Switch to Override Torque Converter Lockup

[TommyM]

Here's what I'm thinking to do, and would like some criticism:

According to the diagrams, the wire that feeds pin "F" of the ALDL connector ties directly into the wire from the ECM to the trans. The ECM grounds this wire to lock the torque converter.

I want to tie a switch into that wire just behind the ALDL, so that a flip of the switch grounds the wire, thus "manually" locking the converter.

I also want to wire a small LED into it so I can see when the converter is locked.

The only downside I can see is forgetting to unlock it for a downshift or when coming to a stop.

The benefits are that I can keep the converter from locking/unlocking going up and down slight grades on the highway.

When I'm wheeling, would I get better engine braking on long mountain trail descents?

Please post your thoughts.

Tommy

 

[TommyM]

A little more background. . . I just swapped in a 4L80E, PCM, and engine harness from a '91 V2500 into my '90 V2500 (originally a TH-400 trans).

Well, I went ahead and bought and hooked up an LED. I'm not sure about the correct +/- terminology, but one lead is tapped into a fuse box accessory terminal, and the other lead to ALDL pin F, which is grounded by the PCM to lock the torque converter.

I'm still wondering whether I will damage anything by connecting a switch to give myself more control over the lockup. I'd appreciate any input on this.

I took it out for a highway run, and was surprised at how and when the TCC lockup signal is on. I know the algorithm is probably a little more complicated, but it seemed to come on anytime it was in 3rd or OD, over about 40 mph, throttle from 5% to 60% (estimated by feel, not measured).

I also am not sure the converter is actually locking when the PCM signals it. I don't have a tach. Since lock/unlock seem to correspond to a substantial change in throttle, or a gear shift, or applying the brake, etc, I can't tell for sure by feel if it's actually locking or unlocking. Is there any way to tell for sure if the TCC is functioning?

 

[kauzenkaos]

i know 4l80s are prone to some tcc problems but without a tach or scantool its hard to see the actual lockup occur. you should feel it in you apply the brake pedal just enough to turn the brake lights on and not enough to slow the vehicle and maintain steady speed u can feel or hear the engine raise about 200 rpm. as far as lockup is concerned the pcm grounds the circuit at the pcm so if u ground the circuit b4 the pcm you would be fine. im not sure about doin it at aldl it dont show that circuit in the diagram.

 

[kauzenkaos]

ok forget the last part i just looked into it more and its a pwm lockup soleniod prolly not a good idea to ground that circuit full ground

 

[TommyM]

I THINK I've ready somewhere that they didn't start the PWM until later years (like '95 maybe?), and that in my '91, the PCM just grounds the circuit.

 

[LVJimmy]

Here's what I'm thinking to do, and would like some criticism:

According to the diagrams, the wire that feeds pin "F" of the ALDL connector ties directly into the wire from the ECM to the trans. The ECM grounds this wire to lock the torque converter.

I want to tie a switch into that wire just behind the ALDL, so that a flip of the switch grounds the wire, thus "manually" locking the converter.

I also want to wire a small LED into it so I can see when the converter is locked.

The only downside I can see is forgetting to unlock it for a downshift or when coming to a stop.

The benefits are that I can keep the converter from locking/unlocking going up and down slight grades on the highway.

When I'm wheeling, would I get better engine braking on long mountain trail descents?

Please post your thoughts.

Tommy

My 700R4 is wired into the brake light switch so when you press the brake the TC unlocks. Otherwise the lock -unlock is controlled by a switch on the dash. The kit came from bow-tie overdrives.

 

[TommyM]

LVJ,

Do you know of any restrictions on when to use the lockup? Like is it okay to leave it on for 30 minutes of steep downgrade in 4-low 1st or 2nd gear, to aid in engine braking?

Tommy

 

[LVJimmy]

LVJ,

Do you know of any restrictions on when to use the lockup? Like is it okay to leave it on for 30 minutes of steep downgrade in 4-low 1st or 2nd gear, to aid in engine braking?

Tommy

I just watch my trans temp. Having it locked will lower the temp. Of course when it's 115 out it is difficult to keep the trans cool.

 

[kauzenkaos]

heres the diagram from mitchell stating that a 91 4l80e is pwm not a straight ground lockup