Painless Performance 700R4 TCC Lockup Kit On Factory TBI?

[Majoraslayer]

Some backstory:

My truck is a 1988 K1500 with a 700R4 behind a 350. In 2013 I rebuilt the truck, swapping my 2WD body onto a K1500 frame. I sold my original engine wiring harness with my original 305 and TH350 since I had a harness with my new (to me) 350 engine. It wasn't until I started installing everything that I realized my wiring harness was for a manual truck, so I had to fabricate wiring for the 700R4 that came with my new frame.

Fast forward to the past month, I've been trying to get my truck back on the road after a few years parked. Driving around town I noticed that the torque converter is constantly locking/unlocking in third gear after the engine warms up. Transmission shifts seem to happen at the right time, so I'm hoping it's not a TV cable related pressure issue. I reset and calibrated it again just to be sure, and the same problem persists. I've also installed a new CTS and brake switch, but neither one fixed the problem.

Recently I also did the cluster swap procedure for a 1991 needle gauge. My original speedometer would intermittently stop working until I tapped on the cluster. Since the swap my new speedometer has worked consistently, but I have a "Check Gages" light with the same problem: it illuminates at random and will go off if I tap on the cluster. User "someotherguy" on ChevyTalk (and on here too...if you see this, hi again!) suggested this can be a common issue with these trucks, and bad grounds or solder joints in the cluster might also cause issues with the TCC lockup. I've not had a chance to dig in and chase my grounds yet, but that's next on my list along with tracing my TCC wires again with a multimeter. When I rebuilt the truck I also hacked in factory cruise control, so I'll also have to chase down and verify how I did that so many years ago too.


I've been wrestling with this TCC issue for a month (including before the cluster swap), so if these things don't fix it I'm at a loss for what to do next. That brings me up to date with the purpose of this post.


I've been doing a ton of reading on the 700R4 trying to understand it better, and these transmissions are frustratingly temperamental. Between the TV cable being so sensitive (there's an on-going online argument on the "right" way to calibrate it) and the reliance on TCC lockup to keep it from cooking itself, I'm starting to suspect this transmission was designed specifically to keep rebuild shops in business. When asking about retrofitting the 700R4's TCC to work like these transmissions did on carburetor setups, I've been told that this would be extremely destructive since the ECM plays such a vital role in determining lockup. I'm hoping to get some more opinions and explanations on why this would be since the 700R4 itself predates TBI. I do know the transmissions from the TBI years are considered an upgrade over the earlier ones, but my understanding is this is mostly due to an improved input shaft and pump design.

Recently I came across a video explaining the installation of the Painless Performance TCC lockup kit, which is typically used to fit a 700R4 into custom applications with a carburetor. Instead of relying on the ECM, this eliminates a couple ECM-controlled pressure solenoids in the late 80s/early 90s valve body, simplifies the lockup solenoid setup, and works off of ported vacuum with an N/C brake switch power source. This seems like it might be a good way to eliminate a lot of guesswork in the TCC wiring for my truck, and possibly help protect my transmission from finicky issues like intermittent gauge cluster grounds or weird sensor-related ECM problems. It doesn't seem like the ECM reads anything from the TCC to change engine behavior, only the other way around. I could be wrong about that, I've just not been able to find verification on it myself yet.


Would installing one of these kits break things if installed with the factory TBI? If so, why?

 

[Schurkey]

I do not know about the Painless TCC kit.

I used a different TCC kit (supplied by TCI, I think) when I crammed a '700 into a '76 Nova. That kit was a mess due to the horse-shiit vacuum switch they used. The switch had no hysteresis, so the lock/unlock vacuum was merely above or below whatever vacuum the switch was set for. The switch was "adjustable" to close at more or less vacuum, but the lock/unlock vacuum levels were the same.

So I'd drive along in OD, and the engine would get some RPM, and build vacuum. TCC locks. The rpm would drop, the vacuum would drop, and the TCC unlocked. That raised the RPM and vacuum, so it locked. Which dropped the RPM and vacuum, and it unlocked. This went on until I stabbed the gas pedal in frustration, got up to cruising speed, at which point the engine might make enough vacuum with the TCC locked to keep it locked.

Ideally, the vacuum switch closes at a certain (adjustable) vacuum level, but stays closed until the vacuum drops well below that level, so the TCC stays engaged.

My advice is to keep the computer in control of the TCC, but figure out why it's so sensitive.

Do as I say, not as I do. My truck disengages the TCC too frequently, too. Anything over ~75 mph (less with a headwind) and the TCC is disengaged.

 

[NickTransmissions]

Some backstory:

My truck is a 1988 K1500 with a 700R4 behind a 350. In 2013 I rebuilt the truck, swapping my 2WD body onto a K1500 frame. I sold my original engine wiring harness with my original 305 and TH350 since I had a harness with my new (to me) 350 engine. It wasn't until I started installing everything that I realized my wiring harness was for a manual truck, so I had to fabricate wiring for the 700R4 that came with my new frame.

Fast forward to the past month, I've been trying to get my truck back on the road after a few years parked. Driving around town I noticed that the torque converter is constantly locking/unlocking in third gear after the engine warms up. Transmission shifts seem to happen at the right time, so I'm hoping it's not a TV cable related pressure issue. I reset and calibrated it again just to be sure, and the same problem persists. I've also installed a new CTS and brake switch, but neither one fixed the problem.

Recently I also did the cluster swap procedure for a 1991 needle gauge. My original speedometer would intermittently stop working until I tapped on the cluster. Since the swap my new speedometer has worked consistently, but I have a "Check Gages" light with the same problem: it illuminates at random and will go off if I tap on the cluster. User "someotherguy" on ChevyTalk (and on here too...if you see this, hi again!) suggested this can be a common issue with these trucks, and bad grounds or solder joints in the cluster might also cause issues with the TCC lockup. I've not had a chance to dig in and chase my grounds yet, but that's next on my list along with tracing my TCC wires again with a multimeter. When I rebuilt the truck I also hacked in factory cruise control, so I'll also have to chase down and verify how I did that so many years ago too.


I've been wrestling with this TCC issue for a month (including before the cluster swap), so if these things don't fix it I'm at a loss for what to do next. That brings me up to date with the purpose of this post.


I've been doing a ton of reading on the 700R4 trying to understand it better, and these transmissions are frustratingly temperamental. Between the TV cable being so sensitive (there's an on-going online argument on the "right" way to calibrate it) and the reliance on TCC lockup to keep it from cooking itself, I'm starting to suspect this transmission was designed specifically to keep rebuild shops in business. When asking about retrofitting the 700R4's TCC to work like these transmissions did on carburetor setups, I've been told that this would be extremely destructive since the ECM plays such a vital role in determining lockup. I'm hoping to get some more opinions and explanations on why this would be since the 700R4 itself predates TBI. I do know the transmissions from the TBI years are considered an upgrade over the earlier ones, but my understanding is this is mostly due to an improved input shaft and pump design.

Recently I came across a video explaining the installation of the Painless Performance TCC lockup kit, which is typically used to fit a 700R4 into custom applications with a carburetor. Instead of relying on the ECM, this eliminates a couple ECM-controlled pressure solenoids in the late 80s/early 90s valve body, simplifies the lockup solenoid setup, and works off of ported vacuum with an N/C brake switch power source. This seems like it might be a good way to eliminate a lot of guesswork in the TCC wiring for my truck, and possibly help protect my transmission from finicky issues like intermittent gauge cluster grounds or weird sensor-related ECM problems. It doesn't seem like the ECM reads anything from the TCC to change engine behavior, only the other way around. I could be wrong about that, I've just not been able to find verification on it myself yet.


Would installing one of these kits break things if installed with the factory TBI? If so, why?

There were several improvements in the 1988+ 700R4s but most were specific to the forward drum (a little better 3-4 clutch pack set up, 3-4 bleed off orifice capsule, 29 element forward sprag), cushion plate in low/reverse, pump (10-vane vs 7 vane), aux valve body (softer engagements into drive), better 1-2 valve train design, eliminated mechanical TCC control/lock up valve train in valve body.

On to your TCC lock up problem...shorts, issues w/the adaptation of the harness or grounding issues can be the source of your TCC issues, you'll find out once you dig in...can also possibly be ECM.

If you hit a wall and can't fix the current TCC lock up, locate an early 82-87 700R4 valve body, purchase Transgo's mechanical TCC lock up kit and install that kit into the 4th bore from the left which is the TCC bore (this bore does not exist in your 88+ valve body that's in your truck at the moment). Put the stiffest spring from the Transgo kit into the TCC throttle valve as that will give lock up at around 50 miles per hour so you're not constantly shifting in and out of lock up in more urban stop/go driving. Install the valve and sleeve kit in that 4th bore and that will give you full mechanical TCC lock up without any need for ECM/Harness/solenoid. You'll need to transfer the two check balls from your existing valve body to the new one (just drop the valve body straight down and you'll see where they go. You can keep the wiring harness and TCC Solenoid in place, just don't plug the external harness into the square plug on the side of the transmission.

I install early 700R4 valve bodies w/Transgo TCC mechanical lock up kits for transmissions I build for my 'resto-mod' customers who want 700s installed in vehicles that originally had two and three speed transmissions but don't want to mess with any electro-mechanical or computer-controlled lock up for the TCC...Alternatively, you can go with a non-lock up converter and Transgo's TCC non-lock up conversion kit but I usually don't recommend it for street-driven vehicles. Some customers who have an electro-mechanical lock up wire in a switch they keep in the cab so they can simply turn on and off lock up manually whenever they want.

I have also installed the Painless kit in numerous 700R4s as well as the B&M kit and gotten good feedback on both.

 

[Majoraslayer]

Just so I don't leave this open-ended, I'll pop in and give an update on my problem. tl;dr I won't need the Painless kit, but it's still interesting to learn about options, so thanks everyone for the advice.

I did manage to find and finally fix this problem, and like most of my problems, it was stupid lol.

In 2020 I developed a problem with the truck where it wouldn't start. First it wouldn't crank, then after I replaced the ignition switch it would crank, but not spray from the TBI or spark. I kept throwing parts at it for the past few years until I figured out the ICM in the distributor had also failed. In the process of troubleshooting in 2020 I picked up a used ECM for a 350 for fairly cheap and tried swapping it out. At one point I ended up with both ECM's in hand and couldn't remember which one I had in it originally, so I just threw one in and figured I would just swap them back if it caused any problems.

Unfortunately I wouldn't get the truck actually drivable until 3 years later....and I completely forgot I may have installed the wrong ECM. It turns out the ECM I put in it had an ASDX PROM in it, which according to Google, is for a manual transmission truck. I got the ECM swapped back and I'm back to rolling smooth as butter.