2005 Chevy Corvette A4 is skipping 2nd gear.

I recently bought this C6 Corvette (Edelbrock E-force supercharger, billy boat headers) about 2 months ago in a no-run condition fitted with a new cam, and head into it. It ran well, I've noticed it doesn't go into 2nd gear and skips into third. Thinking it was a mechanical problem I data logged the condition. When coming to a right turn I did notice it started in 2nd gear, but after revving it out to 4500 rpm it ultimately skipped 3rd gear and went into 4th gear (I have to let go of the throttle for it to shift at all.) Now here's the question, will this be a mechanical or an electrical problem? since I've seen all the gears go in I'm thinking it might be a servo pin problem since the clearances might be off. Or maybe the transmission is just going out. I'll post the data log and see if anyone can point me in the right direction. I do have an upgraded Corvette servo with a longer pin ready to go in but am hesitant to do so in case someone else on here has had the same problem.
Thanks,
Jeff.

You have too much band clearance, most likely the band is worn out. Can't tell much in the log since you did not record any of the transmission PIDs but there is enough in there to see that you have no 2nd but good 3rd and 4th.

Is the pan siliconed on or does it have a cheapo am gasket? Don't remember which gear was affected but the drain hole for the servo is right there and could get plugged.

Robert, I'm probably wrong as it's been a long while since I worked on one, but wouldn't you lose 4th gear too as it's a 2-4 servo? Of course only half of it's that if memory serves. Anchor pins would break too. You have to pull the valve body for that if the band is good.

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Originally Posted by GHuggins

Is the pan siliconed on or does it have a cheapo am gasket? Don't remember which gear was affected but the drain hole for the servo is right there and could get plugged.

Robert, I'm probably wrong as it's been a long while since I worked on one, but wouldn't you lose 4th gear too as it's a 2-4 servo? Of course only half of it's that if memory serves. Anchor pins would break too. You have to pull the valve body for that if the band is good.

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No, because what happens is the second servo bottoms out on the case so you get no 2nd. Then when it goes to 4th, it then pushes on the 4th piston in the cover that pushes directly on the pin straight through the 2nd servo that can't move and goes and apply the band for 4th. You have almost double the travle possible for the 4th piston then the 2nd piston.

Quote:

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Originally Posted by GHuggins

Is the pan siliconed on or does it have a cheapo am gasket? Don't remember which gear was affected but the drain hole for the servo is right there and could get plugged.

Robert, I'm probably wrong as it's been a long while since I worked on one, but wouldn't you lose 4th gear too as it's a 2-4 servo? Of course only half of it's that if memory serves. Anchor pins would break too. You have to pull the valve body for that if the band is good.

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There are two different pistons inside of the servo bore that drive the servo pin 2nd being the weaker of the 2

Robert must be right. I am pulling a 4L apart this weekend. I will be checking if the second apply piston bottoms out earlier than the 4th :]

Well I did say I was probably wrong. I remember there being 2 pistons. Just didn't remember which did what. Been years :) I just recalled one where I put the shorter pin as there were 3 available and just with that little bit of difference I had no 4th or 2nd. Just slipped in those. Swapped the pin back out to the middle length one and all was good again. Also remember you could flip the one piston, although I don't remember which gear you would have issues with doing that either. Been over a decade and a lots happened since then. I do have "GM's" operation and complete tear down books somewhere around here for them that shows the flow charts and everything else, "somewhere" :)

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Originally Posted by Guy With A Chevy

There are two different pistons inside of the servo bore that drive the servo pin 2nd being the weaker of the 2

Robert must be right. I am pulling a 4L apart this weekend. I will be checking if the second apply piston bottoms out earlier than the 4th :]

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The 4th servo area could be bigger or smaller than the second servo depending on which second servo is in there. The 4th is about 5 square inches. Second varies as laid out in this screenshot:
Attachment 142748

When you have the unit apart, put the servo in the empty case with no seals, no return spring between the 2nd servo and case and no cover. Push the servo in until the second servo bottoms out against the case, and then push on the 4th servo and you will see just how much more travel you get. Probably 1/4" or more going from memory.

Update, so I ended up caving and pulled out the trans and inspected. The reverse input drum was toast band looked in ok condition. New drum, and band and frictions/steels while I was in there. Runs like a top. Car was leaking from the trans when I bought it. Previous owner must?ve ran low on fluid.

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Originally Posted by jeff7633

Update, so I ended up caving and pulled out the trans and inspected. The reverse input drum was toast band looked in ok condition. New drum, and band and frictions/steels while I was in there. Runs like a top. Car was leaking from the trans when I bought it. Previous owner must?ve ran low on fluid.

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Glad you got it working. Thanks for taking the time to post the fix.