# 65 Rear Differential



## Stanjco (Jun 28, 2015)

Trying to figure out if this is a Pontiac rear and if so, what is the differential ratio. Tried looking for codes near rear break drum but was unsuccessful. Any help will be appreciated!


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## Pinion head (Jan 3, 2015)

Looks like an early 8.2 BUICK 10 bolt to me. I have one out of a '64 442 post car. Also in the racks, have a '68 BUiCK 8.2 10 bolt out of a '68 GS400. Both have pronounced castings where the plug welds go to attach the axle tubes. That stated, the 68-70 Buick 8.2 10 housing has diagonal ribs & much more "beef" in it's housing.

Buick built their own cast hag 8.2 10 bolts for '64-66 Buick Specials. Olds also used the BUICK 8.2 10 bolts for all '64 Olds F-85's, late intro '64 442's, & most '65 & 66 F-85's & 442's. Eventually Olds engineers realized the single rib design of the cast center secton was weak, & they specified gray iron Pontiac 8.2 10 bolts for the 400-4spd '66 442's. Some Pontiac 8.2 10 bolts were also used in late '65 442's. The gray iron 8.2 Pontiac center section used a twin converging rib design on each side of the front of the center housing. The twin converging rib design continued its use for both gray iron & nodular housing PONTIAC 8.2 10 bolts through the '72 model Pontiac A body's.

Warranty concerns eventually precluded the gray iron 8.2 center housings use under '67 Pontiac A body's with 3.55, 3.90, & 4.33 Safe-T-Track, as Pontiac engineers specified nodular iron 8.2 Pontiac center housings for '67 8.2 A body Safe-T-Track rears with the aforementioned ratios. 

Oldsmobile introduced their "Type O" Olds 10 bolt rear during the '67 model run. These rears are often mistakenly referred to as "Olds 12 bolts" due to their 12 bolt smooth cover. Under the cover is an 8.3" 10 bolt carrier, they are 10 bolt rears.. The Type "O" housing & rebuildable clutch type posi carrier were a major improvement over the previous early8.2 BUICK design, but the most common Type "O"s was not that much of an improvement over earlier offerings & like all gray iron 8.2 10 bolts lacked serious pinion support.

Buick for their '68 model A-bidys totally redesigned their 8.2 10 bolt. These had a '68-70 BUICK 10 bolt specific housing, specific 4 pinion posi carriers, specific (different pitch) 28 spline axles, as well as their own specific ring & pinion sets. 

With all the major difference's, this is why a very experienced GM differential builder does not use such terms as "BOP 10 bolt", I cringe nearly every time I read that uninformed term.


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## Stanjco (Jun 28, 2015)

Pinion Head,
Thanks so much for the quick and thorough reply! I really appreciate it. Do you have an opinion about the performance of this Rear from Buick? Or the rpossible ratios? It handles extremely well on my Goat.
Also, any picks of the '64? That's a sweet ride!


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## Pinion head (Jan 3, 2015)

Stan, as long as the car is an automatic, stock engine build, with 2.93's-3.23's, ought to be fine. the lack of pinion support of the early Buick 8.2, as well as Chevy 8.2 10 bolts becomes very evident with lower gear sets with small pinion gear. With the smaller pinion gear (10 teeth, 9 teeth) pinion deflection is an issue when one side steps a clutch & the power bangs the rear hard. Similar deal with lot more torque, & a loose converter. 

To verify ring & pinion ratio, it's always smart to pull the rear cover & look at numbers inscribed in the ring gear. The numbers will give ring gear part #, ratio (40:13, for example is a 3.08) & date the GM ring gear was mfg. Typically the pinion gear will be mfg same month or within 2 months of the ring gear. Will also have ratio number stamped on the face of the pinion head. As long a you are not having problems with the rearend, nothing wrong with running it in a fairly stock vehicle. I do caution guys that are running quite a bit wider than stock tires/wheels that the sealed axle bearing bolt-in axle rears are a very bad choice to blow money on for lower gear sets & posi units. Just examined way too many sealed axle bearings where the axle bearing seized, chewed up the axle, & the axle either walked it's way out on a slow turn, or rapidly departed under high speed cornering. Pontiac followed Chryslers much earlier lead going with tapered bearing axles, but it wasn't til the mid season '69 Firebirds.


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## Stanjco (Jun 28, 2015)

Thanks! The car is actually a 4 speed with a '68 400 and the "65 tri power setup. The rear tires are 255. So far, runs smooth. Thanks for all the insight. I really appreciate it! The next time I have the car on a lift, I'll pull the rear cover to verify the ratio.


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