1993-1994 Lexus LS400 Front vs Rear Brakes: What Wears First and What to Replace

By Core Brake Parts Tech Team — Circleville, OH warehouse

On a 1993-1994 Lexus LS400 the front brakes almost always wear out first, because the front axle does most of the stopping work. The rear pads usually outlast one or more front pad sets, but the rear brakes hide a second system worth checking: drum-style parking brake shoes that sit inside the hat of each rear rotor. Here is how the two ends differ, how to tell which one needs work, and what to replace together.

How the LS400 Brakes Are Laid Out

The first-generation LS400 uses disc brakes at all four corners. Lexus lists a separate front rotor (part number 43512-50100) and rear rotor (part number 42431-50040) for the 1992-1994 LS400 with the 4.0L V8, so the front and rear discs are not interchangeable. Each end has its own caliper and its own pad shape, which is why you order front and rear pads as separate sets.

The parking brake does not use the rear calipers. Instead, a pair of small brake shoes lives inside the hat section of each rear rotor, and the inside of that hat acts as a small drum. Lexus lists these as separate parking brake shoe assemblies (46540-50010 and 46550-50010) for the 1990-1994 LS400. This drum-in-hat design is common on rear-disc cars: a cable pulls a cam and lever at the bottom of the backing plate, and the shoes are adjusted with a star wheel at the top.

Why the Front Brakes Wear First

When you brake, the car's weight shifts forward. The front tires gain grip and the rears lose it, so the system is designed to send more force to the front. A proportioning valve reduces pressure to the rear brakes, by 20 to 40 percent depending on the application, to keep the lightly loaded rear wheels from locking. On cars with this kind of hydraulic proportioning, the front brakes typically wear two to three times faster than the rear pads or shoes.

The LS400 is a heavy, powerful sedan with a big V8 up front, and many of these cars are now driven in stop-and-go city traffic by their second or third owners. That combination is hard on the front pads and rotors. The rear pads usually keep going, which is why many LS400 owners do two front brake jobs for every rear one.

That pattern is not a guarantee. A sticking rear caliper slide pin, a seized piston or a parking brake that does not fully release can make one rear corner wear fast. Always measure all four corners instead of assuming.

Symptoms: Is It the Front or the Rear?

• Steering wheel shake when braking from highway speed: this usually points to the front rotors, since front rotor thickness variation is felt directly through the steering.
• Pedal pulsation with a steady steering wheel: check the rear rotors. Rear rotor runout shows up in the pedal and seat more than the wheel.
• High-pitched squeal at low speed: the pad wear indicators are touching the rotor. Look through the wheel spokes at both ends to see which pads are thin.
• Grinding: pad backing plate on rotor. Stop driving on it; the rotor on that corner is being cut.
• Dragging or a hot rear wheel after a drive: a parking brake shoe that is over-adjusted, swollen from moisture, or stuck from rust inside the rotor hat.
• Parking brake lever or pedal travels too far: the parking shoes are worn or out of adjustment, independent of the rear pads.
• Pulling to one side: a sticking caliper or contaminated pad on one side, front or rear.

What to Replace at Each End

Front brake job

Replace front pads as an axle set and measure the rotors against the minimum thickness stamped on them or listed in the factory service manual. On a car this age the front rotors have often been machined before, so a fresh pair of front brake rotors is usually the better choice than turning them again. Clean and lubricate the caliper slide pins, fit new abutment clips if the old ones are rusted, and check the flexible brake hoses for cracks, since rubber hoses this old are a real concern. Shop brake pads by position so you get the correct front shape.

Rear brake job

Rear pads come off the same way as the fronts, but the rear rotor has to be pulled over the parking brake shoes. If the parking brake has not been used much, rust can bond the rotor hat to the shoes. Remove the rubber plug in the rotor, back the star-wheel adjuster off with a brake spoon, and tap the rotor free. With the rotor off, inspect the parking brake shoe lining and all the hardware.

For the rear pads we carry the EBC Redstuff ceramic rear brake pads for the 1993-1994 LS400, a low-dust ceramic street pad. Other options are in our ceramic brake pads collection.

Parking brake shoes

Parking shoes wear slowly because they are normally applied only when the car is stopped, but they can crack, delaminate or rust. If the lining is thin, contaminated with grease or fluid, or the springs are rusted, replace the shoes and hardware while the rotors are off. Replacement brake shoes and brake hardware kits make this a small add-on to a rear rotor job.

Adjusting the Parking Brake After a Rear Job

After new rear rotors or shoes go on, the drum-in-hat parking brake must be re-adjusted. The usual method is to turn the rotor and rotate the star wheel through the access hole until the shoes drag, then back the adjuster off until the rotor turns freely. Some manufacturers call for a specific number of adjuster clicks or a drum diameter gauge, so follow the factory service manual exactly rather than going by feel. Too tight and the shoes drag and heat the rear rotors; too loose and the lever travels too far. The clearance exists because shoes can swell with moisture and expand at a different rate than the rotor hat.

How Hard Is the Job?

A front pad and rotor job on the LS400 is a reasonable driveway job with basic hand tools, a torque wrench, jack stands and brake cleaner. The rear takes longer because of the parking brake: freeing a stuck rotor and adjusting the shoes adds time and needs a brake spoon. Tighten caliper bracket bolts and lug nuts to the values in the factory service manual, bed the new pads in with a series of moderate stops, and check the brake fluid level and condition when you are done.

If you are doing both ends, do the fronts first. They are almost always the worn end, and they give you the most stopping feel for the money. Browse everything for your car in our brake parts section.

Frequently Asked Questions

Do the 1993-1994 LS400 rear brakes use drums or discs?

The rear service brakes are discs with calipers. The only drum on the rear is the small parking brake drum formed inside the hat of each rear rotor, which uses its own set of shoes.

Should I replace front and rear pads at the same time?

Only if both are worn. The fronts normally wear much faster, so it is common to replace the fronts alone and do the rears on a later service. Measure all four corners each time.

Are the front and rear rotors the same part?

No. Lexus lists different front and rear rotor part numbers for the 1992-1994 LS400, so order them by position.

Why won't my rear rotor come off?

Rust inside the rotor hat has usually bonded it to the parking brake shoes. Back the parking brake adjuster off through the access hole, then tap the rotor free.

Why is one rear wheel hot after driving?

A parking brake that is over-adjusted or not releasing, or a sticking rear caliper. Check the parking brake cable and shoe adjustment, then the caliper slides and piston.

Sources

1. Lexus Parts Now - Genuine LS400 Brake Disc - front and rear rotor part numbers for the 1992-1994 LS400
2. Lexus Parts Now - Genuine LS400 Parking Brake Shoe - parking brake shoe assembly part numbers
3. Brake and Front End - Adjusting Parking Brakes - drum-in-hat design and adjustment procedure
4. Brake and Front End - Removing a Rear Rotor Stuck on the Parking Brake - stuck rotor cause and removal steps
5. AA1Car - Brake Balance and Electronic Brake Proportioning - proportioning valve pressure reduction and front vs rear wear rates