So, I wanted to take some time to document some things I went through after the transmission was installed that might help with anyone making the swap for a TH350 to the 700R4 or 4L60. Some of these things may seem obvious, but having another person confirm what you are going through and seeing is priceless. So here we go.
First off the transmission took forever to fill to the proper level. I wanted to make sure no damage was done to the transmission as a result of an ATF starvation issue. So, I disconnected the coil to the distributor before I started. I filled the transmission with 5 quarts and then cranked for 5 seconds, another quart, cranked for 5 seconds, repeated until I got to 9 quarts. At that point I changed to running the engine for 10 seconds and adding half a quart of fluid each time and checking the levels. I have a larger external cooler, so I got up to 12 quarts. It took forever, but it was safe.
Cooling and temperature monitoring: If you live in a warm climate, you cannot have enough cooling. I am unfortunate and get 100 to 120 degree summers; as a result I need to over engineer the cooling on most of the systems in my truck. Also after talking with the transmission repair shop he recommended that I do not run the trans ATF through the radiator as he sees them come in all the time for coolant leak contamination. If that happens, your transmission is smoked. So I only ran an external cooler. Also I would not run a rebuilt transmission without a temp gauge, which is cheap and effective and a great trouble shooting device. You want your trans to run between 160-170 F, any hotter and it’s taking miles off the lifespan.
YOU NEED A REMOTE MOUNT TRANSMISSION PRESSURE GAUGE. This is critical because if you have a malfunction inside the transmission or a Throttle Valve (TV) adjustment issue you can burn up your transmission quick, I mean quick! I thought I would be a cool guy and install one on the transmission itself but that only allowed me to read the gauge when stationary, terrible. So I duct taped a Logitech web cam to the frame with a laptop in order to read it while drive testing. Not the classiest thing, but it got the job done.
Stock TV and valve bodies malfunction, and malfunction all the time. These transmissions are OLD, mine was manufactured in 1988 and is currently at 29 years. To put it kindly, my TV-valve body was b-roke. I tried adjusting the TV and doing the neutral TV jerk-clear-clean method so many times. I actually spent 3 days doing that while monitoring the gauge perplexed why it wasn’t responding correctly. In the end I installed the TCI constant pressure valve body and BAM. Absolutely no issues and perfect pressures right out the get go. I wish I hadn’t spent half a week wasting my time with the stock setup. Sure it cost me a couple bucks but with incorrect TV pressures the trans would be smoked and would have to be rebuilt within a week.
After you have the transmission up and running for a while drain the fluid, change the filter, clean the pan and fill with new fluid. To me this seems like an obvious step, but no one talks about it. When you rebuild a motor you change the oil after 100 miles. With auto transmissions it should be the same thing. It is a wet clutch system and anything that comes off the clutches, pressure plates, band, bearings, pump, and gaskets gets circulated right back into the system. Literally liquid sand paper going through your expensive rebuilt transmission. When I pulled the pan to change the valve body and saw that there was already debris in there, I was so glad I did.
