After reading the archives I'm a little confused on this topic. I plan on taking my 8.2" rear out of my 70 firebird and putting in an 8.5". I have a th350 trans, what needs to be done in order for this to fit my car?

Chris

After reading the archives I'm a little confused on this topic. I plan on taking my 8.2" rear out of my 70 firebird and putting in an 8.5". I have a th350 trans, what needs to be done in order for this to fit my car?

Chris

Chris,

I'm studying this same swap now in a '67 LeMans. The differances are that my car is a coil sprung suspension, and yours is leaf spring. From what I can gather, the 8.5" units might be 1 to 2 inches wider from drum to drum. Have not been able to get exact measurements tho. I do know my 8.2" rear is 54.5" from axle flange to flange. The driveshaft may need to be shortened 1" to 2", as the pinion yoke sticks out further from the front of the 8.5" rear. Not sure if spring pads are different locations for 8.2 vs 8.5" leaf spring rears. I do know the brakes from your 8.2 will fit the 8.5. I don't know what cars are good donors for your car. I think you're looking for 72-up firebirds or other BOP cars with leaf spring rear ends from those years. Watch the shock mounts too, as they changed over the years.

I wish somebody would come on here and tell us what years 8.5s will fit our cars, and any length differances there are.

What is the ratio of your 8.2"? I'm thinking of rebuilding my 8.2 if I can find a 3.55 carrier.

robertg

Has the rear end been changed? It should have a 8.5 in there already, unless it's a TA. Then it would have a 8.75

You sure? I've always though it was an 8.2". I didn't think they went to the 8.5" till 73 or something like that.

If it´s a 1970 Firebird w/V8 it should have the 12-bolt rear-end. One-year only.

Chris,

Get the numbers off your rear. ID what you have for sure, then go from there. My money is on 8.2" for a Pontiac produced for US sale. Other countries, canada for example, got different drivetrain packages in the same car.

I am almost 100% sure its not a 12 bolt, I think that was for T/A's and maybe even the formula's. I will check out the ID on it. I did once before, but that was years ago. I'm pretty sure it was the 8.2". If it is, what has to be done to get an 8.5" to work?

Starting in 70, the 350 and standand 400's FB's had a 8.5(10 bolt)rear. TA's and Formula's with RA motors got 8.75(12 bolt)rears. Like Chiphead said, get the letter code off the axle tube. Post here, and we will look it up for you.

Hey Chris, I was thinking the 8.5's didn't start in the F-Bodies until 1971 so I did a search for some of Ol' Pinion Head's posts and found your post from a few years ago where he helped you on it.

http://forums.performanceyears.com/groupee/forums/a/tpc/f/64...106024621#2106024621

It still might not be the original rear end to the car so as Poncho said above, best to check the numbers or post a pic if you can to be more certain. Hope that helps, Rick

Yeah, i stumbled upon that this afternoon. I was pretty certain it was an 8.2". I hope I can get a 8.5 to fit without much hassle.

If you need a source for an 8.5 or need one set up for your car. You might call Gary Parker here in the Plano area as he builds and sells 8.5's. I bought one from him for my GTO a couple of years ago. His number is 972-578-0012

ditto what Rick said,I bought one from
gary and he shipped it to fl.It has held up great through a bunch of drag passes.

Last summer I installed an 8.5 from a 75 Ventura into my 65 GTO. A few weeks ago I purchased an 8.5, at the junkyard, from a 72 Nova. Both these are the shortest 8.5's at around 60 .5 inches(going from memory). The 70's firebirds and camaros had longer axles makeing them wider. Here is a web site with some info http://www.oldsmobility.com/10bolt-tech.htm

Just an FYI...
The Oldsmobility link gets quoted a lot, but the 8.5 r/e article was put together by a guy who seems to know a more about building weblinks, than he does about GM rearends, all the different housings, & what came in what cars http://forums.performanceyears.com/g.../icon_wink.gif Lot of misinfo & missed facts, the whole article needs to be updated.

Chris,
If Gary P is out, I have a 3.42 8.5 posi 2nd Gen r/e with 3R yoke waiting to be gone through. Have business in DFW soon, & might be able to work freshening it up in to my schedule, if interested, drop me a PM.

Chiphead,
The correct 8.5 A-body rear is a direct bolt-in in your '67, & is easily built stronger than a typical $1200 12 bolt Chevy rear. To make a 12 bolt posi rear stronger, it will require aftermarket side gears & spiders, & typically, aftermarket axles. Weak stock spider gears & often weak c-clip axles are the bane of the often hyped 12bolt.

Back to the 8.5... To fit such an 8.5 A-body rear, your factory 8.2 driveshaft will need to be shortened 1". 54.25" wide??? might check your 8.2 r/e for its casting date, & see if it is a '64-mid 66 piece. 8.2 r/e's often got swapped over the years, as most would not hold up. Having blown up more than my share of all versions of 8.2's & 12bolts, many moons ago I stumbled on the 8.5 A-body rear as the vesatile r/e to build.

Narrow vs wide... its only a 1/2 inch on each side. For most, the 1" wider A-body rears will fit easily. One can get in a jamb, however, if running rear wheels with MAJOR positive offset. Over the years of doing 8.5 A-body builds/swaps, managed to even fit an 8.5 A-body rear with 275/60/R15's on 15x8.5's under a '64 Chevelle... no A-body rear wheel houses are tighter than the '64-65 Chevelles.

For comparison, following r/e's are 54.25" backing plate to backing plate:

-'64-67 Chevelle 8.2 10bolt (c-clip junkers)
-'65-67 Chevelle 12 bolt
-'64 (small upper control arm bushings) BOP 8.2 A-body
'65-mid '66 8.2 BOP

55.25" backing plate to backing plate:
-'68-70 Buick 8.2 10bolt
-'68-72 Chevelle 8.2 10bolt (c-clip junker)
-'68-72 Chevelle 12bolt
- mid '66-69 Pontiac 8.2's (sealed bearing axles)
-'7O-72 Pontiac 8.2's (tapered axle bearings)
-'68-70 Type "O" Olds 10 bolt yes it has a 12 bolt cover, but it is a 10 bolt!
- Early 8.5 A-body (all 3 housings/tube versions)... all had bolt-in tapered bearing axle retention.

56.00+" backing plate to backing plate
(upper control arm mounts are cast too wide to use in earlier A-bodys)

-'73-77 8.5 A-body (c-clip axles)
-'73-77 8.5 A-body A-9 bearing bolt-in axles
-'74-77 8.875 M-P series A-body rear (c-clip)
-'77+ B series 7.5, 8.5, & 8.875

1968-70 A-body Buick 12-bolt and 1970-72 A/G-body Pontiac 12-bolt would fall into the 1968-72 Chevelle 12-bolt cathegory, only they use the "big" GM universal joint.

OPH,

Can you ID this rear end for me? Its in my '72 LeMans parts car. I can only find this number cast into the center housing at driver's side rear:

9799100 (maybe 8799100?) First number hard to make out.

what is this rear? 8.2"? 8.5"?

thanks!

Chiphead,
1st number will def be a 9, as the sequence is common Pontiac casting & it is much larger # than the bare '69 housings that we have.

With that large a 9799xxx number, my bet is the housing is the original 8.2 non nodular Pontiac housing to the particular '72 LeMans. Currently have four '70-72 LeMans I'm processing & parting, will ck the '71 & 72's & confirm later today.