Narrowing an 8 1/4" rear end, how is it done?

-
jcwren

jcwren

FABO Gold Member
FABO Gold Member
Joined
Nov 23, 2019
Messages
53
Reaction score
22
Location
Clarkesville, GA
OK, not the greatest title, but whatever.

My '67 Barracuda has a GM 8.2 rear end on it, for who knows what reason. I found a 8 1/4" 3.21 4.5" bolt pattern open rear end that's already had the perches moved for an A-body. Problem is it's supposedly 63" flange to flange, but the guy didn't get around to narrowing it because he found a 8 3/4". The price is too good to pass up. I've never narrowed a rear end, but I do know the axle tubes and axles will need to be shortened. Are the axle tubes something a typical driveshaft shop would do? As far as the axles themselves, shorten them (if it's doable)? Or am I better off looking for a set of new or used axles?

This is going behind an A833 trans with a 360 Magnum engine. No outrageous HP :)
 
I had a 74 Duster crate 380hp 360 4 speed and a 8 1/4'' 3.21 rear.It held up ok meaning I never broke it.
Axle tube ends are the same as the 8 3/4 so no problem buying those.Same with new perches.
Axles I have no idea if the splines are long enough to cut down. It may be possible to get custom length.
Hope your local Driveshaft shop does differentials too.
 
63" flange to flange? Better break out your tape measure and double check that. Not even trucks or Imperials had rear ends that wide. You may be thinking of an outside drum to drum measurement...
To cut an 8.25 housing, you must have a jig to hold the housing ends perfectly square- it uses a caged flat roller bearing that rides directly on the axle (no inner race,) so it MUST be square and on center, or you will eat bearings and axles.
Doubtful that the axles can be shortened, the shaft necks down in diameter immediately after the splines, which doesn't leave enough meat to cut new splines into. In addition, an 8.25 uses a C-clip for axle retention, meaning you'll have to cut a new groove in the splines of each axle at the appropriate length.
All this means you'd probably be better off having new axles made by someone like Moser Engineering, who could also cut the housing for you.
Truth be told, by the time you invest in all this, you'd be money ahead just finding the right rear for your A body.
If, perchance, it turns out you have a narrower rear than you thought, you may be able to get away with just using rear wheels with a deeper backspacing- people have been doing this with B body rears in their A bodies for years.
 
I’m guessing your GM 8.2 rear axle is probably from a Chevy II or 1st Gen Camaro. Unless it’s a complete hack job, I would probably just run it. It’s got 28 spline axles compared to the 8-1/4’s 27, and parts availability and aftermarket support is much better. Aftermarket custom axles (Dutchman makes really good C clip axles for a reasonable price) with Mopar bolt pattern and drum register / stub out length are an option, as well as disc brakes if you wanted.
 
Professor Fate said:
63" flange to flange? Better break out your tape measure and double check that. Not even trucks or Imperials had rear ends that wide. You may be thinking of an outside drum to drum measurement...
To cut an 8.25 housing, you must have a jig to hold the housing ends perfectly square- it uses a caged flat roller bearing that rides directly on the axle (no inner race,) so it MUST be square and on center, or you will eat bearings and axles.
Doubtful that the axles can be shortened, the shaft necks down in diameter immediately after the splines, which doesn't leave enough meat to cut new splines into. In addition, an 8.25 uses a C-clip for axle retention, meaning you'll have to cut a new groove in the splines of each axle at the appropriate length.
All this means you'd probably be better off having new axles made by someone like Moser Engineering, who could also cut the housing for you.
Truth be told, by the time you invest in all this, you'd be money ahead just finding the right rear for your A body.
If, perchance, it turns out you have a narrower rear than you thought, you may be able to get away with just using rear wheels with a deeper backspacing- people have been doing this with B body rears in their A bodies for years.
Click to expand...
Good advice, thanks!

Yeah, 63" made me wonder, I couldn't find anything on the various charts that wide, even allowing for a slight measurement error. But as far as I know (which isn't much...), there's not a 8 1/4" that's too narrow for an A-body. Everything else is wider. Finding the right rear seems to be tricky. 8 3/4" are expensive to start with, and finding one for an A-body seems to be a holy grail. I don't see an 8 1/4" being a problem since this isn't a drag car and a very mild 360 should be well within what it can handle unless I do something really stupid with the clutch. I have a little flexibility in the backspacing, but not much, and I think it's only in 1" increments.
 
Garrett Ellison said:
I’m guessing your GM 8.2 rear axle is probably from a Chevy II or 1st Gen Camaro. Unless it’s a complete hack job, I would probably just run it. It’s got 28 spline axles compared to the 8-1/4’s 27, and parts availability and aftermarket support is much better. Aftermarket custom axles (Dutchman makes really good C clip axles for a reasonable price) with Mopar bolt pattern and drum register / stub out length are an option, as well as disc brakes if you wanted.
Click to expand...
The biggest negative against this rear end is that it's currently a 5 x 4.25" bolt pattern, and the front is 5 x 4.5" (it has spindles, etc from a '73 with disc brakes). One option is to re-drill the axles, and there is someone local I found that can do it. It being a C-clip axle means there aren't any holes drilled in the stud plate, so the new bolt pattern can be drilled halfway between the old one. I do need to confirm the outside drum to drum measurement to make sure the wheels I want to run are available in whatever backspacing that turns out to be. And I would like to put discs on the rear.
 
I calibrate my bandsaw blade to cut perfectly at 90° through a 3" tube. I level the table, and then I level the housing to match the table.

From there, they sell an axle housing fabrication kit that uses bars to center the ends on the axle tubes so that you can weld them on without them shifting too much. These kits are expensive and they're axle specific. Call around and see if there's a 4x4 shop that will let you rent theirs for a day or so.

Burn the new ends on and then weld new perches on to get your desired pinion angle.

Done. Move onto the next thing.

Here's an example of this process on my Dana 60. Those axles tubes were thick!

20210418-125103.jpg


20210418-131941.jpg


20210424-114246.jpg
 
Last edited:
Being a 67 Barracuda and not a Dart, you can use a early "B" like a 1963 Housing.and just install new perches.
It's one of the narrow ones 62-65. Check with Dr.Diff web site for all the information and axle kits to do the job.
You can leave him (Cass) a e-mail. He usually responds in a day or so.Great guy.
 
jcwren said:
it's currently a 5 x 4.25" bolt pattern, and the front is 5 x 4.5" (it has spindles, etc from a '73 with disc brakes). One option is to re-drill the axles, and there is someone local I found that can do it.
Click to expand...
Redrilling the axles is only viable if you’ve got enough material on the outside of the register to move the stud out .125. There should be at BARE MINIMUM 1.5 bolt diameters from the edge of the hole to the outside diameter of the flange, with 2 bolt diameters preferred for tear-out strength. I still recommend a set of new Dutchman axles for the $400 or so (last time I checked) because stronger material and the probable age of your existing axle shafts. You can pull a shaft to tell, but if your at 1/2 spline of twist at the end of the shaft, they’re pretty well done.
 
jcwren said:
The biggest negative against this rear end is that it's currently a 5 x 4.25" bolt pattern, and the front is 5 x 4.5" (it has spindles, etc from a '73 with disc brakes). One option is to re-drill the axles, and there is someone local I found that can do it. It being a C-clip axle means there aren't any holes drilled in the stud plate, so the new bolt pattern can be drilled halfway between the old one. I do need to confirm the outside drum to drum measurement to make sure the wheels I want to run are available in whatever backspacing that turns out to be. And I would like to put discs on the rear.
Click to expand...
In this case, I would seriously consider just going down to the local Pick 'n Pull and grab an 8.25 out of a Jeep Liberty... Why? Many already have 3.55+ gears in them, limited slip, and they already have disc brakes on them.
Width is a touch wide ~55 1/2" flange to flange if I remember correctly (the commonly used B body 8.75 is 54 15/16, so you're only about 1/4" wider than that per side). That can be made up for with offset wheels.
Pros? All the desireable equipment is already on/in the diff, ready to go. No additional cash outlay. (Especially a good deal on Half Price days at the PnP...!)
Cons? There's lots of unnecessary Jeep bracketry that will need to be cut off and properly spaced perches welded on at the correct pinion angle, but you'll probably have to end up doing that regardless of whatever rear you use. Additionally, depending on the year, it may have a flange-type pinion yoke that will need to be dealt with, either by replacing with a U joint yoke or using the driveshaft end adapter from the Jeep, possibly with an adapter U joint. And a little minor fab work getting the parking brake cables hooked up.
 
Last edited:
63” wide would make it an 8.25 out of a ‘71-‘74 B-body. Even for a Barracuda that will be too wide.

I run a ‘68-70 B-body 8 3/4 in my Duster, it’s 60 1/8” wide and can be dealt with using positive offset wheels. I run 18x10’s with a 7” backspace with a 1/2” offset spring kit from DoctorDiff with the perches at 42”.

I would pass on the 63” 8.25”, by the time you narrow that and get new axles you could have done something else. As @Professor Fate said there are more modern 8.25” options. There’s also the Ford 8.8 out of an Explorer. They have the correct bolt pattern, came with 3.73’s and disk brakes. Many were limited slips too. Your barracuda could use one in its stock width, or you can get two “short side” axles and shorten the long tube side of the 8.8”, which is more straightforward. There’s several threads going on using the 8.8” already here to check out
 
Geez, every time I go to do something, it seems like it turns into a dive down a rabbit hole. While I don't mind spending money, I like to spend it effectively and not wind up with parts I can't use because I don't necessarily know what I'm looking at, or it turns out one of the parts I need is no longer made, or whatever. All I want is a dang 8 1/4" sure-grip axle under this thing :) And I want to get it on the road this year.

I think the first option I'll go with is checking if the existing axles can be redrilled or not, followed by replacing the axles with ones on a 5 x 4.5" bolt pattern. If I have to swap the rear end, I'll continue to keep an eye out for a 8 1/4" from a 62' to 65', and if I can't find that in a reasonable time period, then a Jeep Liberty or Ford 8.8 rear end. I know those last two are far more available.

I've done hobby auto mechanic work most of my life, but it's always tended to be service and repair things or replacing like for like, not swapping rear ends (of a different type), converting an automatic to manual shift, replacing a front clip, etc. That puts me at the base of the learning curve, and a lot of things you folks with experience already know, I have to learn, sometimes the hard way. While I've always liked Mopars, the '71 Dart and the '67 Barracuda are my first ones, and I lack a lot of Mopar specific knowledge. I definitely appreciate the help and advice.
 
jcwren said:
I'll continue to keep an eye out for a 8 1/4" from a 62' to 65'
Click to expand...
Just so you know, there were no '62-'65 8.25s. I believe the reference was made regarding 8.75 differentials.
8.25s didn't come on the scene until early to mid'70s.
 
Just for fun. If I remember correctly…73-76 A body 7 1/4 and 8 1/4 are the same width at 54.40”. Flange to flange, not drum to drum.
8 3/4 will be stronger. Find a C body housing and narrow. Buy axles from dr diff.
Or sell the 8 1/4 and put towards A Body 8 1/4 or 8 3/4.
Just some ideas.
 
jcwren said:
Geez, every time I go to do something, it seems like it turns into a dive down a rabbit hole.
Click to expand...
Yup. Welcome to hot rodding in general, and Mopars in particular!
Look at the bright side, it could be worse. You could be into AMCs.
 
jcwren said:
The biggest negative against this rear end is that it's currently a 5 x 4.25" bolt pattern, and the front is 5 x 4.5" (it has spindles, etc from a '73 with disc brakes).
Click to expand...
Near as I can tell, General Mao has never used a 4¼" bolt pattern. GM's car bolt pattern is 5 on 4¾"--larger than Chrysler, Ford, and AMC's 5 on 4½". The Mopar "BVD" bolt pattern is 5 on 4". Ford used the oddball 4¼" pattern on some RWD cars, but as far as I'm aware they were all IRS (Thunderbird, Mark VIII, Continental). The Eagle Premier/Dodge Monaco twins used it, too, but they were FWD.
Whatever the axle is, it ain't a GM 8.2" unless you're off on the measurement.

All A-body 8¾" axles share the same dimensions from 1965-'72 (supposedly 50 1965 cars were built with it for homologation) and fit models through 1976. The 8¼" was first used in 1969 B-bodies, but didn't appear in A-bodies until '73.

The 8¼" just isn't worth the effort to narrow it. The labor & material are less to narrow a C-body/truck 8¾", which is far stronger.
 
NoCar340 said:
Near as I can tell, General Mao has never used a 4¼" bolt pattern. GM's car bolt pattern is 5 on 4¾"--larger than Chrysler, Ford, and AMC's 5 on 4½". The Mopar "BVD" bolt pattern is 5 on 4". Ford used the oddball 4¼" pattern on some RWD cars, but as far as I'm aware they were all IRS (Thunderbird, Mark VIII, Continental). The Eagle Premier/Dodge Monaco twins used it, too, but they were FWD.
Whatever the axle is, it ain't a GM 8.2" unless you're off on the measurement.

All A-body 8¾" axles share the same dimensions from 1965-'72 (supposedly 50 1965 cars were built with it for homologation) and fit models through 1976. The 8¼" was first used in 1969 B-bodies, but didn't appear in A-bodies until '73.

The 8¼" just isn't worth the effort to narrow it. The labor & material are less to narrow a C-body/truck 8¾", which is far stronger.
Click to expand...
Sri, brain fart. I knew it was 1/4" different from the bolt pattern on the front, which is 4.5". I probably had 4 1/4" stuck in my head because of the 8 1/4".

The question is: Can I find an 8 3/4" anything that's within 400 miles of Atlanta and isn't going to cost $1200+?
 
You can contact Stevens Performance Used parts (256-247-1332) I believe they may be the closest.
They are in Alabama if I remember. A body used housing either 8 1/4 or 8 3/4 he may have.
I needed 1 3/4'' small bolt a body 10'' drums before they were reproduced. He had 'um.
Just a thought.
 
How is the overall installation of the GM 8.2 axle? Is it one of the 10 bolt 8.2 axles or one of the BOP axles with the 12 bolt cover? If the installation of the existing axle is well done and operational, redrilling would be very simple to do. I don’t see your combination breaking that axle, and C clip eliminator kits are available, too.
Drill Guide
 
It's a 10 bolt 8.2. It appears to me to be reasonably well installed, but I'm no expert. Haven't driven it yet, I'm waiting for some shift linkages to arrive.

PXL_20230330_003112901.jpg


PXL_20230330_003210233.jpg
 
Sorry, but I had to laugh at the shock plate. It might just work OK, but it reminded me of the E-body air shocks the previous owner "adapted" to my Trans Am by welding a bolt to the bottom of the lower eyering. As if that wasn't enough, he then welded the bolt to the shock plate after securing it with a nut--a nut which he then welded to both the bolt and the other side of the shock mount. I guess in his world, bushings were for the weak and old. :p
 
Last edited:
NoCar340 said:
Sorry, but I had to laugh at the shock plate. It might just work OK, but it reminded me of the E-body air shocks the previous owner "adapted" to my Trans Am by welding a bolt to the bottom of the lower eyering. As if that wasn't enough, he then welded the bolt to the shock plate after securing it with a nut--a nut which he then welded to both the bolt and the the other sideof the shock mount. I guess in his world, bushings were for the weak and old. :p
Click to expand...
Yeah, that's a little sketchier than I realized. I've spent most of my time so far on the top side car fixing a few issues.

PXL_20230330_005855377.jpg
 
Yeah, it definitely could use a set of A body spring plates! But I would check the perch to axle tube welds closely, for definite… On the subject of an 8-1/4, some people have taken them and narrowed them with 8-3/4 / Dana housing ends and ordered Dr. Diff Green bearing axles with 27 splines. It’s also possible to upgrade to later 29 sure grip and axles in the earlier case, too. An LPW cap stud and Girdle make for a nice upgrade on an 8-1/4, too. I do know that an 8-1/4 does absorb less power than an 8-3/4 does. Less housing flex, plus they’re a little more efficient than the late fifties hypoid drive angle.
 
You must log in or register to reply here.
-

Back
Top