New th700 installation

[85 square]

I just got a th700 in my 85 c10. Changed from a th350c. The factory wiring was not compatible so I had to install a tci lock up harness. It includes a vacuum switch that I’m not sure the purpose of. It has a screw to adjust but I’m not sure what to do with it. I would think it should disconnect the tc when the engine lugs. The truck runs great down the highway but at 40-50 mph I need to put in 3rd to keep from luging.
Anyone able to help??

 

[JoeR Jr]

It could be a couple of things.

If you have really tall gears in the diff, shifting into OD at 40-50 will bring the RPMs too low and it will lug. If that's the case, I'd do exactly what you are doing. Keep it in 3rd unless you're on open highway.

The converter is locking too soon(less likely). You can play with the vacuum switch to adjust it to your liking. The vacuum switch is used as an indication of engine load, and it works nicely for that. No load=lock the converter.

Are your shift points ok? You're not shifting too early, right?

Joe

 

[85 square]

Hi joe. My shift points are good. I think it’s locking to soon, do I turn the screw clockwise or counter clockwise to slow down lockup? Right now it locks as soon it hits 4th unless I mash the throttle an it kicks into second or third. Correct me if I’m wrong... the purpose of the switch is to unlock the tc when there is no vacuum in lugging condition.

Joel

 

[84 M1008]

If it downshifts into 2nd from 4th the throttle valve cable needs a be adjusted.

 

[JoeR Jr]

Hi joe. My shift points are good. I think it’s locking to soon, do I turn the screw clockwise or counter clockwise to slow down lockup? Right now it locks as soon it hits 4th unless I mash the throttle an it kicks into second or third. Correct me if I’m wrong... the purpose of the switch is to unlock the tc when there is no vacuum in lugging condition.

Joel

If your shift points are good then your TV cable is most likely good.
I've got no idea which way you adjust the vacuum switch. If it came with directions, give them a shot.
You are correct on the purpose of it.

Joe

 

[85 square]

No directions on how to adjust just say that you can. Guess I’ll try all the way in then all the way out to see what way to go. I think I’ll add a switch also to shut lockup off completely when necessary.

Joel

 

[Matt69olds]

I’m pretty sure turning the screw in increases the vacuum need to close the switch, and lock the converter. It will also unlock the converter earlier with less throttle.

Before getting crazy blindly turning screws, either go a turn at a time, or call TCI for instructions. Those vacuum switches are kinda touchy, it doesn’t take much to damage the diaphragm inside.

 

[85 CA SIERRA 1500]

Hi All,,,,,one of the new guys here.
What is a TH700??? Is it just another name for a 700r4?

 

[Matt69olds]

700, 700r4, 4L60, 4L60E, there is also a 4L65E, and a 4L70E. All the same family, the “E” refers to electronic controls, the 65 and 70 mean they have factory upgrades to improve durability.