C15a front hub bearing
 

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.

Attachment 105454

Attachment 105455 Attachment 105456

So less than....
 

Less than 0.488 mm difference........ how did they fit when you installed them?

Is the difference significant enough to feel the play......? or cause installation problems???

I haven’t installed then yet.

I’m curious with the serial number change where that coincides with production. I wonder if there was an issue that showed up.

Not aware.......
 

why would they make such a small change???

I think either bearing would work fine....... we have parts that are worn out more than that and still acceptable.

Hanno is in the bearing business may be he can shed some light of why such a minor change.


Good Luck

Jordan, this is not so much my area of expertise, so, this might be wrong.
On page 5 of the parts book, 1125 is the number for the hub and drum.
I assume there is what is called a 5 inch hub (not identified as such in the listing) and a 6 inch hub. Each uses a different bearing. It is not quite that simple though as the 5 inch hub is also used with the 6 inch Rzeppa joint.
If you look in the back of the book it tells you all the pages that the base number crops up eg. 1216 crops up on pages 1,2,3,6,and 46.
Does that help?

I'm not a bearing specialist, but looking at the basic dimensions:

Timken Part Number 395-S - 394
Dimensions
d - Bore: 66.675 mm | 2.6250 in
D - Cup Outer Diameter: 110.000 mm | 4.3307 in
B - Cone Width: 21.996 mm | 0.8660 in
C - Cup Width: 21.999 mm | 0.8661 in
T - Bearing Width: 21.999 mm | 0.8661 in

Timken Part Number 399A - 394A
Dimensions
d - Bore: 68.263 mm | 2.6875 in
D - Cup Outer Diameter: 110.000 mm | 4.3307 in
B - Cone Width: 21.996 mm | 0.8660 in
C - Cup Width: 18.824 mm | 0.7411 in
T - Bearing Width 21.999 mm | 0.8661 in

I see differences in d Bore of +1.588 mm like you said, and in C Cup Width of -3.175 mm.

Clearly the Chevrolets after s/n 184–23657 had an axle shaft which was 1.588 mm larger in diameter. While the Cup Width may still fit in the hub, fitting the 399A over the earlier axle would result in a sloppy fit and thus an early failure.

HTH,
Hanno


Attachment 105571

Thanks Hanno for posting the measurements and highlighting the differences.