700R4 Lockup Torque converter control issues solved

[SirRobyn0]

Ok so a few months ago I posted about issue about my torque converter lock up control. I'm going to seriously summarize here but... My truck is a 1984 C-20 with 700R4 that is NOT computerized and it's pretty much a stock truck. It has brake switch to disengage the torque converter and a vacuum switch on the firewall. In the other thread we discussed how this setup should work, and basically the conclusion was that it would probably only lockup in 4th gear, and the vacuum switch should disengage the lockup when under enough load. But that it was common for the vacuum switch to be bypassed, so it would stay locked up anytime it's in 4th. Turns out that's all wrong.

So I've spend a massive amount of time going over wiring diagrams. The trouble is it seems like most GM cars and truck with a lockup converter had at least some primitive computer system, and mine doesn't. So eventually I did find a schematic, there's about 4 different ways they wired the non-ECM lockup converters. The options being 4WD, 2WD, 3rd & 4th lockup or 4th only. Yesterday I went through all the wiring and cleaned up all of the contacts for the lockup circuit. Took it out for drive and got a little surprise. This transmission will lockup in 3rd and 4th. even if the shift lever is left in overdrive it'll still lockup in 3rd. It's actually really impressive to me how well it works for having nothing more than a brake switch and a vacuum switch. So hopefully this post will help someone else that is struggling to get their lockup to work correctly. And now I've got a bit knowledge in this area too, so I might be able to help.

I'll also add from my research that it appears if the the transmission plug has 2 wires it's 4th gear only lockup, if it has 3 wires it's 3rd and 4th lock up.

 

[Snoots]

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[Turbo4whl]

My 1982 also has a thermal vacuum switch for the lock up. The firewall tip-in vacuum switch would only get vacuum after the engine warmed up a little.

The '82 was also built with a Turbo 350C so when I upgraded to the 700R4 I needed to add a ground wire and different plug for the trans.

 

[BRetty]

I have been following these adventures, and I really appreciate you sharing your discoveries, cuz the TC Lockup has been a deep mystery thaty I finally understand. Mostly.

I have a week off, and I'm actually going [back] to my buddy's shop, which is now in another state, which is where my truck is, and we will have about 5 days to fix a bunch of stuff. TC lockup is last on the list, but important if I am going to drive 300+ miles back.
______
My '73 came with many electrical gremlins and many small things just not finished or connected at all. Last summer (with paid work on hold) I dug in and slowly re-wired most of everything. This turned out to be mostly figuring out what all the extra wires were and discovering that I could cut/cap/ignore them.

Being new to the world of vehicle restoration, it took weeks before it sowly dawned on me that the PO had Frankenstein'd this truck somewhat. Finding the VIN of a 1981 Suburban under the dash pad helped explain A LOT. Like why none of my gages worked and why I seemed to have three sets of wiring for HAVC controls. It had switched to HEI, so I could stop looking for the pink ignition wire, had no wipers, and some other wires were for an AC unit....others might have been for emissions sensors my '73 engine did not have.

But the blue and green wires with the broken pigtail on one end and the other ends melted onto the exhaust pipe, those I just could not figure out. Looking in the 1981 wiring diagram just made it worse. Five different possible configurations not matching the reality, but at least I knew it was not an HVAC circuit.

Several more weeks went by before I read "TH350*C*" (either here or on some other forum for obstererous nerds). A few more days before I realized maybe the transmission had come with the dashboard and gauges, transplanted from a donor Suburban. Finally I crawled under and found the "MV4" stamping on the trans case.

More months went by before I slowly understood that you could use a switch in place of the sensors that the wires were looking for like a phantom limb.

ANYWAY, thank you and others here who have helped me learn to love the thick bundle of useless wiring lashed up at various places in the truck. Wiring that came in VERY HANDY the night I dropped a muffler nose-first on the freeway and tried to lash it up with a ratchet strap. We melted through that, twice, before I remembered I had a big hank of wire under the dash!

I'll find a pic of my mystery wiires.

Thanks,
B

 

[ak4life]

Ok so a few months ago I posted about issue about my torque converter lock up control. I'm going to seriously summarize here but... My truck is a 1984 C-20 with 700R4 that is NOT computerized and it's pretty much a stock truck. It has brake switch to disengage the torque converter and a vacuum switch on the firewall. In the other thread we discussed how this setup should work, and basically the conclusion was that it would probably only lockup in 4th gear, and the vacuum switch should disengage the lockup when under enough load. But that it was common for the vacuum switch to be bypassed, so it would stay locked up anytime it's in 4th. Turns out that's all wrong.

So I've spend a massive amount of time going over wiring diagrams. The trouble is it seems like most GM cars and truck with a lockup converter had at least some primitive computer system, and mine doesn't. So eventually I did find a schematic, there's about 4 different ways they wired the non-ECM lockup converters. The options being 4WD, 2WD, 3rd & 4th lockup or 4th only. Yesterday I went through all the wiring and cleaned up all of the contacts for the lockup circuit. Took it out for drive and got a little surprise. This transmission will lockup in 3rd and 4th. even if the shift lever is left in overdrive it'll still lockup in 3rd. It's actually really impressive to me how well it works for having nothing more than a brake switch and a vacuum switch. So hopefully this post will help someone else that is struggling to get their lockup to work correctly. And now I've got a bit knowledge in this area too, so I might be able to help.

I'll also add from my research that it appears if the the transmission plug has 2 wires it's 4th gear only lockup, if it has 3 wires it's 3rd and 4th lock up.

thank you for this, is there anyway you can share pics of the different components and how you wired it to the transmission plug, i bought a universal 4 wire plug that goes into the trans plug but cannot remember if its a 3 or 4 loaded connector....the trans guy only marked a positive and negative on the trans plug and not sure where to wire the third and if there is no 4th on trans plug then ill remove extra wire fro. pigtail.....id love to know what these parts look like regarding the vaccuum switch and how its all wired or connected if possible.....thank you my friend for any help and the for the previous help also....

 

[SirRobyn0]

thank you for this, is there anyway you can share pics of the different components and how you wired it to the transmission plug, i bought a universal 4 wire plug that goes into the trans plug but cannot remember if its a 3 or 4 loaded connector....the trans guy only marked a positive and negative on the trans plug and not sure where to wire the third and if there is no 4th on trans plug then ill remove extra wire fro. pigtail.....id love to know what these parts look like regarding the vaccuum switch and how its all wired or connected if possible.....thank you my friend for any help and the for the previous help also....

I will see what I can do for you. So my truck came factory with the 700R4. From the factory 3rd gear lockup was controlled by the vacuum switch, and over drive is always locked, unless the brake pedal is depressed. So all I really did was disconnected the vacuum switch wiring and wired it to a switch so I could manually control 3rd gear lockup. Still locks in overdrive automatically. Wiring at transmission is factory. If I get the time this afternoon I will snap some photos of the vacuum controller, and the wiring for you.

 

[ak4life]

I will see what I can do for you. So my truck came factory with the 700R4. From the factory 3rd gear lockup was controlled by the vacuum switch, and over drive is always locked, unless the brake pedal is depressed. So all I really did was disconnected the vacuum switch wiring and wired it to a switch so I could manually control 3rd gear lockup. Still locks in overdrive automatically. Wiring at transmission is factory. If I get the time this afternoon I will snap some photos of the vacuum controller, and the wiring for you.

thank you sir, when you have time....

 

[SirRobyn0]

thank you sir, when you have time....

Thank you for the reminder I had completely forgotten and I apologize for that. I have made myself note and will take pictures, hopefully tomorrow if not the following day.

 

[SirRobyn0]

@ak4life I did not drive my truck to work today so no pics. I will have it tomorrow, if you'd be kind enough to post a reminder to me in this thread that will double up on my note and I shouldn't forget then. Thanks.

 

[SirRobyn0]

thank you sir, when you have time....

Ok I took pictures today. I'm not sure if your just after general location type info from the pictures or something more specific so if there is something you'd like that you can't see in the pics let me know.

Below connector on the tranny. I've never had the tranny out nor needed to mess with this wiring so it's pretty dirty, hopefully you'll get what you need from the pic. It's hard to see but there are 3 wires as my transmission will lock in 3rd and 4th, 4th gear only lockups will have two wires only.

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Below on the right of the picture is the plastic tunnel thing that runs above the brake booster, that next thing before the fusible link / electrical stuff is the vacuum switch is between the two. On my truck I decided to disconnect the vacuum switch and have it run to a manual switch in the cab instead. Basically the reason I decided to do this was to give me a little more control over when 3rd gear does and doesn't lock up. 4th gear still locks automatically as is the case with my truck the vacuum switch only affects 3rd gear. That is not the case in all setups there were a number of different ways they were setup from the factory.

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This picture is taken inside that tunnel. That vacuum nipple would normally have a ported vacuum line connected to it with a 3 second vacuum delay in the line. The reason for the vacuum delay was to slow shuttling if you had the throttle right at the cut in point. That electrical connector with the blue wire would normally be connected to the other side of the vacuum switch, but in my case has wiring run to the manual switch inside. There are two wires on that connector it's just that one is obscured. I set it up like this is I could plug it back into the vacuum switch and have it operate automatically when I wanted but discovered that I don't spend much time cruising in 3rd unless I'm towing so it's just easier to leave it setup for manual operation and obviously I got rid of the vacuum line eventually. But hopefully that all makes sense.

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Let me know if you have any questions or need additional pictures.

 

[Stoney]

Hi Rob ....

Hope you don't mind me joining the conversation ...

It appears I have the same setup on my 85 C10 that you have on your truck ... photos look identical ... same brake switch/ vacuum switch setup, so I'm ASSUMING I have the same 3 wire 3rd/4th lockup ... Would that be a logical assumption ... I will verify when I get a chance to get it up on the lift ...

Couple of questions if you don't mind ...

(1) On the road, when driving , how can you tell whether the converter is locked/unlocked ?? ...

(2) On your truck, what is the vacuum source for the vacuum switch ... does the line pickup vacuum directly from a port on the carburetor or does it go through a TVS switch ?? ... Mine goes through a EGR/PURGE/TCC TVS switch which has two vacuum lines going to two ports on the carb (ports J and H) ... so I'm not sure which port actually controls the vacuum switch ???

Thanks,
Jim

 

[SirRobyn0]

Hi Rob ....

Hope you don't mind me joining the conversation ...

It appears I have the same setup on my 85 C10 that you have on your truck ... photos look identical ... same brake switch/ vacuum switch setup, so I'm ASSUMING I have the same 3 wire 3rd/4th lockup ... Would that be a logical assumption ... I will verify when I get a chance to get it up on the lift ...

Couple of questions if you don't mind ...

(1) On the road, when driving , how can you tell whether the converter is locked/unlocked ?? ...

(2) On your truck, what is the vacuum source for the vacuum switch ... does the line pickup vacuum directly from a port on the carburetor or does it go through a TVS switch ?? ... Mine goes through a EGR/PURGE/TCC TVS switch which has two vacuum lines going to two ports on the carb (ports J and H) ... so I'm not sure which port actually controls the vacuum switch ???

Thanks,
Jim

Jim, Your welcome to join the conversation and I see it's your first post so welcome to the forum!

So I assume you read though the thread some? There are a lot of ways that these trannys were setup from the factory, one of the setups used the vacuum controls for 4th gear lockup without a 3rd gear lock, but you'd have the two wire plug on the tranny for that setup. More than likely I'd expect you have the 3rd & 4th lock, setup like mine, but it takes about 30 seconds to look under the truck to verify.

To answer your questions.

#1. You can feel it engage and disengage if you know what to feel for it's not obvious most of the time. If you have a tach in the truck you can see when stepping on the gas lightly at cruse that there is no converter slip (when locked up). Last if your at cruse and tap the brakes, the clutch will disengage your should be able to hear the RPM increase and feel it disengage, if you have a tach you'll see the RPM go up about 200 RPM.

#2. Originally my truck would have run the vacuum for the switch though the TVS. However the former owner removed most of that stuff. So I had it hooked up to ported on the carb. The biggest difference is the converter would lock in 3rd right away, where as the factory setup though the TVS was to prevent 3rd gear lock up until the engine was warmed up. There should be a delay valve in that vacuum line as well between the TVS & the vacuum switch, I think it's either 3 or 5 seconds I'd have to look it up.

Let me know if that makes sense / if you have questions, but that info is correct to the best of my knowledge.

 

[ak4life]

@ak4life I did not drive my truck to work today so no pics. I will have it tomorrow, if you'd be kind enough to post a reminder to me in this thread that will double up on my note and I shouldn't forget then. Thanks.

So sorry my friend i didnt know that you had replied (notifications?) Wow, so i thank you for the reply and the time and also for willingness for more specific info.....ill take a look at all this and will get back to you also with a rundown of my setup and where im a bit confused on my side of things.....thank you and ill be in touch .....

 

[SirRobyn0]

So sorry my friend i didnt know that you had replied (notifications?) Wow, so i thank you for the reply and the time and also for willingness for more specific info.....ill take a look at all this and will get back to you also with a rundown of my setup and where im a bit confused on my side of things.....thank you and ill be in touch .....

Nothing to apologize for. Yes, I saw the notification, just like this one. I will be super busy next week, pretty much Tuesday the 20th though Monday 26th, so if you post back during that time period and it takes me a day or two to respond I don't want you think I'm upset. Just busy and I'll get back to you when I can.

I'll look forward to hearing back.

 

[ak4life]

Ok I took pictures today. I'm not sure if your just after general location type info from the pictures or something more specific so if there is something you'd like that you can't see in the pics let me know.

Below connector on the tranny. I've never had the tranny out nor needed to mess with this wiring so it's pretty dirty, hopefully you'll get what you need from the pic. It's hard to see but there are 3 wires as my transmission will lock in 3rd and 4th, 4th gear only lockups will have two wires only.

You must be registered for see images attach

You must be registered for see images attach

Below on the right of the picture is the plastic tunnel thing that runs above the brake booster, that next thing before the fusible link / electrical stuff is the vacuum switch is between the two. On my truck I decided to disconnect the vacuum switch and have it run to a manual switch in the cab instead. Basically the reason I decided to do this was to give me a little more control over when 3rd gear does and doesn't lock up. 4th gear still locks automatically as is the case with my truck the vacuum switch only affects 3rd gear. That is not the case in all setups there were a number of different ways they were setup from the factory.

You must be registered for see images attach

This picture is taken inside that tunnel. That vacuum nipple would normally have a ported vacuum line connected to it with a 3 second vacuum delay in the line. The reason for the vacuum delay was to slow shuttling if you had the throttle right at the cut in point. That electrical connector with the blue wire would normally be connected to the other side of the vacuum switch, but in my case has wiring run to the manual switch inside. There are two wires on that connector it's just that one is obscured. I set it up like this is I could plug it back into the vacuum switch and have it operate automatically when I wanted but discovered that I don't spend much time cruising in 3rd unless I'm towing so it's just easier to leave it setup for manual operation and obviously I got rid of the vacuum line eventually. But hopefully that all makes sense.

You must be registered for see images attach

Let me know if you have any questions or need additional pictures.

Ok so this did answer a few questions, like what that deelybobber is on firewall...and that with new $900 harness that has bubkiss for it.....ill never waste money on a named wire harness again......absolute waste of money.....sorry i should not get started on that topic. Anyways ill give you a breakdown of my setup....ill try to make it short. Ok its an 1981 body, single cab longbed 4wd k10 w/ 3/4 running gear from 1984 k20. Originally a 305 w/esc and i assume a th350 (3spd.) Now has blueprint 383, w/ built 700r4, 89 column (4spd) those are important details that i never know til its to late. So here is where im stumped, oh and its a 2500 stall. So the trans man, added a lockup in trans for the 4 pin plug, it has a +, -, or ground i believe ( ill snap pics and add later) i bought a 4 pin pigtail, but think it only had 3 wires.....so my first question is if not wanting to be responsible for flipping a switch ( i may forget its on or ? ) what would i wire the wires from 4 pin pigtail to ? And let confuse you and back up a bit, so the original setup (81, 305, th350) had a vacuum deelybobber like yours and also had a brake and clutch pressure pin near brake pedal, but somehow was also wired into a small box up on left side back of steering column frame called by pt.# tcc lockup relay, with doubled wire colors that i can only assume by what wires i could find of original harness go to brake, clutch switches and splice into transfer case wiring and possibly cruise control. Thats when i started getting confused and the dumb/expensive harness does not provision nor give any instructions, and the actual wiring diagrams all 20 something of same components all are confusing or do not detail any tcc relay or where it would be wired to.......... so with all this ive written, im sure ive only confused you more then you wanted....lol. any feedback would be appreciated and will give more precise information and pics next time i get a chance....thank you my friend.....sending pics of what i may have on phone, but probably not what you need for reference