Majoraslayer
I'm Awesome
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?
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?