TH350 Line Pressure

[Chad E532]

This ties into another thread discussing the use of a hydraulic pressure switch for the 2-step activation on the brake system.
Since you need a safety switch in the circuit to only activate the 2-Step in low gear I like the idea of putting another pressure switch in the transmission low gear pressure test port to act as the safety. I see from the TCI website that line pressures would be in the 145-175 psi range when in gear.
But my question is will there be any residual line pressure once the car is in 2nd or high gear or does the pressure on the low port drop all the way to 0 psi?
I think this would be a more robust solution over putting a micro switch on the shifter safe guard the 2-Step from coming on when you don't want it to.
Thanks,
Chad

[art leong]

Originally Posted by Chad E532

This ties into another thread discussing the use of a hydraulic pressure switch for the 2-step activation on the brake system.
Since you need a safety switch in the circuit to only activate the 2-Step in low gear I like the idea of putting another pressure switch in the transmission low gear pressure test port to act as the safety. I see from the TCI website that line pressures would be in the 145-175 psi range when in gear.
But my question is will there be any residual line pressure once the car is in 2nd or high gear or does the pressure on the low port drop all the way to 0 psi?
I think this would be a more robust solution over putting a micro switch on the shifter safe guard the 2-Step from coming on when you don't want it to.
Thanks,
Chad

I think a normally closed switch. In the high gear line would work.
But unsure about what would happen if you throw neutral at the finish. Will the rpms come down quick enough?

[Adger Smith]

Chad,
I think the 3 speed stacks the apply pressures. low stays on when second comes on. A P/G drops the low pressure when hi comes in.

[Alan Roehrich]

I do not advise putting external switches on a transmission, if not absolutely necessary, as it is a place for a leak. A leak that could put fluid on the track, getting you a fine, possibly a wrecked car, and even a fire, should the switch fail and create a real leak.

Yes, I suppose it is possible to use a pressure switch on a line pressure tap to do what you want, but I wouldn't do it, and we do not do that on either car. A switch on the shifter is the correct way to do it.