8 3/4

[Brandini]

Hello I am looking to upgrade my rear end to the 8 3/4 was thinking of shortening a different body rear end and using a big bolt pattern. Will the brake assembly from a small bolt pattern work with the big bolt pattern axles or would I need to buy new brake assembly?

 

[Bad Sport]

What model car do you have?

 

[Brandini]

What model car do you have?

69 Barracuda, I’m not sure what the rear end housing is out of but is wider and a friend is narrowing it down.

 

[318willrun]

8.25 backing plates/brakes are very easy to find and work nicely with the large bolt pattern. Just a thought

 

[Dana67Dart]

7 1/4" rear backing plates are NOT compatable with A B C or E body 8 3/4 axle / housing combos.

If you are narrowing a B C E housing and narrowing the axles you would need the backing plates off of the same or 8 1/4 as noted above.

 

[cudamark]

The backing plates need to match the shoe width and diameter.

 

[Dana67Dart]

The backing plates need to match the shoe width and diameter

And axle back spacing. 5x4 1/2 BBP use a different spacing than 5x4 SBP

 

[AJ/FormS]

Hello I am looking to upgrade my rear end to the 8 3/4 was thinking of shortening a different body rear end and using a big bolt pattern. Will the brake assembly from a small bolt pattern work with the big bolt pattern axles or would I need to buy new brake assembly?

I don't think it will work, at least not without a whole lot of measuring and figuring. I made that mistake and had to fabricate 1/4 inch spacers to push my backing plates out out of the drums . Which made my splines that much shorter.... so I had to widen my thrust spacer. Thankfully, there was still enough spline left to engage my cone-clutches. Or something like that; it was a loooong time ago.

 

[SGBARRACUDA]

7 1/4" rear backing plates are NOT compatable with A B C or E body 8 3/4 axle / housing combos.

If you are narrowing a B C E housing and narrowing the axles you would need the backing plates off of the same or 8 1/4 as noted above.

Not 100% true. The later 10 bolt rear cover Hybrid 7 1/4 Backing plates do work with 8 1/4, 8 3/4, Dana60. They are 5 bolt backing plates and are 10x2 1/2". Will bolt right on.

 

[72bluNblu]

Not 100% true. The later 10 bolt rear cover Hybrid 7 1/4 Backing plates do work with 8 1/4, 8 3/4, Dana60. They are 5 bolt backing plates and are 10x2 1/2". Will bolt right on.

Correct. All BBP backing plates will interchange with any of the BBP axles, doesn't matter if the housing is 7.25, 8.25, 8 3/4 or Dana 60. The axle flange offset was the same for all of them.

What you can't do is mix and match SBP and BBP backing plates. The plates have a different offset from the end of the housing to make up for the axle flange stand off difference.

 

[Dana67Dart]

BBP axles, doesn't matter if the housing is 7.25,

BBP 7 1/4 has a bearing the same OD as the 8 3/4, and 5 bolt holes?

 

[72bluNblu]

BBP 7 1/4 has a bearing the same OD as the 8 3/4, and 5 bolt holes?

No idea on the bearing, I doubt it since the tubes are smaller. The axles don’t interchange, just the backing plates.

As for the flange bolts, the 7.25 only had 4. But the backing plates usually had 5 holes, and the 4 are the same. If a backing plate is missing the 5th hole it can just be drilled.

You can use BBP 7.25” backing plates on a BBP axle 8 3/4. Had a BBP 7.25” in my Duster before I swapped to the B-body BBP 8 3/4. The brakes are the same.

 

[General-Duster]

Tricky subject the 'old A-Bod' 8 3/4.
Even if you find an original A-bod 8 3/4 it has the 4 inch pcd axle shafts.
The narrowest 4 1/2 pcd axle shaft is still too wide for an A-bod unless its a Duster.
You can use a 66-67 B-Bod axle complete in a Duster as it fits real nice.
All pre 70 A-bods need a complete axle revamp to get the 4 1/2 pcd shafts...
By the time you do all the work its gonna get expensive indeed!
Just try and find a done one methinks.
If you was in the UK I could have helped you out with this.
Best wishes from Limey John

 

[General-Duster]

Tricky subject the 'old A-Bod' 8 3/4.
Even if you find an original A-bod 8 3/4 it has the 4 inch pcd axle shafts.
The narrowest 4 1/2 pcd axle shaft is still too wide for an A-bod unless its a Duster.
You can use a 66-67 B-Bod axle complete in a Duster as it fits real nice.
All pre 70 A-bods need a complete axle revamp to get the 4 1/2 pcd shafts...
By the time you do all the work its gonna get expensive indeed!
Just try and find a done one methinks.
If you was in the UK I could have helped you out with this.
Best wishes from Limey John

ps Back in the day we used to re drill the 4 inch pcd shafts to 4 1/2 inch.
You can re-drill the brake drums too and then you have 4 1/2 axle shafts.
Only problem is, the steel wheels don't have a center register sit on.
But if you use long 1/2 studs, and replace the piddly 7/16'', you can safely fit aluminum wheels.
Not recommended for drag race duties...

 

[72bluNblu]

Tricky subject the 'old A-Bod' 8 3/4.
Even if you find an original A-bod 8 3/4 it has the 4 inch pcd axle shafts.
The narrowest 4 1/2 pcd axle shaft is still too wide for an A-bod unless its a Duster.
You can use a 66-67 B-Bod axle complete in a Duster as it fits real nice.
All pre 70 A-bods need a complete axle revamp to get the 4 1/2 pcd shafts...
By the time you do all the work its gonna get expensive indeed!
Just try and find a done one methinks.
If you was in the UK I could have helped you out with this.
Best wishes from Limey John

Yeah that’s definitely not all true. First off, Barracudas, Demons and Dart Sports can all be included with the Duster. They all use the same inner and outer wheel houses and have an extra inch of outboard space compared to a Dart or Valiant.

And you can use a 65-67 B body 8 3/4 in pretty much any A-body, Dart’s and Valiants included. You just need wheels with about 1.25” more backspace than what you’d need for a SBP A-body 8 3/4. Which is a piece of cake if you’re using 17” or larger rims.

Dusters/Demons/Dart Sports and Barracudas can also easily use 68-70 B-body 8 3/4’s. Mine does.

And a complete axle revamp to upgrade to BBP brakes? New axles and brakes are not a complete axle revamp. And nothing is really different between the 8 3/4’s from ‘67 to ‘72, just the breather hole location. And a couple of brake adjuster things on the ‘67, but you’re replacing those anyway. If you need to rebuild your brakes already, you can get it done for an extra $500 or so. New BBP axles are $300 from DoctorDiff, backing plates can be had used for $100. And almost everything other than than brake bars and levers needs to be replaced on a rebuild anyway. Beats rebuilding and re-drilling SBP stuff, especially if you’re actually putting some miles on your car. And you can even sell your SBP stuff to offset the cost further.

 

[General-Duster]

Nice reply 72 Blu.

So you are saying any axle up to 60'' width, can be used in an early A-bod if you use the correct back-spacing?
All you have to do is re-jig the perches.
I only said this about the Demon/Duster because I have worked on those with factory steel wheels.
If you fit a 57 inch axle in, there is still plenty of room so a 66/67 axle will also work.
I heard folks going to wider 60 inch B-bod axles in with custom made wheels, just not in the UK?
Folks here like to use a correct 57inch A-bod axle in an early car as they can get some wheel choice 'off the shelf'.

 

[72bluNblu]

Nice reply 72 Blu.

So you are saying any axle up to 60'' width, can be used in an early A-bod if you use the correct back-spacing?
All you have to do is re-jig the perches.
I only said this about the Demon/Duster because I have worked on those with factory steel wheels.
If you fit a 57 inch axle in, there is still plenty of room so a 66/67 axle will also work.
I heard folks going to wider 60 inch B-bod axles in with custom made wheels, just not in the UK?
Folks here like to use a correct 57inch A-bod axle in an early car as they can get some wheel choice 'off the shelf'.

It just depends on what you want to do. If you want to use factory wheels with factory offsets then you should stay with factory axle widths, with the possible exception of the Duster/Demon/Dart Sport and Barracuda. Their extra quarter room allows a wider axle, but even then it depends on what tire width and backspace you want to run. For example, even with my 68-70 B body 8 3/4 (60-1/8" wide) I was able to run 15x7 cop wheels (4.25" backspace) with 225/60/15's. I couldn't have fit wider tires though. With a 65-67 B-body 8 3/4 I could have managed 235's or maybe 245's.

For 17" and larger diameter wheels, the "off the shelf" backspacing available actually works better with a wider axle most of the time because those wheels are generally intended for modern cars that use a lot more backspace. And if you're trying for a more "pro-touring" look with wider wheels up front, the wider rear axle actually evens up the front and rear track width. A-body's have a wider track in the front then they do the rear, especially with BBP front disks. Again, for example on my car I run 18x9's up front, with a +35 offset. With my B-body rear axle my rear wheels are 18x10 with a +38 offset. If I used an A-body rear axle, that offset would need to be more like +15. My wheels are staggered anyway, but with a factory width rear axle the front and rear offsets for going to wider tires are totally different. Run a wider rear axle and you can run 4 of the same wheels if you do it right.

If you look at the 8.8 Ford explorer rear axle swaps some like to use two "short side" axle tubes, while others have made it work just fine with the original rear axle width. Just depend on what you want to do for wheels. Always better to figure that out first. For me, I always start with wheels and tires. If you're going to modify the rear axle, or are looking for one, it's better to pick wheels and tires first and then figure out the axle width to make them fit. If you already have the axle, then you can spec custom wheels. Just a matter of how you're setting up your car and what your situation is. With as much as A-body axle housings cost these days, it's almost easier to have a longer one shortened than find an original. And yeah, if you're doing that then just pick your favorite wheels and make the axle width fit them.

 

[General-Duster]

Great up-to-date info there 72blu!

I'm just an old school guy with 'old school' knowledge!
Never fitted any fancy wheels, except factory stuff...
Going up to 15 inchers was 'big-news' when we did Mopars lol...
Would really like to get back into A-bods again someday.
I started off in the early 80's with a 1968 318 Barracuda convert.
The motor was tired so we fitted an ex-Jensen 383ci and trans...
One of the factory RHD UK ones, think there is only a handful left now?
They come with an 8 3/4 and a locker from the 'get-go' and small 4'' pcd.
Seen one up in Scotland for sale one of only two 1969's RHD's left I hear.

Happy Christmas to all A-bod folks, from Limey John

 

[george joseph reid]

Going to do this to the 73 Duster. I have a 8 3/4 out of a 68-70 B Body It is not much wider than the 8 1/4 in it now. As it sits it has 8 1/2 by 15s with a 3 1/2 back space and 275 60s. Its tight with a little rubbing. I think after relocating the perches a 15 by 8 with a 4in BS will work. I will be looking for some slotted mags in the future. Also the 8 1/4 will be for sale 3.21s with a SG.

 

[72bluNblu]

Going to do this to the 73 Duster. I have a 8 3/4 out of a 68-70 B Body It is not much wider than the 8 1/4 in it now. As it sits it has 8 1/2 by 15s with a 3 1/2 back space and 275 60s. Its tight with a little rubbing. I think after relocating the perches a 15 by 8 with a 4in BS will work. I will be looking for some slotted mags in the future. Also the 8 1/4 will be for sale 3.21s with a SG.

Yeah that’s not gonna work with that backspace. A 68-70 B rear is significantly wider than an 8.25”. The 8.25” is 56-3/4” drum to drum, the 68-70 B is 60-1/8”.

If you want 15x8’s on a 68-70 B-body 8 3/4 in a Duster you’ll need 5.75” to 6” of backspace with the perches at stock A body width (43” c-c). If you do the 1/2” spring offset then you can increase that to about 6.5” of backspace. I run 18x10’s with 7” of backspace on my 68-70 B-body 8 3/4 in a Duster with the perches at 42” c-c (1/2” offset). The 15’s will take less backspace than that because of the larger sidewall bulge.

 

[george joseph reid]

Yeah that’s not gonna work with that backspace. A 68-70 B rear is significantly wider than an 8.25”. The 8.25” is 56-3/4” drum to drum, the 68-70 B is 60-1/8”.

If you want 15x8’s on a 68-70 B-body 8 3/4 in a Duster you’ll need 5.75” to 6” of backspace with the perches at stock A body width (43” c-c). If you do the 1/2” spring offset then you can increase that to about 6.5” of backspace. I run 18x10’s with 7” of backspace on my 68-70 B-body 8 3/4 in a Duster with the perches at 42” c-c (1/2” offset). The 15’s will take less backspace than that because of the larger sidewall bulge.

Thanks for the info. What I will do is pull the 8 1/4 and do a side by side compare. I thought the B housing is about an inch wider than the A 8 3/4. The car is down for the season and who knows if the 2021 will run..

 

[72bluNblu]

Thanks for the info. What I will do is pull the 8 1/4 and do a side by side compare. I thought the B housing is about an inch wider than the A 8 3/4. The car is down for the season and who knows if the 2021 will run..

Measuring both would be best, especially since there are several different B-body 8 3/4 widths depending on the year. But the ‘68-70 B is more than an inch per side different, even from an A-body 8 3/4. And the 8.25” is narrower than the A body 8 3/4, not all the A-body rear ends are the same width they changed depending on the style of the rear end.

If you really have a ‘68-70 B 8 3/4 you’ll need close to 6” of backspace with 15x8’s if you want the wheels inside the quarters and not rubbing on anything.

 

[318willrun]

I've dropped B-body (65-70) 8.75 rears in Dusters... Nothing to it. I use the B-body perches (lookout! I just ducked a rotten tomato!), all you have to do is oval the hole or drill a new one right next to the original and set it in.
In fact, I made a video of the last swap on one of my current Duster's.
B-body 8.75 Rear End Install In A Mopar Duster - YouTube

 

[72bluNblu]

I've dropped B-body (65-70) 8.75 rears in Dusters... Nothing to it. I use the B-body perches (lookout! I just ducked a rotten tomato!), all you have to do is oval the hole or drill a new one right next to the original and set it in.
In fact, I made a video of the last swap on one of my current Duster's.
B-body 8.75 Rear End Install In A Mopar Duster - YouTube

‘65-‘70 covers two different widths for the B-body 8 3/4 rear axles. ‘65-‘67’s are 59.5” wide drum-to-drum and ‘68-‘70 are 60 1/8”. So if you want your tires to actually fit those axles would use a different wheel backspacing for maximum tire width.

I suppose if you’re jacked up with SS springs or higher in the back and hang the tires outside the quarters it doesn’t matter.

Welding new perches on isn’t hard. You already have the rear axle out of the car, so, even if you can’t weld it’s easy enough to get it done. A-body and B-body 8 3/4’s also use different pinion angles, so, depending on your ride height the B-body stock perches will likely need pinion angle correction. No welder? Set the axle on the perches, loosely attach the U-bolts, rotate the housing until the pinion angle is right, mark the perches, and off the the welder. Piece of cake.

And here’s the real deal, if you’re moving the perches already it’s a great time to install a 1/2” spring offset. I mean, that’s a win-win. You get an 8 3/4, you pick up an extra 1/2” of tire clearance, you set the pinion angle for your car and your ride height, and your springs react faster because there’s no side load. That’s even good for drag racers!

I mean seriously, does this look right? Think about how the spring is gonna sit with the pin in that left hole.

Will it wreck your car? Probably not. But it sure as heck isn’t right. Little things like this add up, bad suspension geometry changes how your car will handle and launch.

 

[318willrun]

‘65-‘70 covers two different widths for the B-body 8 3/4 rear axles. ‘65-‘67’s are 59.5” wide drum-to-drum and ‘68-‘70 are 60 1/8”. So if you want your tires to actually fit those axles would use a different wheel backspacing for maximum tire width.

I suppose if you’re jacked up with SS springs or higher in the back and hang the tires outside the quarters it doesn’t matter.

Welding new perches on isn’t hard. You already have the rear axle out of the car, so, even if you can’t weld it’s easy enough to get it done. A-body and B-body 8 3/4’s also use different pinion angles, so, depending on your ride height the B-body stock perches will likely need pinion angle correction. No welder? Set the axle on the perches, loosely attach the U-bolts, rotate the housing until the pinion angle is right, mark the perches, and off the the welder. Piece of cake.

And here’s the real deal, if you’re moving the perches already it’s a great time to install a 1/2” spring offset. I mean, that’s a win-win. You get an 8 3/4, you pick up an extra 1/2” of tire clearance, you set the pinion angle for your car and your ride height, and your springs react faster because there’s no side load. That’s even good for drag racers!

I mean seriously, does this look right? Think about how the spring is gonna sit with the pin in that left hole.
View attachment 1715658428

Will it wreck your car? Probably not. But it sure as heck isn’t right. Little things like this add up, bad suspension geometry changes how your car will handle and launch.

I was offering 2 ways to get the job done in your screen shot. I'll include a picture of the car on the ground. Looks pretty good, gets rid of the "backwards 3 wheeler look". No pinion vibration at all. Here, I'll include a photo....