C15a front hub bearing

[Jordan Baker]

I’ve just been going through the parts manual and I noticed there is two different bearings listed for the front hub on a C15a

C01Q1216 Timken 395s used before serial 184–23657
https://cad.timken.com/item/all-prod...ri-2/395-s-394

And

C11Q1216 Timken 399a used after serial 184–23657
https://cad.timken.com/item/tapered-...ri-2/399a-394a

When I look over the timken data pages there appears to be no difference between the bearings other then the “d-bore” measurement. That difference is 1.588mm with the 395s being the slightly smaller one. My initial thoughts were that the 399a had a higher load rating or something similar.
I’m curious on the change over in with regards to serial numbers. Was that a significant change in production? It may be interesting to see as various hubs could be mixed and matched on trucks today.

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1D593D9F-9F0E-4F14-B420-3AB17A72936A.jpg 8900C424-91E5-4F22-BFF0-87F154A1DC5C.jpg