70 duster 8 3/4 conversion to 4.5 drum or disk hardware

-
dustadude

dustadude

Well-Known Member
Joined
Jan 30, 2014
Messages
236
Reaction score
29
Location
San Lorenzo, Ca (SF East)
first let me say thanks to anyone taking the time to read this, i appreciate it. So my dilemma is this, I've got a 70 duster with a rebuilt 360, 904 tranny, and an 8 3/4 rear end, 4' lug pattern around.

I've bought the components needed to convert the front drums to disc using 73-75 a-body parts, but now I need to convert the rear end pattern as well. I plan on buying the axles from Classic Industries, but now I don't know what hardware I need to convert the brakes to the bigger 4.5 in pattern in the rear. I don't care about getting disc, I'm on a limited budget and only have drums back there is fine because majority of the breaking will be done up front with the new discs, but if the scavenged parts pricing is close, then I would opt for disc.

Has anyone had any experience with a swap like this, and what parts should I be looking for at the boneyard or online. I seemed to be having the hardest time trying to find some mounting bracket that isn't a part of some ridiculous kit. Can I source it from a junk yard car, or maybe piece a kit together from parts bought from members here?

Thanks for the help guys, really appreciate it!
 
Many owners - myself included - have the original A body SBP 8 3/4" rear setup with the rare bell drums that look to be no longer available.

My thoughts are I would consider contacting Doctor Diff - Cass - who is the Mopar guy - when it comes to A body SBP 8 3/4" alternatives, including rear axle availability, swapping to 4.5" bolt circle, upgrading to rear discs, etc.

I intend to subscribe to this thread to learn what's available out there.

Keep in mind --- the Abody SBP 8 3/4 " backing plates are unique, and any rear brakes have to take that into consideration, unless you intend to locate and use other backing plates. The Bbody backing plates are getting hard to find in my area.

Subscribed.
 
As long as you get your new 5 on 4-1/2" axles set up for the standard Mopar offset, NOT the A body 8-3/4 offset, you can use a lot of different rear brakes.
I picked up a set of axles for my Demon's 8-3/4 from DoctorDiff (highly reccomended)and used a set of 11"x2.5" from a 74 Satellite Sebring Plus I parted. The 11+" discs from the same car are on the front.
I have a couple sets of 10" x 2-1/2" rear brake assemblies available that will work for you, if your interested.
 
Jimacuda, is right. I just did this on a 8 3/4. The backing plates are 10 1/2'' B body. all the shoes(2 1/2''),hardware,and drums are from a 80's Dodge Diplomat.
You can use the Diplomat backing plates, though some only have a 4 bolt attachment and you can drill the 5th hole to bolt to your axle housing.
 

Attachments

  • IMG_1894.jpg
    64.4 KB · Views: 369
A body stock 8-3/4 backing plate will ONLY work with stock offset A body axles. The A body 8-3/4 brakes are unique to ONLY the A body 8-3/4. No other MOPAR rear (post 1965) uses the same backing plate.
If your going with new axles AND large bolt pattern it would be wise to replace the entire rear brake assemblies.
I couldnt get your link to open.
Rear drum brake assemblies from any 1965 up 5 on 4-1/2" bolt pattern will work. The later 7-1/4 and 8-1/4 10"x 2-1/2" brakes work excellent. I have a couple complete sets of those with good drums.
I would use the axle set Doctor Diff (Cass) sells, he knows his stuff.
 
Moser also sells off the shelf A-body 8 3/4 axles for the larger B-body brakes or standard offset for your original brakes. The standard offset axles can be had with both 4" and 4.5" bolt pattern and you can drill the 4.5" holes in the drums you have. One thing I like about the moser axles is you can use the standard tapered axle bearings and dont come with the green bearings already installed.
 
A-body rear brakes on the 8 3/4 are narrower than the B-body brakes. The backing plates and drums do not interchange. Also the distance from the axle housing end and the wheel flange is different or in other words offset.
 
if you want oem rear large pattern brakes you will need new axles that have the correct offset mentioned above

for these probably easiest to buy new...~$350 ish see dr diff you can't go wrong

backing plates from any car or truck with 7.25, 8.25, 8.75, 9.25 rear and the 5x4.5 bolt pattern....say $75 for a core set

new drums...check for your donor application budget $50 each

new wheel cylinders $5 each

new hardware and spring kit...$10 ?

new brake shoes..check your application but budget $30

might want to replace axle seals while you have it apart

your also going to need new rims and potentially tires so bake that into the equation.


or find a lbp b body rear complete... 100 typical price with open diff...and relocate the spring perches.
 
thanks guys, so much good info its hard to know what to do, especially when the prices are broken down for me like that and I can see how expensive it is! I'm heading to the junkyard now to see if I can find a suitable b-body rear end, or maybe see if I can find a donor diplomat. If I end up finding the b-body rear, is the 8 3/4 that I have just a waste of metal to keep then?:burnout:
 
8.25 is a good rear. you will need to move the spring perches and get wheels with deeper back space to run it under your car.

or just snipe it for the brakes,

i wouldn't buy the whole car unless parting is your thing. in the end its just less time working on the car you would other wise want to be driving.
 
You must log in or register to reply here.
-

Back
Top