95 518 pulled from JY and installed in my 70 Challenger.
This is all on jack stands with rear wheels off the ground.

None of the electronics are connected yet (neutral safety switch or OD/LU power).
I have the neutral safety switch grounded so it will start in any gear.
Linkage seems to be fine, shifts through the gears.

Before starting, wheels would only turn when in neutral. Park would hold the tires from spinning by hand.
Added 6 qts ATF4 fluid, ran it for 2-3 min, then added 3 more qts.

With engine running, tranny in N, wheels spin in reverse, same for park.
Even if I start the car in drive, it will spin the wheels forward then stop and start spinning in reverse.  I can even hold down the brakes hard, it's stalls engine but doesn't stop it from spinning in reverse.

Now when I put car in park (not running) and spin the tires by hand, it spins easily and makes a clicking noise.

Never shifted tranny while running, always stopped the car, changed gears, then tried again.

Any ideas?

If you remove the shift linkage and operate the shift lever by hand does it do the same thing? Does the shift lever have distinct detents, no lost motion?

Ok, new symptoms:

I disconnected shifter linkage and moved through the spots by hand.  All had good indents, although there is a "slight" indent between reverse and park?  Like it has a audible click then I can push further back.

Started car in N then shifted by hand, wheels did not move no matter what position of tranny selector.  Checked fluid, it was low, added 2 more qts and tried again, same thing, no movement.

Now when I start car in gear, D or R, tires will spin forward for a little bit then stop, or I can easily stop by hand.

When in park, I can't spin the tires now.

It's possible that the pump has failed, only way to know is to hook up a test gauge to the line pressure test port at the accumulator.

When you installed the converter in the trans did it drop an inch inside the bell housing?

Yes, took some wiggling, but it seated. I went really low budget and just ground off the weight on the 360 TC and bolted it up to my 340. Any chance it's just a TC problem?

It was a long shot that it would work straight from the JY. At least I got all the install issues out of the way.  Time to pull it out and have it rebuilt.  You mentioned the pump might be bad.  Is this a normal item that would be replaced during a rebuild?  Couple more questions to make sure I get it done right.

- What would you suggest for a shift kit, I don't want anything wild, just firm shifts.
- Any suggestions for rebuild kit?  What is normally serviced?
- Any other suggested upgrades that aren't normally covered by rebuild or shift kit?

Thanks for the replies

If the 518 is a lockup trans and you used a non lock up converter that's your problem.

Yes it's a lock up out of a 95 3500 Van. I pulled the tranny and TC together.
I ground the external weight off the 95 TC and that's what's bolted up to my 340.

Everything seemed to bolt up fine, as mentioned, none of the OD or LU solenoids are wired up. Didn't think I needed those to test it on jack stands.

Again, you need to determine if the pump is putting out pressure via the gauge I mentioned earlier; if there is pressure then the likely culprit is the direct clutch in the tail.

Thanks for your valuable input