TR3 & TR4 rear axle modifications for racing
The stock design solid axle will flex in the tapered portion where the hub is pressed on. The car I rolled had stock design axles but made out of very good steel and stock design hubs also made out of very good steel. They were manufactured so that the "stress risers" were removed, but under load the axle, about 1/3 of the way inboard of the outer nut, starts to flex. You can see the fretting inside the hub where that happens. It bends over and over until it breaks.
The "Southwick Rear Axle Conversion" uses Ford 8" axles that are cut down in length and re-splined for the TR-differential. The outer end of the axle tube is cut off and the outboard end of a Ford 8" axle tube is welded on. It is possible that someone sells just that outer end of the axle tube. The backing plates are machined in the center to have a larger diameter hole and holes are drilled for the 4 bolts which hold the axle bearing into the housing.
These axles are a one piece design - the hub / flange is part of the axle shaft. The outer bearing is pressed on and an inner retainer is pressed on to hold the bearing in place. It is a sealed bearing, so acts as the bearing AND the outer seal. There is an o-ring which goes around the outside of the bearing to seal that area too.
My "copycat" Southwick conversion on a TR3 rear axle uses the 9" small Ford housing ends (the housing ID for the sealed bearing is 2.835"). The last step on the housing end is removed and then fit perfectly over the axle tube (2.25"OD) for welding. The Ford axle housing fits right up against the small locating tab which located the outer leaf spring u-bolt, so orientation for track width is easy. Moser engineering sells the 24-spline axles for $370.00, bearings and wedding band retainers installed for $75.00, and they can drill the stud holes on a 4x4.5 pattern for whatever wheel stud knurl diameter you are using.
Make sure to have them drill an access hole in the flange to make it easy to install and remove the axle without taking the brakes apart. Same setup for TR4 but longer axles as you TR4 guys and gals already know. Like Tony mentioned, the brake backing plates will need to be modified for the 4-bolt bearing retainer (backing plate ID needs to be enlarged slightly to slip over the bearing and the 4 mounting holes for the C-shaped retainer need to be drilled). As another patron mentioned, you can mock everything up and do your welding in situ. While your welding, go ahead and weld the axle tubes to the pumpkin for stiffening.
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