[rokit]

I've determined that the engine I got a hold of had a TH400 behind it. The truck I have has a 700R4. Besides changing the flexplate, I am now contemplating what else needs to happen.

The IP has a vac regulator valve on it, as a TH400 shifts according to vacuum. The 700 shifts via the TV cable. In order to go the factory route for lockup, I'd have to get a throttle position sensor installed in place of the VRV.

Help my thought train here: what would the implications of installing a manual lockup switch be?

 

[High Sierra 2500]

You don't really need a switch... You could actually just hook up 12V to the wire that goes to the tranny and be done with it... The solenoids on the valve body will make it unlock at low speeds.

The only problem with running without a TPS is that if you let off the gas all of the sudden it may have a tendency to jerk a bit initially rather than smoothly slow down which is a little uncomfortable and a little hard on things inside the tranny, but if you avoid letting off the gas all of the sudden you should be fine until you find a TPS...

 

[rokit]

It seems like it would actually come in handy for engine braking, but this may be hard on a 700...

Isn't the TCC a switched ground, not a switched hot?

 

[High Sierra 2500]

As I recall, the torque converter clutch solenoid (inside the tranny) is grounded. To actuate it you apply 12V to it. I might be wrong, though... It's been a while since I worked on a 700R4... ):h

 

[jdemaris]

I've determined that the engine I got a hold of had a TH400 behind it. The truck I have has a 700R4. Besides changing the flexplate, I am now contemplating what else needs to happen.
The IP has a vac regulator valve on it, as a TH400 shifts according to vacuum. The 700 shifts via the TV cable. In order to go the factory route for lockup, I'd have to get a throttle position sensor installed in place of the VRV.
Help my thought train here: what would the implications of installing a manual lockup switch be?

I depends on your original transmission control circuitry and where it gets it's engine-speed signal. I don't know what truck you have as GM used many different circuits for the 700R4. 6.2s use different sources for RPMs pickup over the years.
LD 6.2 diesels use the throttle-position to control emmissions. Some HD 6.2 diesels use the VRV to control emmissions (in addition to vaccum control for TH400 shifting).

Manual lock-up works fine. In fact, on some vehicles, I prefer it. My 86 diesel Blazer with 700R4 is kind of underpowered in lock-up mode at highway speeds with lots of uphill grades. It used to shift - in-and-out too much with the standard OEM lockup controls. So, for years I left it unhooked - simply unplugged the wire harness from the trans. Overdrive still worked fine, but with a little torque-converter slippage - it drove MUCH nicer. But, for long trips - especially on flat highways - I wanted to take advantage of the lock-up for the extra couple of MPGs. I finally put in a manual switch, it works fine.

 

[Matt C]

... It's been a while since I worked on a 700R4... ):h

Ya gotta rub it in don't ya.

 

[rokit]

Thanks fellers,
I think I'm gonna put a toggle switch in the dash. I'll likely leave it off in town, and just turn it on when I'm cruising on the highway. Hopefully with the Banks the kickdown meandering won't be a huge issue on the hills. Now I just have to figure out whether it's switched hot or ground.

Is there such a thing as a block-off plate where the vac pump would go? I have no EGR, and nothing else that requires vacuum - I'd just as soon get rid of the thing.

High Sierra, you running a NV4500?

 

[jdemaris]

Now I just have to figure out whether it's switched hot or ground.

Is there such a thing as a block-off plate where the vac pump would go? I have no EGR, and nothing else that requires vacuum - I'd just as soon get rid of the thing.

Yes - there is a sort of "block-off" plate. Your oil pump drive has to be in there, but 6.2 diesel vans and 88 and newer 1/2 ton new-body-style pickups, and a few others have no stuff sticking out in the rear - just an oil-pump drive installed that is flush with the block.

In regard to voltage polarity question - post what type of vehicle you have and I can look up the schematic for the trans.

 

[jdemaris]

Thanks fellers,
I think I'm gonna put a toggle switch in the dash. I'll likely leave it off in town, and just turn it on when I'm cruising on the highway.

One thing I forgot to mention. Make sure, if you add your own switch for the lockup - it's tied into the original source that runs through your brake-light circuit. All the 700R4s are hooked that way so whenever you hit the brakes the lockup disengages.

 

[High Sierra 2500]

Ya gotta rub it in don't ya.

):h Sorry... I won't rub it in anymore...

Thanks fellers,
I think I'm gonna put a toggle switch in the dash. I'll likely leave it off in town, and just turn it on when I'm cruising on the highway. Hopefully with the Banks the kickdown meandering won't be a huge issue on the hills. Now I just have to figure out whether it's switched hot or ground.

Is there such a thing as a block-off plate where the vac pump would go? I have no EGR, and nothing else that requires vacuum - I'd just as soon get rid of the thing.

High Sierra, you running a NV4500?

NV3500... No valve body to mess around with, no plastic governor gears to break, no pumps to fail, no nasty red ATF...

Oh... Sorry... I said I wasn't going to rub it in anymore...

These transmissions are pretty much all wired the same way. The main thing that varied from year to year and setup to setup was the placement of the switches on the valve body...