Stuck as hell: tales of a transmission drain plug

[azucca33]

I bought a 1971 240z back in January. I got it running, replaced most of the braking system, fixed both side windows so that they both go up and down and tended to a few minor details. Long story short, I am ready to test drive it now but thought it would be good to change the trans fluid before doing so. The tranny is a 5 speed from a 280z and seems to be sound but the drain plug is not coming out and to make it worse, someone before me did a good job of messing it up. Can anyone give me any tips? I am not as experienced as many of so I am sure somebody should be able to help. The car is drivable so should I just take it to a shop and let them deal with it?

[Walter Moore]

First get the fill plug out and check the level. (on the right side of the transmission) The plugs are steel and the case is aluminum. There is some tendency for them to corrode in place, and there is a temperature issue as well. If the plug was tightened with the case hot, and you are removing it cold, you will have trouble.

If you are not comfortable with applying lots of force to your car, or don't have really good tools, the professional approach is safer. For the fill plug I have always ended using a pipe wrench and a hammer. (or was it a crescent wrench? maybe vice grips and a cheater bar?) The drain plug in the bottom usually has a recess for a 3/8" drive ratchet I thought.

In any event, do not remove the drain plug until you are sure you can get the fill plug out. Otherwise you can't refill the transmission to get it to the shop.

Also you need to try the search feature, because the transmission takes special GL-4 oil. If you use the more common GL-5 oil the sulfur in the oil will eat the syncros. The most common recommendation is Redline MT-90. I recall that Pensoil also makes an oil that is safe for "yellow metals", but have never used it.

[Arne]

I have actually gone as far as to remove the transmission from a Z so that I could get proper tools and leverage to remove the filler plug. I wish there was a simple trick, but I'm not aware of one.

[Nissanman]

There are a couple of options for you, if the trans. is to remain in the car.

If the fill plug is stuck, the trans can be re-filled through the gearstick hole.

If the drain plug is stuck, I'd be tempted to drill out the centre of the plug as large as possible, say 12mm, and after the oil has dumped out, thread the hole to take the appropriate cap screw fitted with a copper washer.

If the bottom surface of the original plug is rough, smooth it out with a grinder so that the new "plug" can seal properly.

[ajmcforester]

Spray with penetrating oil daily for a while and it might brake free.

Heat the housing with a torch around the plug, maybe even use a little dry ice on the plug after the housing is heated up. You will burn the oil. If you damaged the plug you might want to new one before taking it out

[azucca33]

Thanks guys. Yes i got the filler plug out ( was also very tough to move). I am going to see what i can do, but i am leaning toward taking it to the pros. i don't get a lot of time to work on her and would rather spend it doing other stuff. Thanks for the tip about the fluid. I never would have known. I will check the fluid I bought. Quite poss that its a good thing that plug is stuck. it might have stopped so that i didn't put the wrong stuff in.