I just installed a used 4-speed to replace a 5-speed that is no longer functional (long story). I opened the 4-speed up to replace the input shaft bearing because it had been exposed since the transmission was stored without the front cover and I thought some dirt may of gotten into the bearing. I had to remove the three fork rods to pull the bearing. I noticed that the 3rd 4th rod seemed very tightly stuck into the adapter plate as were the detent balls in the vertical hole between the shafts. I reassembled the transmission and discovered no 1st or 2nd gear. 

I pull the transmission and checked to see if the roll pins were in place and they were. The 3rd 4th fork rod (middle rod) was still difficult to slide through the adapter plate and the detent balls between the upper and middle rods required a long punch and a lot of force to push them through the this section of the vertical hole. 

I've ordered an 8mm hone to try and clean up the vertical hole assuming that the detents are not moving out of the way to permit the 1st 2nd fork rod (upper rod) to move. Is there anything else I should check out. 

This is now transmission #4 so I'd like to make some progress on this one. Between this transmission and my chainsaw, I'm not sure which is more frustrating to get operating. 

Jeff

Edited June 7, 20213 yr by Jeff Berk
wording

I lack expertise in this area. Maybe Chas will chime in

I take it the transmission selected all the gears before you dis,antled it? It will not move (jammed) the 1st/2nd selector or you can't select it, meaning the striker rod won't go over into the 1st/2nd selector? I'm trying to understand you problem a little better.

It could be a problem with the selector interlock balls. You should have 4 interlock balls (two between each selector rod and three checking balls.

The checking balls are installed with the springs and caps after each selector rod is installed, but the interlocks must be fitted during assembly, before you fit the next selector rod. That is in the following order: Insert reverse selector and fit fork in correct direction, drop two interlok balls through the top hole or poke them in through 3rd/4th checking ball hole.

I generally drop something like a philips head screwdriver or round rod, or pencil (something smaller in diameter and  longer than the hole) down in the hole and move the selector rod to see the balls move up and down freely. Then install 3rd/4th selector rod and repeat process for 1st/2nd.

It could be the reverse and the 1st/2nd gear folks. They are the same, but reversed. If you fit them back to front you will lock up the transmission. It they are both facing the same direction (longer tab on fork) then one is not fitted correctly.

EuroDat:

I'm not sure I'm understanding your last paragraph correctly. I've attached 2 photographs of the transmission showing the location of the forks and the striker end of the fork rods. The striker end does not look right but I think I have them in correctly.

I'm not sure if I was able to shift the transmission into 1st or 2nd, but the transmission definitely did not seem to click into those positions.  I might of been in neutral when I thought I was in 1 and 2 gears.

Jeff

 

Aren't the slots on the ends supposed to all line up? It looks like its in reverse in that picture

Can you move the exposed 1-2 shift rod to get in to 1st and 2nd?  Edited, re-read your first post.

Edited June 7, 20213 yr by Zed Head

1 hour ago, Patcon said:

Aren't the slots on the ends supposed to all line up? It looks like its in reverse in that picture

Keeping in mind that this is a 4-sp and the attached diagram is a 5-sp, it looks like I have it right although the alignment looks kind of off.

Edited June 7, 20213 yr by Jeff Berk

8 hours ago, Jeff Berk said:

I've ordered an 8mm hone to try and clean up the vertical hole assuming that the detents are not moving out of the way to permit the 1st 2nd fork rod (upper rod) to move.

You should be able to grab that exposed rod by hand and just shove it back and forth to get in to gear, if the other two rods are in neutral.  A simple test of the detents.  

So the reverse shifter rod has a lot more rod exposed on the end. That seems odd. Maybe that part is reversed. The parts fiche shows all the shifter rod ends being the same

Here's another view.

http://www.carpartsmanual.com/datsun/Z-1969-1978/power-train/transmission-control/4-speed/from-sep-71

Still, the top picture shows the reverse idler gear to be engaged. And Patcon is correct, In the Neutral position all of the slots on the shift forks should line up so the control lever moves smoothly from left to right into a position that would move each/any of them. Remember that the shift lever is a force multiplier - it may take more effort than you think to move the shift forks manually especially with the end of the fork rods dangling in front rather than being held in proper alignment by the front case.

I'm going to hold off working on this until my hone gets here on Friday so my detents move smoothly up and down. Right now, they are really tight in the vertical bore.