RPM Flare After 3 - 4 Shift (4l60E)

[TransGo Robert]

Picture of the old reverse input drum, i replaced it during the rebuild, also very chattered up where sun shell meshes with it

Attachment 150481

The same pressure that applies the 3-4 is what releases the band on the 2-3 shift, so with the shaft pulling out of the drum causing a big leak in that circuit, it fried the band and the 3-4. I highly doubt it is in the valve body, my money is on the servo. I just can't come up with a solid logical reason right now. Since it is not a stock servo it makes it a bit trickier...

[twenglish1]

My mistake, that drum in the picture wasn't from the transmission with the input drum/input shaft issue, I didn't rebuild that one because of bad rear case lug wear, it was so bad i couldnt even get the center support out. That drum was from the junkyard unit I rebuilt. Sorry this is confusing been talking about two different units

I found the old servo, and I have new seals for it, the 1 - 2 shift is very stout, breaks tires loose when giving it more than probably 40% throttle, i tuned it down when I initially installed this in the car, I'll have to confirm but I believe I lowered the 1-2 pressure across the board by 10% or so to soften it up some, so that pretty much would just leave an issue with the 4th piston? Since there are no issues with the 2nd shift right?

[TransGo Robert]

My mistake, that drum in the picture wasn't from the transmission with the input drum/input shaft issue, I didn't rebuild that one because of bad rear case lug wear, it was so bad i couldnt even get the center support out. That drum was from the junkyard unit I rebuilt. Sorry this is confusing been talking about two different units

I found the old servo, and I have new seals for it, the 1 - 2 shift is very stout, breaks tires loose when giving it more than probably 40% throttle, i tuned it down when I initially installed this in the car, I'll have to confirm but I believe I lowered the 1-2 pressure across the board by 10% or so to soften it up some, so that pretty much would just leave an issue with the 4th piston? Since there are no issues with the 2nd shift right?

Not surprised that you had a ridiculous 1-2 shift. That's the problem combining parts like that which were never designed to work together. You probably would be better of in the long run to run a Corvette servo and stock 4th servo with that kit and put the tuning the way it was. The kit was designed and calibrated to work with factory tuning. When you start moving the goal post modifying the command, you are playing engineer doing costly R&D that could take a while before you realize just how costly the experiment was. But for now I would only do the 4th servo and check clearance so that we don't end up with a big headache figuring things out because we changed too many things at the same time.

[twenglish1]

Yeah I completely understand that, the whole end goal was a more robust 4l60e, i am not making any crazy torque currently, was just looking for a more sporty feel, more pronounced shifts. I've definitely been happy with how it turned out for the most part, this issue just had me concerned, like you said it, i didn't want it to turn into something bigger. This is the first transmission i ever rebuilt/upgraded. I had torn them apart and reassembled many times previously though. I just do all this as a hobby, always trying to learn something new. What would you recommend reinstalling the factory servo assembly? I will have a new pin on hand if i go this route incase clearance is way off. Or would it be worth it to go to a corvette servo assembly since it is still OEM? At the same time i will revert the changes to the shift pressures back as well

[TransGo Robert]

Yeah I completely understand that, the whole end goal was a more robust 4l60e, i am not making any crazy torque currently, was just looking for a more sporty feel, more pronounced shifts. I've definitely been happy with how it turned out for the most part, this issue just had me concerned, like you said it, i didn't want it to turn into something bigger. This is the first transmission i ever rebuilt/upgraded. I had torn them apart and reassembled many times previously though. I just do all this as a hobby, always trying to learn something new. What would you recommend reinstalling the factory servo assembly? I will have a new pin on hand if i go this route incase clearance is way off. Or would it be worth it to go to a corvette servo assembly since it is still OEM? At the same time i will revert the changes to the shift pressures back as well

For now I would only go back to the factory 4rh gear servo piston and cover and check clearance.

[twenglish1]

I will try it, thanks again for the help, any preference between OEM style split Teflon seals or sonnax d-ring seals for the 4th piston? I have both

[TransGo Robert]

I will try it, thanks again for the help, any preference between OEM style split Teflon seals or sonnax d-ring seals for the 4th piston? I have both

Six of one, half a dozen of the other in my opinion.

[twenglish1]

So this is interesting, i was doing some more experimenting today and i found that the 3-4 shift torque reduction was causing this RPM flare, zeroed out the torque reduction for the 3-4 shift and the flare went away, roughly a 1/4 way into the log there are a few 3-4 shifts along with TCC lockups and manual downshifts.

No 3-4 Torque Reduction.hpl

[TransGo Robert]

So this is interesting, i was doing some more experimenting today and i found that the 3-4 shift torque reduction was causing this RPM flare, zeroed out the torque reduction for the 3-4 shift and the flare went away, roughly a 1/4 way into the log there are a few 3-4 shifts along with TCC lockups and manual downshifts.

No 3-4 Torque Reduction.hpl

Interesting, I guess the data for the shift solenoid and gear command PIDs on HP Tuners is not reliable for the 4L60E. I almost had you put a voltmeter on the SS1 control wire because it looked so much like it was commanding it to go 3-4-3-4, but I figure surely it can't be that it is not reporting what it is really commanding for the solenoid.... Good job figuring it out!

[twenglish1]

Yeah definitely strange, felt like something was wrong for sure, either the 3-4-3-4 or 3-4-lock-unlock-lock. I tried a few things before finding that the 3-4 torque reduction was it, I had also tried reducing the TCC min and max PWM to 1% and 0%, I almost forgot that I didn't install the valve to disable TCC pwm control from the sonnax shift kit, wasn't sure if this was a feature I might have ended up wanting to use at some point, and it's easy enough to disable it in the trans calibration, my thought here was that it was briefly sending pressure to the TCC during the shift, so I tried removing the PWM signal all together. I'm just happy it doesn't seem like there is anything wrong with the transmission, did not want to pull it again, I already had to install it twice after the rebuild, I found the plastic spacer that goes between the pump and the reverse input drum while cleaning up after I installed, filled and test drove it, not sure if it would have caused problems or not, but wasnt going to take the chance, won't make that mistake again thats for sure! Hahaha

[TransGo Robert]

Yeah definitely strange, felt like something was wrong for sure, either the 3-4-3-4 or 3-4-lock-unlock-lock. I tried a few things before finding that the 3-4 torque reduction was it, I had also tried reducing the TCC min and max PWM to 1% and 0%, I almost forgot that I didn't install the valve to disable TCC pwm control from the sonnax shift kit, wasn't sure if this was a feature I might have ended up wanting to use at some point, and it's easy enough to disable it in the trans calibration, my thought here was that it was briefly sending pressure to the TCC during the shift, so I tried removing the PWM signal all together. I'm just happy it doesn't seem like there is anything wrong with the transmission, did not want to pull it again, I already had to install it twice after the rebuild, I found the plastic spacer that goes between the pump and the reverse input drum while cleaning up after I installed, filled and test drove it, not sure if it would have caused problems or not, but wasnt going to take the chance, won't make that mistake again thats for sure! Hahaha

You should go back in there with the setup from the kit for lock-up, that way you don't change over pressurising the converter clutch piston like so many do with tuning without realizing it. On that trust washer, if you had not put it back in, the unit would have self destroy after driving it a while.

[twenglish1]

I wasn't sure what would happen with that plastic thrust washer not being in there, i definitely didn't want to find out the hard way, i guess the reverse input drum would be hammering against the back of the pump, and im sure it could potentially cause misalignments of some of the fluid passages.

I probably will install the valve at some point just to be safe, at this point i dont think i will ever use the PWM TCC again. It was my understanding that the sonnax pressure regulator valve vs blocking the OEM TCC PWM valve completely, which apparently people have been known to do to "FIX" converter slip codes, in turn it looks like this disables the pressure limiting feature of the OEM valve, the diagram i saw of the OEM TCC valve looks like regardless of PWM duty cycle that it will always be limiting pressure based off of the spring tension on the valves, unless i am not understanding this diagram correctly, but it looks like even with 100% on the PWM overpressures will still exhaust from the apply circuit, i'm not sure if its the case or not but i could see a potential problem from increasing pump pressure beyond what the OEM valve is capable of exhausting preventing it from dropping the TCC pressure down to the safe levels. Diagram below that i was referring to.
900W-Tech-Image.jpg