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Good evening to the forum. For interests sake, do our gurus here know of any other rear axle assemblies from other GM large vehicles can be interchanged with my 66. Or are they unique to the large Oldsmobiles only? The center section has the scalloped on the sides type cover which looks like one found on a Buick or Pontiac (shared). Reason asked is because it would be nice to fit an Anti-Spin unit in the car. Or could a particular case be fitted in the present rear axle. Thanking anybody who can help thank you in advance. Regards, Howie.
What little I know after 35 years: 66 98’s had wider rear brake shoes than the 88’s. Wheels wee 14x6 with 5x5 bolt pattern.
You can swap in rear ends from 65-70. Oldsmobile used types O, P in 98’s, type B was used on some F-85’s (cutlasses) and wagons.
I believe the rear gears were 8.875 in diameter. Common ratios for 98’s were 2.93, 3.08. I think 3.23 was optional and rare.
Anti-spin diffs were/are very rare. They were different in design, but similar in function to positraction. The Olds cone design is difficult to rebuild due to parts rarity. When it wears out, the cones recede into their housings. Then you need a new housing or must shim the cones somehow, but I’ve never seen a procedure to do it.
I’ll defer to those with more knowledge than me. Just what I’ve picked up...
What little I know after 35 years: 66 98’s had wider rear brake shoes than the 88’s. Wheels wee 14x6 with 5x5 bolt pattern.
You can swap in rear ends from 65-70. Oldsmobile used types O, P in 98’s, type B was used on some F-85’s (cutlasses) and wagons.
I believe the rear gears were 8.875 in diameter. Common ratios for 98’s were 2.93, 3.08. I think 3.23 was optional and rare.
Anti-spin diffs were/are very rare. They were different in design, but similar in function to positraction. The Olds cone design is difficult to rebuild due to parts rarity. When it wears out, the cones recede into their housings. Then you need a new housing or must shim the cones somehow, but I’ve never seen a procedure to do it.
I’ll defer to those with more knowledge than me. Just what I’ve picked up...
cf
Thank you very much Cfair, somehow i missed the reply notification about this question. I may have a lead on a 1968 type 'O'. Indeed I have read up on the cone style Anti-Spin differentials. Supposedly by grinding off a bit of the small end of the cones would give back some limited slip action, but I wonder about interfering with what was designed into the parts originally. Nothing is wrong with the unit on our 66, I was asking so I would know what I could do in the MAW's with a perfectly running car. Not that I really care now to lay two strips of rubber with the cost of fuel and tires up in Canada these days. I am also aware of the wider (2.5-inch) shoes on the 98's. Thanks to Joe P and Craig (Mobile Parts) and the book, I learned this and will be getting a OEM set of rear shoes from Craig in the very near future. Just to have a spare set! Regards, Howie.
The 1966 Ninety Eight almost certainly came with a 9.3" Type O. Do not confuse this with the A-body 8.5" Type O. Parts for the 9.3 are even more difficult to find. Lesser Olds full size cars of this vintage also used the Pontiac 8.875" axle (which has nothing in common with the Chevy 12 bolt). The Pontiac is more common and parts are available. It has a 10 bolt cover and a 12 bolt ring gear. Impala axles do not swap. The suspension mounting is different. Most Impalas of that vintage used a three-link rear suspension with a Panhard rod.
The 1966 Ninety Eight almost certainly came with a 9.3" Type O. Do not confuse this with the A-body 8.5" Type O. Parts for the 9.3 are even more difficult to find. Lesser Olds full size cars of this vintage also used the Pontiac 8.875" axle (which has nothing in common with the Chevy 12 bolt). The Pontiac is more common and parts are available. It has a 10 bolt cover and a 12 bolt ring gear. Impala axles do not swap. The suspension mounting is different. Most Impalas of that vintage used a three-link rear suspension with a Panhard rod.
Joe, as always thank you very very much for the information! What I'm going to do, once I get the work finished on the front suspension components, because the front of the car is jacked up so high, even I could not squeeze my scrawny body under the back of the car right now to take pictures of the rear axle and maybe find some numbers and with a pictures perhaps you can give a for-sure definitive answer as to what I have on the car! I do remember the cover being scalloped on both sides where the axle tubes are, it reminds me very much of the cover on the differential of my godson's 1972 Buick Skylark convertible. I am sure the skylarks differential is a smaller one but it was just to give you an idea of what the cover looks like.
Seems like most of the '66 big bodies I've parted out have had the Pontiac 8.875 rear end (the one with the scallops on the sides of the rear cover). All have been Lansing built cars. '66 98 should have 3.08 gears standard if no one ordered something different. I've got 3.23 and 3.42 gears and both open and posi carriers for that rear end. Not cheap. I think Fabcraft makes a 3.55 gear for it and that gear is designed to use the more common 2.73-3.08 series carrier? 3.23-3.42 and above has a different carrier. Big Pontiac '65-'70 had a better gear selection for the 8.875. 2.41 through 3.73 for sure, possibly 3.90 or 4.11 above that.
1965 Olds full size were all Pontiac axles. The Type O did not get released until the middle of the 1966 model year. Once it did, the 8.875" Pontiac was only used on the 330 and 350 powered cars. In any case, it's really easy to tell the difference. Pontiac axles have ten bolt covers and non-parallel ribs on the sides. Type O axles have 12 bolt covers and parallel ribs.
Recently stripped a '67 Delta Custom that had the optional 'Starfire' 425 engine. 375 hp maybe? Heavily loaded car. Unmolested car that had no evidence of any major component replacement. That had a 3.08 open 8.875 rear in it. Not the bigger 'O' rear end.
Recently stripped a '67 Delta Custom that had the optional 'Starfire' 425 engine. 375 hp maybe? Heavily loaded car. Unmolested car that had no evidence of any major component replacement. That had a 3.08 open 8.875 rear in it. Not the bigger 'O' rear end.
Interesting. Maybe it was plant-dependent. My 67 Delta has a Type O. 425 4bbl single exhaust car originally. The parts book indicates that the 8.875 was used on the 330 Delmont that year, and that all Ninety Eights got the 9.3. Keep in mind that the OP is talking about a Ninety Eight, not a Delta. in any case, what matters is what's in his car, and counting the bolts on the cover answers that.
Hi and THANK YOU to all for all the input! I was able to squeeze my scrawny body under the rear of our 66 Ninety-Eight that is jacked up high in the front! I am thinking it is the 8.875! I could not feel the front of the unit to see if the ribs were are parallel or not!
Thank you Joe! Suspicions confirmed! No more mystery Scooby-Doo! Jhoppeolds, thanks to as again the others, and a quick question for you. What would an Anti-Spin carrier go for on this rear axle now that we know what it is indeed?
Thank you Joe! Suspicions confirmed! No more mystery Scooby-Doo! Jhoppeolds, thanks to as again the others, and a quick question for you. What would an Anti-Spin carrier go for on this rear axle now that we know what it is indeed?
Talk to fabcraftmetalworks.com. They specialize in the 1957-64 Olds/Pontiac axles but also support the 1965-up Pontiac 8.875.
I found this thread while trying to figure out what rear end was in my 1966 Ninety Eight because I needed a diff cover gasket for a fluid change. My Ninety Eight also has the 10-bolt Pontiac 8.875 rear end. If anyone with this rear end needs a diff cover gasket, this Fel-Pro is the correct one. I hope this helps someone out in the future.
-Chris
Last edited by IHChris; August 2nd, 2023 at 08:00 PM.
Always good to read these differential threads. I learn something every time.
When I’ve had to replace mine (maybe twice across 40 years with either of 2 cars), I knew about the BOP differences from the factory literature, but I got away with replacements from 65-70 Big Olds rear ends when I needed new pieces. Generally these were boneyard rear ends which bolted up and worked, maybe with new bearings. I came away with the impression that Olds big car owners really didn’t push their cars that hard so the differentials held up well.
Along the way I had a 2.93, usually 3.08 and eventually I found 2 sets of 2.23 gears (open) for both ‘66 big cars. I didn’t like the 2.93 ratio, though the mileage was good. 3.08 was stock from factory for 98’s, and very well chosen by Olds an an optimization between off-the-line and fuel economy. I’m keeping those gears in case gas hits $15.00/gallon down the road…
But like most of us keeping these cars, off-the-line is part of the fun so I stayed on the hunt for 3.23’s just to see if I could find a set, or if I’d even like them. Answer is yup, 3.23’s are best for me - the fun is worth the additional gas cost.
I’m still sorta on the hunt for anti-spin 3.23’s, but don’t ever expect to find them. Even if I did I wonder whether its a good idea to switch to the Olds-unique cone system whose parts are yet more rare than disc brake rotors for a ‘70 big Olds…
Hi Folks, I know my thread here is pretty old, but it is about the continuing saga of fitting a limited slip rear axle onto our 1966 Ninety- Eight LS Sedan. Finally got the limited slip axle sourced from a 1967 Ninety-Eight into a spot in the garage where it is accessible even with 'Ocean Mist' in there as well. There will be lots of scraping sanding and cleaning, as well as new brake lines, wheel cylinders and seals to be fitted. I will be sharing progress along the way. The only uncertainty I will have is if my present drive shaft is the right length, I did ask on CO, and, despite the help from many, no clear answer was available, so it will be measuring C/L from axle tubes to the nose of the two differentials, and take things from there. Drive shafts can always be modified. Hopefully the same universal joint will be useable between the two, can one of our members help with this from parts number books, I get leery of Rock Auto etc as there are errors abundant especially for large Oldsmobiles. Hoping to get this project and changing upper control arm bushings changed, lowers etc were done a couple of years ago. Some sort of carburetor bug needs to be chased down as well, but I will not ask until I have statistics checked out to give clues to fellow members. So far compression checks out to be 175 give or take a few pounds between all cylinders.... To be continued! Ugly Duckling - for now! Lots of lipstick needed for this pig! A pretty big ring gear, and, surprisingly clean inside 3.08, same as I have on the open unit on the car. The recipient, 'Ocean Mist'.
January 27th, 2018, 07:32 PM
