake pedal a little. ( I've always been happy with the vacuum off of the engine. Nice and quiet.) I'd like to pull it out at this point.. Thoughts?
Bob Dunahugh
78 Royale since 2003
4 real COPO Yenkos
 
I have a small PO-added PVC pipe, about a foot long and 2" in diameter, with capped ends and vacuum fittings that will give me an extra pump of the
brakes if my engine quits. Some folks have an even larger PVC tube that is mounted down by the radiator support that serves the same purpose but with
larger capacity. Either one is a step in the right direction, but neither will provide an unlimited source of vacuum to help stop the coach if engine
vacuum is suddenly unavailable.

I'm currently replacing the booster and master cylinder on my coach, and this has afforded me the pleasure of chatting with Dave Lenzi for the first
time. I ended up getting his specially-modified brake parts and also learned that he offers two versions of an electric aux vacuum pump system. I'm
strongly considering adopting one because it seems that the odds of an engine failure while under way are significant enough to warrant such a
countermeasure. I'm pretty sure I couldn't otherwise bring the coach to a stop within a reasonable distance.

So, it seems you have a really good mod already in place. If your biggest issue is the pump noise, perhaps it could be mitigated with better isolation
of the mounts. Or, given that the reservoir is large, maybe figuring out a way to add a bit more hysteresis to the system could prevent the pump from
activating every single time you touch the brakes. In fact, engine vacuum by itself will top up the reservoir eventually, so it may be possible to
avoid most occasions of the pump coming on at all, except in an emergency.

Maybe give Dave a shout and see what he thinks? If you ultimately decide to remove the system, I may be interested in taking it off your hands.
--
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
 
Bob,
Generally an electric vacuum pump for the power brakes is a safety feature. If your engine stalls, the Power Brake Booster has only a couple of pumps
on the brake before the vacuum in the booster is gone. The vacuum pump will continue to give you power brakes as long as you have battery power.

I would definitely keep this feature!

If the vacuum pump is running every time you use the brakes, I'm thinking the vacuum sensor switch must be set too high. Then engine vacuum should be
the primary source of vacuum with the electric pump taking over whenever the vacuum drops below this. I have mine set to 15" of vacuum, so it rarely
runs.

I would check how the engine vacuum and the electric pump system is currently plumbed to be sure the engine is the primary source of vacuum. With the
3 gallon tank, I would expect the electric pump to run for a few seconds upon startup until the engine draws down the tank to below your vacuum switch
setting. After that the engine should keep the vacuum below the sensor switch setting.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Me- I like noisy pumps.

When a bilge pump runs more than you expect, it can tell you that you should pay attention to something right now.
When the potable pump runs when you think that there is no tap open, it is good to find out why before it pumps all your water overboard.
When the air pump runs when you check the ignition, it means you still have not found that leak. Keep trying.
When the air pump does not run when you check the ignition, maybe it is not working.
When the vacuum pump runs when you check the ignition, that means he is waiting faithfully should you need him.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
When the time comes and you are traveling down a mountain side, or in heavy city traffic, or simply need to come to a halt at a busy intersection, and
your engine quits because you ran out of gas, or the ECM died, or the ignition module died, you are not going to care how much noise your vacuum pump
makes trying to keep up with the vacuum demand needed to stop your 12K lb coach. Ernest’s suggestion of a rocker switch is a good one, but in an
emergency situation that Murphy’s Law can inevitably predict, you are assuming the presents of mind and quick reactions to hit that switch on the
immediate need. IMO, keep this back-up system and follow Bruce’s method of making it better isolated to control noise and reduce the running time.
JWID
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
> When the time comes and you are traveling down a mountain side, or in heavy city traffic, or simply need to come to a halt at a busy intersection,
> and your engine quits because you ran out of gas, or the ECM died, or the ignition module died, you are not going to care how much noise your vacuum
> pump makes trying to keep up with the vacuum demand needed to stop your 12K lb coach. Ernest’s suggestion of a rocker switch is a good one, but in
> an emergency situation that Murphy’s Law can inevitably predict, you are assuming the presents of mind and quick reactions to hit that switch on
> the immediate need. IMO, keep this back-up system and follow Bruce’s method of making it better isolated to control noise and reduce the running
> time. JWID

I agree that when the motor stops and you are in a place where you want to be able to stop its nice that the pump runs automatically. I have Dave
Lenzi's vacuum system and sensitized brake booster. It runs a lot. I don't mind because I know that it is working. I'd rather the pump came on when
the vacuum is below a set certain value and not dependent on me remembering where the vacuum switch is located.

--
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com


Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water
heaters.
 
After the engine stops you have vacuum for one stop. At that point I can hit the pump rocker and ask a passenger to start the onan.
It worked well for me in Yellowstone and climbing up the Wyoming and Nevada mountain ranges.
--
1977 Eleganza II
Ogden NY
 
Hi Bob -

I may be interested in that pump if you decide to take it out... and you’ve got a PM too

Thanks,
SW

--
Steve W
1973 : 23'
Southern California
 
Having nearly dumped my 23' and the ratrod toad over the side of Cullawee Mountain for lack of a pump, I consider it the second mod after the reaction
arms, and a case can be made it should be the first mod. At 200+ pounds I can and did anchor my fat ass in the seat and get both feet on the
unboosted pedal and stomp some braking. I question whether a woman unless she's a bit on the big side and/or fairly athletic can generate enough
stomp to stop the coach unboosted. I added a pump and a 3 foot by 4 inch PVC reservoir and some one way valves to the 23'. The 26' has a pump, I
haven't yet added the reservoir, it's on the list.

-0-johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
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