Brak      hek

At brake reline time   relining an axle, with a new set of linings , the S-Cam head and Rollers should be in th is position .  
Simple Installation
"Q Plus"

Brake Wear Indicator

Eliminate unnecessary wheel pulls.
Prevent premature auto brake adjuster damage
Frequent back-off shortens the life of automatic brake adjusters.
Reduce S-Cam brake inspection time.
Monitor brake wear between wheel pulls.

One (1) indicator per wheel-end will add minimal cost to a brake reline. Faster brake wear inspections will save precious maintenance dollars by maximizing brake lining life. Remember the old Maxwell House Coffee advertising, saying? “Good to the last drop”. Enjoy brake lining life to the last drop. Why send useable lining life out with old brake shoe cores?

PMVI (Periodic Motor Vehicle Inspection) is intended to increase vehicle safety.

BWI (Brake Wear Indicator) meters could be called brake cam rotation meters.

The various positions shown above are described, beginning at;
Top left shows brake wear indicator “F”, aimed at yoke pin with brake shoe rollers backed off to Zero during a brake reline.
Top right shows brake wear indicator “F”) at 30 degrees of accumulated S-Cam rotation.
Bottom left, shows brake wear indicator “F” at 90 degrees of accumulated S-Cam rotation
Bottom right shows 120 degrees of rotation. A brake reline is required, when the rotated indicator, notch “F”, is lined up with the Index mark on the Scam and the “E” notch is now pointing at the yoke pin stands for empty.

The easy part about this position is that the condition can be identified without having to remove dust-shields or brake drums.

Brake wear indicators are available in the same sizes as the outer spacer washer they replace.

Back off the slack adjuster until the rollers are in the bottom position of the s-cam. Mark the camshaft, in line with the yoke pin in the slack adjuster. with chalk.

Adjust the brakes to shoe to drum contact, and mark the camshaft. Visually inspect camshaft travel. If the difference between the marks is more than 120 degrees, reject the vehicle.

For a copy of the 2002 Bus Truck & Trailer Inspection Handbook contact:

AAMVA is American Association Motor Vehicle Administrator Tel 703 522-4200

CCMTA is Canadian Council Motor Transport Association Tel 613 736-1003,

After installing Brake Wear Indicators on each wheel end, Brake Cam Rotation identification per wheel-end, takes about 5 minutes.

There is a distinct difference between

“Q” S-Cams and “Q Plus” S-Cams. A “Q” S-Cam will measure                        1 3/8” (inches) across the face, as indicated in the illustration.

A “Q-Plus” S-Cam will measure 1-1/8” (inch). A “Q-Plus” S-Cam is used with the thicker, “Q-Plus” brake lining.

If “Q” shoes are installed in place of “Q-Plus” shoes, the brake wear indicators will indicate a starting position much higher up the S-head ramp after the brakes are properly adjusted.

Brake Reline
At reline time, a properly adjusted brake (.023-.030 shoe-to-drum clearance) the rollers will start life deep in the S-Cam saddles and ride up on the S-Cam, indicated by about 18° of travel on the meter. If during reline and the first brake adjustment procedure, the meters are reading 40 plus degrees of rotation, “Q” linings may have been installed with “Q-Plus” S-Cams.

Whatever shoe and camshaft combination is used to service your S-Cam brakes, cam rotation BEGINS at Zero and ENDS at 120 degrees.

Uneven Brake Wear
If a brake meter on one wheel indicates more accumulated rotation than the others, this could mean one brake is doing more than its share of the braking. Identify why? Don't wait for a wheel fire or other tragic event?

BWI meter technology allows the monitoring of accumulated brake adjustments made by the automatic slack adjuster at each brake.

Each installed meter converts accumulated brake adjustments into degrees of brake camshaft rotation. Visual lining wear inspection is done by a simple glance from a trained brake mechanic. The meter monitors total accumulated brake wear. When the notch on the meter has rotated 120° and the “E” (meaning empty) is facing toward the yoke pin on the adjuster, brake work is required. It may be brake lining, or drum, but 120 degrees means this brake is out of service.

Brake Wear Indicators for S-Cam brakes are not new. They have been on the market for years as “Brake Cam Rotation

Meters”. With the increased focus on brake safety at roadside inspections, brake mechanics need all the training, understanding, and knowledge of tools available to them.

Mechanic must INDEX the S-Cam at Zero degrees of rotation and replace the spacer washer with a meter.

You would not run an engine without a oil dipstick, so why not install BWI meters and monitor brake wear. Change brakes when they need to be changed.