2010 Lexus ES350 Partial Complete Brake Failure
 

A while back I was driving and my brake pedal went straight to the floor as I approached a stop sign. Quickly pumped the brakes and function was restored.

About a week later it happened again. Once again, quickly pumping the brakes brought the pressure back up. However, after this it started happening more frequently.

Brake fluid level was okay, so I bled the brakes thinking that there was air in the lines. After bleeding the brakes they worked fine for a few days, but then the issue returned.

With 220k on the odometer, I decided that perhaps it was time to replace the master cylinder. I purchased a new one online from Grieco Toyota, installed it, bled brakes to get in all new fresh fluid, and my brakes started working again. It has been 2.5 weeks since I installed the new master cylinder, and I have had no issues since.

Because the original issue was happening intermittently, it presented itself as air in the brake lines. I wanted to share my experience just in case someone else experiences the same symptoms.

Thank you for sharing, sthpawil.

Your symptoms were textbook for a master cylinder failure.
Any surprises during the removal and replacement?

It actually went surprisingly smoothly. I watched a YouTube video for bench bleeding the Master Cylinder, as well as a couple of videos for changing the Master Cylinder on a Camry (no Lexus videos to be found).

I lost a little brake fluid as I connected the brake lines to the new Master Cylinder, but otherwise I couldn't believe how easy it was. I went through just over 3 bottles of brake fluid.

I thought about purchasing one of those pressurized bleeding systems for the brakes, but I snagged a helper and we did it the old-fashioned way.

Good call on using an original master cylinder. I had mine replaced for the second time with an OEM unit after the aftermarket one started showing signs of failure after five years. Nothing serious like your situation, but mainly sinking to the floor and having to push down extensively for the car to stop.

I also replaced the check valve and the hose going into it to address a vacuum issue I had. Very doable job.