4l60e no shift attempt to 3rd after rebuild

[Leo330]

Hello,

I have just completed my first automatic transmission rebuild, and while I felt good about all the steps it now will shift 1st to 2nd, but never attempt to shift into 3rd gear. (Never attempts 4th either, but I assume this is because it never gets to 3rd.)

Backstory:
I have a 1995 K1500 4wd with 325k miles on it. I purchased showing 215k and it has been great. As far as I can tell this is the original transmission. Last week I was slowing for a red light that changed to green. The transmission was in 2nd then shifted to 3rd and it acted like neutral. Some research made it pretty clear this would be caused by a burnt up 3/4 clutch pack, and bad piston seals. I dropped the trans and just like I read/you tube showed 3/4 was burnt, and the piston seal was hard/a lose fit. I got a parts kit, new 3/4 frictions and steels and re-assembled. Following the Transmission Bench videos show. I expected success.

Now:
When I went for a test drive I no longer get the 2-3 flair it just never attempts to shift out of 2nd. The 1/2 shift is good. Any ideas what I would have done wrong? I have dropped the trans again and everything looks fine. I am at a complete loss, so any theories would be helpful.

Thanks,
Leo

 

[tayto]

sprag backwards

 

[NickTransmissions]

Hello,


Now:
When I went for a test drive I no longer get the 2-3 flair it just never attempts to shift out of 2nd. The 1/2 shift is good. Any ideas what I would have done wrong? I have dropped the trans again and everything looks fine. I am at a complete loss, so any theories would be helpful.

Thanks,
Leo

Are/were you in Drive4 (i.e. OD) on the column shifter when doing that test drive?

If so, sounds like either Sol B stuck on or 2-3 shift valve/shuttle valve or PCM not commanding the shift or the PCM not issuing the command for the 2-3 shift...

Questions:
- Did you replace all the solenoids, harness pressure switch manifold and torque converter?
- Did you check all the valves to confirm they are moving freely?
- Did you vac-test the AFL and TCC regulator valve for wear?
- Did you air check all applied elements to ensure everything was compressing and releasing, especially the 2-4 Servo assembly?

I wouldn't have dropped the transmission again for this symptom as it's more than likely a 'command and control' problem, not a mechanical one...Once you get it back on the road, plug in a bi-directional scan too to watch live transmission data to see what the commands the computer is giving...If the computer is not commanding a shift, that's a different problem than it is but the transmission isn't responding.

Following the Transmission Bench videos show. I expected success.

This may be a big part of the problem...He puts people to sleep and I can think of at least one critical piece of instruction he gives that's completely ill-advised.

sprag backwards

If he was in D4 and able to move forward, shift 1-2, his input sprag is working.

 

[Leo330]

Are/were you in Drive4 (i.e. OD) on the column shifter when doing that test drive? Yes

If so, sounds like either Sol B stuck on or 2-3 shift valve/shuttle valve or PCM not commanding the shift or the PCM not issuing the command for the 2-3 shift...

I thought the same thing, I actually spend a day checking this out. I was most suspicious of tearing a bit of insulation and having a short to ground causing Sol B to be stuck on. This was not the case. I don't have the scan tool, but used a multi-meter. I also thought there maybe a chance I swapped the 3-2 solenoid and the PWM? Solenoid. The two in the front of the valve body, but they are the same ohms and same part number. I moved them side to side just in case one was bad not change. I ohmed Sol A and B, used a small nail to make sure they moved with a 9V battery and blew on them to make sure they stopped air flow.

Questions:
- Did you replace all the solenoids, harness pressure switch manifold and torque converter? No, since it looks like the 3/4 clutch apply piston I like to change one thing at a time, to the extent it is possible and electronically the trans seemed good going into this rebuild.
- Did you check all the valves to confirm they are moving freely? Yes, although I have a question about one I'll post below.
- Did you vac-test the AFL and TCC regulator valve for wear? I did not, I'll look into how I might do this.
- Did you air check all applied elements to ensure everything was compressing and releasing, especially the 2-4 Servo assembly? I air checked everything in the drum, but not the 2-4 Servo. I did take it out double check all was good and the new taper rings and O-rings all looked good. I made sure to keep blue and green in respective places.

I wouldn't have dropped the transmission again for this symptom as it's more than likely a 'command and control' problem, not a mechanical one...Once you get it back on the road, plug in a bi-directional scan too to watch live transmission data to see what the commands the computer is giving...If the computer is not commanding a shift, that's a different problem than it is but the transmission isn't responding. Is this a tool I can reasonably get from Amazon? (I'll do some searching, but if you have a reasonably priced favorite I'd pick it.)

This may be a big part of the problem...He puts people to sleep and I can think of at least one critical piece of instruction he gives that's completely ill-advised.


If he was in D4 and able to move forward, shift 1-2, his input sprag is working.

Thank you for your response.

 

[NickTransmissions]

I thought the same thing, I actually spend a day checking this out. I was most suspicious of tearing a bit of insulation and having a short to ground causing Sol B to be stuck on. This was not the case. I don't have the scan tool, but used a multi-meter. I also thought there maybe a chance I swapped the 3-2 solenoid and the PWM? Solenoid. The two in the front of the valve body, but they are the same ohms and same part number. I moved them side to side just in case one was bad not change. I ohmed Sol A and B, used a small nail to make sure they moved with a 9V battery and blew on them to make sure they stopped air flow.




Thank you for your response.

You're welcome.

You may have ruled out solenoids themselves as being the source of the problem (I have a special test block that actually tests all those solenoids for mechanical function as well as continuity so can't say if your methods work simply because I never used them). But you really need a scan tool to see the full picture of what's happening when on a test drive ... If the PCM isn't commanding the 2-3 shift, then no amount of continuity testing will reveal that, as all the solenoids will test 'ok'.

Scan tool w/live data on a test drive would be my next step whenever you're ready to do so.

 

[Leo330]

When checking all valves to verify they moved freely all seemed like I expected except for this one. Which I believe is TCC regulation? It moves freely, but the spring is loose. I took it out and the spring is not broken so I assume this is normal?

You must be registered for see images attach

 

[Leo330]

I noticed another, maybe huge, clue last night. It looks like my brand new 3/4 steels got hot and I only drove for ~6miles.

I thought the transmission was never giving the command to change from 2nd to 3rd gear. I'm now wondering if it is possible the 3/4 clutches were applying with the 2/4 band still applied? I feel like this is really stretching but...

(I live on a circle that touches a hwy so I can get a easy drive to the highway and then just enough time to make it to 65 MPH before braking for the second entrance.)
1st Drive: Everything put together, trans in D4 expectations high. 1/2 shift was good no shift to 3rd. When I got to the highway 4k RPM ~65 MPH, feel like 2nd gear.

2nd Drive: Dropped the pan, swapped TCC and 3/2 solenoid. Tested all wiring. Swapped Sol A and B. Exactly the same as 1st Drive. Now feel this not a "new" electronic problem and a result of my rebuild.

3rd Drive: Disconnected Plug on Transmission. It felt like I am taking off in 3rd gear, but when I got to the HWY still 4k RPM and ~65 MPH like second gear. This was very confusing to me. I know you would think it would be obvious if starting from 2nd or 3rd but when paying such close attention and never trying this before it really was not.

If we assume my 3rd drive impression was correct, any chance I was starting in 3rd with the 2/4 band applied? The band shows no wear/heat but the 3/4 steels sure do. I also believe my 3/4 plate gap opened up from .65 to .78. However, the frictions do not look worn.

Do the above impressions point to something?

 

[tayto]

did you air check and/or loctite your input shaft in? would be pretty obvious if you were starting in 3rd vs 1st.....

 

[NickTransmissions]

When checking all valves to verify they moved freely all seemed like I expected except for this one. Which I believe is TCC regulation? It moves freely, but the spring is loose. I took it out and the spring is not broken so I assume this is normal?

There's no spring tension on that valve train, unless you install Transgo's TCC valve or the Fitzall valve (or Sonnax's oversized valve but that requires a reamer to wallow out the bore to fit their os sleeve/valve kit).
Besides, that's not why the 3-4 burned shortly after rebuild.

I noticed another, maybe huge, clue last night. It looks like my brand new 3/4 steels got hot and I only drove for ~6miles.

If we assume my 3rd drive impression was correct, any chance I was starting in 3rd with the 2/4 band applied? The band shows no wear/heat but the 3/4 steels sure do. I also believe my 3/4 plate gap opened up from .65 to .78. However, the frictions do not look worn.

Do the above impressions point to something?

Yes, Im wondering if you forgot to install the green o-ring at the base of the forward drum so you're starting off in 3rd instead of 1st gear - that's exactly what would happen if you leave that o-ring out...Was it there when you took the forward drum apart?

 

[Leo330]

did you air check and/or loctite your input shaft in? would be pretty obvious if you were starting in 3rd vs 1st.....

It definitely was not starting in 1st, but I'm un-sure if starting in 2nd or 3rd.