stumpy is a 71A...as the letter kinda tells you what extension housing it is
apart from the 71c that has 3 different lengths that i know of

It's time for first and reverse gears to go on. First gear on this box, is where 5th would be on an ordinary overdrive gearbox. But this is no ordinary gearbox. Bearing sleeve and rollers go on followed by 1st dog gear, and its spline gear can also go on.




Followed by the selector hub, layshaft spacer and reverse spline gear.




At this point, in reguards to holingers product, you are looking at a blend of old and new dog styles. The dog profile has changed and has been reduced to 6 from 8. Also the selector hub has changed as the broach that goes through the selector ring is the same that is used for many of our selector rings. It makes sense to reuse splines and profiles where you can, even specific parts are the same from different gearbox models, to save on doubling up on parts with minor changes.

On goes 1st Reverse selector ring. The reverse idler and bearings go on but I didn't flood my camera with all the finer details of the reverse idler, but you will see it assembled later.

The forks and rods go on next. Starting from the bottom, 4th 5th rod and fork go on. Followed by the 2 interlock balls. They use 2 standard detent balls to do the job to simplify the process, instead of using an oval detent which would be better.




Followed by 2nd 3rd rod and fork and the last 2 interlocks balls.




Followed lastly by rev 1st rod and fork.




The purpose of the interlocks, on any gearbox, is to prevent you from accidentally selecting 2 gears at once by limitingthe rod positions to one rod moving at a time. This system works well on synchro boxs as there is not enough inertia toover select a gear moving from one selector gate to another as the energising lugs won't allow it. But on a dog box you can accidently select a gear without meaning to if you are too rough, or fast on the gear shift. For example. Changing from 3rd to 4th, when the selector finger comes out of 3rd, into it's neutral position and slips into the 4th rod end, if it has enough inertia (force behind it) the rod can actually keep travelling without your permission and re-select 2nd gear while your shifter is in the 4th 5th selector rod. Basically sticking you in 2nd while you can't select any other gear. Also, this system can only lock out one rod at a time. You can select the 2 outer rods at the same time buy the middle rod will retained in the neutral position. No good if you accidently select 2 gears at once in a race, but awesome if you want to undo (or tighten) the mainshaft and layshaft nuts...

If you thought that you could install a roll pin in any old direction... You'd be dead wrong. This is probably one of the most critical parts of the build. Firstly, only a high quality roll pin should be used. And do not reuse a roll pin either. Not in a race box anyway. Double roll pinning is not always nessicary either, not when you use a quality item. We only use Unbrako roll pins.

This is the direction that they should be fitted and I'll tell you why. The slot should always be in line with the rod. Then you apply pressure to the roll pin the force spreads the roll pin out, strengthening it. If the roll pin were to be installed with the slot facing towards the gearset, the applied load will collapse the roll pin, weakening it.







I hope this is straight forward enough for you guys.

Quote:

Don - Could I use the ca20 pintara 71B alloy centre plate to
replace the cast iron r30 on on the stumpy?, I know itd be weaker
but just wondering as Im anal with weight.

D, that plate is also steel. You'll have to look at earlier bluebird for what you want.Track down an old 4 cyl bluebird box and we'll see if it's alloy, then we'll pull it apart and see. Even if it'a alloy it still needs to be compatible.

I have an 85 ca20e box that has the alloy centre plate but the length of the box
is obviously longer than the stumpy and Im sure its the original box.
Im happy to pay the current industry rates to convert these boxes at your premises
and in your time if possible.

Great stuff Don, very clinical and informative.

Quote:

Bring them over D and we'll suss them out and make sure they are compatible.

Heres a bit of random trivia for you. All this talk about the different series of gearboxs that the humble Nissan/Datsun have. 56, 60, 63 and 71 all refer to the centerline distance of the bearings in mm. So the 71 in a 71 series gearbox is referring to the face that the gearbox has a 71mm centerline distance of the bearings. This is mainly what governs the torque rating. The larger the centerline distance, the deeper you can cut the helical gear, therefore making them stronger.

Heres another interesting fact. Spur gears (straight cut) are not the gear of choice for outright strength. IT is nessicary for a gearbox that has narrow gears and a small centerline distance to have spur gears so that you can cut the root of the gear deeper to get the strength.

All standard Datsun related gearboxs have a single mainshaft nut which is o.k. No problems there, but on high output applications where it is not possible to lockwire a single nut you can use 2 and lock them together. This is what this gearbox uses. W\Here is the first nut fitted to the mainshaft. To get it tight I simply select 2 gears at once. By moving both outer rods and selecting 4th and 1st together I can safely lock the gearbox and apply the correct tension the the mainshaft nut.