700r4 lock-up

[BJedi76]

‘86 GMC 4x4 Sierra Classic 1500 SWB w/305 on a 700r4

I have been looking for the patch cord between the transmission lock up four pin connector & the vacuum actuator switch on the firewall.

I asked a local transmission shop mechanic if he could acquire one.

He told me that simply putting a check-ball all inside the valve (inside the transmission pan) would do the same thing.

sounds elegantly simple to me.

Does anyone have any educated thoughts about this? Meaning, is there anything tragically wrong with this?

thank you

 

[Ricko1966]

That's how I used to do it. It is dirt simple and I never noticed any bad results but It does go into converter lock immediately on the 3rd gear shift. I haven't done a 700r4 swap in over 10 years, closer to 20 but probably if I had to do one tomorrow that's how I'd do it. Wiring the 4th gear switch to a relay to the lockup solenoid is another easy way to get converter lock up.

 

[Itali83]

Not having the converter unlock when under hard throttle would be a pain. My K-10 had 3.08:1 gears and would be a total dog if converter was permanently locked in 3rd and 4th. I wired mine up so I can lock it whenever I want, I can keep it unlocked whenever I want, or I can let mother GM control it through vacuum and brake switch like she intended. Makes me happy to have control.

I personally would not want it to go straight to lock up and be locked unless a drop to 2nd occurs
Ben.

 

[BJedi76]

So with the check-ball, it shifts from; 1st to 2nd to 3rd & then straight to 4th lock up? (Which I call 4th 1/2)

I want all 4 & 1/2 gears.

if this is true, I would rather have the patch cord.

 

[Ricko1966]

With the check ball it goes 1,2, 3rd in lock up, 4th in lock up. With a relay and using 4th gear switch it goes 1,2,3,4 in lockup. You can put a toggle on the relay to disable lockup. So you can control when lockup occurs or a hobbs switch so lockup would come in and out depending on engine vacuum. Did your truck come factory with a 700r4?

 

[Matt69olds]

Read this.

https://gbodyforum.com/threads/200-4r-tc-lockup-kit-build-your-own.58098/

This is for a 2004R trans, but the process is basically the same.

I wouldn’t bother with the vacuum switch, or if you decide to use one, I’d wire it so it UNLOCKS the converter once manifold vacuum drops below a certain point. I have tried to use the vacuum switch to enable lockup at once the engine reaches a certain vacuum, it was always too touchy.


Since your truck came equipped with a 709, you already have the brake switch you need. One pair of contacts are normally open (for the brake lights, it will have a orange and white wire in the connector) the other will be normally closed (and open when you press the brake pedal) that’s the pair you want to unlock the converter when you apply the brakes.


Since your truck is a 86 with the headlight dimmer on the turn signal lever, get a headlight dimmer switch for the floor, and use that to activate the converter clutch. Wire it thru a 4th gear pressure switch to only allow TCC in 4th gear.

Use a vacuum switch to unlock the converter at around 8 inches of vacuum (heavy throttle) that way you don’t need to worry about slipping the converter clutch at heavy throttle.

 

[Matt69olds]

Here is another article with part numbers, this might be useful.

http://www.73-87.com/7387garage/drivetrain/lockup.htm

And another
https://www.thirdgen.org/forums/carburetors/575899-tcc-lockup-budget.html

and another
https://www.thirdgen.org/forums/carburetors/492891-tcc-control.html

 

[Ricko1966]

Nice links Matt. When I tell someone to use a relay and 4th gear switch I guess I need to be more descriptive,and also would like your thoughts. The relay plain old cheapy 4 pin. # 30 and #85 to key on power source #87 to tcc solenoid. #86 to 4th gear pressure switch. That way 4th gear pressure switch is doing the light work the relay is doing the heavy lifting. My thinking is protect the 4th gear pressure switch because a failure means dropping the pan.

 

[Matt69olds]

I would think the pressure switch would easily handle the current draw of the TCC solenoid. You could use a relay to reverse the function of the pressure switch (if the switch on the valve body is a normally closed switch instead of the needed normally open) there are a number of ways to accomplish this. It all depends on how fancy you want it to be. You don’t even have to use a pressure switch, you can control the solenoid with a switch to control the power side, you could run the other wire directly to ground. The concret will then lock when the switch applies power to the solenoid. A 700 is hydraulically capable of locking the converter in 2nd gear if I remember correctly. That means if you leave the solenoid on, as soon as the trans goes into 2nd hear, the converter locks. Needless to say, the truck definitely won’t drive or accelerate very well.

 

[BJedi76]

I fully read through all the links and everybody’s directions and suggestions.

And I have, what I think might be viewed as, a fairly stupid question, but how is any of this simpler than using the 4pin patch cord to the vacuum switch?

i’m sure I’ve missed the point somewhere.

I don’t tow things and I rarely even fill the bed with weight. I don’t see any need to have control over my lock-up, nor the need to have lock-up in second or third. I suppose if you drove 35 miles an hour for half an hour, it might come in handy, but wouldn’t the stock set up do that anyway?

if I wanted control, I would have a stick shift.

i’m just looking for the highway mileage. Was there something wrong with the stock set up or is it too difficult to get the parts?

I do love all of these ideas and they are fascinating, but I think I’m still missing the point.

 

[Matt69olds]

If you want it to lock and unlock automatically, without any driver input, either the factory computer needs to be reinstalled to allow control, or a aftermarket controller will be needed.

You could do the check ball in the solenoid trick, or just ground the solenoid and ally power thru the brake switch. I can almost guarantee you won’t like the way it drives.

If you just want to drive the truck with zero extra involvement, just leave the converter alone. Install the biggest cooler you can reasonably fit snd don’t worry about the lockup. The trans won’t really care, and other than a few hundred rpm of cruise engine speed, and slightly lower mpg, you won’t notice it either.

 

[Ricko1966]

If you use the 4th gear switch as your solenoid ground you won't even have to go through the brake switch.

 

[Matt69olds]

Unlocking the converter while on the brakes helps eliminate the jerky sensation when you get off the gas or back on the throttle. It’s not that big a deal, most people wouldn’t notice it.

 

[Ricko1966]

Unlocking the converter while on the brakes helps eliminate the jerky sensation when you get off the gas or back on the throttle. It’s not that big a deal, most people wouldn’t notice it.

Good to know. I never noticed it.

 

[BJedi76]

“Factory computer”..?

I thought I just had an ECS, but after looking up years of usage, I might have an ECM.

is this two different pieces of equipment at the same time or does the ECM replace the ECS?

And where would I find the ECS/ECM?

there’s a box up under my glove box, but I thought that was the ECS.

I feel fairly uneducated.

can someone please dumb this down a little for me? Sigh…

And does this have anything to do with why my truck dies when it shifts into 2nd, unless I am at less than 10% throttle?