daveb
05-18-2022, 05:05 PM
I have a newly rebuilt 4l60e ('94) that has a very hard 1-2 shift. I have talked to the builder, who took a second spring out of the 1-2 accumulator, didn't help.
Back-story and what's been done to date. Shift problem from day-1. I talked to my Tuner and sent him short video's of the scan tool in real time. The PCM was not commanding higher line pressure during low load acceleration, but was commanding more pressure during a medium/high load take off. Shift at low load is just as hard as high load.
- Shift points are where the Tuner and I discussed, 2-3 shift is perfect, lockup is perfect, 3-O.D./lockup is perfect.
- TPS has been checked and adjusted to 5.6v on idle stop and 4.488v at WOT
- MAP voltage: 5.039v engine off 1.409v engine idling (Lt GRN wire)
- Idle vacuum is 18
As I understand, and this could be a mile off reality, the 1-2 accumulator, separator plate hole #8, and the 2nd gear servo affect this shift. The builder used the "Corvette" servo which has more surface for the oil pressure to act against. The Tuner suggested I swap the Corvette servo for the Truck version to correct the hard shift. I also read that the Corvette servo also does a better job of locking up 3rd and/or 4th (O.D.) which would be a good thing.
Way back in the day, I put a shift kit in a TH400 and part of that magic was to drill out that hole slightly. Made a difference back then. The builder said he drilled out the #8 hole to .070, which he does routinely.
Now, here's what I do not understand. Sometimes the 1-2 shift is beautiful, light/firm with no slide-bump. This happens without fail while the trans oil is cold, first startup of the day. After about 5-6 minutes it starts the severe shifts into 2nd, no matter if I use the absolute minimum throttle to get up to speed or give the throttle a heavy shoe. But, maybe 10-15% of the time it will give me that beautiful smooth, controlled shift, and then go right back pounding the drive train. There is no pattern to when the softer shift is going to happen and I can't seem to repeat it.
Short recap: the 1-2 shift now is what I would want on a full throttle high RPM shift, but not all the time and not poking around town from stop light to stop light.
I would really appreciate help from anyone who has an educated guess as to what is causing this problem, or point me in a direction. The rebuild was total with top of the line parts, the builder does this service for most of the racers around here. He has not stepped up to help me much on this issue though. That's something between the two of us and going back to him is not an option until I have a better understanding of a solution.
Thank you for your time.
Dave
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Back-story and what's been done to date. Shift problem from day-1. I talked to my Tuner and sent him short video's of the scan tool in real time. The PCM was not commanding higher line pressure during low load acceleration, but was commanding more pressure during a medium/high load take off. Shift at low load is just as hard as high load.
- Shift points are where the Tuner and I discussed, 2-3 shift is perfect, lockup is perfect, 3-O.D./lockup is perfect.
- TPS has been checked and adjusted to 5.6v on idle stop and 4.488v at WOT
- MAP voltage: 5.039v engine off 1.409v engine idling (Lt GRN wire)
- Idle vacuum is 18
As I understand, and this could be a mile off reality, the 1-2 accumulator, separator plate hole #8, and the 2nd gear servo affect this shift. The builder used the "Corvette" servo which has more surface for the oil pressure to act against. The Tuner suggested I swap the Corvette servo for the Truck version to correct the hard shift. I also read that the Corvette servo also does a better job of locking up 3rd and/or 4th (O.D.) which would be a good thing.
Way back in the day, I put a shift kit in a TH400 and part of that magic was to drill out that hole slightly. Made a difference back then. The builder said he drilled out the #8 hole to .070, which he does routinely.
Now, here's what I do not understand. Sometimes the 1-2 shift is beautiful, light/firm with no slide-bump. This happens without fail while the trans oil is cold, first startup of the day. After about 5-6 minutes it starts the severe shifts into 2nd, no matter if I use the absolute minimum throttle to get up to speed or give the throttle a heavy shoe. But, maybe 10-15% of the time it will give me that beautiful smooth, controlled shift, and then go right back pounding the drive train. There is no pattern to when the softer shift is going to happen and I can't seem to repeat it.
Short recap: the 1-2 shift now is what I would want on a full throttle high RPM shift, but not all the time and not poking around town from stop light to stop light.
I would really appreciate help from anyone who has an educated guess as to what is causing this problem, or point me in a direction. The rebuild was total with top of the line parts, the builder does this service for most of the racers around here. He has not stepped up to help me much on this issue though. That's something between the two of us and going back to him is not an option until I have a better understanding of a solution.
Thank you for your time.
Dave
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