Okay. Somebody please help me out before I lose my mind. I have 2 trucks and a total of 3 rear axles in my possesion. All 3 I assume are Dana 41's. The number "41" is stamped on the lower right side of the rear housing of all three and the model years should be dana 41's. One of these axles is under an original 49 F1 with the flathead. The second is (or was considering I have the truck dismantled right now) under a 50 F1 that had a 302/C6 engine swap. The third I got out of a very rusty F1 frame that was pretty much shot. The only one of the three that I had even really studied was the one under the 50 with the 302 engine. It has a tag with the following stamped on it: "W 41/11". So I (and a few other very knowledgeable mechanics around here) just automatically assumed that it got a ring and pinion swap to a 3.73 (41 divided by 11, right?) when the PO did the engine swap. BUT, I just noticed tonight that the other 2 rear ends have the same exact tag. So here I sit scratching my head. Either all three rear ends have had the same gear swap (including the original truck with the flathead which I HIGHLY doubt) or I've totally misunderstood the meaning of this tag all along. Can somebody enlighten me please? I would almost bet my life that the 49 with the flathead has the original rear end. Now I'm really really confused. The shop manual gives 2 options for the rear differential on an F1 (page 366). It was suposed to be either a 4.27 or a 3.92. Somebody help me understand this please.

 

It's a mis-print in the shop manual. If you look in the section on rear ends you'll see that 3.73 was the standard with 4.27 as the optional choice.

Ross set me straight on this many years ago.

 

THANK YOU. As a matter of fact, Ross just sent me the link to where you guys hashed this out back in 2009.

https://www.ford-trucks.com/forums/893241-1951-f1-rear-diff.html#post8037040