A Little Trans History . . .
Okay, so the old and tired 39 box in my 32 Cabriolet finally died (sychros are gone) - can't complain, it lasted a year with a very stout engine against it and I wasn't nice to it either. Hey, built it when I was 15 (40 years ago) - drag raced the Antique Nats with it 3 times . . . it paid its dues and I just threw it in the Cab anyway. Time to build a transmission again - should be fun.
So - now I'm building a 'new' 39 Trans - with a NOS set of 25 tooth Zephyr gears and bunch of new parts from Mac VanPelt (his stuff is nice), some custom 2nd gear work from Charlie Schwendler (special bushing fitment), etc.. The best stuff I can find . . . but I'm not happy about the two shafts - they suck! The original mainshaft has .002 wear on it, the best one that Mac could find has .002 wear on it and the repop shafts are pieces of crap (don't buy them!) -- the materials are soft and they are .002 too small right out of the box (the whole shaft length).
Here is the Problem I Wanted to Solve
Take a look at the mic readings for the old and worn shaft - in the worn area - notice it is .747 diameter (.002 under):
OriginalShaft-WornArea copy.jpg
In then measured the non-worn area in the middle - notice the .749 diameter (is what it should be):
OriginalShaft-UnwornArea.jpg
So I ordered a nice new replacement shaft (thought I was ordering the right stuff) - nope, you can cut it with a file and it is .002 under to start with (.747). Not only will it add slop to the cluster, it will leak oil all over the place. And to think - folks sell this crap (didn't get it from Mac)!
NewReproduction copy.jpg
Well - time to get shafted my friends
I have some high quality shaft material, hardened to C60 and micro-polished to a mirror. First I used a carbide milling bit to cut the surface, then drilled the necessary 1/4" hole (carbide drill). Then I cut the shafts to length with a cut-off saw and then turned the ends in the lathe.
Drilling copy.jpg
CutShafts copy.jpg
ShaftTurning copy.jpg
The diameter of my new shafts - exactly .749 - what they should be.
DalesNewShaftDiameter copy.jpg
A New Way to Stop the Leaks . . .
I've seen all the methods that folks use to "stop the shafts from leaking". The typical method is to clean the heck out of the case (front and rear) and dab a bunch of silicone sealer on the ends of the shafts and the cross-link piece that holds them in - see below. This works fine - but I don't like it:
SealingWithSilicone.jpg
I'm just not going to bank on that working for long. Hopefully I'm building a transmission that will stand the test of time and be around long after I'm gone . . . so why not come up with a new (and hopefully better) way - well here goes:
I tapped the ends of the shafts with a 10/32 thread and made a set of three end-caps out of aluminum to place over the ends - they have a recessed area on the back sides. I'll put some gasket sealer inside of them before I put them on and also use a bit of locktite to secure the bolts. This should stop all potential leaks from the two main shafts (but not the lock-in shaft that holds them).
NewShafts2 copy.jpg
NewShaftsWithEndCaps copy.jpg
ShaftsWithThreadedHoles.jpg
RearCaps copy.jpg
FrontCap copy.jpg
Okay, so what about that little lock-pin/shaft that holds them in? It will leak oil as well - so I decided to tap the ends in the case. I'll cut the little shaft down a bit and then use these allen head screws (with sealer) to seal them up.
ThreadedPlugs copy.jpg
So - there yah go . . . two new correctly hardened shafts (with good shafting steel), that are of the correct diameter . . . with a innovative way to seal them from leaking.
Guess we'll find out how all this stuff works . . . time to complete the rest of the tranny!
B&S
Vintage Horsepower