Reserector

***SOLVED*** Jump to this post: https://ls1tech.com/forums/automatic...l#post19752210

You may think this dead horse has been beaten, but after exhaustive searching, I still have not solved this.
4l60e that I rebuilt after the sun shell stripped. Before that happened, the only thing wrong was a slow, slipping 2-3 shift at WOT. But id did shift. It was just tired and in need of a rebuild.

Now, it shifts great during normal driving. It even did a WOT 2-3 shift the other day when passing, and grabbed third like a champ. But from a launch, it will rev to the limiter. I have to let it wind back down to 2K for it to upshift, and continue on.

Here's what I have tried:
Programmed mph and RPM settings changed. MPH lowered, RPM lowered, etc. No improvement.
Scan tool indicates no codes
Scan tool indicates that the PCM is calling for 3rd gear.
I tried overfilling by as much as 1 qt.

I have not put a pressure gauge on it. Mainly because I am fairly convinced that it is not a pressure issue. But I'm willing to try, if anyone thinks that will yield some clues.

I guess my question is this; What is different at WOT that could cause it not to shift? Does the valve move differently? Is there another circuit or clutch that comes into play? What else can I check to give me more clues?

I read one thread where the problem was solved by fixing a knock sensor wire. But I have no codes in any systems at this time.

I'm at a dead end, and need some ideas.

Game ova

How many times have you tried to get it to make the 2-3 shift? I ask because I had a sticking 2-3 shift valve when I first built my tranny that resolved itself after about 10 miles of driving (different transmission same principle). And I saw you say it only happens wot... but sometimes those shift valves do odd things.

Reserector

I've tried several times. I would make an adjustment, and try again. Over and over.

I wonder if a sliver of metal from the stripped sun shell splines remained in the valve body, or something. That's why I'm wondering what happens during wot that doesn't happen normally. That would give me something specific to check.

I am always hopeful that it will resolve itself. I wouldn't be surprised if it did.

01ssreda4

iTrader: (96)

If the computer is commanding it and it aint doing it its an internal problem!

Reserector

I am starting to wonder if the "no 2-3 shift" at high rpm is akin to the 2-3 flare that I had before the rebuild. But instead of being a slow shift, it became a NO shift.
Maybe too much slack in the servo apply pin? Not enough slack?

None of the shifts feel mushy, nor does it slip during the "no shift".

Reserector

I've been going through this Tech Guide, and learning a lot, but still at a loss as to what is different about the 2-3 shift at high RPM. The search continues. The struggle is real.

bbond105

There is more of a load on the clutches when accelerating at high RPMs then there would be if accelerating at a slower rate.

thirdgen rs

I have been struggling with this same problem on my 98 camaro. I bought the car stock and would not shift in to 3rd at w.o.t. and just figured the trans was tired. I Tore down trans and found the 3-4 clutches to be burnt. I rebuilt
trans and installed the sonnax smart tech input drum and had finish line transset the clutch stack with the b/w hi energy fibers and there steels. I used the sonnax performance pack, sonnax smart shell, sonnax super hold 2nd and 4th servo kit.hd 2-3 shift valve kit.wide band,all new sol. installed truck deep pan and filter, 4l70 5 planet pinions. trans now has a precision 3600 lock up converter. After rebuild i still have same issue. It shifts normal part throttlejust will not shift 2-3 w.o.t. fluid looks nice and clean. I did find with mass air flow sensor unplugged trans will shift into 3rd w.o.t. replaced maf and stillsame. I have hp tunner and have adjusted shift speeds way down and rpmsdown no diff. my car is just a bolt on car so have not played with engine tunning. I have recently messaged frost tuning to see if a tune would take care of this issue. he said it sounds like and trans going bad to him.

Reserector

I was suspicious of my servo. I was thinking that if the band is not releasing it will not make the shift. That may still be the case, but I crawled under the truck last night and checked it. Range is supposed to be .075" to .125", and it is right around .100"

I'm intrigued by what you said about the MAF sensor. I will unplug mine and see if I get the same results as you. If I do, then maybe we can go from there.

My scan tool does show that it is in gear 3 when it is supposed to be, but it is not. My tool either doesn't show shift servo status, or I am not using it right, because the readings don't change as it shifts. I may have to hook a test meter to it somehow to verify.

Reserector

I disconnected my MAF tonight, and tried it, but it still didn't make the shift.

Reserector

Just this morning, I was doing 55 when I started to pass on the highway. It kicked down to 2nd, accelerated to about 65 or so, and made a beautiful 2-3 shift. Quick and firm.

It just won't do it from lower speeds.

Reserector

It's been a while since my last update, but I am still trying to cypher this.
I put a pressure gauge on it, and have been monitoring line pressure. The first thing I noticed was that when I start the engine, it goes to 75, but a couple seconds later, it jumps back down to 50. It will rise with throttle, but appears to be regulated at 50.

While driving, I would see pressures as high as 225~250, depending on throttle and engine load. But I also noticed that the pressure was jumping all around for no apparent reason.
I read that the TPS has a major role in controlling pressure, and that when disconnected, would give full line pressure.
With TPS disconnected, pressure at idle was 125.

So, in spite of good voltage readings from the TPS on my scan tool, I opted to replace it anyway.

The old TPS felt a bit loose when I rotated it by hand. The new one had some drag. I suspected it might be moving in reaction to bumps on the road, and it turns out I was right. The new TPS smoothed out the pressure changes.

It did not, however, increase the base pressure, nor did it fix my reluctant 2-3 shift, although is has improved a bit.

Another clue is that reverse has the same base pressure. 50 psi.

That got me searching, and I came across a thread where a guy had a similar problem. He reported the same pressures, but his 2-3 shift had a flare. Here's the link: http://www.justanswer.com/gmc/9y87r-...-pressure.html

One thing he did that helped fix his problem was to adjust the Pressure Solenoid 1/3 turn. He did not say what his pressures were after that, though.

I'm considering making such an adjustment, but I have to wonder if it is a bad solenoid, or another problem.
Could the solenoid just need replacement?

joecar

Can we take a look at your tune file...?

Reserector

I suppose I could download a file from my Diablosport Predator. That's all I have. Would that help? What format should the file be in?
There aren't many variables with it. I mainly got it to correct for gearing and tires.

I also have a Launch C-reader (123) that I can use to read some of the trans data.

joecar

No, that won't help.

Does it have separate parameters for WOT 2->3 upshift MPH and WOT 3->2 downshift MPH... what are these values...?

Reserector

It does. Also has shift RPM, and RPM vs TP . I'll list them after work. I'm still here for a couple more hours.

Reserector

2-3 Upshift RPM 4,500 (It started out at 5200)
2-3 Upshift MPH 42.97
3-2 Downshift MPH 62.98

No other settings are currently altered from stock aside from tire size and gearing. (to make speedometer / odometer corrections)

joecar

Those are upside down... this prevents the WOT upshift.

Reserector

Those settings worked before the rebuild, but nonetheless, I got excited, put on my slippers, and headed out to the truck to swap some numbers and see.

upshift 59.97
downshift 56.98

It still didn't make the 2-3 WOT shift from a low speed start. :-(
I'm going to try some slightly different numbers, and then call it a night. Don't want to do too many pulls this late. Sheriff needs his sleep, too. ;-)

Reserector

Last attempt of the night was:
upshift 64.97
downshift 62.98 because that's a sweet spot for my gearing.

It still didn't make the 2-3 during a hard pull, but from 58 mph it kicked down, pulled hard, and barked the tires at 65 as it shifted into third with authority.

​​​​​​Going to bed now. Beaten, but not defeated.