Converting an Early Jeep CJ to front Disk Brakes

By Steve Lane

Edited for the web by Adam Sparks

Here are the parts I used to convert my ‘48 CJ-2A with a Dana 25 to front disk brakes:

I included the part numbers from our small parts store chain which is affiliated with Federated Auto Parts. It will probably much easier and faster to just order up the parts from the vehicles noted below. The only tricky part is getting the 1-1/8″ thick rotors from the ‘76-’77 Jeep CJ5. They went to the thinner 7/8″ rotor in late ‘77 so be careful!

Parts List

• Chevy parts are from a ‘76 Chevy 1/2 -ton 4×4 truck.(K10)
• • Caliper mounts were $50.00/pair from Mike Kirkus at www.completeoffroad.com
  • Calipers were $16.00 each, plus $15.00 core. Federated part number 18-4046 and 18-4045 see if you can get some junkers cheap from the local U-pull-it bone yard to save you some bucks on the core charges!)
  • Disc Brake pads ran $24.00 for semi-metallic linings. Federated PGD52R
  • New caliper mounting pins ran $13.00 + change. Use the ones with the round outer surface, and an Allen head. (The stock ones have an external hex-head)
  • New anti-rattle clips were $7.50 per set. Help! Part number 5539
  • Brake hoses ran $22.00 each. (2 needed) Federated part number 36761BH
  • Banjo bolts were $4.00 each (2 needed) Edelman part number 13935

• Jeep parts are from a 76-77 Jeep CJ-5 with 1-1/8″ thick rotors.
  (7/8″ thick rotors from a late ‘78 on up will not fit!)
• • Rotors – Federated part number 5356183R
  • Wheel studs were 1/2″ longer than original. (Take an original in and match it up, it is a common 1/2″ x 20 TPI thread, but the splines need to be longer to seat properly in the hub)

Also another parts list, from Jp Magazine Nov. 2001 (a few different PN’s)

• Calipers from a 71-78 Chevy 1/2 ton or light duty 3/4 ton 4×4 w/dana 44
• Caliper mounting brackets from 73-91 1/2 ton chevy 4×4
• Rotors from 77-78 Cj, rotors are 1 1/8″ thick
• 10 longer wheel studs (used Dorman PN 610106)
• Chevy 1/2 ton brake lines (Pro Comp PN 7220)

The toughest single part of doing this conversion is separating the old front hubs from the original brake drum. All I can say here is to use your head here, and remember that it is VERY easy to bend one of these hubs. I wound up putting an oversized impact socket on the backside of the drum, and having a friend help me chuck the whole assembly into a huge vise we have at work. Then, I heated the hub flange slightly and cranked on the vise to press the studs out. Use caution, as they will pop out unexpectedly and the whole mess will try to fall on your toes. After the first one, my friend wore welder’s gloves to be able to hold onto the hub and drum!

The stock Dana steering knuckle will require some grinding to make a relief big enough for the inboard portion of the big Chevy caliper to clear. The area requiring the relief is in the area where the felt outer wiper for the axle tube ball bolts onto the knuckle, and the grinding can be done with the knuckle on the vehicle if you are not doing a full axle rebuild like I did.

This photo shows it pretty well:

Stock Knuckle

At this point, it is a good idea to consider whether you are going to replace the six spindle mounting bolts with studs. If you plan to run big mudders, or do any serious off-roading, then I suggest that you do this. The Mopar #J8124847 studs From a Dana 30 will press in from inside, once you drill out all the threads with a 3/8″ drill bit. (Editor’s note, I did this on my Willys Truck, it’s nice, but I only drilled 4 out, not all 6, for a good write up see Dr. Vern’s Website). I am running 31×10.50 BFG Radial Long Trail tires, and my rig will see almost exclusive street use, so I opted to keep the bolts. Time will tell if I screwed up. In hindsight,I wish I had gone with the studs. Instead, I used Grade-8 bolts that were about 1/4″ longer, and I cleaned the threads out with a tap before reassembly.

When reassembling the steering knuckles, you are wasting your time if you don’t replace the king pin caps, bearings and cups. (Can you say “death wobble?”) The procedure in the service manual for setting the pre-load seems complicated, but it really isn’t. It just takes a little time. I have yet to see an early Jeep that didn’t need to have these components replaced, and with the knuckles apart this is the time to do it, likewise for the felt and rubber seals on the inboard side of the knuckles. I found it easiest to bolt the felt wipers and the retaining ring halves into place, and then grind the relief I mentioned earlier with a 4-1/2″ angle grinder. Clean up the ball ends of the axle tubes with some fine sandpaper, taking care to polish out all the scratches you can without putting your own gouges into the ball surfaces. Use steel wool for a final finish before painting with a good spray paint. Some guys will argue that the paint just scrapes off eventually anyway, but I have found that the paint will a ctually help fill some of the deeper scratches. Really deep gouges can be filled with JB-Weld and then sanded even for a no-leak finish. This little step is really worth the effort, as this is where nearly every closed-knuckle Dana leaks at one time or another.

When you do the final reassembly, you will need to split the inner rubber seal rings to get them over the ball on the axle housing. This is OK, but make sure that the split is at the 12 O’clock position, or your Jeep will once again be marking its territory on the driveway. Use a light film of gear oil or SAE 30 on the rubber seal on reassembly to protect your new seals initially. This seal and the felt wiper is the single biggest source of oil leaks on the Dana 25/27 and it is just plain silly to not replace these seals while you have everything apart.

Once the knuckles are back on, you can bolt the GM caliper mount on with either the studs or slightly longer bolts as mentioned earlier. If you choose bolts, make sure they are grade-8 hardened. The dust shields may or may not be intact on your caliper mounts. Mine were only hanging on by some cracked stitch welds, so I ground them the rest of the way off. These things are worthless anyway in keeping brake dust of anything, so it was no great loss. They tend to get caught up on rocks and weeds anyway. Good riddance! The oil fill plug on the knuckle will have to be exchanged for a flush-type plug; I used an electrical conduit plug with a slotted head, but a pipe plug with a recessed hex or square drive would work also. Fill the knuckle with SAE 140 gear lube before sealing the plug with silicone sealer. NOTE: Even if you are using axle shafts with “lifetime” lubed Spicer-type joints on them, the outer axle stub shaft still turns inside a bushing inside the spindle. Don’t even try to run with DRY knuckles on a Dana 25/27. It is inviting nothing but trouble!

Knuckle back on

Assemble the hubs and rotors, using the slightly longer wheel studs. Remember, they go together ass-backwards from every other American vehicle in that the rotor bolts BEHIND the hub. Depending on the hub, you may need to have a small amount of material removed from the back edge of the hub to provide a true surface for the rotor to seat upon. I had mine done at a small local machine shop; $10 each and about a 1/2 hour total time on the lathe to even things up. Use a set of old lug nuts,inverted, with the new studs to press the hub and rotor together. Works slowly, and tighten the studs in a star-pattern just like you are tightening the wheels on your rig. Once the hub is seated, STOP! Don’t be temped to wail on these with your shiny new 1/2″ drive impact wrench! Do it by hand, so the stud doesn’t spin in the hub and ruin the splines. You are royally screwed if this happens because the stud will just spin and spin and the hub you just had machined is now ruined. Call up KRAGE or whomever and order up a

New hub

Of course, when I got the new hub I noticed that it was machined flat on the backside of the flange, so no further machining was necessary. The photo at right shows the nice, flat surface on the replacement hub.

Install the hub/rotor assembly on the spindle using new bearings, races and seals for the original Jeep application. My $3 bearing packer from Harbor Freight Tools was an excellent investment here, as was the oversized socket for tightening the wheel bearing nuts. If your (wheel bearing) nuts have evidence of ever being tightened via the hammer and screwdriver method as most have, order up a replacement set with the bearings and seals. This is cheap (life) insurance folks! I think I paid about $6 for the correct size socket to tighten the wheel bearing and jam nuts.

Brake pad

With the rotors and hubs installed, mount up one caliper at a time, putting a very light coat of anti-seize compound on all metal-to-metal surfaces, especially the threads on the caliper pins. Slide the caliper back and forth to insure that it will not bind on the knuckle at the ends of its travel. This is important, so that one side doesn’t bind up as the brake pads wear normally,causing uneven braking. Grind additional material from the knuckles as needed to insure good travel, and then do the final reinstall of the calipers, remembering to install the anti-rattle clips on the brake pads. The caliper mounting pins that came with my used mounts were badly corroded, so I opted for new ones. Get the ones with the Allen cap screw heads, as they allow slightly more caliper travel than the stock pins.

New MC

Remember that if you are using a dual master cylinder from a drum-brake vehicle, you will need to remove the 10-lb. residual-pressure valve from the front port of the MC and plumb a 2-lb. unit inline to the front brakes I used a Wilwood PN: 260-1874. (The photo at left is from my incomplete installation). If you don’t remove that 10-lb. pressure valve, the front brakes will drag, as there is no spring to return the calipers like there is in a drum installation. If you just remove the stock valve and don’t install a 2-lb. valve like I did, you may end up having to double-pump the brakes all the time to get any pedal, as there is nothing to stop too much brake fluid from flowing back to the master cylinder when you release the pedal. Note the frame-mounted dual-chamber master cylinder from a 67-71 CJ-5. The purists may cringe; I just couldn’t bring myself to put a single-circuit system back into my CJ-2A when I was going this far with a “restification”. The old saying “no guts,no glory!” just doesn’t apply here I’m afraid.

Also, remember to install the calipers with the bleeder facing UP, so that it will bleed properly. If you reverse the calipers and have the bleeder facing toward the ground (a very common mistake) you will never get the system bled and your pedal feel will be horrible. Simply swap the calipers from side to side to correct this. DUH! Guess that’s why the calipers have different part numbers!

Depending on your specific vehicle, it may be necessary to add an adjustable proportioning valve to the rear brake circuit to restrict hydraulic pressure to the rear brakes. If your Jeep tends to lock up the rear brakes on a hard stop, then this is the case. A Wilwood proportioning valve, PN: 260-2220 is easy to plumb into the main rear brake line, and it will allow you to carefully dial in the amount of restriction necessary to make the front-to-back braking ratio even. If your rear brakes lock up before the fronts do, you need one of these babies. Again, I erred on the side of caution and put one in from the start.

Brake line and hoses

As for the hydraulic hoses, the Chevy truck hoses lined up perfectly to the brackets and hard lines on the early Dana axle in my ‘48 CJ-2A. Some later-model Jeeps have bulkhead fittings on the frame for the brake hoses, and the stock Chevy hoses may not reach. In any case, make sure that your hoses have enough slack in them to reach without binding throughout the entire range of steering and suspension travel. Any parts guy worth a damn can fit you up with a set of hoses that will reach, if the stock Chevy hoses are too short.

The final assembly!

The final assembly

Now that your brake conversion is essentially done, you will need to consider what wheels you are going to use, as the stock Willys rims will not clear the Chevy calipers. You have a wide assortment of aftermarket rims,as well as OEM rims from a Ford F-150 4×4 with disk brakes to choose from. I chose a new set of white 15×8 Cragar “Nomad” wagon-wheel type rims, they ran about $38 each new from Jeg’s. They were a tight fit, but they cleared the calipers and bolted right up. I added new chrome lug nuts for effect, and sprung for 4 new 31×10.5 BFG Radial Long Trail tires at Sam’s club. They were on sale for $84 each, and look really good on my CJ. I rarely go off-road, so performance on the pavement is far more important than off. They should do just fine.

At this point, you have done all the hard work, and your Jeep should be sportin’ some awesome new binders up front. It goes without saying, but I’ll say it anyway: This is not a job for the inexperienced, or the faint of heart. Any work on the braking system of a motor vehicle has the potential to cause serious injury, or even death if not done properly.

If you do not have the skills and equipment necessary to do this job safely, then by all means either hire someone who does, or don’t do it at all. It is as plain and as simple as that.

I learned a tremendous amount about this conversion project, and other subjects simply from surfing the web, and corresponding with other Jeep enthusiasts. Information regarding this project came from many sources, and I will try to name them all here:

• Derek Redmond’s outstanding CJ-3B site: http://www.film.queensu.ca/CJ3B
• Adam Sparks’ Early CJ-5 website: http://www.earlycj5.com/
• Chuck Pedretti’s web site: http://home.off-road.com/~chuckp/
• Bob Notman’s ‘42 GPW site: http://www.42fordgpw.com/
• Ron Fitzpatrick’s G503 site: http://www.g503.com/
• Rick Grover’s Willys site: http://www.public.asu.edu/~grover/willys/

Thanks for reading this, and please let me know how your conversion went. I’m no expert by any means, but I will try to help out if you get really stuck somewhere along the way. Happy Jeepin’!

Steve in Pittsburgh

1948 Willys CJ-2A SN:195945

w3srl@yahoo.com

Update on Parts Availability

Jayhawkclint sent this to me via the forum, as of Aug. 2006. The best deal I could find on caliper parts was NAPA #328 (L&R). It is a caliper, hardware and pads kit that replaces a few of the individual part numbers on the Tech page write up. Cost me $34 a side plus core, which to me seemed pretty cheap. Came with semi-mettalic TruStop pads, new pins with the allen head, anti rattle clips, and beefy reman calipers.

Nickmil adds, If for some reason that doesn’t work for you an easier way is simply to ask for a rotor for a late ’70’s Scout 2 with disc brakes. Same exact rotor as the ‘77-’78 1 1/8″ Jeep rotor. I’ve found this less confusing for some of the “Parts People”. Nickmil.

Elsewhere on the web see:

Disk Brake Swap Tips on the CJ-3B Page