700R4 overdrive question regarding lockup
 

I have read a lot on the forum but I dont understand the concept behind coverter lock up in 4th. I have a rebuilt 700R4 in my 69 C10 with a 350 Crate. It was there when I got it from my son. Where I am a little puzzled is the reason for the wire running from the transmission. I think I am refferng to the lock up wire. When I hook the wire to power and put a light between the lockup wire and power the light glows when it goes into 4th.
Even if the wire is not hooked up to power it still shifts into 4th. Am I supposed to have all 4 gears regardless of whether the lock wire is attached to power?

I have read all the stuff about putting as late model brake light switch with two sets of contact but I dont understand the reason for having a "lock up" if I have all 4 gears with out the lock up wire attached to power?

Some clarification would be appreciated.

Re: 700R4 overdrive question regarding lockup
 

I have this set up with it well lower your rpm ever more when your torq converter locks up

Re: 700R4 overdrive question regarding lockup
 

The trans still has 4 gears and when using the wire actually locks up the torque convertor in 4th gear and the rpm will drop a bit more than in 4th gear, almost like a bit of a 5th gear, don't have to use it but helps gas mileage a bit more than just 4th gear. It only drops about 200rpm but still helps.

Re: 700R4 overdrive question regarding lockup
 

IIRC the lockup actually stops all slippage between the torque converter and the
transmission input, in effect creating a direct drive. This in turn drops the tranny fluid temps down as well as dropping the rpms a bit. the wire should be either to a manual switch to engage the lockup or connected to the brake pedal switch to disengage it, otherwise it would be like braking with out clutching a manual trans when you stopped at a light and you would stall. hope this helps

Re: 700R4 overdrive question regarding lockup
 

Very helpful. Your responses explained a lot. I had actually noticed the drop of a about 200 when I had the lock up wire connected as compared to when I did not. Now I understand why. Dosent seem like there is a lot of gain by installing the late model brake switch to cause lock up if you dont do lot of driving.

Actually bought and installed the swich. One of the ones recomended in the forum. But, I cant get the lock up to work. Brake lights on that portion of the swiitch work but I cant get lock up to work. Guess I got a bad switch or am missing some thing.

My hookup of the switch is hot wire to one pin and lock up wire from tranny is on the other pin. Same hookup as if I had lock up wire directly to hot. Now I just have a switch in the line. Should work. Any ideas wh it dosent?

Thanks
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Re: 700R4 overdrive question regarding lockup
 

Are you sure the switch is adjusted properly
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Re: 700R4 overdrive question regarding lockup
 

Does the brake switch not disengage the lock up? i.e. it locks up in 4th automatically and the application of the brake triggers the switch and unlocks the converter?

Re: 700R4 overdrive question regarding lockup
 

You want to be sure there is a brake switch to disable the lockup in case you have a panic stop.
Here is an image from bowtie overdrives. The left side is your normal setup where it will lock automatically in forth gear. The right side will also lock automatically in forth, or you can lock it yourself in 2nd third and 4th.

Wiring diagram for TCC lockup

Re: 700R4 overdrive question regarding lockup
 

wow.. I learn something new everyday here...

Re: 700R4 overdrive question regarding lockup
 

Find a 1985 or in that general age gas, not diesel gm truck or suburban and remove the brake light switch, the vacuum switch (on the firewall by the brake booster) you really need the vacuum switch, the harness connecting the two that goes down to the trans( has the plug for the trans) hook up one switched power wire and you have the whole correct GM system. I did it to my 68,only cost $15.00 and really simple.

Hope this helps
Bill

Re: 700R4 overdrive question regarding lockup
 

Sorry for intruding.
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Re: 700R4 overdrive question regarding lockup
 

Thank u all for your comments. Brake switch, cruse control side, was defective.
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Re: 700R4 overdrive question regarding lockup
 

why would you want to lockup in 2,3 ?

Re: 700R4 overdrive question regarding lockup
 

I have mine hooked up through a toggle switch. It will only lockup in 4th gear when it's over 45MPH anyway. I had the vacume switch for awhile and then took it off because I didn't need it. No brake switch either. Yes if you are running at speed and slam on the brakes sometimes it want release as soon as it should but I haven't had that many stops like that to borther me.
I can leave it unlocked and it's like a tow mode like on the new vehicles.Normal driving it will unlock at any speed under 45MPH without doing anything.;):chevy:

Re: 700R4 overdrive question regarding lockup
 

I lock mine up all the time in second and third. its a nice option to lock it up in third pulling some passes (with a trailer). Or second gear with it locked when pulling long hills up in the hills on logging roads. Trans doesn't build near as much heat with the torque converter locked as it does unlocked. Same goes going down those hills, locked up in second or third going down hill it slows the truck like a manual trans would. Its a nice option that I use much more often then I thought I ever would.

Sounds like you have your automatic lockup on a toggle.
it varies on when it locks up with the speed and where your right foot is at. Not necessarily a set speed. having it on an actual toggle to where you can lock it up whenever you want (and it stays locked) without a brake switch would be an interesting drive. It will eventually unlock when you get slowed down enough to where it doesn't have enough pressure to have the converter locked up. But until that point, its like trying to stop without pushing in the clutch.

Re: 700R4 overdrive question regarding lockup
 

I have had this 700 R4 since 1992 hooked up and it drives great. It does lock up at 45 MPH if the switch is on. It does unlock at 45mph are less with it on. I don't know what my right foot has to do with it locking up though? It want lock in any other gear that I know of. The truck drives fine well since 1992 it has. It stops just fine.;):chevy: