Slow Acceleration Only - 2nd to 3rd Shift Acts Up

[wildcatgoal]

Only when I'm accelerating slow - like in stop and go traffic and I'm not being Boy Race Driver - my transmission (once hot) will almost skip shift from 2nd to 3rd. Like it comes out of 2nd for sure but then sort of revs up some then finally 3rd catches. There's no jolt or bangs -- it's smooth it's just obvious because I have a louder exhaust and it revs up some between those shifts randomly. Not always. Which servo or doo-dad controls that particular action?

 

[Bill 1960]

I don’t have the answer but I had a similar issue. Mine would shift OK under light throttle but hang in 2 under heavy throttle. I went to 2 shops and all they wanted to do was swap the transmission. Nobody was interested in trying to diagnose and replace the failed part.

 

[wildcatgoal]

Well, what I'm picking up in my research is that it could be a number of things. The 2-3 shift apparently involves a lot of things to work right. One thing apparently overlooked is the servo. If there is wear on the metal parts of the servo, it may not work right causing this issue. I just put in a Corvette servo but that kit doesn't include ALL of the hard parts in the entire assembly like the pin and some of the other metal pieces, just the replacement Corvette pieces. I don't remember seeing wear on my reused pieces, but perhaps there was some wear.

 

[exp500]

Is your MAP sensor reading perfect?

 

[Mudsport96]

Is it the original 60e? It may be that clutches are just worn out.

When was the last flush and filter change? Possible that the 2>3 shift valve is sticky and taking too long to slide. Is there a 3>2 shift lag?


How many miles? Could be a worn separator plate and the check balls arent sealing properly.


And i hate to be the one to ask, but, is the fluid full? Ive been there before, swearing ive checked something and had forgotten to.

 

[wildcatgoal]

Fluid is full, no leaks. 3-2 downshift is as normal as I have the information for... it'll manually downshift from 3-2 and if I need to go from 3-2 in driving it does it just fine. I'm not going to say it's the fastest action, but it's an ancient transmission design... not a Porsche.

I have replaced all the solenoids and all the other doo-dads you can swap from under the car without removing the valve body and what not in a hail mary attempt. Also added a Corvette servo. It did improve after that (1-2 shift is smooth as butter now, for example). During that process, I did a (12QT) bypass fluid flush with Valvoline Multi-Vehicle ATF (Dextron IV compatible). The old fluid wasn't in bad shape (no smells, normal discoloration, no sparklies) and the pan didn't have much to speak of in it. I have no codes. The MAF was cleaned and scan data indicates it's working as it should, based on the information I have. Cleaning the MAF made the truck run a little better and improved fuel economy (by the numbers---I use an app to track). I also - since it was cheap and easy - replaced the TPS with a new AC Delco part... nothing changed from that but I didn't think it would. My thinking is I should find a way to reset the learned trans parameters before I spend big money on a rebuild. Maybe the computer needs to start over from a baseline... going to have to do that if I put in a rebuild anyway. Can only do with a GM tool.

It is the original trans at 204K. Truck was originally owned by a GM mechanic, then sold to guy who drove it to work and spent time literally toothbrush washing the engine bay kind of care. I don't expect the 4L60E to be in brand new shape right now but I am ONLY having this 2-3 shift weirdness after the work I've done to it. Again, it's totally driveable so I'm somewhat trying to avoid spending $1600 on a rebuild and doing all that swap work. I do need a new rear main which is why I'm motivated to consider it.