TCI vacuum switch on 700R4 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

stomper · 08-30-2013, 09:20 PM

My 700R4 installation works great except the lock-up does not unlock with low vacuum. I also have a brake switch wired in the 12v to trans and if I press the brake pedal it unlocks. The vacuum switch does not seem to be working to interrupt the 12v to trans.
I took out the switch, hooked up my multimeter and switched it to the "audible" zero ohms setting. Attached my hand vacuum pump with inHg dial on it. Set the adjustment screw to 'beep' the meter at about 10 inches. (which is the adjusting screw waaaay out)
Installed the switch and when it shifts in 4th it immediately goes to lockup. I can lug it way down below 1000 rpm with my dash vacuum gauge indicating 0 and it will not unlock until it downshifts into 3rd.
Any ideas?

08-30-2013, 09:20 PM	#1
stomper Junior Member Join Date: Jul 2002 Location: Scottsdale, AZ Posts: 1,700	TCI vacuum switch on 700R4 My 700R4 installation works great except the lock-up does not unlock with low vacuum. I also have a brake switch wired in the 12v to trans and if I press the brake pedal it unlocks. The vacuum switch does not seem to be working to interrupt the 12v to trans. I took out the switch, hooked up my multimeter and switched it to the "audible" zero ohms setting. Attached my hand vacuum pump with inHg dial on it. Set the adjustment screw to 'beep' the meter at about 10 inches. (which is the adjusting screw waaaay out) Installed the switch and when it shifts in 4th it immediately goes to lockup. I can lug it way down below 1000 rpm with my dash vacuum gauge indicating 0 and it will not unlock until it downshifts into 3rd. Any ideas? Attached Images __________________ "I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle



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