Odd 1st to 2nd shifting.

[Roilux]

Question for the transmission gurus. I have a 2004 Tahoe, 5.3 flex, 4L60E trans with 168k miles. I’m the third owner and have no previous owner’s service records before purchasing it with 159k on the clock two years ago. Aside from regular maintenance and upgrades during my watch the Tahoe has been trouble free. Now here’s the oddity -

Brisk acceleration from 0 to 70 is predictable, smooth and consistent. Accelerating normally from 0 to 30 (city driving) has smooth shifting from 1st to 2nd about 50% of the time. The other shifts from 1st to 2nd have a little kick to them at what seems to be a slightly higher RPM. It’s more noticeable at normal operating temperatures. Shifts into 3rd and 4th are always smooth and consistent.

Is the intermittent ‘kick’ during shifts a serviceable item that might be cured by replacing a solenoid or ?????

I’m good with a wrench but haven’t been inside a transmission since putting a shift kit in a Turbo350 (admittedly, that's not really 'inside') back when Moses was still a Cub Scout. The transmission fluid appears and smells normal.

I have access to a Tech2 and HPTuners if needed, and also need to become familiar with both.

Thanks in advance.

 

[wjburken]

@NickTransmissions

 

[NickTransmissions]

Question for the transmission gurus. I have a 2004 Tahoe, 5.3 flex, 4L60E trans with 168k miles. I’m the third owner and have no previous owner’s service records before purchasing it with 159k on the clock two years ago. Aside from regular maintenance and upgrades during my watch the Tahoe has been trouble free. Now here’s the oddity -

Brisk acceleration from 0 to 70 is predictable, smooth and consistent. Accelerating normally from 0 to 30 (city driving) has smooth shifting from 1st to 2nd about 50% of the time. The other shifts from 1st to 2nd have a little kick to them at what seems to be a slightly higher RPM. It’s more noticeable at normal operating temperatures. Shifts into 3rd and 4th are always smooth and consistent.

Is the intermittent ‘kick’ during shifts a serviceable item that might be cured by replacing a solenoid or ?????

I’m good with a wrench but haven’t been inside a transmission since putting a shift kit in a Turbo350 (admittedly, that's not really 'inside') back when Moses was still a Cub Scout. The transmission fluid appears and smells normal.

I have access to a Tech2 and HPTuners if needed, and also need to become familiar with both.

Thanks in advance.

At 168k miles, I'd suspect wear in the 2-4 band, broken 1-2 outer accumulator spring and/or TCC regulator valve in the valve body and begin preparing for an overhaul. These transmissions aren't that difficult and don't require too many special tools, just basic stuff and tools to compress the clutch return springs, size teflon sealing rings on the input shaft and pump stator as well as shop air for your air checks.

You could check your servo travel and if found to beyond .125 of an inch, purchase a Transgo SK-4L60E shift kit and install the gold ring/spacer that comes in the kit to reduce your travel. The ring goes just inside the cover, against the rest of the servo. All you need to do is take off the servo cover (the 4th apply piston will be inside of it so don't let it fall out if you don't have a replacement sealing ring for it).

If that doesn't fix the issue, it likely cannot be fixed without just going through the trans.

The other possibility is the TCC regulator valve in the valve body..You can purchase Fitzall's TCC regulator valve for the 2004+ model year 4L60Es and see if that helps. Lastly check the 1-2 accumulator housing for a broken outer spring. I see this from time to time and the result is a very harsh 1-2 shift because you're removing a lot of accumulation from that apply circuit, resulting in a much faster, more aggressive 1-2 shift than what the trans was originally set up for, shift calibration-wise.

 

[Roilux]

At 168k miles, I'd suspect wear in the 2-4 band, broken 1-2 outer accumulator spring and/or TCC regulator valve in the valve body and begin preparing for an overhaul. These transmissions aren't that difficult and don't require too many special tools, just basic stuff and tools to compress the clutch return springs, size teflon sealing rings on the input shaft and pump stator as well as shop air for your air checks.

You could check your servo travel and if found to beyond .125 of an inch, purchase a Transgo SK-4L60E shift kit and install the gold ring/spacer that comes in the kit to reduce your travel. The ring goes just inside the cover, against the rest of the servo. All you need to do is take off the servo cover (the 4th apply piston will be inside of it so don't let it fall out if you don't have a replacement sealing ring for it).

If that doesn't fix the issue, it likely cannot be fixed without just going through the trans.

The other possibility is the TCC regulator valve in the valve body..You can purchase Fitzall's TCC regulator valve for the 2004+ model year 4L60Es and see if that helps. Lastly check the 1-2 accumulator housing for a broken outer spring. I see this from time to time and the result is a very harsh 1-2 shift because you're removing a lot of accumulation from that apply circuit, resulting in a much faster, more aggressive 1-2 shift than what the trans was originally set up for, shift calibration-wise.

Well, hello Guru!

Thanks Nick for the detailed reply. I've items to check

 

[filthysuburban]

I have a tuner and changed those tcc lockup pwms to all 90s and all 100s. This makes it on-off to keep that tcc check ball from rattling around I've heard. But if you have the harsh 1-2 it's probably too late. My dad's van with a 4l60 has the harsh 1-2 shift and so far only did the fluid + filter. It's not terribly bad but sometimes it's quite firm, kind of like what you're having.

 

[NickTransmissions]

Well, hello Guru!

Thanks Nick for the detailed reply. I've items to check

You're welcome, man.

I have a tuner and changed those tcc lockup pwms to all 90s and all 100s. This makes it on-off to keep that tcc check ball from rattling around I've heard. But if you have the harsh 1-2 it's probably too late. My dad's van with a 4l60 has the harsh 1-2 shift and so far only did the fluid + filter. It's not terribly bad but sometimes it's quite firm, kind of like what you're having.

There's no TCC check ball other than the one in the input shaft (perhaps that is what you're referring to?) but what that setting does is increase the TCC apply circuit's duty cycle to max out, basically eliminating the pulse width modulated converter clutch apply. I basically do the same thing in the valve body - see below.

Does your father's van have P1870 or P0894? If so, it's likely to be valve body and there's a few different fixes on the market that can fix it by simply dropping the valve body and replacing the factory TCC regulator valve, etc with the replacement valves. As with @Roilux 's trans, check the 1-2 acc and servo travel...

I did a video on Fitzall's valve on a 2010 4L60E showing how it installs, etc.

If P1870 or P0894 doesnt go away after the VB has been fixed, the cause is likely TC, input shaft-tcc o ring, the shaft itself leaking or a severely worn rear pump stator bushing.

 

[Roilux]

You're welcome, man.

Hi Nick, @NickTransmissions I've a 1-2 Piston Accumulator Housing Assembly with aluminum piston on order. I also located the Transgo diagram showing the gold shim and its location as you've stated. I'll get a new O-ring for the cover as I don't see one in their kit.

With my goal to extend the transmission's mechanical longevity and regaining as much new vehicle feel as possible, should I even consider consider a Corvette servo in lieu of the Transgo shim? If that question makes the hair on the back of your neck stand up, I apologize in advance.

I've watched a few of your YT videos on 4L60e's and subscribed. Nice presentations!

Bruce