'97 Z28 4L60E, no 2-3 shift
 

Hey everyone...first I want to say I've been a long-time lurker, first time poster; just signed up today and looking forward to being part of the forum!

I have a 1997 Z28 w/ a 4L60E, original engine and transmission, 142,000 miles.

Recently I've been having some issues with the shifting...

Some Background:

A couple months ago I noticed that the car would "surge" a little when banking at around 45-55 mph, and also under moderate acceleration. No codes were thrown. I assumed this to be an air issue, so i pulled the K&N filter and cleaned it with their cleaner. No difference. I then replaced the fuel filter. No difference.

The following week, it got worse. I noticed that, when I was in cruise at highway speed, it would seem to hunt b/w 3rd & OD. When I popped it into D it would settle on 3rd gear and the RPMs would stop surging up and down. I drove it like this for a week while researching the issue online, but the following week, while I was cruising on the highway, it suddenly downshifted from 3rd to 2nd, and would not shift back up.

I made it home and decided to try replacing the TPS and cleaning the TB. No difference. In fact, now when I start the car it idles higher than before and slowly comes down to the 1000 rpm range. As soon as I shift it to N it sounds just fine.

Next I decided it may have been a shift solenoid, so I drained the tranny, pulled the 1-2/3-4 and 2-3 solenoids and got a good resistance reading (24 ohm) plus heard them click when I jumpered them w/ a 9V. I decided those were fine (perhaps I shouldn't have?) and I decided to try replacing the manifold pressure switch while I was in there.

So I did this, put on the new filter, gasket, etc...new fluid (RP, found a great deal on it) and tried it out. Still no shift into 3rd, although I must say, the 1-2 shift is smoother now.

So I'm thinking "great, a clutch pack is out and I need a rebuild."

Well, just yesterday I took it out again and, against my better judgement, I romped on it and it (roughly) shifted into 3rd! This makes me think that the clutch pack is probably ok and it's something else altogether. And that's where I'm at.

Also, the speedo is working, so I assume the VSS is fine.

Last week the car threw a P0161 (O2 sensor heater circuit malfunc) but that light went off yesterday when I floored it. Anyway that could be related?

I apologize for the ridiculously long first post, but I wanted to give a clear picture of what it's doing and what I've tried.

Anyone have any ideas? Thanks so much in advance for any insight you can give me!

Most likely seals in the clutch pack are failing. The higher line pressure from the high RPM made the failing seal, seal. Its most likely going to take a rebuild. If you take to someone to rebuild it make sure you take it to them while the car is still running and let them check it out and get their agreement on the issue. Once they agree then pull the tranny yourselfs and carry it in. Most tranny mechanics will feel the issue on a test drive but they can hook up a gage and look for a pressure drop to confirm the bad seal. Atlease we could in the 700R4's.

Thanks Gorn.

I've been fearing the "R" word, lol. I'm going to be taking it to a trans specialist this weekend, but I wanted to get a few more opinions before doing so.

Assuming it does need a rebuild, what else should I have them upgrade while in there? Should I have them replace the sun shell? (Isn't that part notorious for failure?) What do you think about a shift kit? Lock-up TC? Any other recommendations?

Thanks again!