GMC used the Timken axles and they are covered in their maintenance manuals. My preference is Motor's Truck Repair Manual. The 11th edition was printed in 1958. These books were written by mechanics out in the field where factory manuals were written by factory guys that never got grease under their fingernails. Old Motor's manuals appear on eBay regularly. There are still old brake service companies around. San Antonio Brake and Clutch in San Antonio, TX still reline old shoes. They call on us every week.