I just lost fith & reverse!

[Timelapser]

 I found & bought a 1986 Nissan 4x4 p/u ST with the Z24 engine that had been sitting. After a complete tune up, it ran and drove great. But today I jumped in it and all of a sudden, for no reason, I have no 5th gear! Then, when I was turning it around to head back home, I realize that reverse is gone also! It made no grinding noise or anything. I think that the same shifting fork handles fith & reverse gears, so it must be defective. If that is correct, how difficult is it to repair? Thanks ahead of time!

[datzenmike]

 

The early 71B had a tendency for the main shaft nut backing off. It's the one in the fore ground.  It holds the speedometer worm gear, 5th, synchro hub and reverse behind it. As far as I know tightening it back in place will fix it. They switched to a nut with a collar that you could stake into a notch in the main shaft. Similar to the nut above it. You can see where it's bent in.

 

That said I suppose the roll pin holding the 5th/R fork to the shift rod may have sheared. Either way has to come out and the tail removed to get at.

 

Last time I had my transmission apart I was able to turn that nut a 1/4 turn tighter and re-stake it.  

[Timelapser]

Now that sounds logical. Thanks!!

 Sir, since you sound like you know your way around these trannys and since I've got to tear mine apart anyway,

 may I bounce another question off of you? When down shifting, you have to use all your might and SLAM the shifter

 to get it to go in second gear, from third! When shifting normally, from first to second, it goes in smoothly. What should I look for

 that might be causing that problem when down shifting to second? Thanks!

[datzenmike]

By '86 this was corrected I'm sure. Well you'll know on disassembly.

[Timelapser]

On 5/24/2025 at 9:01 AM, datzenmike said:

By '86 this was corrected I'm sure. Well you'll know on disassembly.

Sir, since you sound like you know your way around these trannys and since I've got to tear mine apart anyway,

 may I bounce another question off of you? When down shifting, you have to use all your might and SLAM the shifter

 to get it to go in second gear, from third! When shifting normally, from first to second, it goes in smoothly. What should I look for

 that might be causing that problem when down shifting to second? And, a silly, stupid question: Do I have to take the whole tranny out to fix these problems, or is it possible to take the rear part off with it still in the truck?Thanks!

[datzenmike]

Theoretically you could do that but to get the case back on, the shifter has to be held positioned far to the right in the 5th /reverse gate and the transmission 'gentled' into place with a twisting motion. I have never got it on the first try. Usually you end up with two gears engaged or something. Better take it out and make something to support it with the tail up. 

 

I stopped down shifting into first for that reason and only into second after my turn when the revs are lowest. What you can do is shift from third to neutral, let the clutch out and rev the engine (this will spin up the countershaft, more closely matching the spinning second gear) then quickly push in clutch and shift into second while gears are spinning. Takes some practice as the oil is thick and quickly stops the spinning gears and hand/eye coordination. Another is switch to a synthetic gear oil like  Red Line or Royal Purple. I use the GM Delco Friction Modified Synchromesh Transmission Oil. Up shifts are faster when transmission is cold too. 

 

Down shifting is only really needed if racing where you can go to a lower gear where the engine is revving higher and making more power. Don't use it to slow down. Brake shoes are way cheaper to replace than rebuilding the transmission.

[Crashtd420]

15 hours ago, Timelapser said:

Sir, since you sound like you know your way around these trannys and since I've got to tear mine apart anyway,

 may I bounce another question off of you? When down shifting, you have to use all your might and SLAM the shifter

 to get it to go in second gear, from third! When shifting normally, from first to second, it goes in smoothly. What should I look for

 that might be causing that problem when down shifting to second? And, a silly, stupid question: Do I have to take the whole tranny out to fix these problems, or is it possible to take the rear part off with it still in the truck?Thanks!

Sounds like a bad syncro to me, I had that issue with my 71b 5spd....

I had to double chutch to get it into 5th, 

Later I also broke my 5th/reverse shift fork... so I fixed both while I was in there....

It's not to bad to fix just need to keep things organized... I can try to find the pages in my thread where I was dealing with it....

I have 2 write up, one replacing all the bearings and then another where I fixed the fork and syncro

 

[mmerlinn]

On 5/23/2025 at 8:37 PM, datzenmike said:

 

The early 71B had a tendency for the main shaft nut backing off. It's the one in the fore ground.  It holds the speedometer worm gear, 5th, synchro hub and reverse behind it. As far as I know tightening it back in place will fix it. They switched to a nut with a collar that you could stake into a notch in the main shaft. Similar to the nut above it. You can see where it's bent in.

 

That said I suppose the roll pin holding the 5th/R fork to the shift rod may have sheared. Either way has to come out and the tail removed to get at.

 

Last time I had my transmission apart I was able to turn that nut a 1/4 turn tighter and re-stake it.  

 

 

Since he has an 86 box, that nut should be left hand threads. Early boxes into 81 had right hand threads, with a running change during 81 production to left hand threads.