700R4 Vacuum Switch

[Bruce Wingate]

I have a 1984 K10 with a crate 350 and 700R4. I believe the truck originally had a 305. Most of the emissions and vacuum lines have been clipped or removed.

I have the vacuum switch on the firewall with two wires running to the transmission. I'm assuming that this is the vacuum switch which controls the torque converter lockup. It does not have a vacuum source --> should it get manifold or ported vacuum?

And what is the proper name for this vacuum switch?

Thanks
Bruce.

 

[AKguy]

This example shows manifold vacuum.

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[Bruce Wingate]

Thanks, @AKguy

Going to try to hook this up tonight - let's see if this boost my highway mileage a bit.

 

[scrap--metal]

@Bruce Wingate , did you get the lock up working in your K10 last fall?

I'm currently trying to get a 700R4 lock up system working too.

 

[Bruce Wingate]

I think that I have it hooked up right, but I am still getting pretty bad mileage - 8 - 9, still haven't broken 10 mpg yet. I don't feel the truck shifting into 4th or the lock up kicking in, but I don't have a tach to properly check, just seat of the pants.

 

[Bruce Wingate]

@scrap--metal comment came at about the right time. I suspect that my transmission is still not locking up. Today I check the vacuum switch and it is working (closes contact at about 10 psi, maybe a little more.) I tried to trace this down to the transmission, but just got frustrated because everything down there is a greasy mess. The TCC connector has 3 wires going to it: tan (yellow) and two others of unknown color. I suspect that one of them is from the vacuum switch and the other is from the brake switch.

I have to trace power from the brake switch to see if it is working right and I might but tell tale lights on each to see what and when they are working.

Right now, I can feel shifts at about 15 and 25 mph. I don't have a tach to track RPM any better than my seat of the pants estimates. I just can't tell if I am getting lock up or even 4th gear. (I may be missing a shift down low, but I don't feel three shifts).

My question: do I need power at both the non-ground wires in order to trigger the lockup solenoid or will any one do it?

 

[gmbellew]

on the highway, do you feel it shift from 3 to 4 when you go from D to OD? or the reverse is true, shifting to D from OD will force a shift from 4 to 3.

the TC can lock in 3rd or 4th I think. but this will at least let you know you are getting all the gears.

the TC lock in is a little subtle. but you should be able to feel it if you are paying attention....

 

[scrap--metal]

the TC lock in is a little subtle. but you should be able to feel it if you are paying attention

I have a 200-4R in my Camaro with a functioning lock-up converter. The lock-up is VERY subtle, and I would argue that you usually can't feel it. I really only see it in the tach.

Right now, I can feel shifts at about 15 and 25 mph. I don't have a tach to track RPM any better than my seat of the pants estimates. I just can't tell if I am getting lock up or even 4th gear. (I may be missing a shift down low, but I don't feel three shifts).

Under the right throttle conditions, I believe the transmission can shift right from 1st to 3rd. Don't quote me on that though. @gmbellew's suggestion to manually shift it between 3 and 4 (OD) while at highway speed, or vice versa, is a good one. That will certainly tell you if you're getting 4th gear.

An indicator light in the circuit is a good idea to verify that the switches are working, even if the lock up in the transmission is not.

 

[scrap--metal]

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[scrap--metal]

Above is the factory wiring diagram for an '84 K10 (pulled from the reference library on this site). It makes sense from your 3 wire description with one of them being yellow.

My question: do I need power at both the non-ground wires in order to trigger the lockup solenoid or will any one do it?

If I'm reading the diagram correctly, light blue wire and the yellow wire at the transmission should have power to trigger the lockup. It looks like the yellow wire is spliced from the light blue wire before it runs through some sort of "EGR BLEED" solenoid. I would think that the yellow wire and the light blue wire could be jumpered right at the transmission plug to eliminate that "EGR BLEED" solenoid from the circuit.

I'm not great with these schematics though, so I may be mistaken.

 

[Bextreme04]

I think that I have it hooked up right, but I am still getting pretty bad mileage - 8 - 9, still haven't broken 10 mpg yet. I don't feel the truck shifting into 4th or the lock up kicking in, but I don't have a tach to properly check, just seat of the pants.

My 3/4 ton, with a 350/TH400/NP205, 4.10's, and 35's does that or a little better. Have you had the TV cable adjustment checked?

 

[Bruce Wingate]

My 3/4 ton, with a 350/TH400/NP205, 4.10's, and 35's does that or a little better. Have you had the TV cable adjustment checked?

I've readjusted the TV cable a couple of times, will probably do it again. But it seems like such a stupid adjustment: retract the cable and floor it? Really? For something that important?

[I appreciate your help - its just GM's procedure seems stupid.]

 

[Bruce Wingate]

Above is the factory wiring diagram for an '84 K10 (pulled from the reference library on this site). It makes sense from your 3 wire description with one of them being yellow.


If I'm reading the diagram correctly, light blue wire and the yellow wire at the transmission should have power to trigger the lockup. It looks like the yellow wire is spliced from the light blue wire before it runs through some sort of "EGR BLEED" solenoid. I would think that the yellow wire and the light blue wire could be jumpered right at the transmission plug to eliminate that "EGR BLEED" solenoid from the circuit.

I'm not great with these schematics though, so I may be mistaken.

Thanks for the diagram. I definitely do not have the EGR bleed solenoid.

I'm not too bad with these diagrams, but this makes it seem like the TCC solenoid will be on if either the brake is not depressed or the vacuum switch is closed (high vacuum). Working that out, if the vacuum switch is set to manifold vacuum, the engine should stall at a stop (high vacuum [on] but brakes pressed [off])

First thing, I'll try shifting from D to OD at around 50 and see what happened - hopefully it won't be a loud metallic noise. Then I'll work out jumpering the blue and yellow wire.

 

[Matt69olds]

I've readjusted the TV cable a couple of times, will probably do it again. But it seems like such a stupid adjustment: retract the cable and floor it? Really? For something that important?

[I appreciate your help - its just GM's procedure seems stupid.]

First step in the process is to make sure the throttle fully opens. It’s not uncommon to find the floor mat, linkage flex, carpet, whatever is preventing the throttle from fully opening.

Basically, you want the TV cable travel maxed out at WOT.

 

[Bruce Wingate]

First thing, I'll try shifting from D to OD at around 50 and see what happened - hopefully it won't be a loud metallic noise. Then I'll work out jumpering the blue and yellow wire.

I shifted between D and OD a couple of times on the way to work yesterday. I don't know why, but the shift from D to OD is subtle but the shift from OD to D is very noticeable. So I am getting all four gears.

I noticed that the vacuum line to the vacuum switch was loose so I'm going to replace that with a properly sized line. (Last year all my local part stores were having a hell of a time getting any type of hose or tubing in so I had to get whatever was close. Not close enough apparently.)

Next up is jumping the yellow and blue wire - I bought a set of couplers so I could make the connection on the bench, not worry about mistakenly cutting the wrong wires and I can add the indicator light at the same time. And I can take the whole thing out when I'm done.