700R4 Brake light switch?
 

How do people with under floor brakes make a cut off for power to the lockup converter? If using a swinging brake pedal you can get a brake light switch from an 80's car. I'm trying to figure out wiring to lockup but most diagrams use a brake light switch.

Re: 700R4 Brake light switch?
 

those trucks used a brake switch with a lever that the pedal leverarm contacted during it's pedal stroke. they probably also had a longer pedal stroke due to manual drum brakes all around. here is a link that talks about how the pedal and switch work,with a couple of pics if you notice in the link that the person is having trouble with his switch not contacting the lever properly, and you look closely, you will see that the new pedal arm is pivotted on the new brake booster bracket, further back than the original pedal was. this changes the way that the pedal swings so the switch should also be moved.you could use an original brake switch mounted similar to the original and ensure it is set up so the switch closes as soon as the pedal is moved. that way the lock up disengages before any brake action is possible. also, ensure to have a quality pedal return spring so there will be no problems with the lock up being `locked out`due to the pedal not returning all the way.
http://67-72chevytrucks.com/vboard/s...d.php?t=542546

the switches alsocome as a right or a left from some suppliers.cole hersee I think. anyway,if you don`t have room for 2 switches you could alsoplumb in an electrical pressure switch in the brake system to run the brake lights and then use the brake light switch for your lock up switch. in the link pics there is also no rubber bumper installed on the pedal so the pedal bumper would normally bottom out on the firewall when the pedal is at the top of it`s stroke. the return spring would ensure the pedal rubber bumps there and stays there. that way the pedal stroke is always started at the same location so switch set up becomes easier to figure out. you do need to allow some free play in the brake lever lnkages to allow for a bit of body movement. I suppose you could also run a push button style switch that the pedal would contact when released. the swicth would be open when the pedal pushes the switch and then turn on as soon as the pedal travels away from the switch. some messing around with bracketry would be required.
here is a link to an adjustable universal brake light switch on ebay just as a sample of whats availalble
https://www.ebay.com/itm/Universal-S...-/250358961864
or maybe something universal like this spring loaded affair could be utilized
https://www.autoelectricalspares.co....ake-2718-p.asp

Re: 700R4 Brake light switch?
 

A simple solution might be to use a five terminal relay to operate TCC. Use the normally closed contacts for TCC power. Connect power from the brake switch to the relay coil. When the brakes are applied, the relay engages, and the contacts open breaking the circuit to TCC. With traditional terminal numbers you could connect as follows:

Terminal 85 Brake lights
Terminal 86 Ground
Terminal 30 Ignition Power
Terminal 87A TCC
Terminal 87 No Connection

Re: 700R4 Brake light switch?
 

I was thinking about a relay, but I was thinking of wiring it the way they did in this Hot Rod article. They recommend using a relay for power already. It seems weird to use 2 relays inline. The first would get power from the brake light power and would only send power out of the relay when the brake lights are off. That would power the second relay to power the converter. The article says to use the low current from the relay for the pressure switch and the high current for the TCC solenoid. I may be making this harder than it needs to be. I have new power brake under the floor and a new working brake light switch. They just don't offer the duel switch for this like they do for 80's cars.


https://www.hotrod.com/articles/hot-...hout-computer/

Re: 700R4 Brake light switch?
 

Are you sure that's a dual relay circuit? I see the relay connected to four terminals found on the side of the transmission...

You can incorporate the pressure switch in a single relay circuit by connecting terminal 86 to the switch instead of ground. The relay coil is a low current circuit while the relay points will handle the "high current" TCC solenoid.

Re: 700R4 Brake light switch?
 

That drawing is a single relay, but they don't do anything about a brake switch cut off. That relay is key power. If key power came from brake switch instead it would have power when the brake lights were on only. If brake light power went through a relay it should be able to reverse that and have power out when the brake lights are off. With converter only locking up in 4th I may not bother with a brake cut off.

Re: 700R4 Brake light switch?
 

Hmmm... My apologies. I just realized that I implemented the 4th gear switch incorrectly. And you're correct... no 4th gear switch in the article either.

A single relay and a jumper between A and C at the transmission (using the diagram in the article above) would allow a single relay circuit with brake switch cutoff. I have never had a problem with the 4th gear switch failing, but anything is possible. A relay based circuit to protect the 4th gear switch would look like this:

Relay 1:

Terminal 85 Brake lights
Terminal 86 GND
Terminal 30 Ignition Power
Terminal 87A TCC
Terminal 87 No Connection

Relay 2:
Terminal 85 Ign Power
Terminal 86 4th gear pressure switch
Terminal 30 Ignition Power
Terminal 87A No Connection
Terminal 87 TCC

If you are not using a computer controlled engine then you could probably skip the brake switch.