Hi. In my last post i rebuilt the transmission, a 904, and while doing that, i realized that my lock-up torque converter never locks up because it's electrically activated with a solenoid and that is controlled by the computer, and in my truck someone had changed out the carb before i owned the truck, and disconnected much of the sensors to the computer.

So i was thinking to make a manual lock-up control.

I want to put a toggle switch on the dashboard to bring 12V to the solenoid when i want to go into lock-up and get direct-drive 1:1 ratio with less loss, by cutting out the fluid coupling of the torque converter.

Reed said he thinks it may increase fuel efficiency by 5% or so.

So i've been thinking, what would the manual lock-up be like? Would it be dangerous? When would i turn it on/off?

I figure i could do it, and then put the trans in Neutral and switch it on, and see if i can hear it changing.... then turn it off, and then go into Drive and get up to 40 mph and switch it on.

I figure it would be ok to turn it on above 40 mph, and i must be careful to always remember to switch it off when slowing down.

I am capable of doing this. DO you think it's alright?

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'87 D150 Slant-6 A904 with wooden cap

You need a circuit that will unlock the converter when you hit the brakes.


I think it's an easy circuit to design (I'm thinking a couple of relays, 1 to lock it up, and the other to unlock) , but since it's 3am in CA, my mind can't do it at the moment...................

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Hey that's a great idea. I might be able to do one.

I know some things about electrical circuits.

Thanks!

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'87 D150 Slant-6 A904 with wooden cap

Before you go reinventing the wheel, realize that the turning off the tclu was built into the wiring harness, not the computer.

I have a 87 van w/electric tclu.

The relay pigtail for it has 3 wires. One comes from the brake switch (which is different for so-equipped vehicle).

I do not recall the specifics offhand (this was to be a spring project that got postponed by a much larger project), but I found that a simple relay latching circuit and momentary contact switch may replace the computer, and a second spst relay could be installed in place of the tclu relay.

I dont know if i have a drawing of what I came up with, or if I need to re-reverse engineer it, but it is possible to use the wiring in place to open the latching circuit, and unlock the tc via the brakelight switch.

Iirc the computer switches a wire to ground and an extra set of contacts interrupt that ground when pedal is depressed. The 3 wires at the relay are: (+) out to solenoid, (+) in from the key, and swiched ground from computer and brake pedal, in series.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Ok then, a quick description.

3 relays, 1 Normally open momentary switch, indicator light that's on when tranny locked.


1st relay is so circuit only works when car is running

2nd relay is set on by momentary switch. (loop back output to control input to latch relay)

3rd relay is Normally closed and is on loopback wire of 2nd relay


Hit the brakes to activate 3rd relay, breaking the loopback circuit to shut off relay (and locking)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Only need two relays:

Dpdt under dash for latching circuit and indicator lamp.

Spst at firewall in stock location grounded through first relay.

My 1st relay is so you have an ignition power source that has enough amps to run everything.


Relays 2 & 3 are for the 'circuit'


Add a fuse in front of my 1st relay.......

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

The link Dan provided has #71v2 Adjustable vacuum switch. Two switches in line. First switch opens under low vacuum heavy throttle and closes at higher vacuum medium throttle. Second switch opens at High vacuum lifted pedal decel. This is some thing like the computer did.

You will need a Vacuum switch as shown earlier in the post to protect the transmission during kickdown and to let the lockup clutch loose under heavy load as it is not sized to hold the full power of the engine.