TH400 PROBLEM

shvrolay

Dragway Regular
This TH400 is behind a ZZ502. Transmission has maybe 2000 miles on a 'performance' rebuild by a reputable builder in Columbus, Ohio.
At WOT the trans shifts 1st - 2nd nicely, but 2nd - 3rd it will not engage 3rd gear (acts like it is in neutral) unless I let off the gas...when it does go into 3rd I can get back on the gas and there is no slippage that I can determine. It makes no difference if the trans is being shifted manually or left in Drive. It only does this at WOT........normal cruising - it will shift into 3rd altho that shift is really 'soft'..........softer than it was when behind the 396 mentioned below.
One other thing - after this trans was rebuilt, it sat covered/plugged in heated storage for about 5 years before being put in the car. It was then installed behind a mild 396 and never showed this problem for 2 summers of street driving. It has a Coan 2600 to 2800 converter - http://www.coanracing.com/Catalog.asp?ProductDetail=568 (COA-20210).
Shifter linkage is adjusted correctly, trans fluid appears normal........
Any helpful ideas as to what is causing this?
Thanks for taking the time to read through the post.
 
Last edited by a moderator:

shvrolay

Dragway Regular
Thread starter
I'm hoping it's something along this line. I don't think the trans is hurt since the fluid looks/smells as new, and no 'debris' in the pan.
Thanks for the reply.
 

shvrolay

Dragway Regular
Thread starter
Yes.........this was one of the first things I checked.

After some reading online........looks like it might be either the 2 3 shift valve or the 2 3 accumulator.
Your thoughts ?
I do appreciate you taking the time to answer the post.
 
A sticking shift valve was going to be my next suggestion. I would drop the valve body and check the shift valves. It doesn't take much for one to stick. Usually a simple cleaning and polishing of the valves will do the trick as long as the valves and/or bores aren't scored or worn excessively. Make sure you take careful note of check ball placement if you decide to drop the valve body.
 

shvrolay

Dragway Regular
Thread starter
Thanks Pete. I appreciate the comeback.......
 

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