# Power Brake Vacuum



## TelnetManta (Jun 5, 2008)

Guys,

I have my vacuum pump and tank all plumbed in and since connecting to my brake booster I am unable to get the pump to turn off. The brake booster has a check valve already installed but I wondered if you guys were using something else to maintain vacuum?

Thanks!
Ben


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## judebert (Apr 16, 2008)

I have the vacuum switch from EVParts. It has a screw allowing you to adjust the hysteresis. I've got it adjusted to keep the pump from turning on too much.

I also routed it through the ignition switch; this was a very bad idea. Not only did the pump exceed the current rating on the fuse (for which I replaced the fuse with a slightly larger one, ALSO a VERY BAD IDEA), occasionally something weird happens and drops the main contactor. I can't accelerate again until I get the vacuum pump to turn on.

EVParts mentions that their switch/pump combo requires a relay, because the switch is only 4A and the pump is more. I'm going to try inserting a relay in case this is my problem.

If that doesn't work, I'm going to use the kit from EVSource instead. I'll have to replumb, but that's a worthwhile effort. The $350 doesn't seem that bad, either, considering the importance of the system.

Now that I've given you all the warnings from my experience: you need a vacuum switch, not just a check valve. The switch you choose may require a relay as well. A vacuum gauge is a good idea, too, since it'll tell you if you're leaking so bad that the switch never turns off the pump.


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## fugdabug (Jul 14, 2008)

TelnetManta said:


> Guys,
> 
> I have my vacuum pump and tank all plumbed in and since connecting to my brake booster I am unable to get the pump to turn off. The brake booster has a check valve already installed but I wondered if you guys were using something else to maintain vacuum?
> 
> ...


1. Check the wiring... do you have the switch and the pump fused properly and the relay wired properly?
2. Check for air leaks.
3. Do you have a stuck check valve or is it reversed?
Do you have a Thomas Pump with a microswitch vacuum switch?
if you do, make sure the microswitch is fused about 5V and the pump is fused at 10V and the connections on the microswitch has a power wire to the 'com' off the 5V fuse and the NO* has the switch wire from the relay!
check down the forum list a bit in this section, there is a question I had about the same thing and someone provided the answer...

*Sorry originally wrote 'NC', 'NO' is the correct connection point for the 'switch' position from the relay. 'NC' is wrong didn't want to confuse anyone who was reading for info... -fugdabug


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## TelnetManta (Jun 5, 2008)

I have the switch wired properly, it does turn off at 20in vac when the system is not connected to the brake booster. As I mentioned the brake booster has a check valve and I assumed that it would be all that's needed.

I'll recheck for leaks today.

Ben



fugdabug said:


> 1. Check the wiring... do you have the switch and the pump fused properly and the relay wired properly?
> 2. Check for air leaks.
> 3. Do you have a stuck check valve or is it reversed?
> Do you have a Thomas Pump with a microswitch vacuum switch?
> ...


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## TelnetManta (Jun 5, 2008)

Guys,

I went home at lunch and checked my system. Below is a diagram of how my system is plumbed. If I pull the check valve from the brake booster I can hear the inrush of air and if I clamp off the hose with it connected my pump will cut off.

Do I need an additional check valve in this line and if so which way should it face?













Thanks,
Ben in SC


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## ww321q (Mar 28, 2008)

Sounds like it could be a bad diaphragm in the brake booster . J.W.


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## fugdabug (Jul 14, 2008)

TelnetManta said:


> Guys,
> 
> I went home at lunch and checked my system. Below is a diagram of how my system is plumbed. If I pull the check valve from the brake booster I can hear the inrush of air and if I clamp off the hose with it connected my pump will cut off.
> 
> ...


Your checkvalve should have airflow in the direction of the vacuum pump, and close in the direction toward the brake booster. Also, if you put a check valve on the line to the reservoir (just past the switch/pump junction. And do away with the checkvalve at the booster... This seems to work best for me. P.S. I don't see you wiring in a relay in the diagram... are you using one? Also, the air line goes from the pump, to the switch junction TROUGH the resevoir and from the resevoir to the booster... the resevoir is not doing anything in the illustration you have provided.


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## fugdabug (Jul 14, 2008)

here is a simple diagram of the way I configured my vacuum unit and the power setup...


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## TX_Dj (Jul 25, 2008)

I like the idea of moving the CV between the resevoir and pump, instead of between the booster and resevoir. It seems to me this would be more effective overall.

My suggestion would be to move the CV as recommended, then pump the system down to 20" or wherever your switch shuts down the pump and try to get your head down there and listen for any leaks. Perhaps a cheap electronic listening device will help determine if/where any leaks are at.


Also, too bad it's vacuum and not pressure, could use soapy water in a mister bottle.


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