Issues with 2nd gear

[nonickatall]

If the oil look red, is not burned and there is only that issue with the shifting into second gear while accelerating, while you can shift to second gear manually without problems, i would first look for other electric or control related problems, like a gas pedal or throttle sensor.

I am not common how that is at the gmt820, but i know that from other cars. If you have a dying throttle or gas pedal sensor wich has areas where there is no proper signal then the automatic transmission control unit does probably not know, that it would be the right moment to shift. But if you change acceleration pedal position it knows and shift. And that would probably make as well no error, because the system can not detect that as a false accelerator position.

That is only an idea. But i would check something like this, before i swap the unit.

There is nothing more angry than spend a loz of time and work to find out that it was a simple sensor...

 

[Alex_M]

Unless I'm mistaken, and I don't do a lot of tranny diagnosis so I may be, but it sounds like a stuck check ball in the valve body separator plate to me. If so, ordering a new separator plate and a set of torlon check balls would cure the problem without dropping the trans. I'd put a shift kit and block off the PWM solenoid while I had the valve body out.

 

[NickTransmissions]

Unless I'm mistaken, and I don't do a lot of tranny diagnosis so I may be, but it sounds like a stuck check ball in the valve body separator plate to me. If so, ordering a new separator plate and a set of torlon check balls would cure the problem without dropping the trans. I'd put a shift kit and block off the PWM solenoid while I had the valve body out.

Typically, a stuck #8 check ball (the 1-2 check ball location) results in a very late, harsh 1-2 shift where I believe he's experience a neutral condition in second until the RPMs prompt the 2-3 shift (though @Echo can clarify if need be). Broken 1-2 accumulator springs can also produce that condition as can a worn PWM reg valve, which if that's the cause, DTC P1870 will usually set after two consecutive drive cycles where the condition manifests.

That said, your post is still a great call out as the plate can be repaired via installation of a metal sleeve from Fitzall's plate repair kit and many aren't aware of that check and fix.

I do this all the time on otherwise serviceable spacer plates. If he ends up dropping the pan, VB and spacer plate, he can proactively repair the plate via a sleeve from that kit (if it's not already worn) and install the larger torlon check ball that comes in Transgo's SK4L60E shift kit as well as convert the PWM to 'on-off' using the Transgo PWM valve. Another thing that can be done is blocking the 3-2 downshift valve for much crisper 3-2 downshifts. The SK4L60E doesn't provide a spring for that (the 4L60E HD2 kit does but it's a lot more expensive) but he can use an extra boost valve spring (the small inner spring) or even an aluminum or steel spacer if he's got the tooling to make one. He can also install the Corvette second gear servo to further bolster the 1-2 shift.

He can perform an air check on the 2nd apply once the VB and plate are removed - I show this in one my 4L60E rebuild videos at 4:57.

If none of those things work, its time to pull and overhaul it.

 

[Alex_M]

Typically, a stuck #8 check ball (the 1-2 check ball location) results in a very late, harsh 1-2 shift where I believe he's experience a neutral condition in second until the RPMs prompt the 2-3 shift (though @Echo can clarify if need be). Broken 1-2 accumulator springs can also produce that condition as can a worn PWM reg valve, which if that's the cause, DTC P1870 will usually set after two consecutive drive cycles where the condition manifests.

That said, your post is still a great call out as the plate can be repaired via installation of a metal sleeve from Fitzall's plate repair kit and many aren't aware of that check and fix.

I do this all the time on otherwise serviceable spacer plates. If he ends up dropping the pan, VB and spacer plate, he can proactively repair the plate via a sleeve from that kit (if it's not already worn) and install the larger torlon check ball that comes in Transgo's SK4L60E shift kit as well as convert the PWM to 'on-off' using the Transgo PWM valve. Another thing that can be done is blocking the 3-2 downshift valve for much crisper 3-2 downshifts. The SK4L60E doesn't provide a spring for that (the 4L60E HD2 kit does but it's a lot more expensive) but he can use an extra boost valve spring (the small inner spring) or even an aluminum or steel spacer if he's got the tooling to make one. He can also install the Corvette second gear servo to further bolster the 1-2 shift.

He can perform an air check on the 2nd apply once the VB and plate are removed - I show this in one my 4L60E rebuild videos at 4:57.

If none of those things work, its time to pull and overhaul it.

Awesome info, thanks Nick!

 

[NickTransmissions]

Awesome info, thanks Nick!

You're welcome, Alex!

 

[Mudsport96]

Sounds much like the 60e in my Silverado. Would take 2nd with a manual selection and 4th was okay. But the 2-4 band was shot. Just enough grip that the extra apply for 4th would hold while cruising.

 

[rockola1971]

Sounds much like the 60e in my Silverado. Would take 2nd with a manual selection and 4th was okay. But the 2-4 band was shot. Just enough grip that the extra apply for 4th would hold while cruising.

But the minute you leaned into the throttle even somewhat moderately 4th(OD) would turn to neutral and the RPM's would skyrocket, right?

 

[Mudsport96]

But the minute you leaned into the throttle even somewhat moderately 4th(OD) would turn to neutral and the RPM's would skyrocket, right?

Believe it or not it would hold fine under moderate tip-in. And just kick down to 3rd with any more throttle.
This truck has always shifted odd. To the point that the very reputable shop that installed the new Trans kept it an extra day trying to troubleshoot a perceived issue that 3 different 4l60es have had in it. So I am confident it is a programming issue. I could go into more but not wanting to pirate a thread.