By Core Brake Parts Tech Team — Circleville, OH warehouse
After new brake shoes go in, the shoes have to be set close to the drum by hand before the car goes back on the road. You do that by turning the star wheel adjuster until the drum drags lightly, backing it off until the drum spins freely, then making a series of firm forward and reverse stops so the self-adjuster finishes the job. Skip the manual setting and you get a low, soft pedal that the self-adjuster may never fully correct.
How Drum Brake Self-Adjusters Work
Most rear drum brakes on cars and light trucks use a threaded adjusting screw with a notched star wheel that sits between the bottom ends of the two shoes. Lengthening that screw spreads the shoes toward the drum. A lever, pulled by a cable or linkage, rides on the star wheel teeth and turns it one notch at a time as the lining wears.
The brake-parts manufacturer behind the Know Your Parts technical library describes two common Bendix/Wagner layouts. Type 1 uses a cable attached to the anchor pin and a hook attached to the adjusting lever, with a spring tying the lever to the primary shoe. Type 2 uses a cable from the anchor pin with a spring and guide at the lever, and the lever is pinned to the secondary shoe. A third family, the Delco Moraine style, uses a lever assembly, linkage and adjusting screw with a spring-loaded link.
The key point for anyone finishing a shoe job: the adjuster does not act on every stop. On these designs, adjustment happens when the brakes are applied while the vehicle is rolling in reverse, or when the parking brake is applied. The lever stores the movement and turns the notched wheel when the brake is released. That is why the test drive after the job includes reverse stops.
Why Manual Adjustment Is Still Required
A self-adjuster only takes up small amounts of clearance, one tooth at a time. New shoes installed with the adjuster screwed all the way in leave a large gap to the drum, and the lever needs a certain amount of shoe travel before it can grab the next tooth. If the gap starts out too big, the adjuster may never engage properly. Self-adjusting brakes still need a correct starting position; the automatic mechanism maintains adjustment, it does not create it.
Know Your Parts also notes that for the first 100 miles or more after new shoes go in, the adjuster is at its most active, keeping the pedal at its proper height as the new lining seats. A good manual setting gives it a small amount of work to do instead of a large one.
Step-by-Step: Adjusting Drum Brakes After New Shoes
Work on one side at a time so you always have the other side assembled as a reference, and replace shoes on both wheels of the axle at the same time. Take photos before you pull anything apart.
- Assemble the adjuster correctly. Clean the adjusting screw, then lubricate its threads with high-temperature brake grease so it turns freely. Adjusting screws are often side-specific, so keep the left and right screws on their own sides.
- Start with the screw backed in. Install the shoes, springs, parking brake strut, lever and cable with the adjuster retracted so the drum slides over the new lining.
- Set the shoes close to the drum. With the drum off, you can turn the star wheel to spread the shoes until the drum just slides on with light contact. A drum-to-shoe setting gauge speeds this up: set it to the drum's inside diameter, flip it over, and adjust the shoes to the gauge.
- Fine-tune through the backing plate. With the drum installed, remove the rubber plug from the access slot in the backing plate. Turn the star wheel with a brake spoon or thin screwdriver until the brake drags slightly as you turn the drum by hand.
- Back it off to a light drag or free spin. Turn the wheel the opposite direction until the drum turns freely again. To back off, hold the adjuster lever away from the star wheel with a second thin screwdriver; if the lever stays engaged, the wheel will not turn that way.
- Repeat on the other side and aim for the same feel on both wheels so the car does not pull.
- Center the shoes. Refit the plugs, install the wheels, and torque the lug nuts to the value in your owner's manual or service manual. Pump the brake pedal several times with the vehicle still supported.
- Let the self-adjuster finish. In a safe, open area, back up slowly and apply the brakes firmly, then make several forward stops. Repeat the reverse stops a number of times. The pedal should come up higher and firmer as the adjusters take up the last bit of clearance.
Which way the star wheel turns to spread the shoes depends on the design and which side of the vehicle you are on. On many systems, rolling the wheel upward through the access slot expands the shoes, but that is not universal. Confirm the direction in the service information for your vehicle, or watch the shoes move with the drum off before you trust the feel through the slot.
What About the Parking Brake Cable?
Set the shoes first, then check the parking brake. The cable should not be holding the shoes out against the drum. If the parking brake lever or pedal travel is excessive after the shoes are adjusted, adjust the cable at its equalizer to the procedure in the service manual. Tightening the cable to make up for loose shoes hides the real problem and can leave the rear brakes dragging.
Symptoms of Drum Brakes That Are Out of Adjustment
| Symptom | Likely cause | What to check |
|---|---|---|
| Low pedal that pumps up higher | Shoes set too far from the drum | Star wheel setting; adjuster lever and cable engaged |
| Excessive parking brake travel | Loose shoe adjustment or stretched cable | Shoe adjustment first, then cable |
| Rear wheel hot or dragging after a drive | Shoes adjusted too tight or parking brake cable too tight | Back off star wheel; check cable slack |
| Pull to one side under braking | Uneven adjustment side to side | Match drag on both drums |
| Pedal slowly drops back to low over weeks | Seized or worn self-adjuster | Star wheel threads, lever teeth, cable and spring |
Causes of Self-Adjusters That Stop Working
An adjuster that will not advance leaves you right back where you started. The common causes are:
- Worn lever and star wheel. Know Your Parts points out that a groove can wear into the lever and the notched wheel wears too, so the lever slips instead of turning the wheel.
- Seized threads. Brake dust, water and rust lock the adjusting screw. Cleaning and greasing the threads during every shoe job prevents this.
- Tired springs. Return and hold-down springs go through constant heating and cooling and lose tension. Haynes recommends replacing the retracting and hold-down springs whenever the shoes are replaced.
- Parts on the wrong side or assembled wrong. A side-specific screw on the wrong side, or a cable routed off its guide, can keep the adjuster from ever turning.
- Driving habits. Because most designs adjust in reverse or with the parking brake, a car that rarely backs up with firm braking and never uses its parking brake gives the adjuster few chances to work.
What to Replace at the Same Time
A shoe job is the cheapest time to renew everything that controls adjustment. A complete drum brake hardware kit covers the return springs, hold-down springs and clips, and many kits include new adjuster components. Replacing the adjusters, as the Know Your Parts guidance notes, helps ensure proper brake application and pedal height.
- Brake shoes: both wheels on the axle, always. Browse replacement brake shoes by vehicle.
- Hardware and adjuster: springs, clips, the star wheel screw and lever if the teeth are worn or the threads are rough.
- Drums: check the maximum diameter stamped on the drum and replace drums that are past it, scored or out of round.
- Wheel cylinders: pull back the boots. Any fluid behind them means the cylinder is leaking and will contaminate the new lining.
If you are also servicing the front axle, our full selection of brake parts covers pads, rotors and hydraulics.
How Hard Is This Job?
For someone who has done a disc brake job, drum brakes are a step up in patience rather than tools. The springs take effort to install, and a spring tool plus a brake spoon make the work much easier. The adjustment itself takes a few minutes per side once you know which way the wheel turns. The two mistakes that cause most comebacks are leaving the shoes backed all the way off and forgetting to hold the lever away when backing the star wheel off.
Haynes warns that brake dust can be harmful and that brake parts should never be cleaned with petroleum-based solvents. Do not blow the dust off with compressed air or breathe it; use a dedicated brake cleaner. Before driving in traffic, confirm the pedal is firm and high and that both rear wheels spin without heavy drag.
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Shop Drum Brake Parts →Frequently Asked Questions
Do self-adjusting drum brakes need to be adjusted after new shoes?
Yes. The self-adjuster only takes up small amounts of wear. New shoes must be set close to the drum by hand first, then reverse stops let the adjuster finish the fine setting.
How tight should drum brakes be after adjustment?
Adjust until the drum drags slightly when turned by hand, then back off until it turns freely or with only a light, even drag. It should never bind or grind, and both sides should feel the same.
Why won't my star wheel turn to loosen the brakes?
The adjuster lever is still engaged on the teeth and acts like a ratchet. Push the lever away from the star wheel with a thin screwdriver through the access slot while you turn the wheel with a brake spoon.
How many times do I back up to adjust drum brakes?
Make a series of slow reverse stops with firm brake application, mixed with forward stops, until the pedal height stops improving. If the pedal never comes up, the adjuster is likely not working or the shoes were set too loose.
Can I adjust the parking brake to fix a low pedal?
No. A low pedal from drum brakes comes from shoe clearance. Adjust the shoes first; only adjust the parking brake cable afterward if its travel is still excessive.
Should I replace the springs and adjuster with the shoes?
It is strongly recommended. Springs lose tension from repeated heat cycles, and worn star wheel teeth or levers stop the self-adjuster from working, which lets the pedal sink again.
Sources
- Know Your Parts - The Importance of Drum Brake Self Adjusters - Bendix/Wagner Type 1 and 2 and Delco Moraine layouts, adjustment in reverse or with parking brake, adjuster most active in first 100 miles, worn lever and wheel
- Haynes Manuals - Drum Brake Shoe Replacement - drag-then-back-off procedure, holding the lever off the star wheel, greasing adjuster threads, replacing springs, forward and reverse stops, solvent and dust warnings
- R1 Concepts - How Do Self Adjusting Drum Brakes Work - star wheel and lever operation, adjustment during reverse braking, need for correct starting position
- Phoenix Systems - How to Adjust Rear Drum Brakes With Self-Adjusters - star wheel location and direction caution, light drag target, reverse stops, adjuster cannot engage if clearance is too large
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