74 Duster front drum question
So you think they had a unique spindle to match the unique hub and drum assembly? and they continued using the A1 and A4 bearings from previous years?
They didn't have a unique spindle, they had the
old spindle. And since they had the old spindle, they had the old hubs and bearings.
It's right in the TSB I posted above, the dates and everything, straight from the factory. The conversion to the new 10" drums happened around November 1, 1972. We all know that Ma Mopar used up remaining stock from the previous model year if it was at all possible before starting in with new parts. That would mean that August to October the small upper ball joint spindle would still have been used on the 4 wheel drum cars, with the small ball joint UCA's. Which, in theory, could mean that some of those cars had 9" front drums. Either way, 9" or 10", they'd have been the 67-72 style. After "approximately" November 1st 1972 they all would have had the new 10x2.5" front drums, the larger wheel bearings, and the large upper ball joint spindles.
Again, the TSB tells you everything you need to know. The 10" drum, hub, and backing plate, although primarily B-body, all still had to be re-designed. Which would have also meant re-tooling. Not cheap.
So let's consider the options:
Ma Mopar designed a new drum spindle with a larger bearing and upper ball joint, a new 10" drum, a new 10" drum hub, and a new 10" drum backing plate. And then decided, for some reason, to not roll out the new 10" drum, hub and backing plate until November 1. But, in the meantime, they decided to ALSO design a new 9" drum, hub, and backing plate just to use for 3 months. Oh, and of course the new 9" drum and hub was ready immediately in August, while the 10" stuff that was planned wasn't ready until around November. And, there's no TSB on the new 9" drum stuff they designed, but there is for the new 10" drums.
Or, more likely-
Ma Mopar decided there was roughly 3 months worth of 67-72 style drum spindles, drums, and upper control arms and started production of the '73 model year with the old stuff. And used the old stuff until it was used up, and then switched to the new '73+ design drums and spindles. Also explains why the date is approximate. If the new parts had been rolled out all at once, they'd have the date. But if the new parts were on the assembly line already, just waiting to go into use when the old parts ran out, well, that date would be different at every plant. November 1 was just the catch all date, all the old stuff was completely gone by then.
