TH 400 Question

[gem66]

I have a TH400 transmission problem that I would like some opinions on. It is a reverse pattern manual valve body with (I believe) TCI rebuild components. The problem is this, after 1 run in the eighth mile (or a full 3rd gear pull on the chassis dyno), 3rd gear begins to slip and I lose reverse temporarily. The third gear slip is that the torque converter stalls about 300-500rpm higher. Reverse is like shifting to neutral. After a few minutes of shifting to first, neutral, and reverse it will finally start to work in reverse. It will then shift in with a firm clunk just like the forward gears. I am interested in ideas of what is happening internally rather than 'take it back where you got it' responses. Thanks

[gem66]

I have a TH400 transmission problem that I would like some opinions on. It is a reverse pattern manual valve body with (I believe) TCI rebuild components. The problem is this, after 1 run in the eighth mile (or a full 3rd gear pull on the chassis dyno), 3rd gear begins to slip and I lose reverse temporarily. The third gear slip is that the torque converter stalls about 300-500rpm higher. Reverse is like shifting to neutral. After a few minutes of shifting to first, neutral, and reverse it will finally start to work in reverse. It will then shift in with a firm clunk just like the forward gears. I am interested in ideas of what is happening internally rather than 'take it back where you got it' responses. Thanks

[nasty66gto]

Use the Sonnax PR boost sleeve and PR valve, use red Alto frictions, make sure the bushing in the center support is in like-new condition, keep end-play to minimum allowed, check high gear drum for ring groves
leave the second from the top ring off on the center support .Makes for a lot more apply area and more volume of fluid if all of this checks right
than send vb back to tci may have internal leak

[ErikW]

Leave the TOP ring off of the center support? NO! Second ring!

[superdutydave]

Sorry, but sound like 1st/rev band clutch gone or was a screwey rebuild (I assume it is a tranny you bought/was in car you bought) and/or valve body is messed up. Take to a reputable(?) trans guy and just hav them chk & rebld it.

[nasty66gto]

yes the second my fault leave the second ring off the center support and leave the lip seal out of the drum
this will give more apply oil to the piston

[screamingchief]

Belive if you remove the lip seal in the direct clutch as stated your also supposed to block the reverse passage to prevent backfeeding reverse while in third,this is shown on page 210 of the turbo hydramatic 400 trans book written by Ron Sessions (very good book for anyone into trannies)don't know for sure if thats it but might not hurt to check?

[gem66]

Thank you all very much for your replies. I just bought Ron Sessions book, and will look into this modification.

[nasty66gto]

That is correct you need block the feed off

do this on all my high performance units

[gem66]

If there was a problem with this pressure, would it show on pressure gauge connected to the diagnostic port? If it was the pressure regulator, would it be low pressure in all gears? What would be a 'good' pressure reading in 3rd gear? If I could narrow this down to most likely the valve body, I wouldn't have to take the trans apart. What do you think?

[screamingchief]

In theory the pressure gauge should show it if the problem is fairly major, smaller leaks can sometimes not be picked up,but for the most part it should read it.Yes a pressure regulator problem would be evident in all ranges,could also be plugged filter or cooler, other possible causes too.A "good" reading would probably be a minimum of 150 psi., and probably closer to 200 psi. on a manual valvebody trans,depending on variables like altitude etc.