[Petegto]

Does anyone know if a 71/76 Buick estate wagon posi/rear end clam shell w/leaf springs & 3:42 gears will work in my 67 Catalina wagon? It’s a 5x5 bolt pattern with 65” between backing plates. 10bolt rear with 12 bolt internals like the 67 Pontiac.

Thank you

[Ben M.]

Gonna go with a "no" on this one. I looked into it years ago for my '67 wagon (and also when I had my '71-74 cars) and there were differences that would not make them interchangeable.

There may be parts that can be made to work between the two or just need some machining, but it's not a drop-in-and-assemble job.

[Petegto]

Thanks Ben for your response. I have another guy that has a 81 Buick Wildcat with the 342 gears also but probably won’t work either. It’s an old police car.

['ol Pinion head]

The '65-70 Pontiac B series ran an 8 7/8 "P" series ring & pinion & 31 spline carrier, in both single track & STT styles. Original STT units for these had 3 preload springs & matching steel locater plates. From '65-70 there were 2 different style of housings and all 6 model years used the same sealed axle bearing 5 on 5 axle.

For '71 models, all of GM B series went to a new chassis & body. The 8 7/8 Pontiac rears that went into '71 up Bonneviles & Grandvilles had a Modified 8 7/8 pinion (8 7/8 MP series), Pontiac went to 30 splines on the pinion gear. This style rear was used in TONs of 71-76 Pontiac B series, some had 3.23 & 3.42 gears. The 3.42's are extremely hard to find.

The 455 Buick powered '71-73, maybe 74 model Electras & Centurions received a 9 3/8 Buick rear. These had A10 bearing bolt-in axles. Rivs used these too. Years ago I yanked the posi carrier & gears out of a Stage 1 Riv, believe it was a '73. Just throwing this out as Buick engineers came up with it as a continuation, though different, of their eariier 9 3/8 rears.

The lower horse Chevy, Olds, & Pontiac (think base Catalina's) '71-76 B series received cclip axle 8.5 B series rears. These could be upgraded w posi's & custom 30 spline c clip axles but they won't bolt in a '65-70 Pontiac B series.

For '73-76, as well as '77, the GM A-body station wagons received a c-clip axle version of the 8 7/8 MP series rear. The '77's & later used another style of the c-clip axle 8 7/8 rear. Have seen some GM reference to it as the 8.75. This late style ring & pinion set utilizes a longer pinion. This style rear continued into the mid 80's in certain Buick & Olds B series & Cadillacs, & in lower ratios, with the 200R4 overdrive. Have never pulled one out of an '81 up Pontiac B series, would bet a few were built w them. I have had half a dozen posi carriers of these later style 12 bolt 8.75's. All were out of 3.23 geared rears (had 20r4's).. These have the typical Eaton posi carrier with 4 preload springs & two steel locater plates.

The posi carrier build... Years ago in Pick-N-Pulls, & out of two parts cars, I pulled quite a few '71-73 year range high ratio 8 7/8 posi carriers & temporariy threw them in 8.5 A-body housing cores. Once home, eventually I disassembled those early 70's MP posi units, robbing the 31 spline side gears & spiders, plates, springs , clutches etc. Later, when I had the need, took one of the 80's late style mid ratio "8.75" c-clip carriers, disassembled it & carefully assembled it with the earlier side gears & spiders & best used clutches or new GM clutchs. Care has to be taken to shim the side gear to spider tolerance, that takes an asst of original posi carrier side gear shims. The clutches used in these are the same as used in most regular 12 bolt Chevy rears. Once assembled, the now 31 spline posi carrier could be used in a mid ratio geared '65-70 Pontiac rear. With a 12 bolt Chevy ring gear spacer, Locktite, & the provided longer grade 8.ring gear bolts, this mid ratio carrier can be used in a low ratio '65 Pontiac B series rear. Two of us first stumbled onto this in the late 80's assembling a posi carrier to add posi to a '65 manual tran 2+2. Later, I ended up repeating this carrier swap twice more & sold several other converted 31 spline posi carriers.