Any ideas on the ideal width for a differential in a 37 Plymouth? Planning on 7 inch rims with 4.5 back space. Tire size 225-70-R15. I'm coming up with 57 inches bearing housing to bearing housing.
List of rear end widths so you can select what will work for your application http://www.carnut.com/specs/rear.html
Wheel mount surface to wheel mount surface is a more appropriate number. Put the actual wheels and tires you are going to run under the car just where you want them to be, measure between them, and you will have the size you need. Then compare the charts to see what will work, what you can live with, or what you need to have made.
4 1/2" back spacing will probably set the sidewall of the tire against the inside of the body. 3 1/2" backspacing will be about as deep as will work. The original 5" wide wheels were pretty much centered, and there is more clearance to the outside then there is towards the inside.
If I am remembering correctly, the last one I did I put a Tri-5 Chevy axle under the rear, and ran 6.70-15's, on 15" x 5" wheels.
There have been/are several threads lately about how someone calculated the width they need. Then later they found out that the tire wheel combination they want to use is not available, and what they got rubs their fender or protrudes. Some wheels are not available in 1" wider widths, but are available in 2" or more. Backspacing changes as well between wheel brands. If you want to do it with the least hassle, get the tires and wheels you want to use and set them under the car..........then measure between the wheel mounting surfaces to see EXACTLY what you need. Too many guys found out that they need a 1/2" less than what they thought.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ THIS EXACTLY!!!! A lot of those fat fender late 30's cars don't have much wiggle room to fit tires in right especially if you are going to lower it and run skirts. According to the link that Dick Stevens posted that many of us refer to as it is WMS to WMS http://www.carnut.com/specs/rear.html the 37 axle is 60 inches wms to wms. The 84/01 Jeep Cherokee axle that Orn mentioned on his old build is 60.625 inches (between wheel mounting surfaces) Those are 5 on 4-1/2 bolt pattern and easy to find at least in this area but I'd do the stick the wheels and tires of choice under the car where I wanted them and measure thing and then start going through the possibilities. It was a lot easier in the 70's when we just jacked the back end way up in the air and let the tires stick out ugly as all hell but we thought it was cool .
This is the only reliable way to get it right. The charts are often wrong and it's sometimes not possible to determine what year/make/model a particular rear axle came from and youse gotta know this info to use the charts. Yep. Mock your application up using the ACTUAL WHEELS AND TIRES as the man said. Determine the wheel mounting surface to wheel mounting surface dimention. Then go looking for your axle with a measuring tape, not a chart. Good luck!
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