Transmission thoughts and questions

[Richard McDonel]

Just installed the transmission in my '71. Very lightweight crosspiece I thought, and with only two vertical bolts holding it to 43-year old captive nuts, how much torque would it take to strip one out? I have some parts laying around from a '73 and notice that the transmission mount assembly is much more robust. I have to assume the factory was motivated to make this substantial change. Has anyone had some bad experience with the early mount coming loose?

Installing this transmission reminded of something a wise old mechanic told me many years ago. He said "Only a bad mechanic blames new parts for this problems." I've found that to be 100% true - until now. On my first try, with the cross piece secured to the centre cushion mount, I could not get the end bolts to line up with the captive nuts. Out of line by about one and one-half bolt width. The chassis had earlier been measured as straight, and the engine was secure, so now what? Took the whole thing apart, then lined the brand-new, right out of the package cushion mount on the work bench, alongside two old mounts I had. On each, the centre stud came out at a different angle. Further, if you looked closely, you could see that the metal stamping differed slightly, and finally, the new one was made of a heavier guage metal. Checked the Black Dragon catalogue, and it shows the same piece fitting all 240-280 models. So I took the better looking the two used mounts, installed everything, and it fits just fine.

If anyone is interested in a brand new transmission mount, I have one for sale. Half price.

Cheers All

[Zedyone_kenobi]

You know the same thing sort of happened to me. I center bolt was not positioned right on my mount so I ordered another one. It happens, but also check you have the cross member and mount installed in the right direction. It makes a difference I think. I will have to dig up my old post. Since you got it back on with a used mount you probably have it installed correctly

One more thing, I would not worry about the strength of the bolts. All those bolts really have to hold up is the weight pressing down which is not much at all, as almost life the tail shaft up with your hands with the engine bolted in to its mounts. The engine mounts take up most of the rotational torque as well, and all the transmission mount has to see is the little bit of flexure the engine mounts allow. I would drive without worry.

[Richard McDonel]

Zed,

Thanks for this. Glad I'm not the only one this has happened to!

With respect to the durability of the mounting assembly, I'm still a little nervous about sudden acceleration or downshifting, particularly with those 40+ year-old captive nuts. Motor mounts are rubber, and when the engine rotates in either direction, the transmission has to move with it. I'm wondering if anyone has ever cut open the tunnel, de-captivated the nuts, and installed new - perhaps larger - nuts and washers? I have no plans of racing the car (it's a total frame-up restoration), but would like to be confident taking it out for vigorous drives.

[Zedyone_kenobi]

me thinks you may be a bit too worried.

I am using those captive nuts on my 71 and pushing a strong L28 though it. You will break the rubber mount before a welded in nut on a metal frame breaks. The load is just not that big compared to the yield strength of steel.

[Mark Maras]

I agree with Zed. Another option may be Heli-Coils if the existing threads are suspect.

[Zedyone_kenobi]

eeeewww, that would require drilling them out, tapping them with the correct tap kit and CORRECTLY inserting a new helicoil. May I be so bold as to humbly disagree with you my good man. I have never had any luck with those things and holding torque requires a near perfect installation which has many variables.

I know you were only offering an alternate solution. Trust in the good engineering of Datsun. The car was old, but the engineering principles used on bolt strength were VERY well known even in the early 70's. Do not forget we sent men to the moon before the 71 Z even came out. We were pretty smart. I put lots of faith in those old engineers. I have yet to be let down.