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Old 09-09-2009, 07:52 PM
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700r overdrive unlock

I need to know if anyone knows of a hydraulic switch that I can put in my brake system to open the circuit when pressured up, that will disconnect the lock up converter circuit. What it boils down to is a switch that is normally closed and goes open when pressured up. Thanks Jesse ( preferably 1/8 pipe)

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Old 09-09-2009, 08:01 PM
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Quote:
Originally Posted by 48aero
I need to know if anyone knows of a hydraulic switch that I can put in my brake system to open the circuit when pressured up, that will disconnect the lock up converter circuit. What it boils down to is a switch that is normally closed and goes open when pressured up. Thanks Jesse ( preferably 1/8 pipe)
The Brake light switch from an 80 up Chevy truck that used the TH350C trans would do what you need without tapping your Hydraulics. Trucks/Cars with the TH700R4 and Th2004R trans would work also as they used the same type Brake switch. I do remember reading in the Brake section a while back about someone using a Hydraulic switch in the Brake line for TCC disengagement also.

Last edited by SSedan64; 09-09-2009 at 08:01 PM. Reason: Spelling
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Old 09-09-2009, 08:07 PM
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These are Trans pressure switches, I think they're 1/4" NPT tho'.
Pressure Switch (NC, Two Terminal) GM#8642346
Pressure Switch (NC, Self-Grounding) GM#'s 8642569 or 8634475
http://www.gmpartsdirect.com/

Cruise Control Style Brake Switch GM# 5524845 Unlocks TCC when brakes are applied; also used as part of cruise control in some cases
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Old 09-10-2009, 04:56 AM
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Thanks for the reply. I can't use the typical on the column switch because I'm building a 53 Chev pu with the pedal thru the floor. That's why I would like to find a hydraulic switch that I could plumb off my brake master to unlock the converter. It has to be a switch that is normally closed and goes open with pressure. I'll check out the switches you gave me part numbers for today. Any more info would be appreciated.
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Old 09-13-2009, 06:23 AM
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Just thought I'd let you know I figured it out, for those who might have the same problem. I used a 5 pin relay. I connected pin 30 to batt, pin 87a to the trans feed, 85 to brakelight switch output, and 86 to ground. When the brakes are applied the relay switches to pin 87 and the circuit is broken, thus opening the trans feed. Note 30 and 87a are hot normally.
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Old 09-13-2009, 07:51 AM
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It's been beat to death in this forum, the below example shows a mechanical switch, but the circuit is the same for a hydraulic pressure switch.

Vince
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Old 09-13-2009, 09:07 AM
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I just couldn't find it, I wish I would have talked to you a week ago!! Thanks Jesse
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Old 09-13-2009, 09:53 AM
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as a FYI....

I have posted the image of the wire diagram of 700r4 converter lock up diagram as a "sticky" at the top of the forum here.

this question is asked many times.

I thank you guys for this information and image .


I started a WIKI page for this subject:

WIKI PAGE



lets build this page of WIKI to something we can link to and answer these type of questions for members
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Last edited by Crosley; 09-13-2009 at 10:07 AM.
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