904 Transmission slipping/not engaging - new torque converter

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Trevor B

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1968 Barracuda with 904 behind 170 slant six. Custom torque converter (1967 nose, 1967 rear).

After finally getting this “temporary” donor engine in last month, I tried to test out the car and the transmission wouldn’t fully engage - felt like slipping very badly. Could move a little but obviously something very wrong. Limped up and down block and back to driveway. Did NOT have kickdown cable (Bouchillon) hooked up and assumed it was not fully engaging clutches without kickdown. Looked on FABO and saw “don’t drive without kickdown attached.” So I didn’t drive.

Yesterday finally got the kickdown rigged up and tried to take her out. Same thing. With any throttle she is slipping badly, only seeming to settle at or near idle. Still not really pulling.

What is happening?

Observations:
When installing torque converter, got it all the way into the transmission but when attaching flex plate, the torque converter needed to slide 1/4”-3/8” towards the front of the car to mate up with the holes on the flex plate. Called Dacco (who made TC) and representative told me should be no problem.

Other facts: this transmission has always been a bit funny.
- Kickdown has never worked and I have previously shifted “manually.” Car will try to start in 3rd if in Drive.
- Feels like light shift kit installed at some point.
 
1968 Barracuda with 904 behind 170 slant six. Custom torque converter (1967 nose, 1967 rear).

After finally getting this “temporary” donor engine in last month, I tried to test out the car and the transmission wouldn’t fully engage - felt like slipping very badly. Could move a little but obviously something very wrong. Limped up and down block and back to driveway. Did NOT have kickdown cable (Bouchillon) hooked up and assumed it was not fully engaging clutches without kickdown. Looked on FABO and saw “don’t drive without kickdown attached.” So I didn’t drive.

Yesterday finally got the kickdown rigged up and tried to take her out. Same thing. With any throttle she is slipping badly, only seeming to settle at or near idle. Still not really pulling.

What is happening?

Observations:
When installing torque converter, got it all the way into the transmission but when attaching flex plate, the torque converter needed to slide 1/4”-3/8” towards the front of the car to mate up with the holes on the flex plate. Called Dacco (who made TC) and representative told me should be no problem.

Other facts: this transmission has always been a bit funny.
- Kickdown has never worked and I have previously shifted “manually.” Car will try to start in 3rd if in Drive.
- Feels like light shift kit installed at some point.

Having to pull the converter forward to the plate is absolutely normal, but what I would do is pull the valve body and air test the clutches and bands.
Of course paying attention to the pan contents and fluid condition.
You might just have a valve body problem, or it could be a massive internal fluid leak.
The air test would tell you, but it would be a really good idea to get a gauge on it and test the pressures before you tear into it.
 
Having to pull the converter forward to the plate is absolutely normal, but what I would do is pull the valve body and air test the clutches and bands.
Of course paying attention to the pan contents and fluid condition.
You might just have a valve body problem, or it could be a massive internal fluid leak.
The air test would tell you, but it would be a really good idea to get a gauge on it and test the pressures before you tear into it.

Rats. I was really hoping you'd say I'd installed the flexplate backwards or something I know how to handle. Any tips/link for how to do this? Transmissions are still in the realm of black magic/voodoo for me...
 
Rats. I was really hoping you'd say I'd installed the flexplate backwards or something I know how to handle. Any tips/link for how to do this? Transmissions are still in the realm of black magic/voodoo for me...

Hey, I could be wrong. :D
Look up the service/test ports and put a gauge on it to see what you have, then go from there.
Most any cheap hydraulic pressure gauge works.
 
1967 904s used a 26 spline converter and 1968 used a 27 spline input shaft. At least in the small block 904's.
The slant's could be totally different though.
 
The 904 was custom built to have a 1968 tail and a 1967 nose. It went in pretty smooth.
 
You're positive that the fluid level is full?? Not over-filled or low.

The kickdown is installed so that the transmission lever is in the fully forward position at idle and is fully aft at WOT?
 
Pressure test the L/R first before popping the pan, in gearshift position" Reverse".This will run the pump up to max and you should see about 220 psi or more at 1000rpm. No pressure or very low pressure means pump is bad or broken, or servo is. Now you can take off the pan,lol
 
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Did you check the fluid in neutral or park? Needs to be checked and filled in neutral. If you check it in park it'll be way low
 
Looks like I'm out of the woods. There was a combination of three things messing with the car and with me:
1) Smaller engine (170, not 225) = feels less powerful... duh
2) Brakes were hanging up
3) Needed some transmission fluid - I didn't put enough in the torque converter
Car is driving and shifting. Even the kickdown is working properly.
Thanks for the help!
 
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