So what if a closed-knuckle, drum-braked Jeep axle hasn't been built since 1973. There are over 30 years of closed-knuckle Dana 25,27, and 44 front axles stuffed under many still-running older Jeeps. If you've added bigger tires to your vintage Jeep, frequent the local mud hole and are tired of rinsing out your brakes afterward, or if you just want to stop more quickly and safely, this bolt-on wrecking yard upgrade is right up your alley. We performed our upgrade on a '73 J2000, but this swap works on early CJs, FSJs, Willys trucks, Wagons, FCs, and more.
In addition to the disc swap, we'll show you how to replace the weak spindle bolt assembly with much sturdier studs. Hard use, rust, and age can cause the spindle bolt threads in the stock closed-knuckles to pull out or strip. You'll never have to worry about three-wheeling while driving down the road or trail.
The front drums need to be...
The front drums need to be disassembled. Nearly every early Jeep wheel hub we've opened up has had the hub nuts attacked with a chisel to loosen or tighten the wheel bearings. This Omix-Ada hub socket (PN 16711.01) can be picked up for less than $10 and makes the job so much easier.
The difference in braking performance between 11-inch drums and the new discs is awesome, and the difference between 9-inch drums and discs is unbelievable. If you have a weak leg, consider replacing the single-pot master cylinder found on early Jeeps with a dual-pot system when making the swap. We've run these discs with both single-pot and dual-pot master cylinders with decent results. However, expect the front brakes to drag slightly if you use the single-pot master. To use the single-pot master and avoid front brake drag you can remove the residual pressure valve from the single-pot master cylinder and plumb an inline 10-lb residual pressure valve into the rear brake line.
On FSJs the lower shock mounts can interfere with the calipers at full steering lock. We modified one of our shock mounts and adjusted our steering stops, although it's best to relocate the FSJ shock mounts to retain full steering.
The original backing plates...
The original backing plates and spindles are held in place with bolts. Larger-than-stock tires and heavy use can cause these bolts to loosen and pull out over time. None of this hardware will be reused when doing the disc swap. The bolts are not long enough, and if you are upgrading to discs you really should replace the bolts with studs anyway.
There are two possible ways...
There are two possible ways to add proper studs to the knuckles. Our knuckle threads were in good condition so we used threaded studs. The knuckles need to be removed from the axle. The backside of the holes need to be spotfaced for both methods. We used a drill press and a McMaster-Carr counterbore and pilot (PN 3015A28 and PN 3103A29). If the threads on your knuckles are shot, you'll need to drill the holes out to 3/8 and use a 3/8 pilot (PN 3103A3) on the counterbore bit.
You only need to spotface...
You only need to spotface the bosses down to the main surface of the inner knuckle. This leaves about .390-inch of material for the stud to be threaded (or pressed) into. Threaded holes should be chamfered so the cap screws seat properly.
For threaded holes use 3/8-24...
For threaded holes use 3/8-24 by 1.25-inch McMaster-Carr alloy steel button-head, socket-cap screws (PN 91255A647 for a box of 25), and use plenty of thread locking compound. For holes that have been drilled out to 3/8-inch, use Dana 44/30/GM 10-bolt Spicer studs (PN 36326-2 or PN 36326-1).
Temporarily install the knuckles...
Temporarily install the knuckles to check for clearance between the screw/stud heads and the knuckle end-balls. You may need to clearance the end-balls slightly to retain full steering movement.
After noting where there was...
After noting where there was contact we removed the knuckles and used a die grinder to make room at the 9 and 3 o'clock positions. It was such a small amount that even a rounded or rat-tail file would have worked.
The knuckles can be reinstalled...
The knuckles can be reinstalled and repacked with grease. The factory spindles go on the same as before.
Temporarily install the '74-'91...
Temporarily install the '74-'91 FSJ caliper mounts and brake calipers ('73-'91 GM 1/2-ton 4x4 parts work as well). Mark and grind the knuckles for caliper clearance. We installed flush-mounted 3/8 NPT plugs into the knuckles rather than grind the original plugs flat.
The calipers should fit cleanly...
The calipers should fit cleanly and not contact any part of the knuckles. Make sure they have enough clearance to move freely as the brake pads wear.
The caliper mounts can then...
The caliper mounts can then be bolted up over the knuckles and spindles using the six studs. We used McMaster-Carr conical-top locknuts (PN 92501A430 for a bag of 100) to cinch everything down and make sure it all stays tight.
You'll need to use factory...
You'll need to use factory wheel hubs that are machined on the backside. Most Dana 25 wheel hubs are machined (right). Unmachined wheel hubs (left) are common on FSJ Jeeps with factory 11-inch drum brakes and will not allow the new rotors to seat properly. These FSJ wheel hubs will either need to be properly machined or replaced with earlier wheel hubs, bearings, and seals.
The '77-'78 CJ (11/8-inch-thick)...
The '77-'78 CJ (11/8-inch-thick) rotors are mated to the backside of the original wheel hubs. You'll need new '77-'86 CJ wheel studs to put it all together. We went to NAPA and picked up Balkamp part number 6413103.
The hub and rotor combo fit...
The hub and rotor combo fit right onto the factory spindle. Whatever locking hubs you had can also be reused and bolted up just as they did before the discs were installed. The calipers and pads bolt on just as they would to any stock FSJ or solid-axle 1/2-ton GM 4x4. Some of these calipers use different brake lines and banjo bolts so match them up by model and year.
Early CJs have the hard lines...
Early CJs have the hard lines on the axle. FSJ brake lines go to the frame. We started with '77 Wagoneer calipers and factory rubber lines on our FSJ. In some cases you will need longer brake lines and it's a good time to upgrade. Skyjacker offers longer, high quality, stainless steel braided brake lines for nearly any Jeep. Part number FBL41 works with '74-'91 FSJ calipers. They are long enough to reach the frame on lifted Jeeps, including our '73 J2000, and have 3/8-inch hard line fittings that fit most early Jeeps.
If you have a dual-pot master...
If you have a dual-pot master cylinder it's a good idea to remove the residual pressure valve from the front brake output. Simply thread a machine screw into the brass fitting inside the port and pull it out with a pair of pliers. Remove the spring and rubber check valve, reinsert the brass fitting, and then reattach the front brake line to the master cylinder port. This will keep the front disc brakes from dragging.