late part throttle shift 4L60E

[JD1964]

LT1 with 4L60e in 79 Malibu wagon. 3.73 rear gear and 26" tire.

The initial test drives are encouraging. First thing that needs adjusting is the part throttle upshifts. On normal part throttle acceleration the upshifts are delayed more than normal. In fact, when you get it in to 3rd and up to 45mph or so, you can let all the way off the throttle and it still wont shift to OD 4th. Don't have a speedometer yet but it seems like you have to push it to about 50mph before it will go in to 4th. Other gear upshifts are delayed too. No slipping.

Another thing, on WOT upshift from 2nd to 3rd, it bogs like its skipping 3rd and going to 4th.

Before I start chasing my tail, can I get some review of the attached bin to see if theres anything in there that would cause these symptoms.

Thanks in advance for any efforts that anyone gives

[lionelhutz]

Can you give some background, where the tune came from and what you changed before test driving? Is it possible your speed is off or you adjusted for the tire and rear-end but didn't scale the shift curves?

[LeMarky Dissod]

Minimally adjusted …

[JD1964]

Can you give some background, where the tune came from and what you changed before test driving? Is it possible your speed is off or you adjusted for the tire and rear-end but didn't scale the shift curves?

The initial tune was not done by me. Also, I don’t know the history of the transmission as we bought it used along with the engine. I did have someone else more knowledgeable than look at the initial tune and give me their opinion. They said the speedometer scaler looked good for my ratio and tire size so that was not changed by me. The one thing they questioned was the line pressure. Since I wanted a mild starting point I lowered the max line pressure and also made changes to the main line pressure tables. I used numbers from a bin that was recommended here at this site in another thread.

[JD1964]

Minimally adjusted …

Okay thanks I’ll have a look and maybe give this bin a try. What exactly did you change and if you can give me a reason I want to know. I’m always looking to learn in addition to just finding a solution.

[LeMarky Dissod]

The initial tune was not done by me. Also, I don’t know the history of the transmission as we bought it used along with the engine. I did have someone else more knowledgeable than look at the initial tune and give me their opinion. They said the speedometer scalar looked good for my ratio and tire size so that was not changed by me. The one thing they questioned was the line pressure. Since I wanted a mild starting point I lowered the max line pressure and also made changes to the main line pressure tables. I used numbers from a bin that was recommended here at this site in another thread.

Even if a '79 Malibu wagon weighs a bit less than an F-car, I would not change the max line pressure constant (in part because it's not what you think!), or lower the main line pressure tables. They were already mild to begin with. OE line pressure constants & tables aimed for unrealistic MpGs, at the cost of the 4L60E's longevity.

Okay thanks I’ll have a look and maybe give this bin a try. What exactly did you change and if you can give me a reason I want to know. I’m always looking to learn in addition to just finding a solution.

I adjusted the speedo scalars for 26" tires & 3.73 (more precise tire measurements - between 25.5?" & 26.5?" - would help, or err a wee lil bit on the tall side), and the upper limit speeds in the 'Normal', 'Performance', 'Manual', 'Cruise', & 'KickDown' tables, as well as the 1st gear limit constants. You can do much more to improve the rest of the shift table speeds, of course - GM has always been beholden to CAFE MpG test results. Even GM's Performance Mode table is pretty lame.
At sufficiently high throttle angles, setting the KickDown constants so that shifts reference RpM instead of MpH is safer for the engine.
At lower throttle angles, MpH shift points are fine if the speedo constants are accurate enough.
Raise the max line pressure constant & main line pressure tables back to OE F-car specs, at a minimum.
If your wagon weighs enough, consider using the B-car 9C1 and/or the D-car V4P main line pressure tables; the lesser B- & D-cars also traded 4L60E longevity for MpGs only hypermilers would easily achieve.

[lionelhutz]

That started with the V4B bin then. OK, did you data log and check that the PCM speed is matching the real speed, using GPS or your phone?


Shift curves show that at 45mph it should go into 4th when below somewhere around 28% TPS.

[JD1964]

Even if a '79 Malibu wagon weighs a bit less than an F-car, I would not change the max line pressure constant (in part because it's not what you think!), or lower the main line pressure tables. They were already mild to begin with. OE line pressure constants & tables aimed for unrealistic MpGs, at the cost of the 4L60E's longevity.
I adjusted the speedo scalars for 26" tires & 3.73 (more precise tire measurements - between 25.5?" & 26.5?" - would help, or err a wee lil bit on the tall side), and the upper limit speeds in the 'Normal', 'Performance', 'Manual', 'Cruise', & 'KickDown' tables, as well as the 1st gear limit constants. You can do much more to improve the rest of the shift table speeds, of course - GM has always been beholden to CAFE MpG test results. Even GM's Performance Mode table is pretty lame.
At sufficiently high throttle angles, setting the KickDown constants so that shifts reference RpM instead of MpH is safer for the engine.
At lower throttle angles, MpH shift points are fine if the speedo constants are accurate enough.
Raise the max line pressure constant & main line pressure tables back to OE F-car specs, at a minimum.
If your wagon weighs enough, consider using the B-car 9C1 and/or the D-car V4P main line pressure tables; the lesser B- & D-cars also traded 4L60E longevity for MpGs only hypermilers would easily achieve.

Thanks for all this. Looking forward to loading the bin and doing some test runs.

BTW, I took a short test drive this morning before going to work. No warm up time, just started it up and pulled out. Under light throttle acceleration it shifted normally and timely from 1-2 but when I expected the shift to 3rd, it skipped 3rd and went directly to 4th. So, I pulled the shifter down a notch to force it in to 3rd and it did. Came to a stop and light throttle acceleration with the shifter in that position and it went 1-2-3, normally and timely. Continued to roll in third then bumped the shifter up to the 4th and it shifted to 4th. Came to a full stop with shifter in 4th, again, light throttle acceleration it went 1-2-3-4, normally and timely. Parked it and went to work.

So, for some reason it will sometimes skip 3rd upshift and go to 4th instead. It did this twice the previous day during WOT acceleration.

I have not been able to confirm converter lock up yet either. I think it may be possible that the mechanic who rebuilt the trans not too long before I acquired it may have built it as a non-lockup configuration. I'll try to figure that out but if there's anything anyone can share that might help me determine that, it would be great.

[JD1964]

That started with the V4B bin then. OK, did you data log and check that the PCM speed is matching the real speed, using GPS or your phone?


Shift curves show that at 45mph it should go into 4th when below somewhere around 28% TPS.

Well, it's true that I copied numbers from the V4B bin and modified my original bin with them and loaded it. However, I did not drive the car previously with the original bin. I do have a saved copy of it though. So, I can't say for sure if the V4B bin data has anything to do with the shifting issues or not.

I plan to do data logging and share it as this process continues. Thanks for the tip in comparing GPS speed with data stream speed from PCM. Great idea!

[lionelhutz]

I've read before that the V4P bin transmission control can't be copied by copying the known transmission tables from that bin to another bin because there are differences that are not part of those tables and possibly some unknown stuff that makes it work. I'm not sure how true this is or not.

[JD1964]

I've read before that the V4P bin transmission control can't be copied by copying the known transmission tables from that bin to another bin because there are differences that are not part of those tables and possibly some unknown stuff that makes it work. I'm not sure how true this is or not.

In addition to trying the modified bin LeMarky did I suppose I could also try the entire V4P bin instead of copying and pasting data from individual tables. Of course ill need to set the speedo scaler for my car

[LeMarky Dissod]

I've read before that the V4P bin transmission control can't be copied by copying the known transmission tables from that bin to another bin because there are differences that are not part of those tables and possibly some unknown stuff that makes it work. I'm not sure how true this is or not.

$EE probably still has some undiscovered country left to be defined.

In addition to trying the modified bin LeMarky did I suppose I could also try the entire V4P bin instead of copying and pasting data from individual tables. Of course ill need to set the speedo scaler for my car.

Feel free to copy the speedo scalar from the made-in-crews bin over to whatever bin you use.

[JD1964]

I think I have a problem with the TCC circuit at the brake pedal switch. The circuit remains open even when the pedal is not depressed. I’ve got 12v to one side of the switch but it doesn’t travel through with brake off.

I’m thinking that might be contributing to the weird shifting behavior. What do you think?

[tayto]

you need to run a separate brake switch that has NC contacts. if not your brake switch needs to run a relay and run your TCC circuit through the NC contacts. Those cars came with TH350C or TH200C so you should be able to use factory switch and wiring to make your life easier

EDIT: been a while since i've looked at a factory brake switch but i believe the switch has NO contacts for the brake lights and NC contact for lockup all in the same switch...

[lionelhutz]

I didn't install a brake switch. I have full time power to the circuit. I jumped it because I wanted to drive the car and since it has always worked fine so I have never changed it.

I can't see it affecting the shifts.