CCC PT2:

[Stewart G Griffin]

If the 81-86 pickups did not have computer command control, then how does the torque converter lock/unlock?

[Z28 c10]

If I remember correctly, the torque convertor lockup on the earlier trans is controled via a vacuum solenoid, when you let off of the throttle it sends full vacuum to the switch, that in turn closes the switch cutting out the electric current feeding the torque convertor solenoid. I beleive thats how it worked on the 700r trans at least.

 JayTater

 Z28 C10  

[VileZambonie]

The low vacuum switch was used to unlock the converter. When driver demand is high vacuum drops and the converter unlocks. Lock up is acheived without a computer via pressure switches and in 3rd or 4th gear. The brake switch and low vacuum switch will unlock the converter.  

[Stewart G Griffin]

So where/how does the tranmission get vacuum signal?  Through the modulator?

[VileZambonie]

The 700r4 doesn't use a mudulator. The vacuum modulator on the transmission moves the modulator valve in relation to engine vacuum. Basically if modulator pressure is greater than governer pressure it will force a downshift or delay an upshift in response to engine load.

The low vacuum switch is just a switch that opnes the electrical circuit (open means no continuity) in response to low vacuum so no current will flow to the TCC solenoid.

[Stewart G Griffin]

OK, this is a TH-350, not a 700R.

[roundedline]

There should be a temp-vac switch on the manifold that goes to a vacuum switch on the firewall by the brake booster (think is has 2 green wires on it...)  This is what controls the lockup.  

You can also bypass all of that and put an electrical on/off switch on it and lock it up when you want.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[Lt.Del]

As Chris said, you can bypass all the junk and just throw a 12 volt circuit/current to it via a toggle switch in the driver's compartment like I did.

You don't have a th350, you have a th350C (lockup converter).

As mentioned, the vacuum for the lock up doesn't go to the trans per say, it goes to an electrical switch that sends 12 volts to the trans and takes the 12 volts away.

 

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4