The Foundation Brake Analyzer (FBA) is an innovative S-Cam brake service tool. It allows the mechanic, or any other interested party who wants or needs to establish actual camshaft travel at each wheel end, or to identify the size of a brake drum present in most S-Cam foundation brake assemblies, without removing the brake drum.
This tool eliminates the time consuming and costly removal of the brake drum to determine if the brake drum meets manufacturer’s specifications or is within legal standards.
The system is simple and easy to use. The gauge has three discs that are stacked one on top of the other, with the ever-present stainless steel pointer.
The largest disc is the stainless steel degree disc, designed to measure the total amount of S-cam travel evident in a specific S-cam foundation brake assembly.
The second largest disc is the non-metallic brake lining disc. It is used to convert the brake lining thickness you measure in the specific brake assembly, into a number representing the number of degrees of S-Cam travel used up by the brake lining wear.
The smallest disc is the non-metallic drum disc, which is utilized to determine the size of the brake drum.
The FBA photo above illustrates one actual brake test. The total amount of S-cam travel in this foundation brake assembly is 90 degrees. The brake lining thickness that remained measured ½ inch, which means that 60 degrees of S-Cam travel is used up by lining wear.
Therefore, 90 degrees of total S-cam travel, minus 60 degrees of S-Cam travel as used up by the brake lining wear, the remainder is 30 degrees. The remaining 30 degrees of S-Cam travel is brake drum wear and initial brake lining to brake drum clearance. This 30 degrees has a calibrated measurement beside it of .125. This means that this particular brake drum is worn 125 thousands of an inch.
The FBA is equipped with a magnet (shown above) that is used to secure the analyzer to the S-cam of the foundation brake assembly that is being tested. This design allows the gauge to be portable and can be moved from one assembly to another with ease.
The BLUE discs are used for standard brake lining with standard Q brake S-cams.
The RED discs are used for extended service brakes often referred to as “Q Plus” brakes and S-cams.
The GREEN discs are used when Extended life S-Cams are used with standard thickness brake lining. In other words Q Plus brake S-Cams on an axle, and the choice is made to install standard 4515 lining rather than the more expensive 4707 lining.
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The foundation brake analyzer is a tool designed to measure the amount of S-Cam rotation in degrees present in any S-Cam foundation brake assembly.
By design, the non-metallic (larger) brake lining wear disc and the (smaller) drum wear disc, will help a trained mechanic to identify the condition of any S-Cam foundation brake assembly.
CAUTION: Prior to any foundation brake analysis, the size of the brake drum and the type of brake assembly Standard or Extended Service must be established. Some fleets are mixing Extended S-Cams with standard lining. Then the proper discs must be installed on the foundation brake analyzer.
For a 16.5 inch brake drum:
Standard brake lining with a standard S- Cam assembly use the Blue Discs.
Extended service or Q+ brake assemblies use the Red discs.
Installing standard lining with Q+ S-Cams?Use the Green Discs.
Please consult the manufacturer service manual for proper parts identification.
You MUST know if Standard or Extended service brake parts are in service. If the in service parts can not be identified, the wheels and drums must be removed for an accurate inspection to be conducted.
Step I: Back-off the slack adjuster until brake shoe rollers are seated in the S-Cam lands. Consult the service manual for each brand of auto slack adjuster for adjusting procedure.
Step 2: Loosen the tension nut on the FBA tool to allow the arrow to swing freely. Set the magnet against the splined end of the S Cam. Rotate the stainless degree wheel to align “0” degrees in the view hole in the loose pointer. Gravity will help you find dead center bottom.
Step 3:Adjust the slack adjuster until brake linings contact the brake drum. Note and record the degrees of S-Cam rotation identified through the view window of the (loose) pointer
Step 4:Use an accurate measuring instrument to measure brake lining thickness.
Note the measurement, and then rotate the Lining (middle) disc so the measurement appears in the pointer window. All brake lining thickness measurements on the disc have an associated value beside them. The value is the number of degrees of rotation that is used up due to brake lining wear.
Step 5:Review the measurements that are now recorded on the FBA tool.Total degrees of S-Cam rotation; subtract the Degree value of the lining thickness.The remaining degrees of rotation represent brake drum wear and initial brake lining to brake drum clearance.
Example: In our photo; starting from 0 brake adjustment rotated the meter to 90 degrees.Measuring the lining at the inspection hole, we had ½”, which indicates 60 degrees. Our 90 degree rotation, less 60 degrees, equals 30 degrees. 30 degrees = .125 of drum wear as indicated inline with the 30 degrees shown on the smallest wheel.
Step 6:Rotate the drum wear disc to align with the pointer window to reflect the remaining degree value.The remaining degree value has a drum wear value associated with it. That value will be the oversize or wear of that brake drum.
Step 7: Back-off the brake adjusters to normal running clearance if rotation test is proven to be less than 120 degrees. Record the S-Cam rotation readings for each wheel on the work order.
Guessing at the lined brake shoe dimension or S-Cam rotation will give you wrong readings.
Remember: Any brake that tests beyond 120 degrees of rotation is out-of-service.