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Re: [GMCnet] Ford A426C brake vacuum pump, your opinion please? [message #327578 is a reply to message #327572] Fri, 29 December 2017 15:27 Go to previous messageGo to previous message
emerystora is currently offline  emerystora   United States
Messages: 4442
Registered: January 2004
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Senior Member


> On Dec 29, 2017, at 1:50 PM, James Hupy wrote:
>
> A running GMC engine in good shape, at sea level, will make in excess of 25
> inches of vacuum at 30 mph with your foot off the gas. Like when you might
> be using the brakes. It will make 2 or 3 times more vacuum than your coach
> brakes will ever need.


> So, now we have established that a running coach really does not have
> any need for an auxiliary vacuum pump,

NO we haven’t. How often is the average GMC er going to be driving at sea level at 30 mph with his foot off the gas???

More likely the need to apply the brakes is when some idiot cuts you off at highway speeds when you are at 3000 to 7000 feet elevation. Or if there is an accident in front of you.
What is the vacuum there? Probably closer to 10 inches than 25 inches. The vacuum pump at those conditions will be closer to 20 inches.
Ask Dave Lenzi how much more braking you’ll have with your booster at 20 instead of 10. Or watch one of his demonstration when he has a booster and vacuum pump hooked up to a master cylinder with pressure gauges at one of the GMCMI conventions.
If you are in a panic braking situation you’ll be very thanking that you have a vacuum pump attached to your booster instead of depending on engine vacuum alone.

Now, if your only concern is how many pumps you have for your brakes when rolling backwards on a hill you may be OK without a pump but a lot of people that have been in that situation will disagree with you.

Emery Stora
77 Kingsley
Frederick, CO
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