I have a 1973 Plymouth Satellite w/ a 2BBL/318 and a 904 automatic transmission (the engine does not appear to be original - date stamped 1984 on the block). I've had it for almost 2 years now. Ever since I bought it, it has had a slip in the transmission shift from 2nd to 3rd. I'll try and describe the slip and hopefully someone can give me some tips on diagnosing it.

Under normal/light acceleration, the slip is there but not significant. Under moderate acceleration, the slip is obvious and feels like a trans that is low on fluid and "SLIPS". Under hard acceleration, the slip is severe and the engine will rev high for a second or two then the trans will "slam" into 3rd.

When manually shifting, the slip will still be there under moderate or hard acceleration; it's non-existent under light acceleration or if I take my foot completely off the accelerator pedal, shift into 3rd manually, and then accelerate.

Before I just start throwing parts at it or I pull the trans out of the car, does anyone have any tips on diagnosing this problem?

The fluid levels are normal. The fluid does not smell burnt and it is not dark. I see no debris, shavings or any contamination in the fluid.

Could this be a pressure problem related to a botched shift kit installation? Is it possible that someone has drilled a hole in the valve body separator plate that is too large and it is causing a pressure problem? Maybe swapped some springs and messed up? Could there be check balls in the valve body missing or misplaced? I used to re-build transmissions (almost 20 years ago now...wow!) and I remember installing some shift kits that required specific sized holes being enlarged in the plates, springs being swapped in the valve body and/or check balls being removed. How would I diagnose this without another separator plate and valve body to compare it with?

Is the governor valve something I should be looking into as well? How do I test that or check that it functions properly?

I'd like to eliminate things that can be fixed, changed and accessed from the outside of the trans while it is still in the car before I decide to remove it.

I've rebuilt dozens and dozens of these, but I have never actually had to diagnose one... ironic, isn't it?

Thanks for any help in advance. I appreciate it!

~Angel

Most likely only needs the kickdown rod to the carb adjusted properly. That rod should start to move the instant the throttle is applied.

I have tried adjusting it and even took it to a local transmission shop. They adjusted it as well. Of course, the trans shop suggested pulling it out and re-building it, but if it comes to that, I will do it myself. I realize it might be internal but I want to diagnose it properly.

Anyway, the cable adjustment does change the shift points (earlier or later) but doesn't actually effect the slipping at all.

The trans behaves the same, just quicker or later depending on the adjustment, of course.

Thanks for the suggestion though. I wish it would have been such a simple solution...

You've been driving it for 2 years with it slipping on the 2-3 shift, you've only made it worse over that time.

The only way to fix it is to pull it and rebuild it, an adjustment is not going to fix it.

Sure, you could be right, but it doesn't seem any worse. I check the fluid regularly. I have been shifting it manually from 2 to 3 and it never slips when I ease of the accelerator. I would have to go out of my way at this point to check if it is still slipping (which I'm sure it is; it's not going to fix itself!).

I'll probably have a hard time letting the damn thing shift itself when I do fix it!

Thanks for the reply though. Rebuilding it is not out of the question but how would I be sure the problem isn't in the valve body or separator plate without checking them or replacing them? What if I tear it down and don't see anything unusual? I would hate to put it all back together and still have the same problem because all I did was replace working seals and clutch packs.

Isn't it better to diagnose it first?
~Angel

Alright, I'll try adjusting the band to see if that helps. Then I'll try pulling the VB.

If the front clutch is slipping and it has to be re-built then so be it. I just didn't know if I would be overlooking something simple since I've never actually had to diagnose a slipping trans before.

Thanks for all the help so far. I appreciate it.
~Angel

I can't think of a VB malfunction that would make it slip as described.