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Adding Hub Mount Disc Brakes to 2 1/2-Ton Axles

Posted in How To: Suspension Brakes on August 15, 2019
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Rockwell axles have always been desirable off-road. They are relatively inexpensive, and replacement or upgraded parts are readily available, making them great candidates for fitting big tires under off-road trucks. But one area where performance has always been hit or miss is in the braking department, with woes mainly a concern for on-road use.

Rockwell axles come with huge and heavy drum brakes that are too large for most light-duty vehicle master cylinders to operate. Up until recently the most popular solution to slow the roll on these axles was to add pinion brake to the front and rear axle. By affixing a disc brake and making a caliper mounting bracket to hold a caliper, one smallish disc can easily slow two large tires through the axleshafts. Mechanical advantage for the pinion brake comes from the 6.72 axle ratio. That means slowing even large tires is relatively easy for the pinion brake.

But pinion brakes are less than ideal for a few scenarios. For one, road driving can easily burn up pinion brakes. That's because they spin fast at road speeds (6.72 times per tire rotation) and prolonged light brake pressure (for example, while going down a slight grade) for long periods of time can overheat and destroy pinion brakes. Also, since the pinion brake slows the wheels through the axle gears and in turn the axleshafts, an open differential or other broken axle parts can cause loss of braking action to one or possibly both wheels of an axle. Neither of these scenarios is very comforting when it comes to driving a Rockwell-equipped vehicle on the road. So most folks don't.

We started by playing around with Boyce Equipment's 2.5 Ton Rear Hub Mount Disc Brake Kit (PN DBHMR250, $850). We test-fit the caliper brackets. We knew we would have to clearance some of the rear deuce axle's factory brake backing plate flange to clear the calipers, but we also needed to open up four of the holes for the new caliper brackets. We used our drill and a unibit to open up the holes to 3/8 inch.

If there were another solution there is nothing that says Rockwells couldn't regularly be driven down the road and over long distances, possibly making any Rockwell-equipped rig both capable off- and on-road. Enter Boyce Equipment with its 2.5 Ton Front and Rear Hub Mount Disc Brake Kits. These parts bring disc brakes to each wheel like those of more common axles. This allows each individual wheel to have a brake that spins slower than the pinion brake and creates redundancy that builds confidence for on-road Deuce use. That's perfect for what we have planned for our Deuce axles and fits well with our last story, which was about adding Eaton NoSpin lockers (Nov. 2019; Rebuilding Rockwell Axles for Off-road Abuse). Check out the details while we rebuild our huge 2 1/2-ton axles ahead of getting the project truck for these axles ready to roll.

Truth is we got a bit ahead of ourselves and installed the brake rotor and hub a bit out of sequence. Let's pretend the rotor isn't in this picture; we'll come back to it in a minute. We used a blue paint pen to mark off where we would need to cut back part of the brake backing plate flange.
(Again, ignore the hub and rotor. We promise we will come back to them in the order we should have installed them.) Here you can see most of the trimming we did to the axle brake backing plate flange. We started with the plasma cutter and took more material off with a 4 1/2-inch angle grinder. We then reinstalled the caliper bracket and checked for clearance until everything fit without issue.
The rear rotors from Boyce are held in place on the back of the wheel hub using eight factory-fresh bolts (that also held the drum on the back of the hub). We then installed new hub seals on the spindle by tapping them in place with a hammer and a drift, packed the wheel bearings, added a lot of grease to the hub, and then reinstalled each wheel hub on the rear spindle. There is also seal that goes on the outside of the hub before the spindle nuts and spindle-nut washers are locked in place.
With the hub, rotor, and caliper mounting brackets in place we added the supplied brake pads and clips to the rear calipers and bolted the calipers to the rear axle. Boyce thought about everything and also includes banjo bolts and rubber hoses so you can hook up the disc brakes when you install the axles in a rig.
An engine hoist is a must for working on these axles. This is especially true when you have to pull the centersection to add a locker like we did. After adding the lockers we cleaned up the mating surface of the carrier and axlehousing and globbed gasket maker onto the axlehousing mating surface.
These four nuts are one of the biggest pains in the behind when you're working on a Rockwell. Worst part is you can't just drop the carrier into the housing—you have to hold it just above the mating surface so you can weasel in washers and nuts. They won't fit between the carrier and the top of the studs with the carrier in place. Then use your trusty 11/16-inch box-end wrench to tighten these four nuts. Get comfy; it takes a while.
The front rotors are attached to the factory wheel hubs with these brackets that are held in place by huge wheel studs. New wheel studs are included in the Boyce Equipment 2.5 Ton Front Hub Mount Disc Brake Kit (PN DBHMF250, $1,350). We used our shop press with Swagg Off Road Arbor Plates and a piece of tubing to install the new wheel studs to hold the rotor adapter to the wheel hub.
We then installed the 4340 2.5 Ton Front Axle U-Joint Shaft (sold as a set, PN MFA250CMS, $999.99) chromoly axleshafts with plenty of grease. That's a mostly used 4-pound tub of red grease from our local auto parts haus. We'd recommend getting two of those tubs. The little 1-pound tubs will go quickly with Deuce axles.
The factory spindles are retained using some of the original nuts and star washers, while Boyce includes four new lock nuts for the caliper mounting brackets. You can also see our freshly hand-packed inner wheel bearing, and part of the grease wall we like to try to build between the bearings when packing bearings. Lots of grease. Lots of grease.
For the love of Pete, be careful! When we went through the spindle nut tightening sequence, the front axle jumped off the jackstands we were using to hold it. BAM! That's a lot of weight hitting the ground that could crush a limb to a pulp.
To whoa the front rotors, Boyce supplies these small, lightweight, yet high-performance calipers from Wilwood. They are pretty cool and look tiny on these huge axles. Each caliper has four pistons and can be used on either the driver or passenger side of the axle (because they have four bleeder screws, two per side, one top and one bottom).
We used a couple SAE Grade 8 washers to space the calipers slightly to the outside of each axle. We centered the calipers by eye on the rotor using the center bars of each caliper. Now that these axles are back together, we have to get on the ball with getting the old dualie work truck we want to put them under up and running. Keep your eyes peeled for more on this project with more parts from Boyce Equipment and others.


Boyce Equipment
Ogden, UT

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