Convert from hub rotor assembly to separate parts?


Well-Known Member
Apr 19, 2010
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Lawrence, KS
Like the title implies, does anyone make a kit that converts the original style hub/rotor combo part into two separate parts like modern cars that sandwich the rotor between the wheel and the hub? It would make rotor replacement far easier since you wouldn't have to deal with wheel bearings. Ultimately I'm actually most interested because I'm looking at putting a front wheel speed sensor on my car for a traction control setup and having a hub that is separate from the disc would make life a lot easier for figuring out the installation and clearances. Seems like it could be a fairly straightforward kit with slightly shorter hubs and a different offset on the rotor hat to keep everything in the same relative location, but maybe the rotor diameter isn't big enough to fit a hub inside it with the bolt pattern that is used. Just figured if I was going to go through the trouble of removing the rotor to figure out my sensor that it would be nice to update the system while I'm there if it's possible or not cost prohibitive. I don't need crazy race brakes and $1000+ conversions. It's just a street car and brakes fine today with the system on it (that I think is something like E body parts from what I can tell).
I see no reason why, if you have a once piece setup, you could not machine the old rotor off, pick some rotor that is a candidate, and machine what's left of the hub to fit. You'd have to be "selective" on wheel studs to get it to work and you'd have to watch rotor/ hub offset
It looks like front drum brakes have a separate drum that doesn't have the hub in it, at least from a few pictures I have seen. I can't find a picture of a front corner with the drum off though. I would wonder if maybe I could use the drum hub and find an appropriate disc to go over it, maybe with a little trimming on the hub to make it work. Just need to try to find more info on the drum setup and see if I can find a parts breakdown.
Dr. Diff's Stage 3 & 4 front disc kits (Cobra & Viper) both use separate hub and rotor assemblies, and fit A/B/E spindles (check fine print for the particulars). You'd have to call and ask if parts are available separately.
I think AR engineering made hub assemblies at one time..?
That's a pretty piece, but looks custom machined I'm thinking. I think I found the individual listing for them as well: Mopar Billet Aluminum Hub

Found these on an old for sale ad here. Guessing they are probably still SBP since they are A body, but I've found B body ones for sale as well that I wonder if they would fit: [FOR SALE] - 67-72 A body drum brake hubs $30 shipped

I see them on B body and C bodies sites as well. I think I read the E body and B body front brake setup might have been the same (the Dr. Diff listing seems to make it sound like all the 73+ stuff was the same), so wonder if a set of these might be the ticket. Would still have to find a rotor that would fit over them and still work with the stock calipers though. Wonder if I'd have to turn down the hubs just a tad to make it all work. That or space the calipers out just a bit.
Well, as it turns out it looks like something like this might already exist to some degree. InvincibleExtremes sells a bracket that lets you use a stock drum brake hubs with Mustang rotors and calipers: Disc brake conversion using stock drum hubs and spindles 2 piston, 4 piston or 6

The big question I have now that doesn't seem to be answered anywhere yet is whether the actual spindle between a disc and a drum brake knuckle is different. I'm not talking about the full assembly as I know the factory disc brake knuckle has the caliper mounting included. What I mean is the actual spindle that the hub and bearings ride on. Seems odd to me that they would have changed that between disc and drum brake cars, but I'll have to do some more digging and see what I can find. I think I should just be able to compare bearings and seals between them to get a better idea, but hard to say.
From what I can find on RockAuto and checking bearing and seal sizes, it seems like they all have common shaft/IDs, so I think I should be able to put a drum hub on a disc brake spindle. Seems like hubs are cheap enough, so might be worth a try. If it works out rotors and calipers are $50 each for the smallest setup, so $200 for a full "modern" disc brake retrofit on the front end, plus some extra for hoses isn't too bad. Ultimately probably doesn't give me any more room to work with, but would be nicer dealing with just a hub than a full disc hub assembly.
Looks like maybe I was checking the wrong bearings. The outside bearings I think are common between them, but the inside drum bearings are smaller shaft size than the disc. I looked in the Timken catalog to see if they made a bearing that would adapt between the two, but doesn't look like it. Might be possible to open up the bore on the drum hubs to use the larger inner bearing, but at this point it would probably be easier to just buy drum brake spindles.

I could possibly just use the disc hubs I already have on the car, but it would space the wheel out further once I stack a rotor on the outside instead of the inside. I already have some spacers on the car to account for the backspacing on the wheels I have, so I might just be able to go down to a smaller size, but would have to see if I can find a rotor with that much offset in it, which I think would be a challenge.
The '73+ disk and drum spindle uses the same wheel bearings but pretty sure the cars earlier than that do not. @AndyF used the drum spindle with later 11.75" rotors and Gen1 Viper calipers.

This is what I did:


Some tape and a hacksaw is all it took. I had a shop true up the edge just because, not sure it was really necessary.

But I am running a home built PBR caliper and 13" Mustang Cobra rotor BBK kit, not really a slam dunk for what you are looking for.
BTW, I spent a decent amount of time looking for a drum brake hub that was BBP and used the later bearings and never found one. The A-Body drums are SBP and the B/E cars I looked at didn't use the same bearings, IIRC.

Seems like I found a van (don't remember what year) that used the same bearings, but never found one to figure out if the depth of the hub would work.

Just don't think you will find a hub that will work outside of one from Dr. Diff, one of the aftermarket brake manufacturers or rolling your own.
Just a guess here, but do you have 2 piece rotors now? If so, sounds like you have '72 and older spindles.

If so, I would buy a set of '73+ spindles from Dr. Diff at the very least. If you did that, you could grab a set of rotors from most any later car in the JY and slice off the rotor like I did. I think this would open up much more possibilities than what you have available right now. Even if you didn't cut a rotor down you could run the factory 11.75" setup for not much money.

Not sure what you would have to do to get a separate hub if you stick with earlier stuff.
Yeah, I think I'm just going to have to suck it up and tear my setup down to the spindle to get a better idea of what is going on. I technically have the two piece rotor setup, but I'm not sure that really says much about my car. It was such a mismash of parts when I bought it I think they just kept bolting stuff on until it looked enough like a car to sell it. From the brake hoses it seems like E body calipers, but the rear end and the engine and transmission that were in it when I bought it were more like F body units, so you would have thought the front brakes were too. However, when I bought the hoses to try to flip the calipers front to back, that's when I found out stuff was weird. I've been told I have a C body radiator in it as well, so all bets are off when it comes to guessing parts, lol. I also found out the rear brake shoes are not quite what I expected either as the slot/hole for the parking brake tab was different.

I got to thinking about it some more and got some measurements from the B body forum for some Wilwood drum brake hubs, so I have an idea what the drum brake offset is. I think I'm going to take my hub/rotor off and measure the offset to the hub flange as well and see how it compares to the drum hubs. Maybe they aren't as far off as I think they are. Since I already have the spacers on the wheels I can probably make my existing hubs work, assuming that I can space any caliper bracket accordingly. I just don't want to get things too far away from where they started as that starts putting some goofy loads into things. Honestly, the way things are set up now my brakes are pretty much entirely outside of the barrel of my wheels. Maybe that was typical of the day and age and offered better cooling or something, but they just seem really far inboard with the design.
So I did a little disassembly and some digging and found something rather interesting. Based on the casting number on the back of one of my calipers at least, it appears they are 71 E body. What is more interesting to me is that the spindle I have appears to be the smaller diameter drum size, so swapping over to a drum brake hub would actually be pretty easy if I wanted to go that way. Not sure if what I have is actually worth anything to anyone aside from a concourse restorer looking for correct casting numbers. I did some measuring on the hub as well and it's not way off from a drum hub as far as the mounting flange offset, but looks to be around 3/8" or so if I'm doing my math right. Could probably work since I basically have FWD wheels and a big spacer on my car, but I'd have to make a caliper offset spacer as well, which I'm not as much a far of the idea.