I just came across this article regarding no 4th gear in a 4L80e I rebuilt. It had 4th gear after the rebuild for about 5k miles then lost 4th. At first I thought it was lock-up or a harness issue. I vacuum tested the valve body and checked the valves and springs, also replaced the TCC PWM solenoid, The unit ran fine in 1st, 2nd and 3rd with lockup. It was a stock rebuild with a Sonnax Sure Cure kit installed. I did use a Trans Go AFL reamer and valve instead of Sonnax. I am going to dual feed the direct and possibly delete the accumulators before reassembly. I am still inspecting the unit as of today. Here is the info...



What I did find was that the Sonnax 1-2 spring was much weaker then the OEM spring. Everything else I could test looks good; lip seals on piston and bolt air checked fine, shift solenoids and lock-up work in other gears...etc. No codes. Scanner shows 4th gear commanded. Here are the 1-2 springs, with OEM on the right;



I believe this weaker Sonnax spring to be the culprit. Does anyone have any other insight/thoughts before I assemble the unit and test it? I have a lot more experience with the 4L60e then the 4L80e.

 

1-2 shift solenoid is on when it first gear, and off in 2nd&3rd gear, so sll that seems to be working. I don't think these springs from sonnax are needed if you've repaired the AFL. i don't think it's your problem. have you tried basic things like shifter cable adjustment?

 

The Sonnax 1-2 & 2-3 shift valve springs come in both the sure cure kit and separately. They are different sized than the OE and should have a different rate than the OE. Have you measured the spring rate? Could you have mixed them up? The long one in the picture looks more like the 2-3 spring but i don't have a VB to compare to.
The Sonnax 1-2 is a 1.25" spring and the 2-3 is 1.69" and they have worked well for me in the past.

 

Someone else installed this, but I did tell him to check the shifter cable. He assures me that he did.

 

I thought that as well, but those are the correct springs. I will triple check it though. I will use the stock spring if correct.

 

Upon further inspection of the wiring harness I did find it kinked and a wire showing. Someone else had gone in there to put a longer reverse pin and did not route the harness properly. It's the wire for either the pwm solenoid or EPC. My own fault really, the servo pin was not long enough. It did have 4th gear before that and some time after. But if it had lockup in 3rd, why not 4th?

 

Have you reviewed the ATSG guide page 16? It lists possible causes of no OD.

 

Yes, it was the first thing I turned to. I am leaning towards the pinched wire or shifter cable (after I triple check the valve springs).

 

that wire definitely not good, keep us posted

 

... or PCM.

 

Springs for the 1-2 and 2-3 shift valves were correct.

 

I just wanted to update this post as the transmission now has 4th gear. I believe it was the shift solenoid.

 

seeing this more and more with guys reusing old noids (just too much fiction material has gone thru em and chewed em up. and most of the cheapest of the cheap china noids arent much better.

ask for (this is my bare minimum) rostra harness, pressure switch, rosta or toledo drivetrain for on/off noids (a&b) and borg or delco PWM noids

good luck yall

 

No, these were new solenoids when I initially rebuilt it. GM Genuine and AC Delco, not cheap solenoids. Sometimes even new reputable solenoids fail. I do use Rostra wire harness.