For consistent performance, keep using the same kind of OE linings.

Brake linings are a curious commodity. Intense competition keeps prices in line, but you may never be quite sure what you’re getting in performance unless you stick with a product and supplier you know.

Performance here essentially means how aggressive the linings are and, therefore, how well they’ll work with all other brakes on your rig. Every wise owner also wants long-lasting linings, but not at the expense of weird, perhaps dangerous, performance. To get consistent performance, truck builders urge owners to replace worn original-equipment linings with the same kind.

For S-cam brakes, that ideally would mean brand new brake shoes, but they can cost two to three times what relined shoes do. Relined shoes have new linings installed on used webs; the webs are inspected for general integrity and proper curvature, and some reliners actually re-bend the webs if necessary. So far, so good.

A couple of phone calls to truck parts counters will show that relined brake shoes from a big-name manufacturer may or may not cost more than aftermarket shoes, and in fact may cost less. But how do they perform? A two-letter friction identifier code – known as the ‘edge code’ – such as EE, FF and GH, is stamped on the edge of linings, and is sometimes thought to give a good indication of “aggressivity”. But variations in manufacturing make these questionable, and the edge code is definitely no way to choose one lining over another..

An FF from one maker might not work the same as an FF from another, according to brake experts. If the new material is less aggressive, it won’t do all the work it’s supposed to and other brakes have to work harder. Meanwhile, the stronger brakes might pull the vehicle one way or another. Until recently, there was no way for users to know how a set of non-OE linings would act.

But in 1997, the Society of Automotive Engineers and the Technology and Maintenance Council of the American Trucking Associations adopted a procedure for testing the frictional properties, or aggressivity, of brake linings. Testing on an SAE-approved dynamometer (there are only 16 of these on the continent) simulates brake forces under an exacting procedure specified by U.S. Federal Motor Vehicle Safety Standard 121.
To ensure honesty, manufacturers arrange the testing of their products using an established protocol. The results then go to a committee – anonymously – which reviews the data.

Results are published in TMC’s Recommended Practice 628A. You’ll see lists of linings by company and market name or model, and the aggressivity of each lining is expressed as a torque value, in inch-pounds. These range from about 45,000 inch-pounds to more than 75,000. The current list has 48 products from 10 manufacturers.

If you’re shopping for linings and want to use a brand other than what came on your truck, you can use this list to find a good match. You look up the brand and type of lining that came with your truck, check its torque value, then find an aftermarket product with the same or similar torque. Buy and install those, and they should perform the same, at least in terms of brake balance. They may or may not wear at the same rate.

RP 628A covers 16.5-x-7-inch S-cam brakes, which is by far the most popular size out there. And it lists only those products whose manufacturers want their linings tested and published.

What if the linings now on your truck aren’t in the RP? Find out what was installed there when the truck was new (your dealer can tell you), find it on the list (chances are it will be there because name-brand suppliers to the OEs have been good about such acts of professionalism) and look for a product that performs more or less the same.

You can get a copy of RP 628A from TMC for US$20 if mailed, US$25 if faxed, by calling 703-838-1763. You can also download a ‘pdf’ copy from the TMC website at http://tmc.truckine.com or from an SAE-affiliate website run by the Performance Review Institute at www.pri.sae.org/NADCAP/ brakerep.pdf.

One final word of caution: regardless of the specific lining you choose, don’t even think about having linings with different performance characteristics on two ends of the same axle, and preferably not even on the same truck. Effective braking is about balance within the whole system.