NEED HELP WITH DIFFERENTIAL SWAP

[Julian Sepulveda]

I own a 1970 skylark with gm 8.2. I am currently looking to swap to a gm 8.5. A friend told me that a good swap would be to take a differential from a 77 cutlass. 

 

Question 1: Will this be a direct bolt in? If not, how much would it cost to adapt it to fit? Is this worth the effort or should I look for a different one?

 

question 2: Are any parts interchangeable between the two? I remember reading that the axles and shoe brakes are interchangeable, as they are both bolt in axles, but this sounded like fishy information.

 

Question 3: If this differential will not work, what would be a good donor car to find a proper differential? 

[padgett]

Why do you want to change, are plenty of ratios available in 1970 10 bolts (what you have) and 12 bolts (stronger) ?

[Julian Sepulveda]

18 minutes ago, padgett said:

Why do you want to change, are plenty of ratios available in 1970 10 bolts (what you have) and 12 bolts (stronger) ?

hard to find a 12 bolt around here and a lot of people online are charging and arm and a leg for their shoddy pre owned ones. I am planning to swap the engine in a few years to a 454 (I have a chevy 350 in it currently) and many people have told me that the 8.2 probably won't hold for long with any higher horsepower applications. learned that an 8.5 with a posi would be a good way to go, as it can handle higher horsepower and there is a lot of aftermarket support for it.

[padgett]

and the current rage, Ford 9"s won't work ? Suspect this needs to be asked in a different arena, maybe the Buick forum.

[Julian Sepulveda]

3 minutes ago, padgett said:

and the current rage, Ford 9"s won't work ? Suspect this needs to be asked in a different arena, maybe the Buick forum.

I just got a bunch of dudes getting ticked off that I wasn't a purist

[padgett]

Yes you need to promise to keep all of the original parts in baggies for restoration purposes. (I do, even have baggies of parts for cars I no longer own...)

[bryankazmer]

I think a more realistic approach is to sell the removed parts to others restoring similar cars.  This one's not going to be a future restoration candidate, the remainder of its life will be as a rod.

[joe_padavano]

4 hours ago, Julian Sepulveda said:

I own a 1970 skylark with gm 8.2. I am currently looking to swap to a gm 8.5. A friend told me that a good swap would be to take a differential from a 77 cutlass.

 

Time to find friends who are better informed. The 73-77 A-body cars have a wider track and thus a wider rear axle than do the 68-72 cars. It is not a bolt-in. Any 68-72 A-body axle is a bolt-in.

You'll likely find more useful info on modifications at a site like hotrodders.com.

[padgett]

That's why I have the unsafe 14x6s in baggies and would give to a NO if they want them (have a lot of baggies from sales to people who did not).

[1912Staver]

5 hours ago, padgett said:

and the current rage, Ford 9"s won't work ? Suspect this needs to be asked in a different arena, maybe the Buick forum.

 

 

9 " Fords can be installed but need a lot more work than a A Body housing. 70 Skylarks use  a 4 link set up with coil springs. The most common 9 " typically use leaf springs. Housings with the necessary brackets are available but somewhat pricy. 

Greg in Canada

[jan arnett (2)]

Why not try HAMB.

 

[Matt Harwood]

Find a garden-variety 10-bolt out of a 68-72 V8 A-body and it'll bolt right in. Get one out of a 4-door and it'll have a 2.73 or 3.08 gearset that'll be an easy cruiser. A 10-bolt is plenty strong for street driving. You won't ever break it unless you install some sticky tires behind a serious engine. You don't need a 12-bolt or a 9-inch conversion which will be far more trouble than it's worth. Simple is better and almost nobody drives their collector cars hard enough to justify the heavy-duty parts they think they need.

 

 

Edited February 6, 2020 by Matt Harwood (see edit history)

[Julian Sepulveda]

6 hours ago, joe_padavano said:

 

Time to find friends who are better informed. The 73-77 A-body cars have a wider track and thus a wider rear axle than do the 68-72 cars. It is not a bolt-in. Any 68-72 A-body axle is a bolt-in.

You'll likely find more useful info on modifications at a site like hotrodders.com.

Is there any way to fabricate it to make it fit? roughly how much would that cost?

[joe_padavano]

5 hours ago, Julian Sepulveda said:

Is there any way to fabricate it to make it fit? roughly how much would that cost?

People narrow rear axles all the time. It will cost more than buying the correct one.

[Zimm63]

So Matt, those damn L60s would explain why I broke the rear, tranny, engine, etc on my Camaro as a kid?   Nothing to do with it only having two throttle settings?  As in on and off?  

 

I got real good at changing clutches on that car.  Outside in the winter too.  

 

 

 

[CarlLaFong]

14 hours ago, jan arnett (2) said:

Why not try HAMB.

 

Because The HAMB has standards and OT vehicles and talk of them are quickly deleted by the mods

[Julian Sepulveda]

15 hours ago, jan arnett (2) said:

Why not try HAMB.

 

what is HAMB?

[The 55er]

Google HAMB The Jalopy Journal and find out!

[joe_padavano]

32 minutes ago, The 55er said:

Google HAMB The Jalopy Journal and find out!

 

H.A.M.B. limits cars discussed to 1964-older. I would not recommend that site. Again, as I noted above, your best bet is hotrodders.com.

[Pfeil]

Some history on the carriers used. The earliest Pontiac 8.2 Safe-T-Track carriers introduced for '64 Pontiac A bodies, all were 2 pinion cone type posi carriers. In good shape, these hold up fine in good shape in putt-a-round stock type cars with narrow stock type tires. For '66, the 4 pinion low ratio (3.36-5.57) STT carrier was introduced, as the 2 pinion 8.2 units weren't holding up well under higher torque load applications. The new 4 pinion STT cone type carrier was also avail as a service piece for warranty work on '65 models. Interestingly, Olds manual trans 442's received Pontiac 8.2 10 bolts. When ordered with low ratio gearing, the 442's recieved the 4 pinion STT units. Pontiac's 8.2 gray iron center hsg was cast with much more strength than the Buick 8.2 center housing, thus Olds needed it behind the early 400 Olds and a 4 spd.

Width... Pontiac increased the width of their division's Abody rearends for the '66 models, this same width stayed under Pontiac A body's and most GM Abodys through the '72 models. NOTE: A few of the very earliest usage '66 Pontiac A body rears have been documented to be of the narrower '64-65 width. Last, Chevrolet's Malibus/Chebelles/ Elco's all stuck with the narrower A body rearend through their '67 models.

Pontiac for '67, totally understanding the need for a stronger differential, esp with its stronger and stronger optional engines, and in an effort to reduce warranty claims, began casting its higher performance ratio 8.2 10 bolt housings out of nodular cast iron. Looking back, this was a bandaid in the overall picture, but any effort to reduce center hsg flex in the pinion area helps insure ring and pinion longevity. Have torn down dozens of blown up standard gray iron 8.2 rears that owners spent a lot of coin on hard to find at the time tight 4 pinion carriers, low ratio ring & pinions, and then blew the R&P to pieces at the strip in, for the most part, mid to low 13 sec automatic GTO's and early F85's. Picking up the pieces, and starting over, one eventually gets smarter.

More timeline history... Sometime between '67 and '68, the HD Safe-T-Track Pontiac 8.2 10 bolt rears were introduced. These included the nodular center hsg, the 4 pinion STT carrier and newly introduced HD forged axles. The HD Safe-T-Track 8.2 Pontiac in Pontiac A body's was only avail with 3.90's and 4.33 gearing. Have gone through the rebuilding of over a dozen HD STT's, not something one runs across very often.

By the '68 models, Pontiac became the only GM division using the Pontiac 8.2 10 bolt. Due to neccessity, Buick came out with their own strengthened BUICK 8.2 10 bolt for '68-70. Housing design, carrier design, ring and pinion design, axles spline pitch, all are different than the Pontiac 8.2 10 bolt. Note: the much strengthened BUICK 8.2 was used under the heavy and often very quick '70 Buick GS Stage 1's (stock 500ft lbs of torque)

Olds, also for '67, came out with their own rearend design, the Type "O" 8.4" 10 bolt. The Olds guys love to refer to them as 12 bolts, but only the smooth cover has 12 bolts, in actuality, the ring gear is an 8.4" diam 10 bolt. The type "O" Olds design was used through the '70 model year Cutlasses and 442's, and again only under Olds vehicles. Both the Buick and Olds designed rears are relatively strong in top condition, stronger than the previous gray iron 8.2 Buick and 8.2 Pontiac provided rears that were under the Buick and Olds A body's from '64-67. Desirable ratio ring and pinion sets and posi's are expensive for both, more so than parts for the Pontiac 8.2. I've rebuilt quite a few of each, and up till recently, for the BUICK version there were no aftermarket gear sets.

Like Pontiacs 8.2 10 bolt, both the Type "O" and the late BUICK 8.2 had rearend housing ends which were changed slightly for the '70 model, as GM went to tapered axle bearings in all their bolt in axle A body rears. This move coincided with the introduction of wider 70 series and 60 series tires beginning in '69 in OEM applications. GM's performance A body's and early Firebirds with sealed axle bearing rears were not designed for the increased side loading, thus the move to much more positive axle retention with a splash lubricated tapered axle bearing and external seal. The great thing about tapered axle bearings, they don't seize and chew up the axle mating surface like the preceding sealed style axle bearings.

1970... new decade, some would say the pinnacle year of the first Musclecar Era... for '70 model Pontiac GTO's built with the 455 engine, Pontiac engineers gave up on the 8.2 Pontiac 10 bolt rear and specified a McKinnon built 12 bolt rear, complete with slightly stronger cc-clip axles and a larger 3R joint flange than was used on standard usage Malibu/Chevelle 12 bolts. The major weak spot... the Eaton posi units used in the 455 application 12 bolts is they still had the same brittle spider gears and side gears as was used in nearly every oem application chevy 12 bolt Eaton Posi. Unless the rear is going back in a Putt-A-Round car, in a build, I prefer to always replace the side gears and spiders in these factory Eaton 12 bolt carriers. Have ran across too many high 12 sec cars that have shattered the small brittle spider gears.

Buick and Olds for '71 models introduced the 8.5 A body rearend under their A body product lines. Firebirds and Camaro's for '71 also received their own version, but with c-clip axles. Designed with a longer pinion and more pinion support in the center hsg than any previous GM A body differential, the '71-72 8.5 A body rear wasaver on three different housings, and was avail with two different size tapered axle bearing axles. In repetitive abuse on the street and strip, as a GM offered rearend, very hard to beat the 8.5 A body rear both in strength, availabilty of parts, and in total cost to build. Interstingly, the same strength stock axles that found themselves behind a 6cyl Skylark were also run behind '71 Stage1 and W30 models. Buick and Olds joint effort didn't cheap out on the metalurgy of the axles.

[joe_padavano]

32 minutes ago, Pfeil said:

Some history on the carriers used.

 

Great summary, thanks. One minor correction and some additional trivia. The Type O A-body axle was released in May 1966 and was installed in some late 1966 cars. The 1966 version actually has the 64-66 style spring perches and is quite rare. The 67 Type O housings are the same part number (and thus the same width) as the 1968 housings. Another tidbit is that while the Type O only has an 8.5" ring gear held by ten bolts, those bolts are larger than the ones used on the vaunted Chevy 12 bolt and the ten of them will actually carry more axle torque than the twelve bolts holding the Chevy ring gear. Clearly, this is only one area when comparing strength - bearings, gear tooth contact pressure, and axle shaft diameter are all important. The Olds axles DO have the shafts retained at the outboard ends, not with those stupid C-clips, however. And this obviously only applies to the A-body cars. The Olds full size cars used a different Type O axle that had a 9.3" ring gear held on by twelve bolts.

[Pfeil]

9 minutes ago, joe_padavano said:

 

Great summary, thanks. One minor correction and some additional trivia. The Type O A-body axle was released in May 1966 and was installed in some late 1966 cars. The 1966 version actually has the 64-66 style spring perches and is quite rare. The 67 Type O housings are the same part number (and thus the same width) as the 1968 housings. Another tidbit is that while the Type O only has an 8.5" ring gear held by ten bolts, those bolts are larger than the ones used on the vaunted Chevy 12 bolt and the ten of them will actually carry more axle torque than the twelve bolts holding the Chevy ring gear. Clearly, this is only one area when comparing strength - bearings, gear tooth contact pressure, and axle shaft diameter are all important. The Olds axles DO have the shafts retained at the outboard ends, not with those stupid C-clips, however. And this obviously only applies to the A-body cars. The Olds full size cars used a different Type O axle that had a 9.3" ring gear held on by twelve bolts.

 

" The Olds full size cars used a different Type O axle that had a 9.3" ring gear held on by twelve bolts."

 

 Tell me Joe, a 9.3 in a post 1964 Salisbury axle?? If so would that include Pontiac / entire GM line sans Cadillac?

[joe_padavano]

12 minutes ago, Pfeil said:

 

" The Olds full size cars used a different Type O axle that had a 9.3" ring gear held on by twelve bolts."

 

 Tell me Joe, a 9.3 in a post 1964 Salisbury axle?? If so would that include Pontiac / entire GM line sans Cadillac?

 

The 66-up Type O 9.3 is unrelated to the 57-64 Olds/Pontiac axles. No parts interchange. Yes, it's a Salisbury axle. Technically it's 9 3/8". The 66-70 9.3 Type O was used in full size Olds and I think Buick cars. I'm pretty sure Pontiac stayed with the 8.875 Pontiac axle (12 bolt ring gear, ten bolt cover). Olds used the Type P axle under lesser full size cars for 1965-68 model years.

[Pfeil]

23 minutes ago, joe_padavano said:

 

The 66-up Type O 9.3 is unrelated to the 57-64 Olds/Pontiac axles. No parts interchange. Yes, it's a Salisbury axle. Technically it's 9 3/8". The 66-70 9.3 Type O was used in full size Olds and I think Buick cars. I'm pretty sure Pontiac stayed with the 8.875 Pontiac axle (12 bolt ring gear, ten bolt cover). Olds used the Type P axle under lesser full size cars for 1965-68 model years.

 Well I never! thanks for that information. Being into Pontiac's I don't think I ever paid attention. I always knew about the 8.875. So it seems the "B" bodies got the 8.875 and the "C" bodies sans Cadillac got the 9.3.

Learn something new here all the time.

[joe_padavano]

4 hours ago, Pfeil said:

 Well I never! thanks for that information. Being into Pontiac's I don't think I ever paid attention. I always knew about the 8.875. So it seems the "B" bodies got the 8.875 and the "C" bodies sans Cadillac got the 9.3.

Learn something new here all the time.

 

Well, at Olds, the Type P was used on all 1965 B/C-body cars. The 9.3 Type O did not get released until part way through the 1966 model year. At that point, there was a phase in. The 1966 Jetstar 88 still used the A-body derived axle. The 425 2bbl cars got the Type P. The higher HP and heavier cars got the Type O. Delta 88s with the 365 and 375 HP motors got the 9.3. In 67-68 the Delmont with the 330 got the Type P and all other B/C-body cars got the 9.3. My 67 Delta 88 came with a 9.3. By 69 Olds stopped using the Pontiac axle and only used the 9.3 on all B/C-body cars. I am not that familiar with what other divisions did.

[Pfeil]

16 minutes ago, joe_padavano said:

 

Well, at Olds, the Type P was used on all 1965 B/C-body cars. The 9.3 Type O did not get released until part way through the 1966 model year. At that point, there was a phase in. The 1966 Jetstar 88 still used the A-body derived axle. The 425 2bbl cars got the Type P. The higher HP and heavier cars got the Type O. Delta 88s with the 365 and 375 HP motors got the 9.3. In 67-68 the Delmont with the 330 got the Type P and all other B/C-body cars got the 9.3. My 67 Delta 88 came with a 9.3. By 69 Olds stopped using the Pontiac axle and only used the 9.3 on all B/C-body cars. I am not that familiar with what other divisions did.

 

  I will have to get into my library and check on those Grandville's and Bonneville's that had  455's. I would think they would have a 9.3 Type O. You probably remember that at this point in time GM was getting into the powertrain standardization phase like T400 for all, even BBC. My guess is Pontiac has it in the big cars. We'll see.