Jerry, the above experts have a valid observation, me as a none expert will say that if she was popping out of gear as you mention on post #1, the tranny is F*&%k up, man after all the wait and mula, but these complications is what makes this hobby entertaining

Edited November 4, 201212 yr by 72 OJ

Jerry, sounds a lot like something in the transmission to me. Did you inspect all of the gears or have the transmission rebuilt?

m

Mike, The transmission was a total rebuild from what I understand and at this point I agree with you and Arne it is internal. Les, said that when he first got the car under it's own power that it was fine in reverse. He said that he had an incorrect straight shifter in the car and when he changed to the correct shifter the problem began. I acquired another shift lever, correct to the "B" box inspected it put in new bushings and installed it. It shifts great but the noise in reverse is still there. It is somewhere between a loud knock and a clunk, it is rotational, and it changes cadence with speeding up and slowing down. I can feel the knock in the shift lever but when I place my fingers on the drive shaft just at the back of the transmission I can not feel transfer of the knocking. It is similar to a bad universal but only in reverse and I can not imagine what it could be in any other part of the drive line. Differential? I believe that I am going to have to pull the transmission out.

So I understand that the tranny shifted fine before putting the correct shifter in? After installing the correct shifter the problems occurred? I guess maybe I'm not understanding what was wrong with the original shifter that worked fine in reverse.

So I understand that the tranny shifted fine before putting the correct shifter in? After installing the correct shifter the problems occurred? I guess maybe I'm not understanding what was wrong with the original shifter that worked fine in reverse.

Steve,

I don't know how that relates, it may not. Les just said that he had installed a straight shift lever temporarily when the car was first put under it's own power. He said that it shifted fine. He said that the problem occurred after he installed the correct shift lever. One most likely has nothing to do with the other. My guess is that a mistake was made or a bad part was installed upon rebuild of the transmission and did not show up initially. I changed shift levers to a known correct part and it did not change the problem. Just my thoughts at this point. jlp

I can't remember the exact details - so I'll call a couple guys that rebuid trannies monthly... However, as I recall - one of the transmissions had a large nut that secured the shaft that 1st & Reverse are on - and that nut can come lose. This was corrected by reverse threading that nut on later transmissions so it tightened with rotation of the shaft. {or viseversa}. I just don't remember if that was a 4 or 5 spd. that had the problem

I have had some "clunking" in reverse - usually it was caused by rear brake shoes hanging up - and putting additional strain on old weak U-joints in the half shafts. But in that case someone standing outside the car as I backed up - could hear the clunk at the rear of the car.

Let you know if I find any useful info.

Carl B.

Edited November 5, 201212 yr by Carl Beck

I can't remember the exact details - so I'll call a couple guys that rebuid trannies monthly... However, as I recall - one of the transmissions had a large nut that secured the shaft that 1st & Reverse are on - and that nut can come lose. This was corrected by reverse threading that nut on later transmissions so it tightened with rotation of the shaft. {or viseversa}. I just don't remember if that was a 4 or 5 spd. that had the problem

I have had some "clunking" in reverse - usually it was caused by rear brake shoes hanging up - and putting additional strain on old weak U-joints in the half shafts. But in that case someone standing outside the car as I backed up - could hear the clunk at the rear of the car.

Let you know if I find any useful info.

Carl B.

Thanks Carl, I will have someone listen to the rear as I back later today just to see if it could be that simple. With all being new I don't think it would be the case. Any further input from you trany guy would be appreciated. I may have to find someone to rebuild this rebuilt trany. JLP

I agree with Carl, the nut on the main shaft might be loose. We have opened a couple of 4-speeds and the nut was loose on both. Loose drive shafts, worn u-joints, or brake problems won't force the transmission out of gear.

Jerry, I doubt the box needs another "rebuild". As noted above, there are several things here that might only need to have it opened and a small correction made. I suspect the solution will be fairly simple once it is out and the case is cracked open.

Jerry, I doubt the box needs another "rebuild". As noted above, there are several things here that might only need to have it opened and a small correction made. I suspect the solution will be fairly simple once it is out and the case is cracked open.

Thanks for the input. I just got an email from Les, he has sent me the original shift lever he had in the car when all was working fine. When it arrives I plan to install it, only take a minute, and see if that cures the problem. If so I will have to see what the difference is and go from there. I am not very confident about this I just believe that I have the correct shift lever in the car. jlp

Hi Jerry:

Ok talking to John Williams in Atlanta - The nut on the main shaft can come lose, if it isn't torqued properly and peened strongly enough. In that case the entire gear cluster can move rearward and it kicks the shifter out of gear. Both said that it was far more common in the 5spd. than the 72/78 4spd. with original transmissions from the factory. Early 72 production Z's had the problem show up - but by later production it seemed that Nissan was peening the nuts with more force - and they rarely come lose.

If the tranny has been rebuilt -it is a different matter - - it is as common in both 4&5 speeds if the nut is not penned in place strongly enough.

You have to pull the tail housing off - see if the nut is lose. If so, you have to torque it back down, and properly peen it in place. Both said that when that happens they replace the nut with a new one.

The clunkiing you hear is most likely the whole gear cluster hitting the shift fork.

FWIW

Carl B.

Thanks for the input. I just got an email from Les, he has sent me the original shift lever he had in the car when all was working fine. When it arrives I plan to install it, only take a minute, and see if that cures the problem. If so I will have to see what the difference is and go from there. I am not very confident about this I just believe that I have the correct shift lever in the car. jlp

I received the shift lever from Les yesterday. It is shorter and straight, obviously not the correct shift lever for a 1972 Z. I installed it and it works fine with no clunking from the transmission or popping out of gear. The difference is that the short straight shift lever is approximately .25" shorter from the tip of the ball on the end to the center of the pivot hole than the one from a 1972 "B" box. I am taking a correct shift lever to a local machine shop to have it modified to the specifications of the short incorrect shift lever. Carl, any thoughts? Anyone?

Hi Jerry:

The only thing I can think of - is that it must not be a 4spd. from a 72 240Z. Thus the longer extension from the pivot point is moving the shift forks too far and they are hanging up on the gear clustor. j

Good to hear that you have solved the issue.

Carl B.