904 wants to downshift, or slips out of gear with additional throttle

[Aeronet]

My 904 has been acting up lately. It will shift through the gears when in D, but after a while cruising on the highway it will downshift or slip out of 3rd with any application of throttle. I don't know if the front clutch pack is overheating and then slipping, if it's a valve body malfunction, if the line pressure is falling and letting the clutch slip, a leaking seal, or what.
I rebuilt the transmission four years ago and it has worked flawlessly until a few weeks ago.
Fluid level is good, fluid doesn't smell burned.
It's hard to tell if the front clutch is slipping or if it's dropping into 2nd. When I give it some gas in 3rd and the tach shows the rpm jumping up wildly when I drop it into 2nd the rpm is roughly the same. The car continues to accelerate when it does this, but not like it should and I don't push because if the front clutch is slipping I don't want to burn it up.
Anyone else had a Torqueflite act like this? It's a new one on me.
It's a full-throttle downshift valve body.

 

[wyrmrider]

fluid full?
then crap in the pan?
if so remember most coolers can't be cleaned

 

[Aeronet]

Yeah, the radiator is suspect. I'm going to drain the fluid, clean the valve body and check the line pressure setting, check to see if the front clutch pack engages.
I'm going to add an auxiliary cooler. I had thought about it when I overhauled the transmission, but decided against it.
A better description of the problem might be that after awhile the front clutch pack quits holding. I say front clutch because every other gear works fine.

 

[Demonic]

I might do a temperature check after a long drive first, then do some hydraulic pressure tests - line pressure and front servo- per the factory service manual. A 4" face liquid filled gauge and some high pressure hose, about 4-5", with 1/8" mpt adapter at one end and matched to the gauge - likely 1/4' at the other.

 

[Aeronet]

Good idea. Thanks.

 

[dvw]

Is the kick down linkage bound in the rearward position? There should be a light spring holding it forward. This could cause it to downshift at lighter throttle. Also posible if this valve body has part throttle kick down the valve could be stuck. If its realy slipping instead of down shifting something is broke. Stator seal rings, high clutch piston or seal. Needs to come apart.
Doug

 

[turbine68rt]

Yeah, the radiator is suspect. I'm going to drain the fluid, clean the valve body and check the line pressure setting, check to see if the front clutch pack engages.
I'm going to add an auxiliary cooler. I had thought about it when I overhauled the transmission, but decided against it.
A better description of the problem might be that after awhile the front clutch pack quits holding. I say front clutch because every other gear works fine.

In high gear both the front and rear clutches are applied. In 1st and 2nd gear the front clutch is off. If you have good reverse your front clutch might be ok since only that one is applied. I'd still pull it to do a full inspection like Doug said.

 

[Aeronet]

Is the kick down linkage bound in the rearward position? There should be a light spring holding it forward. This could cause it to downshift at lighter throttle. Also posible if this valve body has part throttle kick down the valve could be stuck. If its realy slipping instead of down shifting something is broke. Stator seal rings, high clutch piston or seal. Needs to come apart.
Doug

Linkage is fine and adjusted properly. I'm going to flush the transmision and clean the valve body, but yeah, it's not looking good. The transmission is behind a bone stock 318 (dual exhaust is only modification) and I don't hot rod it or abuse it.
Overhauled 4 years ago.
I overhauled it because it got to where it wouldn't shift into 3rd. The front clutch pack was burned up. This isn't the same and I shouldn't be having any trouble. I change the fluid and filter once a year and keep the throttle rod adjusted properly.
Frustrating.

 

[wyrmrider]

not your problem here but use ATF +4 from here on
I just run a remote cooler on mine but
I run a filter in my from trans to cooler
do not want to plug the cooler if converter clutch lets go
if your tank cooler is plugged post back
mopar has a spec on flow
so man ounces jn so much time
pull off the return line and check flow into a gallon container