DanielCr

I own a 2017 GX 460 with approximately 70,000 miles on it. I purchased it used and certified from Lexus when it had 55,000 miles. Recently, the dealer conducted a service on the car and observed that all four rear brake pads had 30% life remaining, whereas all the front pads were at 90%. This struck me as unusual because they claimed to have replaced all the pads at 55,000 miles. I requested a technician to investigate the rear brakes further to identify any potential issues. They reported that everything was functioning correctly, there were no signs of binding, and the pads exhibited "normal wear". However, I am fairly confident that Lexus OEM rear brakes should last longer than 20,000 miles.

Upon closer observation, I have noticed a few things:

1. Periodically, my rear brakes emit a hot smell, and the calipers feel hot to the touch after driving without engaging in hard or aggressive braking.
2. I experience a slight tapping sensation on the brake pedal during gentle braking, such as at stoplights or signs. This sensation never occurs during hard braking or when under heavy load. It resembles a brief, soft ABS vibration that lasts only half a second.

I am puzzled as to what could be causing my rear brakes to bind. The calipers and slide pins appear to be in good condition, and all components are moving smoothly, yet the binding persists. Could it be an ABS issue? If so, where should I begin troubleshooting to address this problem?

skeener

Maybe a stuck piston? Any evidence of brake fluid changes in the vehicle history? Old fluid can corrode pistons, causing sticking, especially when close to fully extended.

DanielCr

Thanks for the reply Skeener.
The fluid was changed at 55k. I would agree that it could be a sticky piston. However, both sides are wearing at the same rate. This is why I am led down the rabbit hole of ABS. If pistons on one side are stuck would it cause the other side to stick as well?

ASE

Very unlikely where calipers seize in pairs ... with even pad wear on both sides ...

Agree ... fluid pressure is potentially not backing-off ... or front-to-rear brake fluid pressure is not being properly regulated (proportioned) ...

On the latter ... if the front-to-rear brake fluid pressure is being regulated (proportioned) properly ... under hard braking as a test ... there will be minimal rear-end lift ... or minimal rear-end "squatting" ... meaning that the vehicle will remain close to level.

DanielCr

Thanks ASE. I will try that this afternoon and see what happens.
Hypothetically would that be an ABS pump that regulates that front to rear brake pressure? Or would it be a sensor that is sending the wrong information?

ASE

Not sure how the GX regulates (proportions) front-to-rear brake fluid pressure. Physics ... the front brakes provide 75-odd % of the braking power ... given when braking hard, there is significant forward weight transfer ... so the front of the vehicle dives ... increasing the front tire-to-ground traction ... with the rear of the vehicle lifting ... meaning less rear wheel traction to the ground ... so the system adjusts the front-to-rear brake fluid pressure to compensate for even braking for maximum traction to maintain as close to level weight transfer as possible under these conditions. That's why the rear brake pads for the GX and 4-Runner and FJ Cruiser Platforms (or for any vehicle) typically last 3 times longer than the front brake pads.

I was actually surprised ... never-ever replaced the rear brake pads on a GX-470 ... multiple 4-Runners and an FJ Cruiser before 85,000 + miles. My 2019 GX460 rear pads were gone in 30,000 miles ... well before the 38,000 mile front brake pad replacement. Maybe Lexus has changed their rear brake pad material ...

skeener

I wonder if stability control is faulty for some reason and thinks it needs to bias braking to the rear?