Relining and Rivets
In the early days of BRAKE & FRONT END, the brake job was known as a reline. The technician would pull the drum and attach fresh friction material to the shoes at the shop. In 1931, a complete reline with adjustment could be had for $10.00!
The shops could buy friction material in a roll. The woven materials were typically made of fibers like asbestos, wool or steel. The strands of the fabric were impregnated with resins and abrasives that were not fully cured.
The technician would cut the material so that it would cover the shoes. Next, the material would be fastened with rivets to the shoes. The typical shoe had between four to 12 rivets. The riveting process would involve cutting a hole in the material and pressing in the rivet with a clamp or press.
After the material was secured, the technician would grind the shoe to match the radius of the drum. It could be a very dirty process that could send asbestos fibers into the air and the lungs of the technician. It was a very labor-intensive process.
This approach in the brake business had its benefits when it came to inventory. With only three or five widths of material, a shop could service 99 percent of vehicles on the road. But, if the core was not serviceable, you had to order a new set.
As the performance of vehicles increased, the friction materials changed. The woven style lengths of material were not able to stand the heat generated by more vehicles that had twice the power of just 10 years ago. Fully cured molded friction materials were the answer and soon replaced woven materials. These materials could not be cut to length at the shop, so it required more inventory. These were called “matched sets.”
Relining was an equipment intensive process that required a riveter, shoe grinder and a device to drill out the old rivets. If the previous linings were bonded with glue, it might require grinding or soaking in toxic solvents to remove the old material.
This approach to the passenger car brake business was killed by bonded shoes, asbestos regulations and disc brakes. The relining strategy is still used in the heavy-duty trucking industry where the drum is still the dominate braking method. But even large trucks are moving towards the disc brakes.
Got Brake Tools?
If you were a shop that relined its own brake shoes, it required some tools that might be completely foreign to new technicians or maybe found in the antiques listings on eBay.
In the early days of BRAKE & FRONT END, many of the advertisers were the tool companies. Two tools were essential for relining shoes:
Brake Shoe Radius Grinder: This tool would grind the arc of the shoe to match the drum. The radius was taken from the diameter of the drum. If the radius of the shoe was not right, it could cause uneven braking. This was critical in the days before hydraulic brakes when the forces were not equalized by the fluid pressure. The grinder would send large amounts of brake dust into the air.
Riveting/Grinding Press: Brake shoe and clutch rivets where typically made of brass or other malleable metal. The c-shaped presses typically had two functions. First, to serve as a press to drill out or grind down the old rivet. Second, with a foot-operated pedal the operator could set the new rivets into place. Some linings were not pre drilled and countersunk for new rivets, so the installer had to do this before the rivets were installed.
The Rise of the Bonders
Even in the 1930s, the brake friction industry was moving away from relining shoes in-house. The trend was driven by increased vehicle performance and better roads where higher speeds could be achieved. Also, the number of friction materials and shoes were increasing and shops found it difficult to carry an inventory to cover the entire vehicle population.
Because of World War II research, adhesives had improved dramatically. Chemists were able to create synthetic adhesives that could out perform organic glues under extreme heat. To use these modern adhesives, it required heat and curing time to make a rivet-free brake shoe. Some of these ovens were out of the reach of the smaller brake shops.
Seeing the opportunity in these converging trends, many larger brake shops and parts suppliers became brake bonders/jobbers. With more volume, they were able to use new bonding techniques while keeping the prices low. Also, bonders introduced a new four letter word to the aftermarket — “core.”
In the late 1960s, the market began to shift to disc brakes. Many smaller brake bonders were not able to keep up with the changes. By the mid 1970s as the number of brake relines diminished and with increased competition from larger manufacturers, the local brake bonder/jobber practically disappeared.
In 1976, the EPA/OSHA report on asbestos in the workplace put the nail in the coffin of some bonders and manufacturers.
In the past 20 years, friction material and attachment technology has advanced more than during the previous 20. The driving force in these changes has been the evolving vehicle and customer expectations. Premium-grade pads contain more testing, research and development than ever before. In the waning years of the 21st century, aftermarket brake pad manufacturers started to make more brake pads that were focused at a specific applications that were problematic at even the OE level.
While backing plates and attachment methods have not received the same level of marketing attention as the friction materials, they have improved dramatically. Rivets are still used in a few applications where the performance and economical parameters call for it. Integral molding where the friction material is pushed through the holes in the backing plate (in conjunction with glue) is the most common method of attachment.
On some demanding applications where noise and safety are critical to the performance of the entire brake pad, some manufacturers are turning to new attachment methods. Some manufacturers are creating stronger bonds with the backing plate through special surface treatments that create more surface area for bonding. Another approach has been new methods of mechanical attachment.
One brake backing plate manufacturer is able to put hundreds of small hooks on the plate that grab the friction material. The hooks increase the shear strength and can prevent edge lift of the friction material. Not only can it increase overall safety, but it can decrease incidents of unwanted noise. What is the future? While racing once pointed the direction of future innovations of brake systems of road-going systems, it is now influenced more by fuel economy and customer expectations.
With new fuel economy standards on the political chopping block, it is possible that brake systems could a due to shed some weight. This will mean lighter rotors and possibly brake pad backing plates that are made out of exotic composite materials.