700r4 lockup???

[45acp]

This question is related to towing. I have a 1984 k1500. When I'm in overdrive an shift to drive manually does this lockup the torque converter? I appreciate you input!

 

[Matt69olds]

The torque converter lockup is controlled by the PCM. It uses inputs like engine temp, vacuum, throttle position, vehicle speed, etc to determine when to lock the converter.

 

[PrairieDrifter]

If you are downshifting from overdrive to drive you would be going to 3rd gear.

 

[PrairieDrifter]

If you are downshifting from overdrive to drive you would be going into 3rd gear, lockup is only in overdrive, when above 45mph and cruising. If you tap the brakes, while in OD with the converter locked, the converter will unlock with a touch of the brakes.

 

[gmbellew]

Not sure if all years operate the same. My 1990 suburban 700r4 will lock up in 2nd, 3rd, and 4th gear.

For towing, definitely keep it in D.

 

[PrairieDrifter]

Not sure if all years operate the same. My 1990 suburban 700r4 will lock up in 2nd, 3rd, and 4th gear.

For towing, definitely keep it in D.

I'm not sure on the specifics, but this is true. But he did say it's for an 84, and thats how my 84 700r4 is.

 

[45acp]

The torque converter lockup is controlled by the PCM. It uses inputs like engine temp, vacuum, throttle position, vehicle speed, etc to determine when to lock the converter.

Thank you for your input! My truck has fed./high alt. smog,no ecm or pcm so it IS controlled by engine temp and vacuum. What I am concerned about is running a 180 thermostat when 195 is what's called for. I guess I need to find out at what temperature the thermostat vacuum switch opens. Thanks again!

 

[45acp]

Folk, I'm not very good at asking questions. I guess what I should have asked is will a 180 temp thermostat still lock up the torque converter?

 

[Goldie Driver]

Folk, I'm not very good at asking questions. I guess what I should have asked is will a 180 temp thermostat still lock up the torque converter?

I am not sure on this but will say that it probably depends on where the lockup switch draws its vacuum from.

If it is from a thermal vacuum switch, then you may have a point.

If it is from manifold vacuum then I suspect it won't care about temp as it is looking for high vacuum from cruise.

 

[PrairieDrifter]

I'm running mine off of just manifold vacuum. I don't think it's operating like "factory", I say this because it basically locks up and drops rpms without me hearing 4th gear, at least what my head and ears say, I have no idea in all reality.

But I can say I've had no problems, and if worried about it you can wire in an optional switch that way you can decide when the converter locks or not. You just have to be careful with a switch, as to not leave the converter locked up at any other time than when needing to use it.

I do believe it was factory operated off a thermal vacuum switch off of the thermostat housing. From there on I'm clueless lol I just ripped all of the emissions crap off right away.

 

[45acp]

I am not sure on this but will say that it probably depends on where the lockup switch draws its vacuum from.

If it is from a thermal vacuum switch, then you may have a point.

If it is from manifold vacuum then I suspect it won't care about temp as it is looking for high vacuum from cruise.

It is from the thermo vac switch.

 

[Matt69olds]

I have no clue how the TCC is controlled on a 84 truck, or the specifics of Fed or California emissions.

The 700 is hydraulically capable of locking in 2nd gear, meaning if the solenoid sticks, or the wiring is screwed up, the converter can lock as soon as the trans shifts to 2nd gear. Some transmission (depending on original application and calibration) had a 3rd and 4th gear pressure switch.

I’m betting there is a thermal switch that delays converter clutch until the engine reaches a certain temp. To met the ever more restrictive emissions standards, I’m sure GM would want the engine to get to operating temp ASAP. Keeping the engine speed up until it warms is a perfect way to accomplish that.

I don’t know what the coolant temp threshold is to allow the converter to lock, but I’m betting a 180 thermostat would be warm enough.