Drilling a crown gear for a differential

[Grant T]

I need to drill the existing bolt holes on a differential crown gear out to a size larger to fit a gear change on a 1953 Chev pickup. He has the replacement gear. I doubt that I can re-drill the holes with standard good quality drill bit on my milling machine. I expect the gear will be hardened. I don't have any carbide drill bits. I don't know if a HSS end mill will do the job either. Any thoughts will be appreciated.
Thx. Grant

 

[phaxtris]

I assume you mean the ring gear ? I would give it a try with what you have, good chance only the tooth side is hardened

 

[Chicken lights]

what are you working on, Dana or an Eaton or factory GM?

 

[Kernel Sanders]

MOPAR ring gears are left hand threaded... not sure about GM but you should check if that's what your wanting to drill/retap.

Of course if your just drilling the rotating assembly that has the sure-grip/locker/posi/open etc, drilling the through holes a little larger shouldn't be a problem as long as the ring gear fits/located properly onto the rotating assembly.

 

[Grant T]

Thanks for your replies I was able to drill out the carrier which is a casting with no issues.
I did not need to drill the hardened gear
Thanks Grant