Datsun Roadster Forum-311s.org

Working on a transmission for my 1970 2000 restoration. Need some help identifying what I have here. I see a single nut on the main shaft, not a double nut arrangement. The car came with engine and trans removed, and there were 3 transmissions in total included with the parts.....
How can I identify exactly what 5 speed I have? Are there any markings on the cases that would help?
And how can I determine if it would need/want to have the welded 5th gear replacement?

The center case is what would be on an early servo synchro box, the late box has an egg/milk crate looking web on the case. Some are servo and most are Warner boxes.
Dave

The center case is what would be on an early servo synchro box, the late box has an egg/milk crate looking web on the case. Some are servo and most are Warner boxes. The box on the left is an early 5 speed on the right is a Warner box.
Dave

The case markings are not definitive. The servo assembly can go in a late style case- and plenty have been mixed and matched over the years.

The only thing that is definitive is the synchro itself -brass vs. steel (and the coupling sleeves are a bit different too (1-4 only).

All the roadster 5th gears are servo type.

As I recall, there is no way to ID the splined 5th externally (I don't recall any different machining marks etc.) you just take it apart and look at it. (It is possible there is something externally visible on the splined 5th gears, but if so I do not recall it.)

All the posted photos indicate an early/mid run steel servo synchro box-not late. Most likely a pressed 5th(non-splined) unless someone updated or welded the 5th gear at some point.

JT68 wrote: Wed Jan 03, 2024 9:13 pm The case markings are not definitive. The servo assembly can go in a late style case- and plenty have been mixed and matched over the years.

Correct: I currently have two servo boxes apart, and they came with those different cases.

Not sure how the bent-tab washer in the photos would serve its intended purpose of locking the single nut (used in place of the oem caulked double nut arrangement), since the shaft it rides on is only threaded there and does not have splines or keyway.

Dave, JT, ever seen this used successfully before? Also, IIRC, you recommend a bit of welding on the two nuts, Dave -- correct?

Thank you.

Jon

I always put a single tack weld right on the threads at the nut, so it touches both the nut and threads. It’s easy to undo, just use a small grinder with a cutoff wheel and grind off the tack weld and it ready to come apart. When done correctly the double nut never backs off. I have seen the folding tab and it’s a 50/50 chance it will work. What I used to do with the single nut boxes years ago when I could get them was to use the 240Z nut with a sleeve that would get staked into grove it would grind into the shaft. Those always worked great!
Dave

jhayden wrote: Thu Jan 04, 2024 11:25 am

JT68 wrote: Wed Jan 03, 2024 9:13 pm The case markings are not definitive. The servo assembly can go in a late style case- and plenty have been mixed and matched over the years.

Correct: I currently have two servo boxes apart, and they came with those different cases.

Not sure how the bent-tab washer in the photos would serve its intended purpose of locking the single nut (used in place of the oem caulked double nut arrangement), since the shaft it rides on is only threaded there and does not have splines or keyway.

Dave, JT, ever seen this used successfully before? Also, IIRC, you recommend a bit of welding on the two nuts, Dave -- correct?

Thank you.

Jon

Yes, the lock tab for the big nut is normal for the single nut shaft. We actually have a heavier duty version of the lock tab/washer in stock.

It works because it has ears that lock to the thick washer and the thick washer cannot rotate since it is anchored to the main shaft with a steel ball.(so the washer, tab and nut are all locked to the shaft.) j

Is this the actual 5th gear? If so, how do I get it apart to inspect? The outer snap ring is meaner than any tool I currently have to remove it...

The Hypoid gear portion spins relative to the straight teeth....

That is a gear that was running too tight of a clearance. There is a thrust washer that goes under the large nut on the main shaft. The washer needs to be replaced every time the transmission is torn down or have it blancherd ground before reassembly. From what I can see in the picture, it looks like you need to have 5th gear welded.
Dave

This is what JT is talking about

Is this what happens when the 5th gear fails? I don't fully understand how the rest of the pieces in this gear assembly work....

Well I see the thrust block, break bands and synchro ring but I don’t see the anchor block. Is that all the pieces that were there when you took it apart? The anchor block is missing in your photo. The reason the 5th gear needs to welded is the early gears were a pressed fit not splined and slip under the torque of the engine.
Dave

Yep, the toothed wheel is a press or splined fit on the gear-it should never come off, As Dave pointed out the gear in the photo got very hot and had a rough life. I’d get another 5th or do some serious work to that one- including welding and additional work.

I have to explain more about what I've been doing, Long story.. The friend I bought the car from reported that when he drove it home from Colorado 35 or so years ago, it didn't have 5th or reverse. I got 3 transmissions with all the parts I brought home, all of which were out of the vehicle. So I was trying to determine which trans was bad and how it was bad.... The pictures so far, have been from one of the transmissions that I believed was what had been in the car when he drove it home. And after I got the 5th gear off as shown above, it confirms that it was the one with the spun pressed in gear. That was also my "practice" Roadster trans for how to disassemble and check the 5th gear. As a note, I have rebuilt a several 240Z 4 speed transmissions that we used to race in SCCA's ITS class. So being inside a Datsun box was somewhat familiar.
So having done this, one of the other transmissions that came with the car, looks absolutely pristine and was completely together. So I wanted to see whether the 5th gear in that one, was a pressed or splined gear. So I got it apart this morning and it has a splined 5th gear! Will not need to get a welded one.
So now I'll need new gaskets and grease seals, and will have to decide on retention of the single main shaft nut on this one. I have heard using a thicker tab washer, Loctite, Spot weld, 240Z nut with some sort of sleeve. I measured .003" clearance at the 5th gear before I took it apart. (it's not clear how I would increase that if I thought it wanted to be greater,,,, Maybe someone can advise).
So here's some pix of the gearbox I will intend to use. And I sure appreciate all the input!