Which size dropped axle to use in my 39 Ford?

[39 Ford coupe]

Help! I am confused about the length of 4" dropped axle to use in my 1939 Ford traditional style hot rod. I have see lengths from 46" to 47 3/4 " wide. I don't know why there are different lengths. I will be using disk brakes. Which make of axle should I buy? Also... instead of a split wishbone, can I go with hairpins and bat wings like the earlier Fords use? I was told by a local rod shop hairpins are the way to go. I have never seen them used on a fat fendered Fords so I have my doubts. If not, why? Thanx.

[Bib_Overalls]

Help! I am confused about the length of 4" dropped axle to use in my 1939 Ford traditional style hot rod. I have see lengths from 46" to 47 3/4 " wide. I don't know why there are different lengths. I will be using disk brakes. Which make of axle should I buy? Also... instead of a split wishbone, can I go with hairpins and bat wings like the earlier Fords use? I was told by a local rod shop hairpins are the way to go. I have never seen them used on a fat fendered Fords so I have my doubts. If not, why? Thanx.

Call Chassis Engineering at 1-319-643-2655 and ask them to send you one of their FREE catalogs.  They have 10 pages of 35-40 Ford chassis products.  And I have found their technical folks to be quite helpful.

When you say "traditional" are you talking flathead and closed drive line?  In that case I would use the stock wishbone and Chassis Engineering dropped steering arms.

Hairpins are not the way to go in my opinion. The 40 Ford front spring is mounted ahead of the axle.  So the traditional bat wing will not work.  You need a mount that incorporates a spring perch and this needs to be quite substantial. The spring will be exerting force on the mount that the wishbone or its equivelent must resist (The pins will work like a hinge.).  I think hairpins would flex.  I have seen a parallel bar setup that looked well engineered.  It may have been a Posies product.  But it had 1" or heavier bars and they were quite short.   And there is a possibility that your tires will contact the hairpins when you make tight turns.

Chassis Engineering recommemds their 47" I beam axle which they describe as "ideal for pre-1941 Fords.

[enjenjo]

The axle width needed is determined by tires, and how low it is. A real low car with wide tires will need the narrower axle for fender clearance. You also shouldn't use hairpins with a tube axle, too much stress on them.

[39 Ford coupe]

First of all, thank you guys for all your help. I appreciate your replys to my questions. I was wondering, Is a 4 bar front suspension the same as hairpins?

[enjenjo]

No, a 4 bar puts very little stress on the axle. Best bet for a 39 would be to use a wishbone, split just enough to clear the trans.

[Topsterguy]

I used a 46" axle in my '40 coupe and it worked perfect with disc brakes, 14x 6 solids and 185/65 x 14 tires.