Can Small Bolt spindles run Big Bolt rotors?

-

Dingos Garage

Member
Joined
Mar 29, 2016
Messages
21
Reaction score
2
Location
CT
Hello, I have a 75 Duster with Big bolt pattern front drums that Im trying to convert to discs. I have the front suspension (spindles, upper/lower control arms, etc) from a 71 small bolt pattern Dart, is it possible to run big bolt pattern rotors/wheels on this combination of parts? let me know, thank you
 
With one of the Scarebird kits, yes.
 
There are kits that use the drum spindle. SSBC, Baer and Wilwood I beleive make some.
 
So, a couple of things to note here

1- A-bodies never came with BBP front drums. So, if you actually have BBP front drums, you probably have spindles from a different car (B/E body)
2- Your '75 Duster has the more desirable large ball joint upper control arms. You do not want to switch those to the small ball joint UCA's your other set up uses
3- There's no need to switch the lower control arms, they're the same unless they have sway bar tabs

By far the easiest thing to do would be to buy a set of reproduction 73+ disk spindles and run factory 73+ disks. You swap out the spindles, get the BBP brakes, and everything still uses factory parts for a '75.

10.95" Front Disc Brake Kit (Stage 1)

Looks like the full kit is currently out of stock for some reason, although the disk knuckles show as being available. I'd call DoctorDiff on Monday and ask what the ETA was on the kit.
 
Hello, I have a 75 Duster with Big bolt pattern front drums that Im trying to convert to discs.
This is proof that these cars are subjected to some strange parts swapping.
When I converted my '70 Charger to front discs, I saved the 10" drum assemblies and used them on a stunt car that I had. I wanted the big bolt pattern for it to have a wider selection of wheels.
 
This is proof that these cars are subjected to some strange parts swapping.
When I converted my '70 Charger to front discs, I saved the 10" drum assemblies and used them on a stunt car that I had. I wanted the big bolt pattern for it to have a wider selection of wheels.

Which is exactly why you can’t assume something was factory just because you saw it on a car at a yard 30 years later.

Not the first time I’ve heard of a BBP drum swap though. The later cars especially are easy to do this with because of the large ball joint UCA’s, you just swap on the B-body spindle and brakes. I guess if you have the parts on hand it’s one thing, but the 73+ BBP disk swap is exactly the same amount of work and you get disks.
 
Hello, I have a 75 Duster with Big bolt pattern front drums that Im trying to convert to discs. I have the front suspension (spindles, upper/lower control arms, etc) from a 71 small bolt pattern Dart, is it possible to run big bolt pattern rotors/wheels on this combination of parts? let me know, thank you

Yes, the spindle on the late model drum brake knuckles is the same as on the disc brake cars. So all you need to do is slide a big bolt pattern rotor on the spindle. You'll have to use a special bracket to mount the caliper though. Doctor Diff has this stuff if you want it although I think a better solution is to just swap on a set of disc brake knuckles.
 
Hello, I have a 75 Duster with Big bolt pattern front drums that Im trying to convert to discs. I have the front suspension (spindles, upper/lower control arms, etc) from a 71 small bolt pattern Dart, is it possible to run big bolt pattern rotors/wheels on this combination of parts? let me know, thank you

Here is how I did it 20 years ago. Late model A body drum knuckles, custom adapter plate, Viper calipers, and 11.75 rotors from a B body. It all bolts together. Worked pretty good too for some wrecking yard engineering.
AR011a (Large).jpg
AR011b (Large).jpg
 
Yes, the spindle on the late model drum brake knuckles is the same as on the disc brake cars. So all you need to do is slide a big bolt pattern rotor on the spindle. You'll have to use a special bracket to mount the caliper though. Doctor Diff has this stuff if you want it although I think a better solution is to just swap on a set of disc brake knuckles.

Here is how I did it 20 years ago. Late model A body drum knuckles, custom adapter plate, Viper calipers, and 11.75 rotors from a B body. It all bolts together. Worked pretty good too for some wrecking yard engineering.
View attachment 1715594845 View attachment 1715594846

The only issue I see with all of this is that you’re assuming he has late model drum spindles. He said he has BBP drums, which means it’s possible he has pre-‘73 B or E body spindles. Which use different bearings than the 73+ stuff.

I’m just going off the OP’s post, if he has BBP drums then he doesn’t have A-body drum spindles.
 
The only issue I see with all of this is that you’re assuming he has late model drum spindles. He said he has BBP drums, which means it’s possible he has pre-‘73 B or E body spindles. Which use different bearings than the 73+ stuff.

I’m just going off the OP’s post, if he has BBP drums then he doesn’t have A-body drum spindles.

Perhaps, just depends what he has on there. The OP doesn't seem to really know what he has so we'll have to wait until he pulls it apart. The car should have late model A body knuckles on there but someone could've swapped on B body drum brakes.
 
-
Back
Top