Vicious 1-2 Shift on 4L60E.

[Fireball5657]

what is the # on your accumulator housing? 94 should NOT have dual springs unless you are using a late housing. do you know the colours? with the piston against the separator plate a stiffer spring actually makes a softer shift in this instance...

did you play around with the separator plate holes or install an aftermarket servo? was the 2-4 servo pin travel checked? a loose band can cause a harsh 1-2 shift...

Not sure of the part number, the inside spring was green and the outside spring was black. I didn't touch anything else, and I'm not familiar enough with transmissions to tell you about the servo pin.

 

[Fireball5657]

Update: New PCM installed, PROM swapped, absolutely nothing changed. Still shifts crazy hard 1-2.

I may try testing the EPC solenoid itself next, if it's not that then it must be something deeper in the transmission.

 

[1997]

did you follow the service manual for checking the all the solenoids when you had the ECU out?
it gives you the specs (ohms) for them, might save you digging into the trans.

 

[tayto]

i don't think this is going to be an electrical or sensor issue. i would get an extra set of servo seals and servo cover seal, so you can pull the servo out and measure the servo pin travel. anything over 1/8" is to much..I don't care what GM or any run of the mill transmission shop says. I run them .060-.075" on a new band.

running the sonnax pinless accumulator piston isn't helping things either. by design its taller, so the stroke is reduced and a firmer shift is the result. like I said, you want to run a STIFFER spring for a SOFTER shift with how you have the 1-2 accumulator stacked up. i have a feeling you have the 2nd design housing and the inner spring is causing the piston to bottom out (shorten the stroke). the 3rd design actually has a pocket for the springs to sit into. if you are going back into the pan get the numbers off the accumulator housing and we can verify.

the last thing i would check is what the 1-2 shift hole is drilled at in the separator plate. this will require dropping the valve body unfortunately.

 

[E-gads]

I've been through what you are going through. 1999 Yukon new reman 4L60E with teeth rattling 1-2 shift. All other shifts were perfect. It can really grind you down. I found myself clinching and letting off the gas before every 1-2 shift. I tried taking the kit out of the 1-2 accumulator and returned it to stock, new trans electrical harness and new pressure switch and solenoids throughout. Nothing seemed to fix it. I had all but given up as I am not a transmission guy. Was actually getting ready to get a 4L80E from the junkyard and do that. Saw a video, I hate to admit that a Youtube video save the day, but The guy said to replace the throttle position sensor. I was skeptical and my TPS sensor seemed to be operating normally watching it on the scan tool. At least in a linear fashion, as far as I could tell. But desperate times call for desperate measures and I replaced it with an ACDelco one and it cured my harsh 1-2 shift. Now keep in mind that this was on a 1999 Yukon. I don't know if that will be the same for a 1994. Just thought I'd throw that out there. I know, feels a little crazy, but if you think about it, there is definitely some logic behind it. I just don't know if that applies to a 1994. I've owned a 1997 Hoe and a 1999 Yukon and there are differences between those years. You have Throttle body injection, I think, and its OBDI vs OBDII. The sad part of my story is that I really wanted to do the 4L80E upgrade and now I don't have a legit reason to do it.

 

[Urban Cowboy]

I have a 97 with a 4L60e that was supposed to have been rebuilt. I drove it for a couple weeks when I got it and it began shifting hard from first to second.
Forgive me as I don't really know the component terms, but the technician checked everything, and the problem was line pressure was not within acceptable parameters.
He said over time there was a valve/solenoid? that had worn it's cylinder from round to an egg shape. He got a kit which required boring the hole back to round, and replacing the part with a slightly larger diameter one.
That fixed the issue and it's been good for over two years now.

Hope this helps a bit.

 

[tayto]

I have a 97 with a 4L60e that was supposed to have been rebuilt. I drove it for a couple weeks when I got it and it began shifting hard from first to second.
Forgive me as I don't really know the component terms, but the technician checked everything, and the problem was line pressure was not within acceptable parameters.
He said over time there was a valve/solenoid? that had worn it's cylinder from round to an egg shape. He got a kit which required boring the hole back to round, and replacing the part with a slightly larger diameter one.
That fixed the issue and it's been good for over two years now.

Hope this helps a bit.

i am going to guess he was talking about the AFL valve. this is the problem with remans. they just put new clutches and seals in and send it.

 

[Scott Davison]

what is the # on your accumulator housing? 94 should NOT have dual springs unless you are using a late housing. do you know the colours? with the piston against the separator plate a stiffer spring actually makes a softer shift in this instance...

did you play around with the separator plate holes or install an aftermarket servo? was the 2-4 servo pin travel checked? a loose band can cause a harsh 1-2 shift...

You're on the right track. I've seen the check ball worn through and stuck in the seperator plate before. If it blew through the hole you'd have an enormous feed to the servo.

Hydraulics Fundamentals Part VIII: Check Valves

Read Part I , Part II, Part III, Part IV, Part V, Part VI and Part VII of the Hydraulics Fundamentals series.Some of the smallest valves in an automatic transmi

www.sonnax.com

 

[scott2093]

I just wanted to update the thread with some more information I've found.

Inside the transmission is an EPC solenoid. From what I've read, it controls the line pressure for the whole transmission. The PCM controls the amperage for this solenoid, as the amperage gets lower, the line pressure gets higher. As the amperage goes up, the line pressure gets lower. Sometimes the PCM can fail and set the EPC amperage much too low, causing the line pressure to go much higher than it should.

I watched a video of a guy who had a 1994 G30 with the TBI 350 and 4L60E, just like my truck has. He was diagnosing a harsh 1-2 shift. He hooked up a multimeter to the EPC control wire and a pressure gauge for the transmission fluid. Wouldn't you know it, the amperage from the PCM was closer to 0.3a rather than the 1.07a that it's intended to be at. This of course set the line pressure to well over 100 psi at idle. He swapped the PCM for a new one, changed the PROM chip, and now amperage was at the intended 1.07a, which made the line pressure go down to normal.

I figure it's a long shot, but I'll stick a multimeter to the wires tonight. Regardless of what I find, I'll probably just swap the PCM with a new one just to see if it changes anything. I don't want to tear into the transmission again just yet, so I'm trying everything I can think of on the engine and electrical side of things.

Let me know if anyone has any ideas, I'm determined to fix this now!

I got a pcm from ebay and I'll be darned if this wasn't exactly the case for me. With my computer everything was fine. Put the Ebay one in and it felt like I'd drop the transmission on the road every time it would shift. Did the test and 340mA on the circuit. 1.06A with my computer.
And scanner read everything was fine for both.
Here's the video of that guy doing the test..

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[fj40mon]

Update: New PCM installed, PROM swapped, absolutely nothing changed. Still shifts crazy hard 1-2.

I may try testing the EPC solenoid itself next, if it's not that then it must be something deeper in the transmission.

Fireball5657 I'm having this exact issue with a 95 silverado. What did you do to fix yours?