4L60E Misbehaving on the highway - Drivability

[swearingencj]

I went back and looked at it and it never even goes in lock-up once in that log, so the pump RPM never went low enough under light load to cause the unit to downshift from 4th to 3rd.

I have to run out, I'll go back on the highway and will command it on when it's slipping. You'll see it stop right away.

[TransGo Robert]

I have to run out, I'll go back on the highway and will command it on when it's slipping. You'll see it stop right away.

It really does not matters, your problems is a fairly common one and clear as day in the normal driving lot. It is falling out of overdrive into third gear while the command remains steady. It's in the valve body.

[swearingencj]

I went back and looked at it and it never even goes in lock-up once in that log, so the pump RPM never went low enough under light load to cause the unit to downshift from 4th to 3rd.

Had to run to the store so I pulled another file. I left the TCC PWM engage the whole trip except for a few times on a downhill and you'll see the RPMs jump. What I see here is that when the TPS is between 20 and 25% the TC flickers all over the place. TPS above 25% and it locks. It still allows some slip between 20 and 25% but only about 150 rpms instead of 800.

Toggling that solenoid turns this behavior on and off.

The only exception is that when I mess with it, sometimes it will act right without the TCC PWM toggle on for just a minute or two and then it'll go back. This is my work and home route every day so I've been seeing this for a while and can definitely tell that the toggle fixes the behavior.

032124953tccpwm.hpl

[TransGo Robert]

Had to run to the store so I pulled another file. I left the TCC PWM engage the whole trip except for a few times on a downhill and you'll see the RPMs jump. What I see here is that when the TPS is between 20 and 25% the TC flickers all over the place. TPS above 25% and it locks. It still allows some slip between 20 and 25% but only about 150 rpms instead of 800.

Toggling that solenoid turns this behavior on and off.

The only exception is that when I mess with it, sometimes it will act right without the TCC PWM toggle on for just a minute or two and then it'll go back. This is my work and home route every day so I've been seeing this for a while and can definitely tell that the toggle fixes the behavior.

032124953tccpwm.hpl

800 is not TCC slip, it's third gear. I don't think I can find a way to tell you what you want to hear unfortunately. This is 100% a valve body issue, I can't help you beyond that unfortunately.

[swearingencj]

800 is not TCC slip, it's third gear. I don't think I can find a way to tell you what you want to hear unfortunately. This is 100% a valve body issue, I can't help you beyond that unfortunately.

I appreciate your help, I'm not trying to get a particular answer really. Just don't want to throw money at the problem. I just don't get a few things that I asked and still am curious. Why is the log showing 4th gear if its actually in 3rd? Isn't third commanded when the 2-3 solenoid is on and fourth is commanded with 2-3 off and the band is applied by the external shift solenoid (cant remember the name)?

What I hear you saying is that the trans is not slipping and is in 3rd even though it shows TCC Slip is on, Gear is 4th and the 2-3 solenoid is off. I admit I don't understand how these things really work which is why I bought this scanner, but you're telling me that the logs are reporting false information. I'm all for swapping the part or swapping the valve body under warrantee but just want to fix this once and for all. This trans has been completely rebuilt by a very public and reputable shop but the shop is pretty far and that warrantee is expired already

[TransGo Robert]

I appreciate your help, I'm not trying to get a particular answer really. Just don't want to throw money at the problem. I just don't get a few things that I asked and still am curious. Why is the log showing 4th gear if its actually in 3rd? Isn't third commanded when the 2-3 solenoid is on and fourth is commanded with 2-3 off and the band is applied by the external shift solenoid (cant remember the name)?

What I hear you saying is that the trans is not slipping and is in 3rd even though it shows TCC Slip is on, Gear is 4th and the 2-3 solenoid is off. I admit I don't understand how these things really work which is why I bought this scanner, but you're telling me that the logs are reporting false information. I'm all for swapping the part or swapping the valve body under warrantee but just want to fix this once and for all. This trans has been completely rebuilt by a very public and reputable shop but the shop is pretty far and that warrantee is expired already

I am in between two flights right now on my way to give a class and I think I will use your log to help transmission guys understand this tricky problem to diagnose on 4L60E. So typing this on my phone will try to make it short, if it is still not clear let me know when I get back I'll explain better. This transmission does not have a sensor for the input shaft so the computer is unable to tell what gear / ratio it is in. What you see in the scanner data is what it commands and what it thinks it is doing. You can see the command for both pick-up and 4th remains steady. Nothing at all command wise is changing when it has the big flare ups. The converter at cruise when it unlocks would only cause a 300-400 rpm increase. The way to know what is really going on is to compare the engine RPM to the output shaft RPM. Before the spike up if you divide the engine RPM by output RPM you will see it is real close to 0.69 which is overdrive ratio of the 4L60E. Then when the RPMs go up, do the same math and you will see that both numbers are just about identical giving 1.00 ratio aka direct, aka 3rd gear. Now the computer is not that smart, it assumes the unit is still in 4th gear, so it displays the difference between the expected engine RPM and what it is swing as converter clutch slip. In reality, at light throttle, if it was the converter that was unlocked the RPMs would only be 3-400 higher then expected and the ratio between the two would be something in between 1.00 and 0.69, an impossible ratio for this unit. Bottom line here is that the transmission is not doing what it is asked to do, if you hard it rebuilt just take it back to them and have them fix it. It could be a few different things, the most common is AFL valve issue in the valve body, but don't just throw parts/money at hit, let them it diagnose the problem first. You can show them your log it just the screenshot I sent before showing the problem and let them take it from there. I hope this helps clear things up a bit.

[swearingencj]

I am in between two flights right now on my way to give a class and I think I will use your log to help transmission guys understand this tricky problem to diagnose on 4L60E. So typing this on my phone will try to make it short, if it is still not clear let me know when I get back I'll explain better. This transmission does not have a sensor for the input shaft so the computer is unable to tell what gear / ratio it is in. What you see in the scanner data is what it commands and what it thinks it is doing. You can see the command for both pick-up and 4th remains steady. Nothing at all command wise is changing when it has the big flare ups. The converter at cruise when it unlocks would only cause a 300-400 rpm increase. The way to know what is really going on is to compare the engine RPM to the output shaft RPM. Before the spike up if you divide the engine RPM by output RPM you will see it is real close to 0.69 which is overdrive ratio of the 4L60E. Then when the RPMs go up, do the same math and you will see that both numbers are just about identical giving 1.00 ratio aka direct, aka 3rd gear. Now the computer is not that smart, it assumes the unit is still in 4th gear, so it displays the difference between the expected engine RPM and what it is swing as converter clutch slip. In reality, at light throttle, if it was the converter that was unlocked the RPMs would only be 3-400 higher then expected and the ratio between the two would be something in between 1.00 and 0.69, an impossible ratio for this unit. Bottom line here is that the transmission is not doing what it is asked to do, if you hard it rebuilt just take it back to them and have them fix it. It could be a few different things, the most common is AFL valve issue in the valve body, but don't just throw parts/money at hit, let them it diagnose the problem first. You can show them your log it just the screenshot I sent before showing the problem and let them take it from there. I hope this helps clear things up a bit.

Wow, thanks! I follow, so that gives me a lot to think about. We're driving to FL today and we did some logging. Interesting that when the trans was in forth gear the line pressure registered as 10% but when we started going downhill it dropped to 0%. I toggled the TCC PWM back on and it bumped back up to 10.

I'm starting to think the last shop that worked on it might not have put my new valve body in and just charged me for it. I'll call transtar next week and see if the part they sent has a serial number that I can see and compare.

I had this trans rebuilt by precision transmission in Amarillo TX and it ran like a top for about 18 months, no issues at all. Then on a trip to Alabama it started throwing p1840 codes and going to max line pressure. Three shops told me to replace the TC and valve body. I did that and picked a shop base on reputation and talking to the owner. Unfortunately, the owner sold his business and backed out so I'm back to square one with this. I've taken it to my mechanic and a local tran shop that's been serving my area for 25 years and no one has any ideas. Mostly because we believe the last shop actually swapped the valve body.

I'm going to call transtar to see if I can tell if that unit is really the one they sent. If not I'm out the $550 plus labor and I'll have to get another.

Really appreciate the time you took to explain, for now I'm going to enjoy my vacation this week and tackle it when I get back.

[TransGo Robert]

Wow, thanks! I follow, so that gives me a lot to think about. We're driving to FL today and we did some logging. Interesting that when the trans was in forth gear the line pressure registered as 10% but when we started going downhill it dropped to 0%. I toggled the TCC PWM back on and it bumped back up to 10.

I'm starting to think the last shop that worked on it might not have put my new valve body in and just charged me for it. I'll call transtar next week and see if the part they sent has a serial number that I can see and compare.

I had this trans rebuilt by precision transmission in Amarillo TX and it ran like a top for about 18 months, no issues at all. Then on a trip to Alabama it started throwing p1840 codes and going to max line pressure. Three shops told me to replace the TC and valve body. I did that and picked a shop base on reputation and talking to the owner. Unfortunately, the owner sold his business and backed out so I'm back to square one with this. I've taken it to my mechanic and a local tran shop that's been serving my area for 25 years and no one has any ideas. Mostly because we believe the last shop actually swapped the valve body.

I'm going to call transtar to see if I can tell if that unit is really the one they sent. If not I'm out the $550 plus labor and I'll have to get another.

Really appreciate the time you took to explain, for now I'm going to enjoy my vacation this week and tackle it when I get back.

It must have been the usual code P1870, there is no P1840 on this application. The valve body was not new from Transtar by the way, you cannot buy new valve body for those from anywhere, even the dealer sell remanufactured valve bodies. What you bought was a remanufactured valve body, lots of defects with those no matter what company you get them from. It is normal for the pressure control solenoid to be commanded to lower line when you lower the throttle or coast down, it goes hand in hand with the load. That's why it comes out of fourth too, there is an ALF or solenoid issue so when the pressure drops a bit not enough pressure can build up between the solenoid and the 3-4 shift valve to overcome the valve spring force. Many guys will band-aid the problem by simply enlarging the solenoid feed hole, but what it really need is to have the AFL valve bore wear issue address, it needs be machined oversized so that an oversized valve can be fitted and restore the hydraulics so that it can work as intended. I would be good money the shop did put that Transtar valve body in it, and no they don't put serial numbers on them to be able to identify it but some company will put a tag on them. Either way it would be much cheaper and a much better repair to have your valve body fixed instead of just trying you luck with another reman valve body. If I was you I would print all this out, bring it to your transmission shop and have them read it and I bet you after that the light will go on and now they will know how to fix it. If not or if anything is not clear, you can have them email me at [email protected] or call our product support line and I can help them.

[swearingencj]

It must have been the usual code P1870, there is no P1840 on this application. The valve body was not new from Transtar by the way, you cannot buy new valve body for those from anywhere, even the dealer sell remanufactured valve bodies. What you bought was a remanufactured valve body, lots of defects with those no matter what company you get them from. It is normal for the pressure control solenoid to be commanded to lower line when you lower the throttle or coast down, it goes hand in hand with the load. That's why it comes out of fourth too, there is an ALF or solenoid issue so when the pressure drops a bit not enough pressure can build up between the solenoid and the 3-4 shift valve to overcome the valve spring force. Many guys will band-aid the problem by simply enlarging the solenoid feed hole, but what it really need is to have the AFL valve bore wear issue address, it needs be machined oversized so that an oversized valve can be fitted and restore the hydraulics so that it can work as intended. I would be good money the shop did put that Transtar valve body in it, and no they don't put serial numbers on them to be able to identify it but some company will put a tag on them. Either way it would be much cheaper and a much better repair to have your valve body fixed instead of just trying you luck with another reman valve body. If I was you I would print all this out, bring it to your transmission shop and have them read it and I bet you after that the light will go on and now they will know how to fix it. If not or if anything is not clear, you can have them email me at [email protected] or call our product support line and I can help them.

Thanks Robert,

I'll shoot this over their way and get on the schedule. Can't thank you enough for jumping in here and sticking with me on this.

Chad

[swearingencj]

Well the builder got into it today and pulled the valve body, it already had the new afl valve installed in the reman'd unit.
On to find where else it could be loosing pressure. Tomorrow they are dropping the trans out and going through it.

[TransGo Robert]

Well the builder got into it today and pulled the valve body, it already had the new afl valve installed in the reman'd unit.
On to find where else it could be loosing pressure. Tomorrow they are dropping the trans out and going through it.

I don't see what could be gained by pulling the transmission at this point. Whose AFL valve is in there and what is the spring or springs lenght, diameter ane wire diameters?

[swearingencj]

Here is what he found:
photo_2024-04-11_20-22-14.jpg
photo_2024-04-11_20-22-26.jpg

That torque converter was installed about 6 months ago. Don't know if the bearing was replaced at the time, id have to check my invoice.

Shop says everything inside the unit looks perfect except this. They are investigating what might have caused the bearing failure now.

[TransGo Robert]

Here is what he found:
photo_2024-04-11_20-22-14.jpg
photo_2024-04-11_20-22-26.jpg

That torque converter was installed about 6 months ago. Don't know if the bearing was replaced at the time, id have to check my invoice.

Shop says everything inside the unit looks perfect except this. They are investigating what might have caused the bearing failure now.

Missing dowel pins or bad ground, had to tell without seing the bushing all the way around.

[swearingencj]

Bad ground to the harness? or externally? I know the harness that is in there is new but recently new.

[TransGo Robert]

Bad ground to the harness? or externally? I know the harness that is in there is new but recently new.

Engine ground. When you have an insufficient engine ground, while cranking the huge amp draw of the starter causes the electrons to use the transmission as a ground path to go back to the battery. When it when it jumps from the converter hub to the pump bushing it arcs adn damage the bushing. It usually looks different then what you have in your picture but it is still a possibility. It would be very useful to see a good picture of the whole bushing instead of just one side. Also, is hte converter hub damaged like that all the way around or just on that one side?

[swearingencj]

Thanks Robert,

Shop inspected for arcing and was pretty familiar with how to inspect for that issue and did not see any evidence of arcing anywhere in the unit. I believe the TC is damaged all the way around.

photo_2024-04-12_16-07-07.jpg

[TransGo Robert]

Thanks Robert,

Shop inspected for arcing and was pretty familiar with how to inspect for that issue and did not see any evidence of arcing anywhere in the unit. I believe the TC is damaged all the way around.

photo_2024-04-12_16-07-07.jpg

OK good you can see in the picture that it is an alignment issue, it wore the bushing on one side. That's usually because one of the two dowel pins is missing. If it had been a converter hub runout issue or ground issue it would have chewed up the bushing the same way all the way around.

[swearingencj]

Well she's back together and shifting perfectly. The shop looked for anything that could have caused that misalignment and failure but couldn't pinpoint a smoking gun. It needed a rear main seal and looking at the flywheel, it was not oe and had some pretty ugly inconsistent welds so it was replaced. They replaced the worn items and made sure it all looked good.

I put the stock GM tune back in there for now but will be thinking about how I can try to squeeze some extra highway miles from this beast.

Can't thank Robert enough for your patience and explaining. Learned a lot. Long way to go 😜

[TransGo Robert]

Well she's back together and shifting perfectly. The shop looked for anything that could have caused that misalignment and failure but couldn't pinpoint a smoking gun. It needed a rear main seal and looking at the flywheel, it was not oe and had some pretty ugly inconsistent welds so it was replaced. They replaced the worn items and made sure it all looked good.

I put the stock GM tune back in there for now but will be thinking about how I can try to squeeze some extra highway miles from this beast.

Can't thank Robert enough for your patience and explaining. Learned a lot. Long way to go ��

Glad it is working good now. Scary that they did not find the alignment issue, hopefully it does not happen again. Thanks for taking the time to post this update.