AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Thorough Brake Inspections Are Comeback Preventers And Profit Builders

How many times have you seen a hand-painted sign in a shop window that advertised a menu-priced brake pad replacement for “$XX.95 per axle.” Of course, a menu-priced brake replacement would be good if a simple brake pad replacement would cure all...

Read more...

Automotive Pet Peeves 2: Reader Feedback Is Overwhelming

How many auto repair pet peeves are out there? Well, enough of them that one article wouldn’t hold them all. I’ve received so many emails, texts and phone calls about my article in the February issue that I thought: why not put everyone’s pet peeve...

Read more...

Air Filter Show & Tell: Seeing Is Believing

Air filters are normal wear items that ­require regular checks and ­replacement. Their role is to trap dirt particles that can cause damage to engine cylinders, walls, pistons and piston rings. In fuel-injected vehicles, the air filter also plays...

Read more...

ZF 8-Speed Transmission Replacement

The ZF 8HP transmission made its debut in 2009, and since its introduction, has been one of the top choices for international car manufacturers. BMW, one of ZF’s largest customers, uses the 8HP across its entire product portfolio. BMWs featuring...

Read more...

Shop Folds After Shoddy Brake Work Endangers Woman

A Florida woman was thankful to walk away without injury after her vehicle’s brakes went out for the second time in as many months due to negligence on the part of her local repair shop, ABC Action News reported. Shelly Darling of Zephyr Hills, FL,...

Read more...

Air Ride Diagnostics: Reservoirs and Compressors

Just about every Asian and European luxury import nameplate manufacturer has a 7- to 10-year-old vehicle on the road with an air-ride suspension at all four corners. Chances are one of these vehicles will be coming to your shop sooner rather than later. Regardless...

Read more...

Can Cordless Power Tools Replace Pneumatic Tools?

I recently attended Milwaukee Tool’s annual media tool preview event where they unveiled over 80 new products that will be available later this year and early next year. Milwaukee Tool is known primarily as a leading supplier of professional-grade power...

Read more...

OTC's Technician Challenge Tour Will Award Ultimate Diagnostics for Life

The OTC Technician Challenge is going on tour with dates in six states, showcasing the Encore with new Bravo 2.0 software. Technicians nationwide will compete to win one of three Ultimate Diagnostics for Life packages. Ultimate Diagnostics for Life winners...

Read more...

New Productivity Features Added To Coverage In Snap-on Software Upgrade 15.2

Snap-on has increased its vehicle coverage in the new Software Upgrade 15.2 for the Auto-ID, One-Touch Full Vehicle Code Scan and the One-Touch Code Clear features to provide effective, accurate and fast diagnostics out of the box and miles down the road. The...

Read more...

BMW Recognized for Engine-Building Excellence

BMW Group’s engine-building prowess was recognized with four wins at the latest International Engine of the Year Awards. The drive unit in the BMW i8 earned two class wins as well as being declared overall winner, with a further class win being garnered...

Read more...

Diagnostic Dilemma: The Case of the Missing Code

When doing mobile diagnostic work, no-code stalling complaints are a major part of your agenda. In most cases, the client shop is simply too busy to duplicate the failure or, in some cases, a long test drive will yield nothing in the way of useful...

Read more...

Secondary Ignition: The Art of Spark

What is a coil? From the beginning of the internal combustion engine, several different ignition systems have been used to create a high-energy spark. The most popular system, and the one that’s in use today, is a step-up coil. A coil is nothing...

Read more...

Home Brakes Drum Brake Self Adjusters: Understanding These Ancient Devices

Print Print Email Email

d bridge bolts.

Opposing piston calipers are bolted to the knuckle and have pins to position the pads. Drum brakes have return springs to return the shoes to a rest position and hardware to hold the shoes to the backing plate. The shoes return to a fully retracted or rest position when the master cylinder releases pressure to the wheel cylinder. There is no compensation for lining wear.

In some cases, the master cylinder may contain residual check valves to prevent air from being drawn past the wheel cylinder cup seals when the shoes are retracted by the return springs. Before 1955, drum brakes required periodic adjustment. As the linings wore, the piston in the wheel cylinder would have to travel further to engage the shoe with the drum friction surface. The return springs would retract the wheel cylinder piston to its rest position. This caused the brake pedal to move closer to the floorboard when the brakes were applied. This was commonly referred to as low pedal.

Adjusting the brakes would move the shoes closer the drum friction surface and reduce the travel of the wheel cylinder piston. It also required more fluid in the wheel cylinder to apply the brakes. Adjustments were made by manually turning the notched wheel on the adjuster with a brake spoon for the self-energizing type.

The dual-servo drum brake with leading and trailing shoes requires a wrench to adjust the eccentric adjusting cams located on the backing plate. It took a good “sense of feel” to adjust the brakes evenly. The process was to tighten the adjuster or eccentric adjusting cam to a point where the shoes contact the drum friction surface and backing off the adjuster or eccentric adjusting cam to where the shoes just cleared the drum. It’s all in the “feel” as you turn the wheel and move the adjuster or eccentric cam.

Bendix/Wagner
The Bendix/Wagner self-energizing brake has a single anchor pin located above the wheel cylinder. The primary shoe is identified by its length and position on the shoe. The lining segment is shorter than the lining segment on the secondary shoe and is positioned toward the adjuster or heals of the shoe. When the brake is applied, the master cylinder applies hydraulic pressure to both wheel cylinder pistons.

The primary and secondary shoes engage the friction surface of the drum. The wrapping motion of the primary shoe transfers pressure through the adjusting screw and drives the secondary shoe against the anchor pin and friction surface of the drum.

The secondary wheel cylinder piston is held in its rest position as the secondary shoe is driven against the anchor pin.

The adjuster mechanism is attached to the secondary shoe. It is a mechanical device that is made up of the three components.

First, an adjusting screw that is a threaded device like a nut and bolt. The head of the bolt is a notched wheel with a cylindrical pin. A washer and slotted cap fits over the pin and engages web section of the secondary shoe. The nut is also a slotted cap that threads onto the bolt and engages the primary shoe.

Second, a lever moves on a pivot to engage and turn the notched wheel.

Third, a cable or linkage is attached to the lever and the anchor pin to move the lever at its pivot point. There are springs and retainers to hold the mechanism in place.

The adjustment takes place when the vehicle is in reverse and the brakes are applied or when the parking brake is engaged. The cable or link attached to the anchor pin pulls the lever mechanism based on the movement of the secondary shoe.

When the brakes are applied, the lever cannot move the adjuster screw because the brake pressure is being used to apply the shoes. The adjuster lever mechanism must store the adjustment and turn the notched wheel when the brake is released.

There are two types of Bendix/Wagner self-adjusters. Type 1 uses a cable attached to the anchor pin and hook that is attached to the adjusting lever. A guide holds the cable in place. A spring connects the lever to the primary shoe to contain the adjuster. Type 2 uses a cable attached to the anchor pin with a spring and guide that attaches to the lever.

Type 2 uses the same cable guide as Type 1. On Type 2, the lever is connected to the secondary shoe with a pin and return spring. A spring connects the primary and secondary shoe to contain the adjusting screw.

On the Delco Moraine type, the adjuster uses a lever assembly, linkage and adjusting screw. The lever assembly is made up of the adjusting lever with spring-loaded link. The linkage is attached to the anchor pin and spring-loaded link of the assembly. The lever is attached to the secondary shoe at the shoe hold down. A lever return spring is placed between the lever assembly and shoe. A spring connects the primary and secondary shoe to contain the adjuster.

Dual Servo
Dual Servo brakes use two primary shoes and two anchor pins. The pistons of the wheel cylinder apply both of the shoes. The adjuster is located under the wheel cylinder. The adjuster uses an adjusting screw and notched wheel and lever in the same way as the Bendix/Wagner. A lever is attached to one of the shoes to adjust the notched wheel. The lever is usually part of the parking brake assembly.

There is no pressure on the adjusting screw when the brakes are applied allowing the lever to turn the notched wheel. A return spring is used to contain the adjuster in the same manner as the Bendix/Wagner type. This is different from the Bendix/Wagner type where the adjustment takes place after the brake is released.

Adjuster Inspection
The lever and notched wheel are in contact and move against each other every time the secondary shoe moves off the anchor pin. A groove can be worn in the lever and the notched wheel will also wear. A grove worn in the lever can prevent the adjuster from working properly. The wear on the notched wheel can easily be determined when it is compared to a new adjusting screw. The cable can be stretched or frayed.

Springs and linkage can also become worn. Don’t forget that there are left and right adjusting screws. If you install one on the wrong side the lever, it will turn the screw the wrong way.

In a disc/drum application, the automatic adjusters play an important role in maintaining proper brake balance during the time when the shoes are seating to the drum. The linings on most premium replacement shoes are eccentrically ground to produce a clearance at the shoe’s heel and toe.

This allows for a closer drum-to-shoe clearance. As the brakes are applied, the center of the lining contacts the drum first. As hydraulic pressure increases, the shoe will flex allowing the lining to completely contact the drum friction surface. As the shoes wear in, there will be less flex in the shoe and it will closely fit the contour of the drum.

For the first 100 miles or more, the adjuster will be the most active and keep the brake pedal at its proper height. After the shoes have seated, the adjuster will turn the notched wheel in small increments. Replacing the adjusters can provide your customer with a repair that ensures proper brake applications and pedal height.

The following two tabs change content below.

Gene Markel

Latest posts by Gene Markel (see all)

Latest articles from our other sites:

ZF 8-Speed Transmission Replacement

The ZF 8HP transmission made its debut in 2009, and since its introduction, has been one of the top choices for international car manufacturers. BMW, one of ZF’s largest customers, uses the 8HP across...More

ACDelco Unveils Training Recognition Program For Technicians

ACDelco is rewarding technicians and aftermarket service centers for making the commitment to enhance their skills through ACDelco training. The ACDelco Technician Training Recognition Program awards technicians...More

ZF 8-Speed Transmission Replacement

The ZF 8HP transmission made its debut in 2009, and since its introduction, has been one of the top choices for international car manufacturers. BMW, one of ZF’s largest customers, uses the 8HP across...More

Shop Folds After Shoddy Brake Work Endangers Woman

A Florida woman was thankful to walk away without injury after her vehicle’s brakes went out for the second time in as many months due to negligence on the part of her local repair shop, ABC Action News...More

Homak Has Serious Tool Storage Covered

Homak has introduced its new 35" seven-drawer Service Cart. It has plenty of storage for all your tools and is offered in three unique, high-gloss finishes. Featuring full-extension gas struts in...More

Alert Stamping Introduces Versatile Rechargeable Hood Light

Alert Stamping’s new rechargeable SMD LED Hood Light offers dual brightness levels: 1,200 lumens on high and 700 lumens on low. Its bracket extends up to 88" and can stand on flat surfaces. The bottoms...More

Chicago Auto Show Display Takes 1.0L EcoBoost Apart

One of many highlights in the Ford booth at the 107th Chicago Auto Show was a large layout of the pieces that make up the first-ever Ford three-cylinder EcoBoost engine. This 1.0 liter turbocharged, direct-injection...More

Performance V6 and Four Bangers

Any engine builder worth his or her torque wrench keeps their eyes open. They’re looking for anything and everything to make work easier, better and, of course, more profitable. And just as important...More