<VV> 1960 aluminum three speed transmissions

[Crawford Rose]

All, there was a TSB on this topic from Chevrolet, DR#440, dated June 16, 1960. The rear axle pinioon bearings were faling on Corvairs equipped with 3 speeds.  The countershafts became loose from the fully seated position against the statkes at the front othe transmission case. The countershaft was unable to maintain a light press fit into the bore at the front of the case to prevent rotation and/or fore and aft movement.  When shaft movement occurred, lubricant leaked from the shaft bore and due to the common lube supply for the transaxle the axle oil level became low, causing the pinion bearings to overheat and seize. 
 
The transmissions built after April 28, 1960 have a pin in the shaft to prevent movement of the shaft.
 
In 1961, the use of cast iron eliminated this looseness problem.  The 1961 shop manual discusses the changes in the design from the 1960 design, one of the most interesting being a concentricity face which the 1960 case did not have. This helped center the bore of the concentric mainshaft when the case was mated to the differential pinion nut. Anyway, an aluminum shortage was not the problem as much as aluminum weakness was.  Possibly the April discovery of the cause of the transaxle lubrication failures derailed the four speed until 1961 because the problems with ALL manual transmissions had to be addressed.  The whole transaxle was redesigned and fortunately the four speeds don't have annoying loose countershafts.
 
Crawford Rose