[Grant Bowker]

C8, C8A and C15 follow a bit different pattern as they use more Chevrolet parts.
Bsed on parts list 175 dated January 1941 the C8 and C15 use 5300869 for the front, C8 uses 5300866 for the rear while C15 uses 5450071.
The same parts list shows all C15A to C60 and CGT using 92Y2261 front and 91T2261 rear. This is consistent with the listing above showing a difference between early and late production of the C60L as this is an early parts listing. Parts lists C15-02,C15A-04, C30-03 shows the same wheel cylinders throughout (i.e. no change between early and late production or small/large axle joints) while C60S-03 shows the same pattern shown in C60L-03 of using 1-3/8", then 1-1/2 but suggests they then switched back to 1-3/8 for large joints and tires (no mention of 10.50x16 tires on later production). I suspect one of the lists may have a typo??? CGT-03 lists more variants but follows the 1-3/8, 1-1/2, 1-3/8 front with 1-1/2 rear cylinders, I didn't find it 100% clear on first reading which CGT got which size front wheel cylinders..
List C8A-04 for the HUP shows 92Y2261 front and 5450071 (replaced by 5451208 when stock depleted) Based on Rob Clarke's late 1945 1C11 "staff car", there may be a later list that could be even more informative as there are inconsistencies between that vehicle and the C8A-04 list.
List C60X-04 gives 91T2261 as used all round throughout production, regardless of which master cylinder and booster system were employed.
One odd thing observed is that Parts list 197 dated August 1942 lists the cylinders for C8 and C15 (same as parts list 175) but I can't see the listing for C15A to C60 and CGT. Does anyone else with the list 197 see it the same way or am I missing pages or going blind?
I don't see anything in the service bulletins (incomplete set) I have about converting from one wheel cylinder size to the other as a maintenance modification.

The Chevrolet Master Parts List 1928-1949 lists 5300869 as being front 1-1/4", used on all 1936-48 comm. and util. (except DS ES and FS - all 1 ton trucks). 5300866 is listed for 1936-48 comm. rear 1-3/16 and GD, HD, JD, KD, AL, BL (all 3/4 ton trucks with 11' brakes) and 5450071 for 1936-48 rear 1-3/8 GE, HE, JE, KE (all 3/4 ton trucks with 14" brakes), KF, AM, AN, BM, BN, DR, ER, FR (mixture of 3/4 and 1 ton). 1-1/4 seems to be the largest front wheel cylinder Chevrolet used in this period. For 1-1/2 and 2 ton utility (includes truck and school bus, both regular and COE cabs, single and dual rear wheel) they used a 1-1/2 rear wheel cylinder assembly 5450553. Original costs were $4.00 or less.