Fs5c71a 5 speed

[Stitebunny]

I think it gets welded so it won't come apart again if the nuts loosen up. Not sure though. I hope it can all be pressed back together and the splines are not damaged.
I did fashion a puller and got the bearing off. Still need to remove counter shaft gear so I can get the syncro half off.

The nuts and shaft threads are pretty mangled but I think I will be able to clean it up enough to work.
Also, I see where there should be a ball at the thrust washer. But there wasn't one. I wonder if that had anything to do with the double nuts coming loose. I'll try to track down a ball for that spot.

Appreciate all the tips, help, and comments.

[jrusso07]

The original 5th gear was a press fit with no splines. It would spin free when it failed (5th gear neutral). Those are the ones typically welded. Assuming you can get the spines pressed back, you shouldn't have to weld it but if you do, make sure the welder doesn't overheat and distort it.

Maybe the cause for the nuts coming loose was the thread damage? What came first - hard to know? The nut torque is really high. 165 ft lbs if I remember correctly. I bolt a 3 foot piece of angle steel to the center plate top and use it as a handle while torquing the nuts. Have to lock the gears too...which means if have to take the spring-loaded shift rod ident locking balls out of the center plate so you can engage two gears at the same time. You might consider some red loc-tite on the threads. I did. You can still find the main nut for the FS5C71B...for the Z. It has a ring shoulder that you put divots in to help it from rotating. Those divots on your nuts were done for the same reason

https://datnissparts.com/main-shaft-nut ... 354-e9803/

[Stitebunny]

Thanks Joe. Good info. There is no major damage to splines that I can see, now that I have it all apart. There is some very fine blemishes I will try to file out and then press them together.
It seems odd that it would come apart in the first place. But I think I will skip welding and just make sure the nuts are torqued correctly.
Good tip on the use of a long handle bolt to the transmission. Thanks!
Your comment about removing the spring loaded shift rod locking balls worries me. I have been able to lock the gears by engaging the 5th/reverse shift for and the 1/2. Is it possible there are more locking balls missing if this is the case?
Thanks for linking to that lock nut. Do you think using that would be preferable to the 2 flat lock nuts I have now?

[jrusso07]

hmmm, my understanding is that the locking balls prevent you from having two gears engaged at once. I recommend pulling them all out. Use a magnetic pick up took to remove the spring and ball. It tends to precent the balls from falling on the floor and the usual colorful language uttered while trying to find them.

Dual locking nuts are preferred in my opinion. They were added after the single nut would come use - so essentially an improvement along with the splined 5th gear. If your dual nuts have usable thread, I would use them. I have used the Z car nut with good results. The puzzling part is how those nuts got so loose. Bad threads or under applied torque...??? Use loc-tite if you have any question on thread integrity

[jrusso07]

hmmm, my understanding is that the locking balls prevent you from having two gears engaged at once. I recommend pulling them all out to confirm their presence. Use a magnetic pick up took to remove the spring and ball. It tends to prevent the balls from falling on the floor and the usual colorful language uttered while trying to find them.

Dual locking nuts are preferred in my opinion. They were added after the single nut would come loose - so essentially an improvement along with the splined 5th gear. If your dual nuts have usable thread, I would use them. I have used the Z car nut with good results. The puzzling part is how those nuts got so loose. Bad threads or under applied torque...??? Use loc-tite if you have any question on thread integrity

[Stitebunny]

Thanks again. I will check the springs and balls.

Being that the lock washer is missing along with the lock ball for the thrust washer, I will also assume improper torque on the nuts. That's what I'm hoping for anyway. I'm hoping to be able to find those parts and get this put back together correctly.

[theunz]

If using double nuts, the procedure is to tighten the first nut to 20 ft.lbs. Then tighten the second nut to 15 ft.lbs. Now hold the second nut and tighten the first nut against it at 215 ft. Lbs. use a crows foot wrench to allow you to facilitate the usage of a torque wrench. Be sure to use the formula for using a crows foot with a torque wrench, as it will be somewhat less than the 215 ft.lbs.
Scott Scheelers “The Datsun Roadster Book” has a very comprehensive write up on rebuilding both the four and five speed transmissions. Highly recommended.

[23yrRebuild]

1+ ....on what Mike M just advised....that's exactly the torqueing procedure I used from Scotts' book, crow's foot, and some math,...the Internet has many references on how to apply simple math with a torque wrench, to achieve the correct torque readings....I also used a new lock plate, and updated, and "improved" second lock nut from Rallye, which has the "extended collar" as shown in the above link for the nut used in the other Nissan vehicles....I don't know if it's the exact same one, but the photo looks like the one I used....the lock tabs were bent over 3 times on alternating flats of the first nut, and followed up with a small tack weld at the seam between the two nuts....because of the extended collar of the second nut, there really wasn't enough room to put a tack at the second nut and mainshaft, even if I had wanted to....if anyone wants to see a pic of the lock nuts in place....let me know....I have some good ones...
Mike

[Stitebunny]

Thanks guys. Hoping to have all the parts on order soon. Found a forum member who may have a lock plate and that will be the final part ordered.
What fluid do you guys like?
I’ve read several threads about it and still not sure what I will choose.

[23yrRebuild]

I'm using one of the two, that the guys on the Porsche Forums recommend....Kendall NS-MP Hypoid 80W90.
I like it, it shifts smoothly, without any more than a minute or two of warming a cold engine, to settle the idle...the other recommended oil is the Swepco 201....I've never tried that one, but others on 311s seem to like it a lot.

[redroadster]

The way it shifts has much to do with the taper area of the speed gears ( where the brass blocker ring grabs the gear ) new it is mildly rough like a a new brake rotor face but years of use polish it and the ring has trouble grabbing it to slow down or bring the gear up to speed to mate thinner fluid helps glazed taper work better

[Gregs672000]

Regarding fluids, I used to run the swepco and really liked it but it got drained due to some work on the box. I recently added and commented on the Royal Purple, and while it did seem to help initially with smoother shifting vs the Valvoline I had in there, that has not continued all the time, and it appears to leak more than the swepco... not sure how accurate an observation this is as the box may have been low before (part of the reason it was pulled was to address leaks at the shifter plunger/side springs... fix didn't work as well as hoped). The RP is a thinner base oil, and it may be that the 90w is a better match. Nevertheless, it does leak more at this point... grrrrrr. So, if oil weight has anything to do with leaks, I'd stick with the thicker oil.

[Stitebunny]

Thanks for the input and ideas.
I think I will try the swepco.
Anxiously awaiting parts in hoping for a drive before the rain sets in.

[funkaholik]

... if oil weight has anything to do with leaks, I'd stick with the thicker oil.

Good advice. I was told the same thing by Steve Pettersen. My trans is leaking a bit at the shift shaft input, and he advised me to try running 90 wt vs the 75-90 that I have in there now.

Stitebunny, let us know how the Swepco works for you.

[Stitebunny]

Well, don’t tell me it’s wrong because it’s now back together.
Getting closer.

Next step is the shifter. Does anyone have a photo of how it is supposed to look like?
I got the new delrin bushings and it seems like the top one sits too high. And I don’t think I have the correct hardware either.