Sterling Disc brake Swap and Related Info

Part I

Even though I was running one-ton axles (88 Ford 60, 90 Ford sterling) and their respective one-ton brakes, my braking has always been less than adequate in my opinion. Granted, the fault could lie in the 40” tires or the 7000+ pound weight of the rig, but I wasn't satisfied. Long ago, I switched to a 94 F350 Booster, and 1 1/8 bore master cylinder, and ditched the 4WABS computer. I've been running the stock axle brakes with upgraded booster and MC for a few years, and never felt like the bronco would stop well in a panic stop. With a baby on the way, and desires of him and the wife coming on my wheeling trips, I wanted some better braking. I want to stop RTFN (right the F now) when I need to. With that, however, I also want decent modulation, reliability, and ease of maintenance. My solution was a disc brake swap, but, that lead to several other changes as well.

• BACKGROUND INFO

  First up was deciding what disc brake “kit” to use. I priced out TSM and a few other vendors, and while their kits are supposedly bolt on, I didn't like the exorbitant cost. I had also read of some quality issues with the TSM kit in the early days of its production. Other vendors, such as Great Lakes Off Road wanted to sell “bolt on” kits that required making your own spacers, and either machining or hand grinding the back of the sterling hubs down, so that you could use a 70's Chevy K20 front axle rotor.

Factory Hub	Required Grinding to fit Chevy rotor	Another Pic

 The other issue I had was that it required the use of a late 70s 3/4 ton Chevy 12.5 rotor that would press on from the back of the hub. I looked at using several different rotors for this application, and they all ended up with nearly the same result. The Chevy k20 rotors (Napa part number 4886242) are 12.5” diameter, with a 2.75” height (measured from the back of the rotor face to the front of the mounting side on the hat). They are designed to press onto the backside of a front axle hub. If you look at the center hole on the rotor, it has a chamfered edge, which is designed to press against the backside of the hub, which has an equal but opposite chamfer.

These opposing “miters” (for you construction people) are designed to locate the rotor hub-centrically. The wheel studs are then pressed through the rotor, and into the hub. People who do similar brake conversions on 14 bolts and 60's will usually find a lug that has a longer and bigger diameter knurl, so that their stud (and its knurl) actually presses into the hub, in addition to the rotor. The problem with the sterling hub is that the factory studs are the largest 9/16 studs available, and in fact, are the ones that 14B and 60 guys use. The Dorman number for our lugs is 610-303, and is for an 85 to 97 ford. It's a 9/16 –18 stud that is 3 and 9/32 long, with a .677 knurl and 15/16 shoulder.

Ford sterling lug 610-303

Other common studs. 610-301,610-194 and 610-189. Note the larger shoulder on the 2 Chevy studs to the right of the Ford

The Rotor material is also not strong enough to hold the stud IMO (as well as a machinist I spoke with), for repeated bolting/unbolting of the wheels using an impact gun, which is something I like to do. In addition, because the stud would barely engage the hub, the stud would likely, wobble out the hole in the rotor. Some people have run it this way and JB welded their studs in place. That might work, but isn't the “right” way to do it in my humble opinion.

Another issue with the Chevy rotor and our studs are that if you look at the shoulder size of 15/16, the shoulder area where the stud is supposed to sit in the Chevy rotor is much larger, and in a machinist's opinion that I spoke with regarding machining my hubs, the stud would wobble, and wear away at the rotor which is made of a very soft material in comparison to the hub.

As stated, the GLO bracket was built for a 12.5 rotor diameter and recommends the Chevy rotor. I believe it went with the Chevy stuff based on price and commonality. One of the nice things about using a 12.5” rotor is it allows for 15” wheels. I tried a variety of rotors with varying hat depths to see if I could get away from having to use a spacer. The spacer is required to move the caliper bracket back to the proper location so the caliper aligns properly on the rotor. Here are some rotors and their specs.

Older Rotors

78 Ford Napa #85731 12.5” with 3.225 height

78 K30 Napa # 85843 is 12.875 by 3.080

80's Dodge Napa # 85864 is 12 and 13/16 by 3.26

70's K20 Napa # 86242 is 12.5 with a 2.75

Newer Rotors

02 Chevy P/U Napa # 86242 12.5 by 2.75

96 Ford E350 Napa # 86799 is 12.83 by 3.87

05 Chevy Van Napa # 86999 12.795 by 3.51