TOOLBOX
Small sledgehammer
Ball peen hammers
Inch-drive air gun and sockets
Hydraulic or air jack
Heavy-duty jack stands
Combination wrenches
Bushing drivers
Trouble lights
Dial indicator
Anchor pin press
Half-inch socket set
Grease gun
Penetrating fluid
Cleaning solvent
Anti-seize compound
Locking pliers
Eye protection
Shop towels
Steel brushes
FOR MORE INFO
ArvinMeritor
(800) 535-5560
arvinmeritor.com
Bendix
(800) 247-2725
bendix.com
Carlisle
(800) 867-7992
carlislemotion.com
Eaton
(800) 826-4357
eaton.com
Brake job proficiency is a sort of status symbol among do-it-yourself truckers, indicating a grade of mechanical expertise that commands awe among greenhorns and respect from seasoned professionals.
Reaching this level of know-how has become easier in recent years, with the widespread use of outboard brake drums, which can be removed and replaced without disturbing hubs and wheel bearings. This development significantly reduced the time, mess and effort needed to swap brake shoes. Today, an experienced shop mechanic with the right tools can reline a set of brakes in about four hours. That would amount to roughly $240 to $330 worth of labor – a sizeable sum to save for anyone willing to spend an afternoon turning his own wrenches.
The biggest cost for backyard mechanics is the drum, selling for $75 to $170 each. Drums will normally last through two linings before their metal is worn beyond safe or legal limits. After that, they make excellent supports for bird feeder poles. The trucking industry used to be fond of cutting, or turning, drums during a reline job, to smooth the accumulated grooves and to prevent them from quickly gnawing into the new linings, or blocks. The procedure, however, has now fallen out of favor because it weakens drums, diminishes their heat-holding capacity and requires the use of expensive, oversize linings.
Without drums, brake parts cost about $50 per wheel end. That price includes two shoes and the hardware kit containing the necessary springs, pins and bushings. The instructions below apply to one outboard-drum wheel end, fitted with quick-change brakes.
THE JOB
1. SECURE TRUCK, REMOVE WHEELS. Park the vehicle and chock two wheels. Before setting the parking brake, back off the slack adjusters and cage the maxi cans – if so equipped – of the wheel ends you’ll be working on. Some slack adjusters require considerable force to back off. Do not use an impact wrench for this task. ArvinMeritor (Rockwell) adjusters have a locking pawl device that must be pried out or removed before they can be backed off. Lift the axle until the tires are off the ground. Use an inch-drive air gun to remove wheel lugs.
2. REMOVE DRUM. Use a small sledgehammer to loosen the corroded bond between the hub and drum. Several good whacks around the outer surface are usually enough to free these parts. Slide the drum off the brake shoes and carefully lower it to the floor. Drums are heavy – as much as 80 pounds – so you might want help.
3. DISASSEMBLE BRAKE COMPONENTS. Use a sturdy pry bar to raise the top shoe off the S-cam so the roller pin can be removed. Repeat the process on the lower shoe. This should provide enough slack to unhook the return spring(s) near the S-cam, allowing the shoes to be twisted off the spider. Some mechanics prefer to remove the retainer (anchor-pin) springs instead of the return spring(s). These are easily popped out with a hammer and long chisel-like tool.
4. DISLODGE ANCHOR PINS. This often requires the use of an anchor-pin press ($90 to $110). The press, which looks like a big C-clamp, is a worthwhile investment for do-it-yourselfers because it prevents accidental damage to a spider. You simply crank it down tightly on an anchor pin, then hit it hard with a hammer. Lacking this technology, you’ll need to heat the spider with an acetylene torch, douse the pins with cold water and try to dislodge them with a sledgehammer. Manufacturers warn against this technique, however, because of the high risk of bending and weakening the spider. The anchor pins should be followed by the anchor pin bushings. For them, you’ll need a hammer and an appropriate-sized driver. You may leave these bushings in place if the anchor pins had fit snugly but came out easily.
5. INSPECT S-CAM AND BUSHINGS. You might need a dial indicator ($30 to $50) to measure wear. Grab the camshaft and try to move it up and down, forward and backward, side to side. Excessive endplay (greater than .045 inch) can be corrected by adding spacers (washers) to the shaft, on one or both sides of the slack adjuster. However, if there’s too much vertical or horizontal movement (greater than .03 inch) you’ll need to replace the camshaft bushings and, possibly, the camshaft.
To do this, disconnect the slack adjuster and air chamber’s pushrod yoke. Remove the snap ring and washer(s) from the camshaft’s end. If there are several washers, and if they differ in any way, wire them together and note their location. Then slide the slack adjuster off the shaft, using a puller if necessary. Remove the remaining washers and spacers. Wire-tie and label them as well.
S-Cams on tractors are enclosed by metal tubes that are bolted or (rarely) welded to the spiders. Bolts are preferable, from a repair standpoint. Otherwise you’ll need to cut the weld seams with a high-speed carbon disk and reweld them later. The bushings are press-fitted into each end of the tube. They can typically be coaxed out with a small crow’s foot or other sturdy prying instrument. Trailer S-cams are much easier to rebush because they’re completely exposed, except for a pair of two-piece bushing housings, each held together by four small bolts.
6. CHECK COMPONENTS. Thoroughly clean the spider with solvent and look for cracks and signs of damage. Wipe off the hoses leading to the air chambers and inspect them for cuts, chaffing and other potential problems. Give equal attention to the slack adjusters. On all brands except ArvinMeritor, the adjusting bolts should move freely in one direction and stubbornly in the opposite direction. The locking pawls of ArvinMeritor slacks should be in place and intact. Clevis pins should fit snugly in their bushings. Finally, inspect the drum. It’s obviously a candidate for the scrap heap if it is badly grooved, glazed, heat scored or cracked.
Of course, gauging these wear traits is a little like reading tea leaves: the more you’ve seen, the better you are. Some mechanics use expensive dial indicators to measure the interior diameter of used drums. Others rely on their own judgment. In general, if you can hook the cracks with a fingernail – moving around, not across the wear surface – the piece is junk. It’s no better if the shoe track just inside the outer ridge is deeper than .06 inch, roughly the thickness of a dime and a nickel.
7. REASSEMBLE S-CAMS. Clean the housings or tube holding the S-cam bushings. Follow the manufacturer’s instructions for replacing your particular style of bushing. Attach any necessary parts and apply a generous coat of grease to the camshaft’s bushing surfaces. Slide the cam through its hole in the spider, but be careful to avoid damaging the grease seals in the bushing tube or housings. The cam should be in a non-apply brake position. Install the spacers and slack adjuster in the reverse order that they were removed. Use a new snap ring to hold the assembly together. Connect the air chamber’s pushrod clevis and slack adjuster. Be sure to use the correct hole in the adjuster. Pump grease into both bushings until it starts oozing from the seals. Grease the adjuster. Do not lubricate the S part of the camshaft.
8. MOUNT SHOE ASSEMBLY. Install new anchor pin bushings if the old ones were removed. This job will require a hammer and appropriate-sized driver. Slather anti-seize compound on the new anchor pins and slide each into an installed bushing. Both should fit snugly and be centered in the spider. Install a return spring pin in the web, or frame, of each new shoe, if required for your brand of brake. Hook the return spring(s) to both shoes and carefully drape the assembly over the wheel end, positioning one end of the top shoe on the upper anchor pin, the other end on the S-cam. Some manufacturers recommend dabbing a small amount of grease on the anchor- and roller-pin recesses of each shoe. Never grease the area of the roller pins that touches the S-cam. Install a retainer on each of two roller pins and snap them into place. Connect a retaining spring to one shoe and firmly grab the spring’s other end with locking pliers. Put a short, sturdy bar under the pliers to pry the spring open, guiding its unattached hook to the appropriate hole. Repeat the process on the other retaining spring, if necessary, for your brand of brake.
9. INSTALL DRUM AND WHEELS. Guide the drum over the shoes until it bottoms out on the axle flange. Mount and tighten both dual wheels. Remove the jack stands and lower the tires to the ground.
10. ADJUST BRAKES. Perform this step after you’ve finished relining your brakes. Pressurize the vehicle’s air system and release the brakes. Uncage the maxi can, if necessary. Manually set up the slack adjuster until push rod travel is 11/2 inches. Have an assistant repeatedly apply the brakes while you watch the new parts move. Everything should operate smoothly and freely. Test the new brakes in a parking lot before heading down the road. Monitor the brakes for the first few hundred miles. N
