Model 'A' Rear End Rebuilding - Additional information
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Bearing Pre-load
There have been many excellent articles produced on the subject of
rebuilding or restoring the rear end. This page is intended to
supplement those articles with information that has been overlooked.
Much as been discussed on the subject of setting the pre-load on the tapered roller bearings that support the differential carrier. While the only way to be absolutely certain of the pre-load adjustment is to measure it, knowing the original configuration is extremely helpful.
Ford originally assembled all the rearends the same, relying on the individual components to be within tolerance. In mid 1929 it was determined the pre-load on the carrier bearings was inadequate. The correction was made by altering the axle housings. The depth of the seat for the bearing cup was reduced by .005" in each housing. The new measurement was 1.365"-1.367" as shown in the drawing above.
All units were assembled at the branch with .009" thick axle housing gaskets (A-4035). When the housings were changed the gasket became A-4035-A and a new gasket A-4035-B measuring .004" thick was released. The new gasket was strictly designed for use when servicing the previous assemblies to increase the pre-load to the new specification.
With the proper combination of undamaged original parts and new quality bearings, the pre-load will be within the range Ford determined was suitable. Unfortunately, the only housings that can be identified without checking the above measurement are the housings with the riveted perch ball. These were introduced in early 1930.
Backlash
My experience with replacement ring and pinion gears is limited to
3.54-1 gears. In each case it required moving the ring gear and carrier
assembly .004" closer to the pinion by adding .004" shim behind the
bearing cup in the left axle housing and an additional .004" housing
gasket on the right side. In each case the gear contact was excellent,
the assembly was quiet, and no heat was generated from the rear end.
IMPORTANT
Original axle housing bolts (20 pcs.) were machined with a larger
diameter pitch than standard. NEVER chase the threads on these bolts or
in the housing. If the bolts will screw in with your fingers DON'T USE.
You don't want to be the one on the side of the road with loose bolts
and no gear lube!
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