Installation Wiring for TH350C

[houston54]

I had a TH350C (lockup) rebuilt and am now trying to identify the vacuum switches needed to initiate the lockup.  I already have the brake switch needed for this application.  Can anyone provide a part number for this part?  I could not identify it on any of the FLAPS websites.  

The wiring scheme I plan on using is 12v to the vacuum switch in series to the brake switch which is wired to the solenoid switch on the trans.  This would activiate the lockup upon reaching a predetermined constant RPM and disconnect it at the application of the brakes.  Please advise if I have this backassward.

The system would be the same as used on 80 model G bodies or corvettes according to the information I have.

This is being installed in my 54 Chevy pickup.

[houston54]

I either stumped everyone with this question or nobody gives a hoot.  Probably the later so I will share the solution I have found.

The lockup feature in the trans is activated by pump pressure so as long as 12v is provided to the solenoid in the trans the converter will lock up. The problem is getting it to unlock when needed to keep the engine from chugging to a stop.  The parts needed to interrupt the 12V are readily available from the parts house.

The required parts are:
GM #25524845 - Brake Switch
GM # 14032087 - Vacuum Switch
GM # 14020691 - Vacuum Check Valve

The price of these AC Delco parts from the dealer was quoted at $107 but I sourced them from XL Auto Parts for $58.  When you look at them you feel you were overcharged at that rate for what they are.  You could probably scrounge these same parts from the salvage yard if you can find any mid 80s GM truck or passenger car that ran this tranny.

The installation is very simple.  The vacuum is taken from the ported connection on the carb located on the right side of the carb base (Edelbrock 1406).  This is plumbed to the check valve which is then plumbed to the vacuum switch.  The 12v switched power is wired to one side of the vac switch, then from the other side of the switch to the brake switch from there it is wired to the trans connection.  

The lockup will now deactivate either through brake application or low vacuum caused by deceleration.

Should be pulling the old trans tonight and stabbing the new on in this weekend during the storm.  

Hope this helps someone else who chooses to use the TH350C at a later date.

[Crosley.In.AZ]

hmm, I thought I answered this thread.

forget the vacuum switch stuff. Un-needed.

12 volts through the brake light switch is good as needed  for lock up cancellation  .

Not using the lock up on a t-350C will not cause any adverse problems like it can on a 700-r4 ttans.