Shifting Issue 99 Z28
Thread Starter
Registered User
Joined: May 2014
Posts: 14
Likes: 0
From: Concord, NC
Shifting Issue 99 Z28 So quick question for everyone, I have a 99 Z28 has the 4L60E. On occasion it shifts hard normally but when it rains its even worse sometimes it will make the whole car jerk rain or no rain. Anyone ever heard of this? I'm not getting any trans codes or anything on testers. Could this actually be an axle or gear issue?
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
If it really is related to rain, I would suspect a bad connection, perhaps to the VSS.
If the VSS (and speedometer) briefly read a low value, the PCM may detect that as slippage and set max line pressure in an attempt to reduce slippage. The max line pressure will give you hard shifts.
If it is only the 1-2 shift and not related to rain, and no codes, I would suspect a cracked piston in the 1-2 accumulator.
If the VSS (and speedometer) briefly read a low value, the PCM may detect that as slippage and set max line pressure in an attempt to reduce slippage. The max line pressure will give you hard shifts.
If it is only the 1-2 shift and not related to rain, and no codes, I would suspect a cracked piston in the 1-2 accumulator.
Thread Starter
Registered User
Joined: May 2014
Posts: 14
Likes: 0
From: Concord, NC
Hmm I might have to look into that. I know when I manually shift it and i get up in higher rpms and shift from 1st to 2nd or 2nd to 3rd it makes a slight almost like blow off valve wease. Its just a real quick sound. My traction control does click on when it shifts hard in the rain though. I thought it could have been a tire issue and no traction cause my tires were wore down but i got new tires and it was still doing the same. Thanks for the response I'll look into what you mentioned.
As odd as it sounds, I had a pcm that wasn't sealed properly and would leak water into the case... it would cause all kinds of shifting issues in the rain, and only in the rain... The way I found it, I was on a trip to Orlando, it rained hard over night... we got up to head to Disney the next day and halfway there, the car went nuts... 2nd gear only, misfiring, dash lit up like a christmas tree... during troubleshooting, we pulled the pcm to swap into my buddies car which was also a Trans Am, when we pulled it out of the holder, water started running out of the pcm... I will say that after we dried it out with a hair dryer from the condo, it worked perfectly and lived in a walmart bag for the duration of the trip... after being sealed up properly, it's still in the car to this day...
Thread Starter
Registered User
Joined: May 2014
Posts: 14
Likes: 0
From: Concord, NC
Nice I'll look into that to. At this point in time I'm accepting all ideas. I just want to get the issue fixed. Thanks for the help so far. I'll look into these things within the next few days and let you all know what I find.
