snoopybg

My car has 2 brake switches. The one for the stop lights and the other one for the cruise control.
My question is which one does the ECM monitor to engage the TCC lockup? The one without the vac line has two connectors. Is the two-wires one for the ECM, if not what is it for?
Basically I wanna know if I need the vacuumed switch if I don't want the cruise control.

1987 camaro

snoopybg

Is this correct?

n1ffer

Snoop - The 700R4 trans uses vacuum for lock up of the over drive function of your transmission. The brake switch works to interrupt the vacuum switch mounted next to the brake switch when the brake is applied.

When you hit the brake the system assumes you are stopping and need to downshift so the vacuum switch cuts vacuum to the TCC and drops the trans back into drive to allow proper downshift.

I do not believe the vacuum switch on the brake pedal has any inputs to the cruise control. I believe it is dedicated to dropping the trans out of lock up when you hit the brake.

The vacuum related to the cruise control is underneath the hood located by the steering box on the driver side. It looks like a very large EGR valve with throttle cables and vacuum lines running to it.

If you want lock up overdrive on your transmission, do not mess with the vacuum switch on the pedal. That much I am certain.

astrosurfer

I thought the 700r4 was locked up electrically from recent study here. I have a trans problem. However I think it's clutches and not lockup. No 3rd or 4th.
I have no vacuum line to my transmission. My th350 did though.
Could someone clarify this.

snoopybg

Well, I too did some reading in many other threads that stated the TCC lockup in 700r4 is performed by an electric coil, controlled by a switch on the brake pedal. I only am not sure which switch.

DENN_SHAH

iTrader: (1)

the 700 has no vacuum controls on it.
the shift points are controlled by the TV cable and the governor.
TCC is electronically controlled by the ECM.
the TCC gets power thru one of the brake petal switches.
i don't have a wiring diagram handy, but i believe one side of the switch with the vacuum hose on it is for TCC, but i could be wrong.

the vacuum part of that switch is a safety to insure the cruise control releases the throttle.

vetteoz

iTrader: (13)

Correct

snoopybg

Thanks a bunch. So the ECM does not monitor this switch, but the switch disengages the clutch directly.

Where do you get these diagrams?

vetteoz

iTrader: (13)

As previously noted above ; the ECM operates the TCC by grounding the TCC wire (at ECM).
Obviously when the power supply is broken at the brake switch the TCC solenoid disengages

That is from a GM FSM ( factory service Manual ); the best investment you will ever do if you want to save $$$ on your car
Some more basic diagrams here

http://www.austinthirdgen.org/index.php?pid=19

snoopybg

Thank you