Hey all,

I've got a GMC vacuum pump to assist my power brakes. I'm right at the edge with my cam, and want more vacuum for my brakes, even though it is "OK" the way it is now.

Pump I have is on/off only, there's no vacuum-dependent switch.

Here's what I'm thinking:
Wire the pump to my brake switch, so when I hit the pedal the pump goes on for a pre-determined length of time, say 5 or 10 seconds max. This will prime the booster for the next time I brake, and the cycle will repeat itself as needed.

The pump pulls more than 3 amps, but not certain exactly how many. As a result, I'm thinking a relay would be the best way to wire it up, and I'm still looking for a reasonably hidden mounting location.

So, with these parameters, can anyone help me out with wiring suggestions? I suck at electrical stuff, so don't be afraid to be specific.

Thanks!

Are you sure there is no internal vacuum switch in the pump? All the pumps I've ever had have switches built in.

Some info:

http://www.gmcmotorhome.com/tech/vacuum_pump/index.html

I'm sure if there is one it's not functioning, as I tested the different ports with 25lbs vacuum and ran the pump. The pump itself pulls 22lbs.

If it matters, there's only 2 electrical connections, not 3 or 4 as the link suggests.

Take a look at these guys: whitmancontrols (http://www.whitmancontrols.com/vacuum-switches.asp?gclid=CK_LgKvLipoCFRBbagodswmmFA)

I'm sure you could rig something up. You'll still have to use a relay for the pump, these switches won't carry much current.

After reading this post I went down to the salvage yard and picked one up for $15. I believe it was an 82-84 chevy caprice wagon. It had a 2.8fi badge on it. The pump was accessed from the driver's side wheel well towards the bumper. The hose went from engine to pump, then pump to brake booster and had 3 wires. Looks promising. I had to go to the salvage yard for a seat slider anyways.

Those vacuum switches are a good idea, as they are adjustable.

I'd have hit the junkyard myself, but time isn't my friend nowadays - too much to do with work/home/play, and not the greatest salvage yards within 1/2hr..

I'm thinking this is an easy hookup with the brake switch, I just don't want it to run all the time - the one I have is 2 wires only, so I'd need to either hit the yard for another pump or figure something out.

72, if you hook it up soon let me know where you decided to hide it.

With no inner fenders at the moment, trying to hide it isn't much of an option. But both lines to and from it were well over 2ft long. When I get it done I will take it out and check braking distances with and without at something like 45mph. I can take a pic of the unit and send through email. I just don't have pics hosted online to put on here.

With no inner fenders at the moment, trying to hide it isn't much of an option. But both lines to and from it were well over 2ft long. When I get it done I will take it out and check braking distances with and without at something like 45mph. I can take a pic of the unit and send through email. I just don't have pics hosted online to put on here.

Most of the GM ones look pretty much the same (see link above).

LOL, no inner fenders would certainly help. I was thinking of somewhere directly on the frame under the firewall and out of sight, or the inside of the frame along the bottom of the car. Really, it could even go in the back of the car somewhere.

Any ideas using one of these in the circuit with the brake pedal switch?

http://www.crutchfield.com/p_607528T/DEI-528T-Relay-Module.html?tp=153