automatic transmission

[68 Wagon]

Can someone provide info on the automatic that's in my 72 4 door? I have recollections that they are crap but the wife wants an auto so thought I'd see if anyone knows a lot about them. Most everyone (including me) swaps them out for a manual of some sort.

Any help would be great, thanks.

[okayfine]

Kinda help? They are a period 3-speed auto trans. Nothing wrong with them, lots of survivor cars still turn up with autos and they still work fine. Not the last word in performance or refinement, but then neither is a 510. The 3n71b was used forever. Couple different trans' in 510s depending on year.

Making the best of the automatic requirement, you could look for and swap in one of the later L4N71B. DQ 11.4 has some details.

[datzenmike]

After April '71 the JATCO 3N71B was used. This was Nissan's 'in house' transmission and a refinement on the older Borg/Warner 35 that's been around since the '50s. It's tough little unit and with almost no servicing will last the life of the car. Just check the ATF level and never tow or otherwise over heat it. Fluid should be changed every 30K miles.

The 3N71B does have coolant lines and a heat exchanger in the lower tank of the rad. The torque converter is infinitely variable from 1 to 1 up to 2 to 1 to multiply torque as needed. The automatic's only sin is that it's so good at what it does that it's boring. My L18 '74 710 with a 4.11 rear end easily did 90 MPH

[68 Wagon]

Thanks guys. Before we parked it, I drove it for several months. Sometimes it would hesitate going into drive and slipped a little too if memory serves. I have a transmission shop not 200 yards from me, the owner is a cool dude, and they do excellent work. So if need be I have someone close to lean on. I'll post my progress.

[okayfine]

Fluid level? Fluid condition? Or, what Mike says^

[datzenmike]

It's probably in need of a change and a clean new filter. Fluid should be deep red and clear. Discoloration (brown) could be from over heating (think McDee's three month old fryer oil) Black could be clutch material. Once the fluid and filter is changed, pull one of the coolant lines off the rad (the pass side I think, and start the engine. Old torque converter oil will pump out. Collect half a quart, stop the motor and top up the transmission. Repeat several times and the new oil will displace the old. It will be mixed in the spinning torque converter but you will be diluting it with several quarts of fresh ATF. The 3N71B uses DEXRON ATF.

[68 Wagon]

Just checked the tranny oil and it is black. O'Reilley's has the service kit so I'll change the oil via your instructions and see where I am.