700R4 LockUp Troubleshooting

[pjmoreland]

Hopefully it's just the solenoid and not the TCC!

[sick472]

Well, when I was 18 I thought I knew it all, and at 52 I should know twice as much right?, but maybe not, lol. It turns out that the shudder was a product of a misfire in the engine. When the lock-up would occur in 4th gear...it was too much load on the engine (about 200hp) and caused the miss to exaggerate and it was actually the motor shuddering. Thankfully, a faulty sparkplug wire was the problem and not the solenoid, or worse, the torque converter. I am embarrassed that I did not notice the misfire myself, but thankfully my transmission guy picked it up during a test drive. To make matters even more embarrassing, some guy standing around the transmission shop, not knowing anything about my truck, out of nowhere from 20 feet away, says...that truck is misfiring! I'm a doof.

That's good news and I now have enough power to spin both tires which takes me back to 18 years old again. I'm happy and I THANK YOU PJ for teaching me a few things along this thread...I learned a lot!

The only downfall, minor albeit, is I really don't know how the transmission is actually wired internally regarding the available schematics. I am happy that it locks up in 4th only as lock up tends to lug even in 3rd and, lets face it, how much mileage can be saved during the short time that the truck spends in 3rd gear. Historically, the truck gets about 12 mpg.

[pjmoreland]

That's great news! It's such a pain to try to diagnose an issue when there are multiple causes. My truck got 10mpg when I had a TH400, and now it gets 12mpg with the 700R4. Hopefully your mileage will improve now that you've got that spark plug wire fixed and your TCC is engaging.

I think the best TCC lockup system would have a speed component to its logic so the TCC would never lock at speeds under, say, 50mph. B&M makes a controller that does this, but they want way too much money for that thing, in my opinion. I'm working on building my own from a cruise control speed sensor and an Arduino controller. The speed sensor is back-ordered right now, so the project is on hold.

https://67-72chevytrucks.com/vboard/...=822382&page=2

Have fun spinning those tires!

[LT7A]

Originally Posted by sick472

Well, when I was 18 I thought I knew it all, and at 52 I should know twice as much right?, but maybe not, lol. It turns out that the shudder was a product of a misfire in the engine. When the lock-up would occur in 4th gear...it was too much load on the engine (about 200hp) and caused the miss to exaggerate and it was actually the motor shuddering. Thankfully, a faulty sparkplug wire was the problem and not the solenoid, or worse, the torque converter. I am embarrassed that I did not notice the misfire myself, but thankfully my transmission guy picked it up during a test drive. To make matters even more embarrassing, some guy standing around the transmission shop, not knowing anything about my truck, out of nowhere from 20 feet away, says...that truck is misfiring! I'm a doof.

That's good news and I now have enough power to spin both tires which takes me back to 18 years old again. I'm happy and I THANK YOU PJ for teaching me a few things along this thread...I learned a lot!

The only downfall, minor albeit, is I really don't know how the transmission is actually wired internally regarding the available schematics. I am happy that it locks up in 4th only as lock up tends to lug even in 3rd and, lets face it, how much mileage can be saved during the short time that the truck spends in 3rd gear. Historically, the truck gets about 12 mpg.

Thanks for coming back and telling us the outcome even if it isn't fun to admit. Still helps the rest of us, and a pretty cheap fix which translates to a win. If it makes you feel any better, I had taken my car back to the shop which had installed the clutch. It's little German thing that I struggle to work on. Won't buy another one. Anyway, they put in the clutch awhile back and I felt like it was slipping. The owner of the shop took a ride with me and said that's an ignition problem. I'm like huh? We got back to the shop and he pulled the codes and it had misfires on two cylinders... That's half of them. Being turbocharged, it ran okay at lower speeds and boost pressure. But then the spark would fail as it spooled up. Needless to say, I felt like a chump having blamed the clutch when the coil packs and spark plugs were overdue. Spent over $200 replacing those even though I did it myself, but that's another story... Did I mention I won't be buying another one of these cars?

[pjmoreland]

Originally Posted by sick472

Well, when I was 18 I thought I knew it all, and at 52 I should know twice as much right?, but maybe not, lol. It turns out that the shudder was a product of a misfire in the engine. When the lock-up would occur in 4th gear...it was too much load on the engine (about 200hp) and caused the miss to exaggerate and it was actually the motor shuddering. Thankfully, a faulty sparkplug wire was the problem and not the solenoid, or worse, the torque converter. I am embarrassed that I did not notice the misfire myself, but thankfully my transmission guy picked it up during a test drive. To make matters even more embarrassing, some guy standing around the transmission shop, not knowing anything about my truck, out of nowhere from 20 feet away, says...that truck is misfiring! I'm a doof.

That's good news and I now have enough power to spin both tires which takes me back to 18 years old again. I'm happy and I THANK YOU PJ for teaching me a few things along this thread...I learned a lot!

The only downfall, minor albeit, is I really don't know how the transmission is actually wired internally regarding the available schematics. I am happy that it locks up in 4th only as lock up tends to lug even in 3rd and, lets face it, how much mileage can be saved during the short time that the truck spends in 3rd gear. Historically, the truck gets about 12 mpg.

Maybe your transmission has a TCI 376600 lockup wiring kit installed inside it. That would explain why connecting pin D to ground makes it lock up in 4th gear only.

https://www.tciauto.com/amfile/file/...product/43784/

[sick472]

LT, No, not fun to admit, but my goal is to keep learning and share that learning. Besides the wiring lessons that I learned from PJ's posts and the research it encouraged, I thought it best to share that a misfire can causes some problems that sure seemed to be transmission related. And, I am now more able to identify a misfire, troubleshoot, and correct.

PJ, That particular diagram would certainly explain why my transmission acts the way it does. However, my guy seems to remember a 4-3 downshift stitch to be present which is rather confusing since the transmission does not lock-up in 3rd at all. With my limited electrical knowledge, I have found no diagram that would include the 4-3 switch which implies that it would also have a switch to engage in 3rd that matches my transmission's actions. There are still the electrical unknowns of what is actually going on in the pan...bad switches, bypassed components, & what switches are actually in there.

Bottom line and a good lesson learned...when putting in a 700R4 from a different vehicle...Always understand how the replacement unit is wired to function and how the receiving vehicle is wired as well. This would have saved me over a week of daily efforts in making it work correctly and I still don't know all the details.

These 700R4's were wired at least 23 different ways from the factory over the years (82-93) that they were produced. This does not count the other ways that people have changed the wiring during the junk yard transmission's history.

Here are some documents (700R4 Technical Service Indentification and Diagrams) that I have discovered during this journey which don't seem to be easily available on the net, up until now...

[sick472]

Some more and many more to come...

[sick472]

More...

[sick472]

And more...

[sick472]

Still more...

[sick472]

Last 2 pages, ENJOY...

[Bloodhound]

Thanks for posting these! I have been trying to verify for a while that my 700R4 I installed in my 1981 C10 back in 1995 or so was out of a 1989 Corvette and this confirms it. I thought my memory was tricking me. Now I can use this schematic to get the TCC wired up and finish this restoration.