Transmission Problem?
Climbed over the southern Rockies in extreme heat the other day on I8 and in to San Diego. Tranny overheated and went in to fail safe on that long eastern climb, even though the engine temp was OK or ...
Forum Discussion
Just for fun, a little more on the 4L80E trans. The ECM monitors the input and output speed. It also knows engine RPM. In the old days, as the trans would wear, you would very slightly loose coupling. Over the long term, you could adjust the bands to take up this wear. In the 4L80E, since it is monitoring slip all the time, it tweaks the pump pressure based on slip. This way the trans will shift the same regardless of wear, throughout the life of the trans. One other trick they did was inventing a very unique clutch design for the TC. The pad is very porous, and allows fluid to run through the pores. This keeps the pad cool so that it can slip continuously, but not over heat. The valve is pulse width modulated. The design scheme is that you never feel the TC go into lockup, because the slip is variable based on conditions. If you recall, in the early days of TC lockup, it was always very annoying every time you let up on the throttle, the TC would kick out and then back in again. It still does, but you never feel it, because it never fully kicks out. There is a small amount of clutch pressure even in second gear. It also means that GM has a patent on the clutch material design. This means when you rebuild the trans, you have to use a GM TC, or the rebuild company must buy a GM TC and then modify it. Any other TC will burn up. Of course that means the after market TCs are very expensive. The early 4L80Es didn't have this scheme, so they can use any TC. It is only the later versions that matter.
Very early in my trans swap, I ended up manually operating the trans, because I could not get it to shift properly. Since I had a critical trip I needed to take, I ended doing a ton of reading on how this thing worked, as I did not want to damage anything. I ended up manually operating the TC lockup, with a variable resistor in series, as it was too difficult to build a PWM circuit in the short time that I had. Full on will eventually burn up the valve. I had wires going everywhere on that trip. I think I was more nervous that trip than my maiden voyage with the coach. Aren't RVs fun?
Very early in my trans swap, I ended up manually operating the trans, because I could not get it to shift properly. Since I had a critical trip I needed to take, I ended doing a ton of reading on how this thing worked, as I did not want to damage anything. I ended up manually operating the TC lockup, with a variable resistor in series, as it was too difficult to build a PWM circuit in the short time that I had. Full on will eventually burn up the valve. I had wires going everywhere on that trip. I think I was more nervous that trip than my maiden voyage with the coach. Aren't RVs fun?
