Thanks for the info Cory,at one time I thought that I read something about two
different differentials being used for the Roadmaster. They were both 10 bolt rears,but the difference was in the ring gear diameter, possibly I am thinking of another situation,please confirm. tks ed
The Caprice SEDAN's used the smaller 7.5" rear. They got it behind the 5.0(305, 91-93), 4.3 V6(265, 91-93... EXTREMELY RARE), and the 4.3 V8(265, 94-96). This was only on Civilian models. AND, there were some civilian models with the smaller motors, that got the larger 8.5" rear. Most of them also had the F40, "Ride Handling" suspension package. But (as far as I know), all of the police cars, regardless of engine, had the larger 8.5" rear, and also the towing package Caprice's also had the larger 8.5" rear. But from what I have gathered, every Wagon, and Every Roadmaster had the larger rear axle.
It's not just the ring gear. The 8.5" 10 bolt is bigger in almost every way, when compared to the 7.5" 10 bolt. Axle tubes, axle shafts, pinion diameter, bearing diameter, brakes, etc. Pretty much the only thing the two shared, was a 5x5 bolt pattern(91-96), and the "10 Bolt" designation. The 7.5", is what gives the 10 bolt a name as being weak.... yet many guys are running 10's, & faster in the 1/4 mile, on basically stock 8.5" rears. Many do this, whill still weighing in at over 4000lbs... That weight puts ALOT of stress on an axle.
Another thing you might be thinking of, is that the Sedan, and Wagon used different WIDTH axles. The Sedan used a "Skinny" axle housing, that was 1566mm IIRC. Where as the Wagon axle housing was about 1650mm.(that's not the exact). The wagon used a larger outer axle shaft bearing, which makes the flange bigger. The axle tube doesn't neck down. Which means you can't take the backing plate off a Caprice 9C1/Impala SS, slap it on, and have rear disc brakes. The axle shafts are also longer. The lower control arm mounts are spread slightly farther apart, and the spring perches are in a slightly different spot. This is good to know, when you try to sway in a sedan axle. Some have done it, and noted that the LCA's are angled slightly, and the springs don't line up perfectly. There also was another Sedan axle used, that was the "wide" axle housing. It was 1598mm, and was used on Caprice Sedan's(Not Fleet or Police cars) with the 8.5" axle, and the Impala SS.
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