700R4 questions

[84chevk10]

Right now my truck, 84 K10, has the 700R4 in it. I'm going to put a mild shift kit in it and do the servo update, corvette servo. My trans has 3 wires on the plug on the left side of the trans, what controls the lock up on this year truck? The reason I ask is that there are wires cut and things unplugged and I'm trying to sort some of it out. If the lock up is unhooked will it cause the trans to run hotter?

 

[84chevk10]

Anyone got a diagram of the oil pressure switch deal? That sounds like my best bet. Also, where the 4th gear port is and what pressure switch to get.

 

[VAL]

This might help you out.
http://www.gmsquarebody.com/forum/showthread.php?t=10246

 

[84chevk10]

Thanks, they had some good info. I ordered a external switch set up. My solenoid is a 1 wire, since I don't need any other wiring in the trans, except for lock up in 4th, I thought about using 1 of the 2 prong sensors in the trans in the 4th gear port and doing it all internally. Figured I'd try the external switch to be safe. On my firewall there is a vacuum switch, toward the right side, I presume it was for the lock up. It's not hooked up at the present. Would I be better off hooking this up? Some say to run one, and some say to run the brake switch also. My truck had cruise, could check that out and wire it through the brake switch to kill the cruise.

 

[1987 GMC Jimmy]

It's way better to run lockup. The lockup avoids slippage by directly engaging the transmission to the engine thus allowing cooler and more efficient operation of the transmission and the vehicle. I say absolutely run it, especially it being an early 700R4. I'll also add that some people comment on the corvette servo being lackluster in the face of their expectations over the old servo. They say that the billet servo is much better. Are you upgrading the sunshell?

 

[84chevk10]

No, just the shift kit and the servo. Wanted to get the lock up working. I'm getting a 350 turbo built, already have the spacer, but I wanted to get the truck on the road and keep this trans for awhile if I could.

 

[1987 GMC Jimmy]

I gotcha. Well, here's some more food for thought. If you're building a TH350C, it'd be nice to get the factory lockup stuff working so it's all neat, and it can do its thing on its own. However, if it's a pre-1980 TH350 without lockup, then I'd just do the external switch and get rid of it when you swap over to the 350.

 

[74 Shortbed]

If the lock up is unhooked will it cause the trans to run hotter?

Definitely not, 400's, 350's never had a lockup and never got hot from day one, 700 is no different, BUT, it could run hotter if you were cruising at a low enough speed that rpm's were lower than the converter stall speed, now you would have converter slippage and that heats up the oil, other than that it won't get any hotter than any other trans..

 

[1987 GMC Jimmy]

I agree on the TH400's and the pre-'79 TH350's, and they're great examples of doing it right without lockup, but the 1979-1984 TH350 units did get lockup. I can't speak to the payoff of doing that in a three speed trans, but those TH350C's are out there.

 

[74 Shortbed]

but the 1979-1984 TH350 units did get lockup. .

I have a couple of them and they are 350C, and they're is a difference in the valve body and the case, all else is identical, they do help drop the rpm some with lower rear gears.