My tranny does the usual occasional shift into or out of OD without taking enough time to unlock the TC. It has been rare enough that I didn't worry too much about it. We recently got a 13k lb trailer and the problem has been magnified and does it very regularly. While towing, it will bang into 4th (or downshift into 3rd) so harsh that it literally shakes the truck. I can't imagine it's very good with a GCW of just over 20k lbs.
Has anyone come up with a solution to this?

 

No one?

 

Triple disk, correct?

Is it shifting like its locked in TH and normal mode both or just TH?

The OE program for 3-4 and 4-3 shift\lock strategy happens too fast for a triple to unlock correctly in TH. It should be better in normal mode but under heavy throttle you may have the same problem. Have to find some way to soften up the shifts if normal mode is a problem.

 

I quit using T/H after the tranny build. It does this in normal mode. Yes, it is a triple disk. It would seem that I need to delay TC lockup a sec. Do the shift enhancers do this?

 

Its not only delay lockup on upshift its speed unlock on downshift. Not possible as far as I know in the ECU. Shift Enhancers basically ramp the TV pressure faster and higher to stetch shift points which is going to make the problem worse. I think you may have to go back to the VB, back the line pressures down and try to figure out how to slow down the 3-4 and 4-3 shift so the lockup has time to release.

Dave can figure it out if anyone can but its a bugger when things are not just right.

 

You can get a harsh shift with a modded tranny while locking up in 4th There is one part of the VB that you don't want to drill out due to it making this issue worse. The best advice I can give you is back off of the go pedal a little when it shifts into 4th and then roll into the throttle. This will make the TC stay unlocked until you reach around 50-55 MPH and you will get a much smoother lockup. If you get in a hurry pulling out in traffic this will not doubt make it shift harsh.

 

I didn't drill the holes for harder lockup. It sounds like I need to measure line pressure. I'm sure that's the first thing Dave will ask. Are there other circuits that need to be measured, too?

 

Run the standard pressure test and record the values the FSM points out. That will be the best snapshot of what is going on.

 

Which port is it?

 

Port 1 - rear servo pressure

Port 2 - governor pressure

Port 3 - accumulator (line) pressure

Port 4 - front band apply pressure

Port 5 - OD apply pressure