Have you even driven a dynaflow? What model? Properly functioning it will perform. Here is a fun site: http://www.automobile-catalog.com/m...ries_60_century_1gen_riviera_2-door/1955.html Now search 56 Oldsmobile with a step gear auto trans and similar engine specs and the performance is worse. For increased performance for short runs install 3.9 rear gears out of a standard trans car. If yours is Special with 264 a four barrel will help All of the 55's with the eliminated torque tube ride like crap...still waiting for a well engineered setup.
As was asked earlier, what engine? If it's a Special it will have a 264. Add the four-barrel setup from a 322 and you will gain more performance then you will get by swapping transmissions, and if you have all of the proper parts, it won't take an hour. The '56 Dynaflow is a bit more efficient than the '55 and earlier units, and will bolt in. Any other transmission will be a project. If the engine is a 322, the '55 is 236 hp, the '56 is 255. Going from the 264 to the 322 will gain you power, but a really well set up 264 with a 4-barrel carb can perform better than you would think.
When I was a kid I remember riding in my brothers 56 Buick at 110 mph. it felt like the rpm of the engine was really low for that speed. does the dynoflow keep the revs down because the way it operates?
Supposedly, the '55 Century was the first American regular-production sedan that would do 0 to 60 mph in less then 10 seconds. I'm not sure whether this was with the Dynaflow or the stick shift. A good Dynaflow is rugged and reliable. Switching a torque-tube Buick to any other gearbox will be a very big deal. If I were going to go that route, I would install an open-driveline 401 or 425 Nail. You are going to need to totally re-engineer the rear suspension, driveline, and while you are at it, brakes. This has been done many times before, but is not a job for someone who is not fully familiar with suspension and brakes. You will find yourself doing some significant engineering. I don't know if the frames will interchange exactly, but it might be possible to use a '54, '55, or '56 Oldsmobile 88 or super 88 frame, or graft the rear portion onto the Buick frame. Of course this begs the question "Why not just use the Oldsmobile?" Having owned both '55 Buicks and a '55 Oldsmobile, I can tell you for sure that the Buick is the better riding car of the two.
And that's because of the suspension design & torque tube. A seemingly difficult but relatively easy rear conversion is a Jag rear set-up. Comes with discs, springs for the weight, shocks, etc. Not that hard to do. Could also use a '61-'65 full size car rear or a '63-'70 Riv. rear. Must transfer ALL the nec. brackets etc. Also a pretty easy swap IF you have the nec. skills. Tom T.
lots of good reading here about the dynaflow, like John said the 55 went under 10 seconds, 9.8 seconds and it was with an automatic 1/4 mile was 17.5 sec. also if correct like it was mention I would want a 56 tranny since they are an upgrade over the 55. then have a good rebuilt on it by someone who knows these trannys. not sure what stock gear ratio is but, would want more rear end gear because i was reading that with a dynaflow at 70 mph the engine is turning less then 2000 rpms so even with more gear it still would be a hell of a highway cruiser plus better acceleration. if taking out the torque tube makes it ride bad, I would never do that would ruin the whole car. just some stuff to think about.
The 56 tranny is about 2 inches longer (due to bellhousing/torque converter) than the 55 Special/Century, but about the same length as the Super/Roadmaster. You are right about it being an upgrade, since the switch-pitch in 56 worked also in Low. Years ago when I did not know any better I installed one in a 55 Special and wondered why the rear wheels were further back, the springs rubbed the pockets and and the panhard bar rubbed the diff cover. But if I could get traction it could not be beat in stop lite to stop lite drag races.
I'm almost positive that '55 and '56 wheelbases are the same. The transmission length issue can be solved by installing a '56 torque tube setup. I believe that there are internal differences between the '55 and '56 differentials. Also the '56 used oleo strut shocks in the rear, the '55 had lever-action (Houdaille) shocks. You would have to fabricate upper shock mounts if you use a '56 differential/torque tube. Many folks would consider this to be an upgrade. It won't hurt the ride.
John, my father swapped in a 56 trans and they are closer to one inch longer at the bellhousing to accommodate the improved converter. He slotted the strut bars which pushed the rear wheels back. Not really noticeable. Also didn't the output spline count change around then too ?
The only '56 that I had was a stick shift; there are likely others here who would know more about splines on the Dynaflows then I do.
I would rather have a good working dynaflow than any other trans,you got the switch pitch which gives you an edge to start,i have a 55 special which I put 4 barrel holly,and pertronix ign.thing goes really good.i outran many a car with a 57 century,from a dead start in low and shift at 80 mph,wish I had that car now.dynamite