Yesterday I pulled the center section on the rear end from my 1955 Fairlane Club Sedan to check ratio and condition.  I was expecting a 3.89:1 as it is an 8 cylinder car with manual transmission. This is what I found on the ring gear.  AG-4210 -B-"C"  Ford  10X37.  This would be 3.70:1.  My confusion is that neither the shop manual for '55 or the 1949-1959 Car Parts Catalog list a 3.70:1 differential.  The 4210 is confusing as the parts catalog shows the number for the Ring and Pinion as 4209 (unless 4210 is the ring gear alone).  Also etched on the ring gear in hand writing is 8536 although the 8 looks like a S with a diagonal line.  The differential case looks like the '55-56 model although I understand the earlier cases are the same. The parts catalog lists a 3.70:1 but only for the '57.  I believe this would be a 9" rear end.  Anybody know what I have here?  Also I feel the 3.70 gears would work well with the T5 transmission.  I can get a 3.89 center section What do you think?




Mark

1956 Mercury M100
1955 Ford Fairlane Club Sedan
Delta, British Columbia