2003-2009 Lexus GX470 Parking Brake Problems and Adjustment

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 2003-2009 Lexus GX470 does not use its rear calipers to park. It has a separate drum-in-disc parking brake: two small shoes inside the hat of each rear rotor, pulled by cables from a center-console lever. When the lever travels too far, the SUV rolls on a slope, or the rear drags, the fix is almost always shoe adjustment, worn or glazed shoes, or a stiff cable, and Lexus gives a clear specification to check it against.

How the GX470 parking brake works

Lexus describes the GX470 system in the owner's manual as a "drum-in-disc type parking brake system." Each rear rotor does two jobs: the outer friction ring is clamped by the rear pads during normal braking, and a machined drum surface on the inside of the center hat serves the parking brake. A pair of parking brake shoes sits on the backing plate inside that hat. When you pull the lever, cables pull a lever and strut that spread the shoes against the drum surface. A star-wheel adjuster between the shoes sets how close they sit to the drum at rest.

On the U.S. GX470 the parking brake is a hand lever between the front seats, not a foot pedal. The owner's manual says to set it by pulling up the lever, and to release it by pulling up slightly, pressing the lock release button and lowering the lever. For better holding power, Lexus says to hold the brake pedal down while you set it. If you have read that you press a pedal a second time to release it, that describes the later GX460, not the GX470.

Because the parking shoes only work when the vehicle is stopped, they wear very slowly. Their biggest enemies are rust, disuse and misadjustment, not mileage.

The factory specification: lever clicks

The GX470 owner's manual lists service specifications for the brakes. These are the numbers that matter when you judge whether your parking brake needs attention:

Count the clicks as you pull the lever up with firm, steady effort. Around 5 to 7 clicks is in spec. Many more than that means the shoes sit too far from the drum. Fewer, or a rear that drags with the lever down, means they are set too tight or something is not returning.

Common GX470 parking brake problems and their causes

Lever pulls up too high and the truck rolls

This is the classic complaint. The shoe-to-drum gap grows as the linings and drum surface wear, and on a parking brake that is rarely used hard, the adjuster does not keep up on its own. It also shows up right after a rear rotor replacement: a new rotor has a fresh, full-diameter drum surface, and if the shoes were backed off to get the old rotor off and never readjusted, the lever will travel well past spec.

Parking brake does not hold even at normal lever travel

If the clicks are in range but the GX470 still creeps, the shoes are usually glazed, contaminated or worn to the lining limit. A leaking rear axle seal can soak the shoes in gear oil, and a leaking rear caliper can put brake fluid on them. Contaminated shoes cannot be cleaned back to full grip and should be replaced in axle sets. A drum surface that is rusted or scored also cuts holding power.

Rear brakes drag, heat up or smell hot

Shoes adjusted too tight, a cable that sticks and will not fully return, or a broken return spring can leave the shoes rubbing. Lexus warns in the manual to make sure the parking brake is fully released and the reminder light is off before driving. A drag on only one side points to that side's cable or hardware.

Lever feels stiff or will not release cleanly

Cables on a truck that sees salt, mud or water crossings can corrode inside their housings. Brake and Front End notes that the equalizer linkage on these systems can rust and interfere with proper application and release. A cable that stays stiff with the rear wheels off the ground needs lubrication or replacement.

Brake warning light stays on

The red brake light on the GX470 does more than report the parking brake. The manual says it also comes on for low brake fluid and for a hydraulic brake booster fault, and that if the light stays on after the parking brake is released with the engine running, or the buzzer sounds with it, you should stop in a safe place and have the vehicle checked. Do not assume a lit light is just the lever switch.

How to adjust the GX470 parking brake

Adjustment happens at the shoes first, not at the cable. Tightening the cable to take up worn-shoe slack leaves the shoe lever partly applied at rest and causes drag. The general procedure for a drum-in-hat parking brake, as described by Brake and Front End and Wilwood, is:

1. Chock the front wheels, release the parking brake, raise the rear on stands and remove the rear wheels.
2. Locate the access hole in the rotor hat and rotate the rotor until the hole lines up with the star-wheel adjuster.
3. With a brake adjusting tool or a thin screwdriver, turn the star wheel to expand the shoes until the rotor will not turn by hand.
4. Back the star wheel off until the rotor turns freely. A very light, even rub is acceptable; a drag you can feel is not.
5. Repeat on the other side. The adjusters are mirror images, so the direction that tightens one side loosens the other. If the rotor gets looser when you expect tighter, go the other way.
6. Pump the lever several times, then count the clicks. Aim for the 5 to 7 click specification. Only if the shoes are correctly set and travel is still out of spec should the cable adjuster be touched.
7. Spin each rear wheel with the lever down to confirm there is no drag, then refit the wheels.

Brake and Front End stresses that you should never estimate a parking brake adjustment, and that some manufacturers call for a drum gauge rather than feel. The feel method above gets you close; the lever-click check is the final proof.

Replacing the shoes, rotors and hardware

Replace parking brake shoes when the lining is at or near the 1.0 mm wear limit, when they are contaminated with oil or fluid, or when they are cracked or glazed. Always do both sides. It is also the right time to replace the springs and adjuster hardware, which rust in place on this truck; a brake hardware kit and new parking brake shoes cost little compared with the labor to get back in there.

Because the parking drum is part of the rear rotor, a scored or rusted drum surface, or a rotor whose outer face is worn out, means new rear rotors. For the GX470 we carry the EBC GD Sport slotted rear rotor set GD7161 and the EBC USR7161 slotted rear rotor set, both listed for the 2003-2009 GX470 4.7. Browse all brake rotors or matching brake pads if you are doing the full rear brake job at once.

After new shoes or rotors go in, Lexus says the drum-in-disc parking brake needs bedding-down of the shoes, both periodically and whenever the shoes or drums are replaced, and recommends having a Lexus dealer perform it. Bedding seats the new linings to the drum so they reach full holding power. Until that is done, do not rely on the parking brake alone on a steep grade.

How hard is the job?

Checking lever clicks takes a minute. A star-wheel adjustment is an easy driveway job with the rear wheels off. Shoe replacement is moderate: the rear caliper and rotor come off, and the shoe springs and hold-down hardware take patience and the right spring tools. Anything involving rusted cables, a leaking axle seal or a caliper that has soaked the shoes adds time. If the brake warning light is involved, have the hydraulic booster and fluid level checked before you blame the parking brake.

Frequently Asked Questions

How many clicks should the GX470 parking brake lever have?

The owner's manual specifies 5 to 7 clicks when the lever is pulled with 196 N (about 44 lbf) of force. Noticeably more clicks means the shoes need adjusting or replacing.

Does the GX470 use the rear calipers as the parking brake?

No. It uses a separate drum-in-disc system: small shoes inside the hat of each rear rotor, operated by cables from the center lever.

Should I tighten the cable to fix a loose parking brake?

Not first. Adjust the shoes at the star wheel so they sit just clear of the drum, then recheck the clicks. Tightening the cable to cover worn or loose shoes can leave the rear brakes dragging.

Do I need to adjust the parking brake after new rear rotors?

Yes. The new rotor carries a new drum surface, and the shoes are usually backed off during removal. Reset the star wheels, check the clicks, and have the shoes bedded as Lexus recommends.

Why is my GX470 brake light on when the parking brake is off?

On the GX470 that light also warns of low brake fluid and a hydraulic booster problem. If it stays on with the lever down and the engine running, or the buzzer sounds, stop safely and have the brakes checked.

What brake fluid does the GX470 take?

The owner's manual specifies DOT 3 fluid meeting SAE J1703 or FMVSS No. 116.

Sources

1. Lexus 2004 GX470 Owner's Manual (OM60B55U) - lever operation, drum-in-disc parking brake and bedding-down, 5-7 click adjustment spec, lining wear limit, DOT 3 fluid, brake warning light and hydraulic booster warnings
2. Brake and Front End - Adjusting Parking Brakes - drum-in-hat construction, star-wheel adjustment through the hat, never estimate the adjustment, rusted equalizer linkage
3. Wilwood - How to Adjust the Internal Drum Parking Brake - star wheel to lock, then back off until the drum turns with minor drag