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1947 Differential gear set


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Hello everybody, 

 

I am in the stage of acquiring a 1947 Buick Super that still has the 4.45 differential in the rear axle. The car is very original and therefore has the synchromesh transmission as dynaflow was not available then. 

 

This 4.45 does not seem to be the best gear set to cope with modern traffic, right? I am for sure not an extensive high way driver, but lower RPMs at a given speed is for sure desirable. 

 

My question is, what gear sets are recommended and interchangeable with the car? Is it something you recommend? I know it is a lot of work to get it done. There must be a good reason Buick installed this in 1947. I am sure you guys have more insight than I have. 

 

Maybe someone even has a good set available and would like to part with it?

Anything else that I need to consider?

 

Thanks a lot for your help and suggestions!! This will be my first stick shift Buick.... 

 

Best, 

 

Hans 

 

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Hello, I have a 49 Super with Dynaflow with the same gearing,The Dynaflow is some want slow on acceration so it has the lowest gearing they made, rpms are high at highway speeds .At the time they were built 50 mph was top speed limit except on the Pennsylvania  turnpike where it was 70 mph. Some people have equipped an overdrive in the older cars to cruise at higher speeds, or as you mention replace the differential,If you can replace it with the whole carrier, it will be a bolt in operation that way , A shop manual will help the 1948 49 manual covers rear axle repair quite well . I had to replace the differential in mine with a used one as it was bad . 

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If I recall correctly, the internal gears or the "pumpkin" will interchange up to 1955 models.  The best would be if you can find a good 4.10 or 3.90 ratio.

I have my own theory of why Buick used the 4.45 for the post war years in the Super and Specials.  The Olds and Cadillac had the Hydramatic since 1940 and 1941 but Buick did not get the Dynaflow automatic transmission until I believe 1948 and then only on the Roadmaster.  With the 4.45 and for most local driving you could drive around and not have to shift once in third gear because of the high torque of the Buick engine.  Of course coming to a stop would require the operation of the clutch and shifting into low or first but sometimes you could start in second on a flat road.  The problem was on the open road where you would want to get to 55-60 MPH.  However, back in the day, as stated above, the speed limit on most parkways, not modern interstates that did not exist then, was 45 MPH or so.  Also, back in the day with the suspensions, bias ply tires and handling of most cars, the parkways often had many scenic turns and twists so 45  MPH was all you would want to go.  Do any of you old guys remember what I am talking about?

Joe, BCA 33493

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I agree with Joe. Start in second, shift to third at 20, and you're done. But you are well over 3000 rpm at 60 mph.

I looked for a 3.9 because that was the ratio used in '52, the last full year of the straight eight but I couldn't find one at the time. I had a 3.6  from a '53 Roadmaster V-8, so I tried it. It works fine. You have to use every gear now, but it is much better on the highway. It's not going to win any drag races, but that wasn't going to happen with the 4.45 either.

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