Thread: Gear conversion

My plan is to convert the intermediate gear bearings in the transfer case in my WW2 Jeep . The original setup has a 3/4" hardened shaft and caged needle bearings running through the bore of the gear , this setup was a major design flaw , the shaft wears and thus creates a noisy unreliable Jeep. In the 1960s somebody here in Aust. came up with a good conversion, you bore out each end of the gear and use tapered roller bearings , Holden wheel bearings were a perfect fit. My first Jeep had this conversion and it never gave any trouble. Simple washers provide the pre- load. Question is: would this job be better suited to a lathe or a vertical Mill ? Accuracy is paramount.

Originally Posted by morrisman

the shaft wears and thus creates a noisy unreliable Jeep.

I didn't know there were other types of Jeep Sorry, couldn't resist that one.

I'd be inclined to go to the lathe, you won't get a flat bottom to the counterbore with a boring head and I reckon it's easier to clock up a 4-jaw than a mill table.

Personally with my home gear, I'd go my lathe. Easier to set up and dial in.

I would go the lathe. But then I don`t have a mill or access to one anymore.

Its a good mod to do. Even though I changed my gearbox and transfer case to the latter T90 setup with the larger 1 1/8" intermediate shaft I still had to rebuilt it after about 10,000 kms. (Towing an over weight trailer did not help). I carried spare bearings in one of the boxes in the back along with a spare water pump.


I met a guy in Adelaide that had done this to several Jeeps. He would machine the rear opening out in the transfer case then fit a carrier that supported the end of the shaft and pushed on the bearing. It had a three bolt flange on it. Shims could be fitted between the flange and the transfer case housing. Made the whole thing a lot easier to setup.

Tony

That gear would be pretty hard in the bore if it was running needle rollers.....
That will be the biggest problem that i can see.
Have you measured it to work out how much material you will have left behind the new outer brg shell bore? Looking at the pic it looks to me that the gear won't be hanging on by much.

Thanks for the replies. Yes I figured the bore would have been case hardened, like the the teeth . I would have to start the boring deep enough under the hard surface. A chap in the club I was in did a few of these conversions , I wil give him a ring , I'm pretty certain he used a lathe , a robust solid lathe is required . Yes the T90 was a popular conversion , the little T84 has its weaknesses, mine has worn thrust washer faces each end of the case, I'll have to figure out how to fix it.

Similar tapered roller conversions were done to '80's vintage Landrover boxes.
At one stage I dialled up an unmodified gear in my 14" Takisawa lathe and had a crack at creating a bearing recess with cheap carbide WNMG tooling.
Dialled in a decent cut and it worked well albeit with a few sparks and some smoke (no coolant used). It was definitely case hardened.

I was mainly just testing whether the carbide would actually work so didn't bother chasing a nice final dimension but my thinking at the time was if I needed to do it for real I'd probably just get close and finish off with some sort of jury-rigged grinder, but it might be easy enough to hit the required size just by turning once under the case.

Edit: re the thrust washer wear in the case a flanged steel bush is probably a good repair method. If you're converting that intermediate gear to tapered roller you should only need enough flange to support the bearing cone - ie if the wear area was 12mm wide on each side of the bore you might only need 6mm wide flange for the cone to bear on. Should be easy enough to make a line-boring style counterbore tool to cut the recess for the flange to sit in, and run it in the existing bore before opening up for the flanged bush.

Steve

Gee more problems .. The transfer case housing is scored on the flats where the thrust washers have been spinning, the washers were originally held in by a tang but over time it all becomes loose and the washer spins thus scoring the faces . I'm hoping to reface the scored faces but not sure how to ?

It doesn't look too bad to me, rub off any high spots with a stone.
The new thrust washer just needs to sit flat

Originally Posted by shedhappens

It doesn't look too bad to me, rub off any high spots with a stone.
The new thrust washer just needs to sit flat

One side is worse than the other . Yes I was thinking of using a stone . Maybe fitting a thin flex shaft down through the 3/4 hole and somehow fit a stone on the shaft !

I assumed Shed was meaning just a hand stone. That’s what I’d be using. The washer only sits against it so it doesn’t need to be a nice running surface.

Steve

Originally Posted by OxxAndBert

I assumed Shed was meaning just a hand stone. That’s what I’d be using. The washer only sits against it so it doesn’t need to be a nice running surface.

Steve

I overthink things alot but totally agree, don't make a job out of something that doesn't need it. Spend the time and worry on something that does.

Ok I think i have a solution. The casing has had a hard life, somebody has bushed the original 3/4" shaft holes with bronze bushes , the original holes must have worn elongated due to a sloppy shaft. Anyway if i make a new bush with a flange on it, I can replace the plain bush with the flanged bush thus creating a flat surface on the inside face. The opposite face is less scored, so i will use a stone and see how it goes, on this face i can adjust the pre load for the tapered bearings with a shim/washer, I can adjust the thickness to correct pre load . I will have to test assemble the thing so that the gears line up correctly . Rather fiddly but it should work OK

Sounds like a plan.
Since it’s been repaired previously don’t just assume that the existing bush is concentric or true with the shaft axis. Hopefully it is - as that means you can just interference fit the new flanged bush and ream to final size, but if it isn’t then the best way forward would be to sort it out before bushing.

Steve

This guy is doing the same conversion . The Pie jaws are new to me and expensive to buy

https://www.youtube.com/watch?v=IY2LFzHYItg