76 620 Trans Issues

[76loooongbed]

Well here's the story........

 

I bought a 76 620 w/ auto trans that had been sitting for a while. Got it running with no problems. Drove it for a couple weeks and it drove great aside from having it rap out before it would shift. Vacuum line on the side of the trans causes this from what I've read. Then one day I'm driving it and it seems to jump out of gear and into nuetral. I don't feel or hear anything, but the rpms climb with no forward movement. I pull over and put it park and turn it off. After a minute or so I start it back up and it shifts into gear and I start to head home. Made it two blocks and it happens again, but this time it never goes back into gear. I check the fluid and it's nasty brown and purple and smells burnt. I chalk this up to the old trans just being on it's last leg and pull the old trans out.

 

Got another one from a buddy that worked fine he just put a manual in his. I put the new one in along with a new filter and pan gasket. Fresh fluid as well. Also I blew out the lines and made sure nothing was clogged up. I fire the truck up and this one doesn't do anything either. It feels like it shifts fine and locks into park, but will not spin the drive shaft. I've tried everything I can think of with no luck. I put fluid in the torque converter when I put the trans in. I have triple checked everything from the flywheel to the torque converter to the input shaft, etc, etc.

 

I'm out of ideas as well as patience at this point. Any ideas? I'm all ears. Thanks in advance.

[datzenmike]

Warm it up and check the fluid level in park and engine running.

[76loooongbed]

I checked it and it's just a hair under HI.

[datzenmike]

Well you have nothing to loose so pull the right cooler hose from the tranny off the rad and have a pail handy to catch any fluid. Have someone start the truck. Does any fluid squirt out the line???

 

If not then the oil pump inside isn't working

[76loooongbed]

I'll try that tomorrow after work and see what happens. Thanks.

[datzenmike]

For the automatic to work it has to have hydraulic pressure from the oil pump. Left over oil from the pump is fed to some components to lube them but most goes through the torque converter to cool it and then on to the rad to cool the fluid.

[76loooongbed]

Anything else you can think of to check if the pump is working? And when you say the right hose do you mean passenger side?

[datzenmike]

Yeah, I think the pass side in the out from the tranny. No matter it will eithr come out the hose or out of the rad one way or the other. If circulating the pump is likely working.

[76loooongbed]

Well, I had some time after work to finally get underneath the truck today. No fluid coming out of either hose. Pulled both off and blew out the lines and cooler again. Nothing clogging it up and nothing coming out still. So is there anything else it could be instead of the pump at this point? Did different years have a different length input shaft?

[datzenmike]

Well if you swapped the tranny it's easy for this to fall out. It's the input shaft but I don't think it drives the pump.

 

[76loooongbed]

What does it drive? The flywheel/torque converter is what spins the pump right?

[datsunaholic]

Did you take the flexplate off? I put it on backwards once... no go.

[76loooongbed]

I thought about that too and check it out. I couldn't get the bolts in if it was flipped around. They'd be too short.

[datsunaholic]

I had no problem putting the bolts in with the flexplate backwards. It's just thin sheet metal that's been stamp-formed. It's just crankshaft flange + spacer + flexplate. Doesn't change the bolt length/fit at all.

[datzenmike]

It's the same thickness if on backwards.

[76loooongbed]

Hmmm It wouldn't spin if it was on backwards would it? Wouldn't the teeth be off?

[datsunaholic]

The teeth will be a little off but not enough to prevent the starter from engaging, though mine was a little loud since it was grabbing teeth that had been worn the other way, and the backspacing wasn't right. What it does is sets the torque converter off by just a little bit, and the fluid flow passages then don't line up.

[76loooongbed]

So if it was in backwards...I could have the plate off and still see it spinning? I wasn't sure it was in backwards or not, but I saw it was spinning and figured I had it right. Could this be my problem then? Also, there's a lip on one side of the plate. Should that lip be facing the rear or front side of the truck?

[dropped620]

did you say that you pulled a line off and started the truck and no fluid came out?

[datzenmike]

Well, I had some time after work to finally get underneath the truck today. No fluid coming out of either hose.

[dropped620]

i work for a local tranny shop and if you started the truck and NO FLUID came out then the pump is bad. possible broken veins or pump gear internally. could have been caused by a stack convertor.  That is only if you pulled the lines off the tranny and started it.