# Vacuum Assist Brakes



## [email protected] (Jun 14, 2011)

vacuum assist brakes.

My vacuum pump runs continuously. 

The pump turned off as designed when I disconnected the hose and place my finger to create vacuum.

Has anyone out there had their pump damage the internal diaphragm on their donor car?


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## gdirwin (Apr 7, 2009)

I just had a similar problem when I mounted my VW vac pump - worked fine on the bench, but ran continuously when in the car.

I mounted the pump on a rubber gasket, which was pinching a very small air intake vent - thus the pump was not getting any air, and not developing vacuum.

Probably not your problem, but something to check.


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## EVfun (Mar 14, 2010)

The vacuum brake booster eventually leaks and needs to be replaced. It is unlikely to be caused by the vacuum pump. Leaving a car in a non operating state for a year or so while converting it can encourage the failure of rubber parts.


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## NZero (Jan 30, 2010)

EVfun said:


> The vacuum brake booster eventually leaks and needs to be replaced. It is unlikely to be caused by the vacuum pump. Leaving a car in a non operating state for a year or so while converting it can encourage the failure of rubber parts.


What he said, its usually a decrease in vacuum anyway from ICE to EV.


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## gojo (Feb 1, 2011)

I just had a similar problem. The car is a 1983 Mazda RX7. 

I adjusted my vacuum shut off switch to shut off at 22#s. When I connected my brake booster the pump kept running, however when I pulled up on the brake pedal, the pump would shut off. 

The pedal seems to be coming up better on it's own, but the pump only shuts off for about a minute, and then will come on for about a minute. I would be interested in knowing how often an average pump would come on and off (cycles).


In this case the power booster probably hasn't been used for 10 years or more, and I haven't driven much with it (just up and down my long diveway). It may get better or worse with use.

Good brakes are a must.


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## piotrsko (Dec 9, 2007)

sounds like you both need a new booster assembly


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## [email protected] (Jun 14, 2011)

Thanks for all your replies.

I seem to have two problems. That always makes troubleshooting difficult.

The booster diaphragm is leaking slightly and the vacuum switch is not working properly.

James


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## gojo (Feb 1, 2011)

piotrsko said:


> sounds like you both need a new booster assembly


In my case, is this because the pump cycles on and off about every minute? Without appling the brakes, how often would the pump just come on with a good booster?

Or is it because the pedal was sticking? The pedal has pretty much quit sticking, after just working it up and down a few times.


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## steven4601 (Nov 11, 2010)

Was about to start a similar thread with the same question. What interval is acceptable without causing annoyances?


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## piotrsko (Dec 9, 2007)

annoyingly, the on interval quality is set by the manufacturer. BUT back in the day.... all my cars with boosted brakes would hold vacuum for at least a day without the ICE being on, until I used the brakes. Saying that, I think that once the pump shuts off, the system shouldn't turn back on until the brakes are applied.


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## steven4601 (Nov 11, 2010)

piotrsko said:


> annoyingly, the on interval quality is set by the manufacturer.


On interval ? Minimum on-time after it is triggered?


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## dtbaker (Jan 5, 2008)

the pump should NOT cycle at all, for many days, unless you use the brakes. You either have a leak, and bad check valve, or the check valve installed in the wrong spot allowing vacuum to escape back thru the pump itself.

It is highly unlikely that any of these little pumps pull more vacuum than the ICE manifold, so are unlikely to damage anything. In fact, at altitude the pump is de-rated significantly, so you have to set the vacuum switch considerably lower, or the pump never 'finishes'.

my pump is supposed to pull 23" at sea level, but at 7000' I had to set it down to about 13" so that it would 'finish' relatively rapidly.


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## EVfun (Mar 14, 2010)

steven4601 said:


> Was about to start a similar thread with the same question. What interval is acceptable without causing annoyances?


Manual brakes provide a suitable interval.


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## dtbaker (Jan 5, 2008)

EVfun said:


> Manual brakes provide a suitable interval.


but are pretty hard to find.... or replace master cyl with an appropriate unit not needing vacuum. Probably NOT a good idea with a lead build trying to stop the extra weight without a little help. 

I am looking at retaining the stock vacuum-less brake master for my Alpine build, but might upgrade to a shiny new Wilwood or something along those lines as the stock brakes are in need of a major rebuild anyway.


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## steven4601 (Nov 11, 2010)

Just build a 555 based pump timer relay/mosfet .
Circuit works nicely but sadly the new reservoir has a hiss. 2 minutes and 10 seconds is when the vacuum switch triggers the pump timer.

Ill have to install hose clamps tomorrow & apply thread lock to the vacuum reservoir connections.


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## gojo (Feb 1, 2011)

dtbaker said:


> the pump should NOT cycle at all, for many days, unless you use the brakes. You either have a leak, and bad check valve, or the check valve installed in the wrong spot allowing vacuum to escape back thru the pump itself.
> 
> It is highly unlikely that any of these little pumps pull more vacuum than the ICE manifold, so are unlikely to damage anything. In fact, at altitude the pump is de-rated significantly, so you have to set the vacuum switch considerably lower, or the pump never 'finishes'.
> 
> my pump is supposed to pull 23" at sea level, but at 7000' I had to set it down to about 13" so that it would 'finish' relatively rapidly.


Are check valves always needed? 

I have a Gast vacuum pump, and no check valve. I maybe need to experiment a little more with it. I used a gauge to set my switch, and the vacuum seemed to hold ok, but maybe I should have waited a little longer to see if it cycled before I connected it to the vacuum booster.

It would be great if I didn't have to replace the vacuum booster. Besides the work, the're getting hard to find for an 83 RX7.


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## dtbaker (Jan 5, 2008)

gojo said:


> Are check valves always needed?
> 
> I have a Gast vacuum pump, and no check valve. .



yes.
add a check valve BETWEEN pump and vac resevoir. the Gast and most other vac pumps will leak when not running.


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## gojo (Feb 1, 2011)

dtbaker said:


> yes.
> add a check valve BETWEEN pump and vac resevoir. the Gast and most other vac pumps will leak when not running.


Thanks. That should be easy enough. 

Can I just get a check valve at the local auto parts store?


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## dtbaker (Jan 5, 2008)

gojo said:


> Thanks. That should be easy enough.
> 
> Can I just get a check valve at the local auto parts store?


if your local store doesn't have them, you can get'em from kta-ev.com or some other ev parts people, or ebay.... for less than $10.


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## Old Goat (Jun 28, 2011)

My problem is that I ordered a used vacuum pump (Audi) and it arrived in good shape, but I was surprised to learn that it didn't come with a built in control switch. I am in the market for a controller that senses vacuum and turns the pump on when vacuum is below a set point (maybe 14 inches of Mercury?) and it keeps pumping the vacuum down until it gets to the high set point (maybe around 25 inches?). Where can I find such a switch/controller?


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## dtbaker (Jan 5, 2008)

Old Goat said:


> ...in the market for a controller that senses vacuum and turns the pump on when vacuum is below a set point (maybe 14 inches of Mercury?) and it keeps pumping the vacuum down until it gets to the high set point (maybe around 25 inches?). Where can I find such a switch/controller?


the 'D Square' vacuum switch unit and reservoir have proven dependable... available at KTA-ev.com and other places.


d


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