[Car!]

1972 TH 400 Trans. Professionally rebuilt (by a friend who's now out of the business)New clutches, shift kit installed and a big (BIG) trans cooler on 3/16's cooling lines. Fluid is up, no leaks, but it just started slipping.
When I start the car, drop it in drive I can feel the clutches try to engage but not quite get the pressure they need. If I shift into first it builds pressure and then can be shifted into drive and drives normally until I shut it off again.

My concerns are that the trans is running too cool, or that the valve body is coming loose.

[Car!]

1972 TH 400 Trans. Professionally rebuilt (by a friend who's now out of the business)New clutches, shift kit installed and a big (BIG) trans cooler on 3/16's cooling lines. Fluid is up, no leaks, but it just started slipping.
When I start the car, drop it in drive I can feel the clutches try to engage but not quite get the pressure they need. If I shift into first it builds pressure and then can be shifted into drive and drives normally until I shut it off again.

My concerns are that the trans is running too cool, or that the valve body is coming loose.

[PROBRD]

Don't worry about the tranny running too cold. Heat is what kills transmissions. Very well could be that the valve body has come loose. Pull the pan and check the bolts. Could also be the 1-2 accumulator valve is stuck or damaged in the valve body. Also could be a problem with the pump. Several things it could be. Try the easy ones first. If you still can't find the problem you may have to tear it apart and check the forward clutch pack and piston. Good luck.

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1/8th mile 6.56 @ 104
1/4 mile 10.43 @ 127

[Scott Misus]

It could also be those tiny 3/16" cooling lines....

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"Lord knows I can't change..."--Ronnie Van Zant

[Car!]

doh! 3/8's
Scott you never change do ya?
Good to know you're still on the board

[Brian Baker]

What?! No Rink-A-Zink modulator references?! You disappoint me, Misus (LOL)!!

[Ccass]

I know this doesn't solve Car!'s problem, but it reminded me of an old trans problem I had.
Back when I was just a kid, my GTO trans. developed a scary slipage going thru all 3 gears. A Cottman place looked at it and said..."yep, trans has to be rebuilt" $700. Well I couldn't afford it so I limped out of the lot and had a buddy take a look. He noticed that the modulator line was hooked up to a non-constant source of vacuum. 30 seconds later the trans was as good as new and never gave me another problem for the 5 years I drove the car.

[Half-Inch Stud]

Was the torque converter dry?
Best practice is to pre-fill the converter.
...Keep adding fluid.
12 plastic containers is about 12 Quarts.

Real advice: Add fluid while running the motor. Stop motor, Pull Vac-Modulator out and figure the tranny is full when fluid starts to come out from the modulator hole.
Drive the car around to fill the converter and exercise the air out of the clutch packs.
Refill, check for overflow from Vac Modulator.

Forget the dipstick.

I'm not sure if there is a better or more reliable way.