no i dont really know all that is implied with this conversion. ive been reading on it for days......all info appreciated thnx james
As you may already know, the driveshaft on your Buick (and other Buicks up to 1960) is enclosed in a "torque tube" which connects the rear axle to the transmission. This tube is part of the rear suspension design and performs two essential functions. First, It resists the rear axle torque reaction (when power is applied, the axle housing wants to rotate in the opposite direction to the wheels). Second, it transmits the rear axle driving thrust to the frame by means of the thrust pad mounted on the transmission crossmember. The axle is pushing on the torque tube when you are driving forward and pulling on it in reverse. At full throttle in 1st gear, this thrust can amount to more than a ton, assuming the rear tires can get sufficient traction.
If you want to run any transmission other than a Dynaflow or a stock manual, you no longer have a way to connect the torque tube to the transmission. This means you must now convert to open drive and replace the rear suspension with a design which can perform the same functions that the torque tube used to do.
The most commonly used arrangements for this are 4-link, ladder bars, and "truck arms". Truck arms are called that because most people are familiar with the design used on 60-72 Chevy half ton trucks. However, the same basic design was also used on Oldsmobiles up to about 1950 and possibly other cars before that. With most of these designs you will keep the existing panhard bar, which is a crosswise link that locates the axle from side to side (look under your car and you will see it just behind the axle). At least one type of 4-link design does away with the panhard. You can see this on GM A-body cars from the 60s and 70s.
I won't get into the debate of which design is better because most builders have their own preferences, and an opinion is an opinion. If cost is a concern, truck arms will likely be the least expensive, because these Chevy trucks are still fairly easy to find in salvage yards (don't bother looking for the Oldsmobiles though). Truck arms are also available from aftermarket vendors if you want all new parts, but then the cost will be about the same as the other designs.
Because you are fortunate enough to have a 56, the one point I will take a stand on is, keep your present rear axle. This is because 56 was the first year for the axle design which was used until about 65. These were open drive from 61 on, and the center sections from those will bolt into your present axle housing without modification. First choice would be a 61-62 chunk because those have the same shaft splines as your 56. Later years can also be used, but then you will have to swap the side gears to match the splines on your shafts. The reason I am raving on about this is that you get to keep your stock brakes and you avoid the hassle of cobbling your parking brake cables to work with the brakes that come with a different axle. This can be a much bigger annoyance than you might think.
Ok, I know I have babbled too long already, so I will shut up now. If you have any questions, please feel free to ask.
Ray
