The Stovebolt Site Forums The Parking Lot Big Bolts Disc brakes for 1.5, and 2 ton trucks

For the single wheel trucks not only would you need to adapt the spindles and caliper brackets from an 8 lug P-30 to the 2 ton axle, but you also need to find a single wheel hub and rotor to fit the spindle and caliper/bracket.

I've searched and searched and the best possible rotor/hub that I can find is a NAPA part number 4885580. It's a GM combined hub and rotor that has the same 12.5"x1.5" rotor that the dual wheel version that comes on the P-30 axle has.
Here are the critical dimensions, look at this sketch for clarity.
https://picasaweb.google.com/lh/photo/WPE6TH44cNiB2d-tiFQ0ptMTjNZETYmyPJy0liipFm0?feat=directlink
Measurements in inches are from rear surface of rotor, from WMS, and from outside faces of installed inner and outer bearing cones

_________________ "A" ____ "B" ____ "C"
P-30 dual hub ___ 7.289 __ 0.955 ___ 3.995
NAPA 4885580 ___ 3.823 __ 0.938 ___ 3.990

As you can see the rotor position in relation to the inner bearing is essentially the same, so the rotor sits where it's supposed to and fits in the caliper.
Also note that the dimension "C" distance between bearings is the same.
The big and expected difference is position of the wheel mounting surface, and in this case it is 3.45" per side, or 6.9" narrower for the whole axle.

Now, don't get to excited because this single wheel hub and rotor won't fit...
It uses a different smaller inner bearing, NAPA LM501349 and won't slide on the spindle.
But luckily enough the outer bearings, NAPA 15103-S are the same!

The P-30 spindle uses a (inner or large) bearing with a 1.688" ID.
The new single wheel hub uses a bearing with a 1.625" ID.
A 0.063" difference.

The way to make this fit a good way is to turn that 0.063" off the inner bearing journal on the spindle. Then off the shelf bearings and hubs work in the future.
More/better/different bearing option of a larger bearing and thin adapter sleeve, keep reading or click to skip right to it. https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=778876#Post778876

An alternative method might be to adapt the hub to fit the larger P-30 bearing cup, this is a 0.109" difference, and I'm not sure about the depth, or if there is enough material in the hub. Not a good plan because you have to modify parts to replace rotor/hub.

The grease seal intended for the new hub fits the P-30 spindle perfectly. It's very common and 1/3 to 1/4 the cost of the P-30 seal, so that's a good thing.
NAPA seal # 21771

Now the big question, is this whole thing narrow enough to fit in an AD truck?
Starting from an 8 lug P-30 axle WMS to WMS of 81.625: the new WMS width could be 9.125" narrower with an AD 2 ton axle beam swap, and 6.9" due to the hubs, for a total of 65.6"
That's 7.35" wider than an original AD 1 ton, and that's disappointing

To start with the original axle could be wider and the tires could still fit, but not that much wider... The limiting factor seems to be the 68" width measured inside the front fender lip at bottom of opening, same both front and back edges.
Some different wheels with a little more inset might work?
I'm still going to see what this all looks like, but not sure how it'll turn out.

One thought is to narrow a 2 ton axle I-beam 5.25" because then half he U-bolt holes could be reused, and a plate made like this to land the springs on and the other two U-bolt holes.
That would leave the resulting axle about 2" wider WMS to WMS than original, which would be fine, 1" per side might not be noticeable to the untrained eye.
Admittedly not a simple or fun solution, but could be a workable one.

Another thought is narrow a P-30 axle beam a lot and still use spring mounting adapter plates like above. Narrowing it 16" results in original single wheel WMS to WMS, but several inches narrower at the kingpins, so less steering angle, and not much (enough?) room for the P-30 steering arm to not hit the springs. Narrowing it about 14" might improve the situation, but then the 2 ton axle narrowed (as above) looks easier/better for same final width.

Grigg