Vacuum switch, break switch, and wiring for 700-R4

scrap--metal

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Like the title says, I'm looking for the lock up converter stuff for a 700-R4 in a K20. I need the vacuum switch, the brake switch, the relay, and the associated wiring if that's available too. My K20 has a 700-R4 and it's not plugged into anything. I'd like to try and get the lock up converter working.

A buddy across town is parting out his old plow truck because the frame cracked, but that truck had a TH400 so he doesn't have the stuff I'm looking for. Then, there was a Suburban being parted out last month about an hour away from me, but now I don't see it on C-list anymore. :confused: If only I knew I needed these parts a few weeks ago...

Anybody able to help me out?
 

scrap--metal

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So I found the guy parting out the '88 Suburban I mentioned in my previous post. The truck had an automatic (guy said either 700R4 or 4l60). I don't think they came with 4l60's, so I'm optimistic that it had a 700R4. He sent me a pic of the firewall where I though the vacuum switch should be, but it doesn't look like it's there.

Is the vacuum switch mounted someplace different on a 'burban vs. a K10 or K20?

Here's a pic of the part-out:
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Itali83

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What year was the suburban? If it was 87-91, it’s tbi and no vacuum switch.

Ben
 

78C10BigTen

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Pretty sure its on the pass side firewall...
 

scrap--metal

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What year was the suburban? If it was 87-91, it’s tbi and no vacuum switch.

Ben
It's an '88, so that explains it. Thank you for the insight.

It there a TPS to control the lock up in a TBI system? What replaces the functionality of the vacuum switch in earlier 700R4 applications?
 

scrap--metal

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Pretty sure its on the pass side firewall...
He sent me another pic with some of the passenger side firewall visible, and I didn't see it over there either. Thanks though, Ted.
 

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It's an '88, so that explains it. Thank you for the insight.

It there a TPS to control the lock up in a TBI system? What replaces the functionality of the vacuum switch in earlier 700R4 applications?
The ecm controls lockup. Looks at throttle position, map sensor and coolant temp.

Ben
 

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Slightly off topic but how do you tell when the lockup on a 700R4 is engaged? 1991 Suburban
 

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Slightly off topic but how do you tell when the lockup on a 700R4 is engaged? 1991 Suburban
I have a 1990 burb. 350tbi. 700r4. 4x4. 3.73 gears. 33in tires.

I can feel lock in in the highway in 4th. it feels almost like a subtle gear shift...drops RPM about 200 or so. also, unlock should be noticeable on slight inclines before any 4-3 shift would occur.
 

ballencd

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Just realizied that I never responded to this. Thanks for the info. Do you know if there is a way to light a lamp when it is in lockup and/or in OD?
 

AuroraGirl

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So I found the guy parting out the '88 Suburban I mentioned in my previous post. The truck had an automatic (guy said either 700R4 or 4l60). I don't think they came with 4l60's, so I'm optimistic that it had a 700R4. He sent me a pic of the firewall where I though the vacuum switch should be, but it doesn't look like it's there.

Is the vacuum switch mounted someplace different on a 'burban vs. a K10 or K20?

Here's a pic of the part-out:
You must be registered for see images attach
technically speaking, 1991 the 700r4 was renamed 4l60 so technically squares did lol but 700r4 is a more meanignful way to refer to it because there was overlap with the 4l60e and the distinction between the two is enough to warrant the old name. kinda like 440t4 instead of 4t60
 

scrap--metal

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Do you know if there is a way to light a lamp when it is in lockup and/or in OD?
Yes, there is a way to do it. I'm not exactly sure how though. The schematic below is one example of how our trucks could be wired. The low vacuum switch and the brake switch can both interrupt the lock-up. That's what confuses me on where the indicator light should go. Lot's of aftermarket lock up systems are simpler with just a brake switch and a relay to control the lock up.

You must be registered for see images attach
 

gmbellew

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Just realizied that I never responded to this. Thanks for the info. Do you know if there is a way to light a lamp when it is in lockup and/or in OD?
you can monitor TCC lock with ALDLDroid and a Bluetooth OBD hookup or a scan tool.

the only way to know 4th vs 3rd gear is by feel or by selecting D vs OD on the column shifter. D won't allow OD (4th gear).
 

wlwarnke

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An easy test:

While driving down the road, in 4th while holding steady throttle, tap the brake pedal ever so slightly. (Just enough to turn on brake lights)

RPM will pickup and then drop a second after you release brake.

If it does this, your TCC is working.

Switch on non TBI is located next to the normal brake switch. It’ll have wires as well as a vac hose connected to it.

Back when I was building and swapping 700r4s into stuff, I didn’t use brakes switches or vac switches. I would simply wire the solenoid through a pressure switch (usually one that’s already in the VB) so it would lock anytime the Tranny is in 4th gear.

That being said, when towing a heavy load with a 700r4 I would also pull it down into 3rd if it was constantly down shifting out of 4th.
 

SirRobyn0

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An easy test:

While driving down the road, in 4th while holding steady throttle, tap the brake pedal ever so slightly. (Just enough to turn on brake lights)

RPM will pickup and then drop a second after you release brake.

If it does this, your TCC is working.

Switch on non TBI is located next to the normal brake switch. It’ll have wires as well as a vac hose connected to it.

Back when I was building and swapping 700r4s into stuff, I didn’t use brakes switches or vac switches. I would simply wire the solenoid through a pressure switch (usually one that’s already in the VB) so it would lock anytime the Tranny is in 4th gear.

That being said, when towing a heavy load with a 700r4 I would also pull it down into 3rd if it was constantly down shifting out of 4th.
And you have to be careful with that, wiring directly to 4th. It's simple but not the best for everyone at least. When I got my truck it had been wired that way even though all the vacuum controls were present and functional. So what tipped me off was #1 I couldn't feel it engaging, and #2 my trans temps would spike when towing in 3rd without it locking up. So I set up the vacuum controls to function for third initially. I wanted more control, so I set it up so anytime the transmission is in overdrive it locks up. And then for third gear lock up I have a switch in the cab. so I can hold it in lock up longer if trans temps start to creep up.
 

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