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Old 08-08-2019, 11:06 AM   #20 (permalink)
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Originally Posted by me and my metro View Post
Computer controlled transmissions can be tricked into firmer shifts by adding a resistor to the line pressure solenoid wire. Running at high line pressure all the time is not necessary.
4L80 GM transmissions will break the case if the line pressure solenoid sticks high for too long. There is a preemptive fix for this from Gill Younger.

The shift kit in the old days was done with springs and hole sizes on the valve body separator plate. Now it is done with resistors and programming. You have combined old and new technology by working around your computer. I would probably add a “sport/daily driver” switch so you can choose easily. I think your transmission will last longer.

In the previous version of my 700R4 my builder flipped the 2/3 accumulator piston and used a Chrysler spring to firm up the shift. In a performance car that weighs 2500 to 3000 lbs this would be fine but in a 6000 lb truck it was quite harsh. This transmission would shift from 2nd to 3rd with the converter locked and with no accumulator it would snap your neck back and was uncomfortable.

This latest version of my transmission we went back to a stock accumulator setup and it still shifts locked up but it is very nice now.

The previous version of my transmission lost the low planet set and GM has come out with a heavy duty 5 pinion planet since we built the previous version 10 years earlier.

Sorry about the long dissertation but I have been running performance transmissions since the 70s. I hope this gives some old school knowledge.
Thank you for your help. I don't think I am going to break anything due to the high line pressure because I didn't modify anything mechanical (like springs) and from my understanding, the PCM already commands maximum line pressure at full throttle to keep the clutches from slipping. Maximum line pressure is also commanded in "limp mode" to prevent the clutches from slipping and burning up if there is a problem. So it's designed to handle maximum pressure, at least intermittently. The shifts are never "harsh" by my standards as long as the converter isn't locked, so I don't think I'm going to break anything from hard shifts either.

My concerns would be if I am working the pump harder it may possibly shorten its life. Also, I imagine that holding a high pressure might require more power from the transmission's oil pump, reducing MPG and creating more heat in the transmission. Am I right?
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