Rear end recommendations

[Art Newland]

I'm not a 9 inch hater by any means, my 49 F1 has one and it works great. 3.70 gears are a nice trade off. My stock 239 won't ever hurt it!

The numbers published in National Dragster, in a tech article by Evan Smith show:

Dana 60 - 5%
GM 12-bolt - 7%
Ford 9" - 10%

Since the losses are very heavily dependant on the offset of the pinion shaft centerline from the ring gear centerline, the 10-bolt and 12-bolt would likely have similar losses, since they have similar geometry.

With a drivetrain consisting of a steel FW Street Twin, stock T56, 3" chrome moly DS and a Strange 12-bolt w/ 3.73 gears, and 17" wheels with 275/40-17 street tires, we measured total drivetrain losses in the range of 12.2 - 12.5% for power levels ranging from 490 -760 flywheel HP (measured in 1:1 4th gear). Subtracting the nominal 7% value for the rear axle assembly would leave only 5% or so for the rest of the drivetrain. The tranny is not going to have a lot of losses in the direct drive gear, since there is little or no power transmitted through the gear teeth. Its mainly some friction losses in the bearings. The rear eats up power because of the fact the gears are transmitting the power through a 90-deg bend, and involve a lot of friction losses as the gear teeth slide on each other. The trend now is to reduce those frictional losses with the Mikronite treatment of the gear teeth faces.

[40 Deluxe]

Originally Posted by Art Newland

I'm not a 9 inch hater by any means, my 49 F1 has one and it works great. 3.70 gears are a nice trade off. My stock 239 won't ever hurt it!

The numbers published in National Dragster, in a tech article by Evan Smith show:

Dana 60 - 5%
GM 12-bolt - 7%
Ford 9" - 10%

Since the losses are very heavily dependant on the offset of the pinion shaft centerline from the ring gear centerline, the 10-bolt and 12-bolt would likely have similar losses, since they have similar geometry.

With a drivetrain consisting of a steel FW Street Twin, stock T56, 3" chrome moly DS and a Strange 12-bolt w/ 3.73 gears, and 17" wheels with 275/40-17 street tires, we measured total drivetrain losses in the range of 12.2 - 12.5% for power levels ranging from 490 -760 flywheel HP (measured in 1:1 4th gear). Subtracting the nominal 7% value for the rear axle assembly would leave only 5% or so for the rest of the drivetrain. The tranny is not going to have a lot of losses in the direct drive gear, since there is little or no power transmitted through the gear teeth. Its mainly some friction losses in the bearings. The rear eats up power because of the fact the gears are transmitting the power through a 90-deg bend, and involve a lot of friction losses as the gear teeth slide on each other. The trend now is to reduce those frictional losses with the Mikronite treatment of the gear teeth faces.

Several internet sites listed the additional loss at 2-4%. One (Strange Engineering, a 9" specialist) said that they had done tests with Ford that showed a 3 to 4% loss. Keep in mind that these losses are at full throttle, full load and peak RPM. In the real world, cruising along at 60-70 MPH, actual losses will be much less (Less power output needed=less friction==less power loss). To maintain 60 MPH on a level road takes about 20 HP, as I recall. So that would be less than one horse power lost to the 9".

[RalphM]

Well, I’m still putting a 9” in my 35 coupe, only problem I see is how to fit my wire wheels and still keep them under the fenders.

[bobH]

Originally Posted by RalphM

Well, I’m still putting a 9” in my 35 coupe, only problem I see is how to fit my wire wheels and still keep them under the fenders.

I put a 9-in in a 34... should be similar for a 35. I used a 9-in from a 57-58 Ford station wagon, which provided 'large-flanged' axles (and big bearings). Eric Vaughn (the wheel guy) changed the lug pattern to 5-on 5.5. (Was able to do this because of the large flange used for 57-58.) This should work for a 35 and for 35 wire wheels. Probably would need support rings??
(I've been told that 57-58 Ranchero used the same 9-in as the station wagon.)

[V8COOPMAN]

Originally Posted by RalphM

Well, I’m still putting a 9” in my 35 coupe, only problem I see is how to fit my wire wheels and still keep them under the fenders.

The early Broncos supposedly had the narrowest 9", plus they had the 5-1/2" bolt pattern. No matter what, if need be, Curry can build you a housing ANY width you want, with axles to match, AND with the correct bolt circle! For bobH above, the Rancheros and wagons BOTH had the big bearings. DD

[40 Deluxe]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by V8COOPMAN

The early Broncos supposedly had the narrowest 9", plus they had the 5-1/2" bolt pattern. No matter what, if need be, Curry can build you a housing ANY width you want, with axles to match, AND with the correct bolt circle! DD

The problem with the early Bronco rear end is that the entire drive train (engine, trans, T-case, differential) is offset 1 1/2"-2" to the right. So your driveshaft will have a little zig-zag in it. Not a problem as long as the driveshaft tunnel is wide enough.
Also, they came in both small and large bearing axle shafts.