I want to change the standard ratio of 4.44 to a 3.90 as was used in the 36 Centurys. What do I have to modify on the third member or the carrier to do this? Also, is it possible to replace the ring and pinion of the 36 with a much later ring and pinion.... like maybe a 3.6 from a dynaflow? Are the splines different on the pinion? I would also like to do this on the 1941 Special I have. I do believe the 3.90 of a 41 on up to some later year will work, but I'm not clear how late and which models interchange. My Hollander only goes to 1948.

The 36 and 41 will not interchange, but the rear ends from 1940 to 1955 are the same. You can get the center section from a V8 Dynaflow (3,3-3.6) and put it in your rear axle. The axle splines are the same, so it is a bolt in operation. The only real job is removing the drive shaft if it is a different length.

I still am wondering what modifications are necessary, if any, that are required, to add a 36 century differential, ring and pinion, and or carrier to the 36 special. Sometime back I was told that the ring of the century is too large to clear the housing of the special but that with a ground notch it can be made to work. I just don't want to spend the trouble to get a century diff only to find out that they were not telling the truth. Has anyone done the exchange, or can tell from the Buick master parts book that they do interchange? Sorry to have confused the issue by making the 41 a question of interchange in this scheme. I was sure that the 36 parts are unique compared to the 41's. I did exchanges to the 41's in the 40's and am not real familiar with the 49 on up models that would exchange with the 41 specials.

The complete third member from the Century will fit the special.Just remove the Special rear axle and torque tube and replace it with the Century unit. The extra wheelbase for the Century is from the tranny up