I was wondering if someone could help me ID the rear differential in my 1970 Skylark Custom convertible. I cannot find any stampings in the axle tube. The diff cover has 10 bolts with the eyebrow from 12 to 3. The differential casting has two parallel ribs on each side. The only markings on the differential casting itself include the following: front passenger side passenger: 407298, front center: CFD, front drivers side: 1, driver's side between webs: BD. The ring gear has 10 bolts and a part number of 1234477. The gear ratio numbers are 40 13, which I assume means a gear ratio of 3.08. The carrier is an open type. The body tag on the car indicates that it was built in Flint, MI but the only differential that I can find in the assembly manual that had the parallel ribs was the one assembled by McKinnon Industries in Canada for Canadian built cars. Any help would be greatly appreciated.
The axle code is on the pass axle tube about 3" from where it enters the pumpkin. Your pinion has bolts and straps for the rear u-joint. Also there is an "O" on the driver's side cast into the carrier.....I think Monzaz told me that is indicates and Olds rear for Lansing Olds built cars. Contact him and he can tell you.....from what I can see, I would guess and 8.5" from a 71-2 Cutlass built in Lansing. Monzaz will know for sure.
Thanks for the information. I will contact Monzaz and see what he thinks. The O looking shape that appears on the driver's side also appears on the passenger side. I attempted to measure the circuference of the ring gear and came up with something a little less than 26", which would seem to suggest the diameter of the ring gear is 8.2 (26/3.14 = 8.28"). I have added an additional pic of the inside of the diff.
10 bolt 8.5 from a Olds 1971 1972. Jim Bearing caps are the give away here. Plus the O and then the mounting points. A oicture of the yoke ...should have 2 straps and 4 bolts. the upper t-chassis brake hose should bolt into the top of the center section casting bewteen the upper control arm mounts. It usally comes with a round cover with a half oil bend in the cover to the upper right of the cover. Jim
Jim, When you say the mounting points are a dead giveaway, what do you mean. Is the mounting geometry different between a 70 buick and a 71-72 Cutlass? The only reason I ask is that my rear coil springs have a pretty severe curve in them in order to meet the body spring perches. This is my first A body car so I am not sure if this is correct or worn springs or incorrect geometry. Thanks for your help!! Chris
Mounting points....t-arms, shocks are the same for the 68-72 GM A-bodies...your springs are curved because they are probably the wrong ones.
Chris, I mentioned mounting points becuase ONLY 1971 1972 were 8.5 in the early a-body cars 64-72 era. Once 1973 -1977 car came out the mounting points were totally changed and they used the same as the 1978-1996 full size cars . There are a TON of those corp housing and alot still have posi units you can fit into your 1971 1972 buick/olds rear corp. Remeber you can use c-clip or bolt in axle posi units in your 1971 1972 skylark/olds housing.
That's a good rear.Keep it.Add a posi,or build it. All of the Cutlass/442's that were built in Lansing had that style of 8.5" 10-bolt.The one that cames from other plants mostly had the other style,which is what most of the Buicks have.There is the "A" casting,which most Buicks have,and there is the "O" casting,which is what you have.The "A" casting will have the cover with teh notches at 9:00 and 3:00. The "O" casting has the cover that you pictured,with the rib or lip running from 12:00 to 3:00.
