Ok, I have a banjo rear in my model A that has some stripped threads on one of the axles. No I didn't do it. Anyways I have pulled the axles and what I have are 18 tooth axles 35-38 I believe. I have aquired some new axles with center (ring and pinon gears) to go into the car that are 16 tooth axles. All are the same length, I know that. Question #1 is do I have to replace the center of the rear (the one in the car now that went with the old ring gear) also with the one that came with the new axles or can I use my existing center piece? Note: the tooth count is different on the two ring gears. I can't remember which is which, but one is like 34 tooth and the other is like 36 or 37. Question #2 is why did Ford go from 18 tooth to 16? What are the advantages? Or should I just look for another 18 tooth axle and just replace that one? Hopefully this makes sense.
First you have to identify what year rear axle was installed in your car. If you have removed the rear axle measure the length and the tooth count on the end of the axle. 18 tooth axle is common to 1933-1938 but the length of the axle shaft is important. The 1933-34 axles measure 32.18" long where as the 1935-38 axles measure 32.85 " long. If your damaged axle measures 32.85" it can be exchanged with the 1939-41 16 tooth axle shaft if that to measures 32.85" and the use the corresponding 16 tooth spiders . If your replacement 16 tooth axle measures 33.70" then its the later 42-48 version and will not work.
Both axle shaft lengths are 32.85". My old 18 tooth axles are 32.85". I'm pretty sure the rear in my car now is 1935-38, and my new one is 1940 with the 16 teeth. I have the center section with the pinion and all that for the new one, but I was just wondering if I could just change the axles without removing the old center section. Basically just a swap of axle shafts and ring gear without changing the pinion that's already in the car. I mean both centers are in great shape, it's just more of a time saving thing. I just didn't want to remove the existing center section from the driveshaft if just a simple swap would work. I'll check on the pinion tooth count and widths.
As DS said, just the spider gears need changing...even the inner differential case is the same. By the way, if your threads are not too bad...this is a judgement call, of course, and remember they have to survive a lot of torque on the nut...they can be rethreaded outward from the good threads at bottom. This has some tendency to roll battered metal back into place and not just cut like a thread file. There is a fairly common special tool for this, and in modern stuff Little Giant makes 2-piece dies with an adjustable holder to move in towards finished size in stages.
I've solved the problem by just changing the ring gear on the new axles with the ring gear that was in the car that matches the pinion that's already in the car. Does anyone know why Ford went to 16 tooth axles instead of 18 tooth. Are the 16 tooth axles better axles? Just curious if anyone knows the reasoning.
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