Hi everybody I'm new here. I've searched Google and here and I can't seem to find somebody with the same trans issue.

First the background: 94 Z28, 54,043 Miles. The guy I bought it from didn't test drive it due to weather. When he does drive it home he gets on the highway and he said the trans was slipping. So he takes it to a trans shop and has the following done (he gave me the invoice) from the invoice: Transmission rebuilt, stage 1 shift kit, Corvette servo, 6 clutch plates and upgraded solenoids.

Now I buy the car with 55,200 miles on it and it drives perfect..... Until I floor it from random cruising speeds including 70-75 mph on the highway. Intermittently it acts like it goes to neutral and just pegs the rev limiter. Other times under the exact same conditions it performs the kickdown properly! I am stumped.

The trans was done in Sept 2013!

Fluid is up and clean no engine light on the dash and always shifts properly just driving the car regular.

So I'm leaning towards the rebuild didn't address the problem at all?

Thank you in advance for any insight or suggestions.

 

Sounds like the forward clutch sprag is slipping.

 

Thank you for your opinion.

 

Overfill the fluid by 1/2 quart and see if the problem goes away. I just had this problem on my transmission.

 

If the 1/2 quart overfill doesn't work, try to determine if it is slipping in all gears or only e.g. 3rd gear.
We've had a few cases of the forward sprag slipping, but usually it just breaks and then you have no forward motion in [D3] or [OD].
Slipping in 3rd gear is the most common complaint mentioned here.

 

I will try that. FWIW it really is like it's going into neutral, it just pegs the limiter and the car does not try to accelerate.

I do appreciate the help, I will follow up once I decide on a trans shop, I'm a little leery of going back to the shop that already did it once!

 

Years ago when I worked at a Chevy dealership and the 700R4 was a couple of years old this issue occurred.The customers complaint was when trying to pass another vehicle at wot, the transmission would go into neutral.
After disassembling the unit, I found that the reverse input drum was flared out so bad it was cutting into the transmission case. The forward sprag would hold by hand, and when normal driving. I'm sure 700R4 and 4L60E builders have seen this happen many times.

 

Whoa! Could that happen in such a short time? Or is that input drum not replaced on a rebuild?

 

So far your issue does not sound like a problem with either the input drum or the reverse drum. The input drum is rarely replaced during a rebuild as it is not a wear item. The reverse drum is sometimes replaced because the band wears against it.

Give us more info about what gears slip and we will go from there.

 

Other than acting like going into neutral instead of kicking down, it really does perform perfectly. Light turns green it shifts 234, light turns red it shifts 321. Basically if I never floored it I wouldn't know I have an issue. I'm meeting with the guy that rebuilt it Monday morning. Even though I'm not his customer I'm giving him the opportunity to stand behind his work. It's just over 621 miles on the rebuild!

 

Hooking with the trans builder is a good plan.
Presumably he will connect a scanner and a pressure gauge and take it for a test drive.
It is hard to diagnose these problems from just a description.