Brake pressure 2 step switch help needed
 

I am trying to run my 2 step via an adjustable fluid pressure switch mounted in the front brake line. It is the first thing in line from the master cylinder, before the adjustable proportioning valve and line lock solenoid. The switch states it is adjustable from 250 - 1000 psi. I have installed pressure guages at the RF caliper and the RR caliper to set the proportioning valve front/rear bias and looking at the front guage i am getting 600psi to the front caliper. I can adjust the brake pressure switch all the way to either end of its adjustable limit and still not get it to activate. Two things i am curious if i am doing incorrectly:

1 - I have the pressure switch mounted vertically in a brass tee. Line comes from master cylinder in one side of tee, switch is mounted vertically in the top port, the line comes out of other side headed for proportioning valve. Does the pressure switch needs to be mounted at least horizontally if not upside down due to needing to make sure there is no air trapped in the switch. There is no way to bleed the switch itself and i am thinking maybe i have air trapped inside and therefore not letting it activate whatever plunger that must be inside this thing.
2 - Wiring. These switches come with three wires. Black, Red and a third color. I have two different brand switches, one has the third wire as blue and the other has as green. Does this need to be grounded? I would not think so. I wired in a blue LED light in the dash to show when the pressure switch is activated. I originally had black to ground, red to 12 volt, and the third wire going to launch on my MSD 7AL3, which actually teed to the blue LED also. I can jump 12 volt to the launch terminal on the 7AL3 and the blue LED will come on so i know the light is working.

I am thinking i need to mount the pressure switch sideways or upside down to make sure there is no air trapped but not positive that is the problem. I dont think it needs to be grounded either??

Any help would be much appreciated, Thank you!

Kurt

Re: Brake pressure 2 step switch help needed
 

On the switch I use the blue is not used although I could probably hook it up to light. The red is power in and the black is power out, Not ground. When the switch is activated it just completes the trigger circuit to the two step. Chad probably does it differently due to his expertise in the safety of race car construction.

Re: Brake pressure 2 step switch help needed
 

I had to get air out of the line leading to the switch to get it to activate. The line came down from the dash to the top of the switch, which is mounted vertically in my case, but inside the car, mounted lower than the master cylinder. The tee is before the line lock and proportioning valves, as you have done.

As there was no bleeder, the flare nut that connects the line to the switch's fitting was loosened to allow fluid to spill out when the pedal was pressed. Tightened it while the pedal was down, then repeated.

Re: Brake pressure 2 step switch help needed
 

Kurt, if you are using an industrial style switch the three wires should be:

1 will be a common wire the other 2 will be 1 NC (normally closed) and the other NO (normally open) both of which will be in the normal state (no Pressure) the trick is to figur the common then OHM out the other two to get the NO open set which you want.

Re: Brake pressure 2 step switch help needed
 

Do you want to have the two-step on during the burnout?

Re: Brake pressure 2 step switch help needed
 

No. The 2- step rpm for launching is usually much lower than the burnout rpm.

Re: Brake pressure 2 step switch help needed
 

Correct.

Which is why I asked. Typically the switch will go in the rear brake line. With the switch in the front brake line it's going to be on during the burnout. Unless you turn the activation pressure way up on the switch, then you risk the potential of it not coming on when you are bumping it in and staging.

Re: Brake pressure 2 step switch help needed
 

If you put the pressure switch between the master cylinder and the line lock, it should not activate during the burnout. At least that is how I see it. If the switch is mounted after the line lock then yes it will be activated during the burnout.

Re: Brake pressure 2 step switch help needed
 

Robert is right.The line lock will hold the pressure on its output side, not the input.

I have this setup in real life., it is not theoretical.It works very well.

Re: Brake pressure 2 step switch help needed
 

Might be off thread a little, where or who did you get the switch from?
Perko