Well guys, here is my story. A year ago I did a h/c combo on the car and have been pushing 450+rwhp on the stock tranny. Afew months ago I did a sk-4L60E shift kit from Transgo and the trans felt really strong. A few weeks ago I noticed that I no longer had 4th gear, or OD, 3rd would just keep climbing. This was expected as I had done plenty of 4th gear runs on the car and I knew its days were numbered. So, we did a simple rebuild but we added more clutches, a stronger sunshell from a 700r4, a wider 1-2 band, drilled out wider fluid passages, pump, booster valve, rev kit and a Jet billet servo for 4th gear. When we put it in the car right off the bat 2nd gear would tag the limiter before getting into 3rd. We tried to mess with shift points and nothing. We dropped the pan and found the filter was cracked at the base of the neck that goes into the valve body. Valve body checked out ok, new filter, and the car ran really strong. Then, 3 days later, driving normal, BAM, broke the lugs off the drum, no 3rd or 4th. I said "maybe the damage had been done with the cracked filter starving the trans". Ok, rebuild number 2. Got it back into car, ran great and shifted nice and firm.Ran perfect for a whole week then all of a sudden 2-3 shift got really really hard. I even thought I hit a pothole! This was only happening at partial throttle not WOT. Next day I was test driving it going slow then all of a sudden no 3rd or 4th, broken drum again. Rebuild #3!!! We're really scratching our heads on this one. All parts and valve body looked good and air tested fine. No symptons or problems from the get go, problems seem to just ahppen all of a sudden. No codes or anything. Rear diff is fine, torque tube is fine, fluid level has always been good. This time we are replacing most of the valve body components back to stock since we feel it may be a vb pressure issue. I hope this takes care of the problem. Has anyone here experienced this before? Ive done many searches in many forums and the net and have found nothing exactly happening like it is in my case. If anyone has any suggestions or has been through this before please let me know. Thnx.

 

SOUNDS Like you need to send it to rpm for a upgrade

 

loctite?

 

Your car is a Coupe and your mods list Z06 - 3:42 gears. Did you ever reprogram the new gear ratio into the PCM? Did you change tire sizes?

Just throwin' out ideas here.

Good Luck.

 

Sell the car and buy one with a manual tranny. Autotrans are for Buicks and Caddys not Corvettes.

 

Sounds to me like you are using inferior parts or are making some kind of assembly era. To keep breaking the same part over and over at your power level seems, strange.

A well built 4L60E should last a long time at your power level. Guys are putting 800 -1000 rwhp not to mention torque thru their 4L60's without busting them up the way you do.

I think it's time to send it out to a professional shop like RPM for a proper rebuilt.

 

Yeah, long long time ago. That was all done at the same time.

 

Hardy har har. I'll put my stalled auto vs any stick, let me fix it first.

 

It was done by a very reputable builder. We used all the best parts I assure you. This is why its so wierd. Im wondering if the ecu is having brain farts and thinks the car is slipping so it boosts the pressures up too high. IDK. Just got the car back, shifts softer but still feels firm. All good so far.

 

Wasn't implying that you or your builder were not reputable. Sometimes it takes an outside person to figure out what you're doing wrong, if you know what I mean.

If your ECU was having brain farts you'd be getting a crap load of codes and since you aren't, I don't think that's where you problem is.

Obviously, if using to much line pressure, that could cause some problems, but to keep breaking the lugs of the drum tells me there some type of tolerance problem or you're very unlucky.

 

I noticed that if you do not change your shift time table in your tune to "0.00" and bring your shift pressure tables closer to stock level, this will happen on most 4L60E's that have a shift kit.

It will burn up 3rd and 4th every time.

 

I know what you mean and I have had another tech/builder look at it and he's just as confused as us. As for tolerance, I think I'd feel it right away but the car drove fine for a whole week this last time. I think a tolerance problem would evidence itself right away.

 

I was thinking the same thing but this time around most of the shift valves and vb components are stock with a few exceptions. This should mean that the vb psi should only be 10% higher than stock(we brought it up with the tuner before). If I feel something wierd I'll bring those tables down to 0 right away.

 

That's why it's better to go with one that has a warranty, instead of racking your brain out.

 

I hear yah but the guy has been really cool. He did the second rebuild at no charge and this time I only paid for a few parts. He does back his stuff up even though we arent exactly sure where the problem is. Still, I like knowing and figuring out whats going on or what went wrong.

 

Not saying he ain't a great builder but sometimes you need to try something else. I would like to know what is causing the problem too, so that I can avoid that pit-fall too.

 

I will post what we find if anything. I havent seen anyone else post something like this so I'll try to lend a hand and voice of advice as one of the first...I guess.

 

As a second opinion, may I ask you why this might be needed? Thnx

 

shift kits are never the way to go. Im speaking back even from the early 90s with IROCs and TransAms..transgo shift kits ruins the tranny

 

Have you checked line pressure? I have a ST3500 with an RPM trans with 430 RWHP and I can tell you it doesn't shift hard. It sounds to me like a hydralic problem and not ECU as you are not setting codes. If the ECU detects slipage it will raise the line pressure and set a check engine light.

Good Luck and keep us updated as this is a unusual problem.

Mike V