2002 Lexus RX300 brake/braking problems - Intermittent

Our car has about 135k miles. It is a great car, except in the past year we have started to have braking problems. Not sure if this is relative, but we live in Hawaii. About a year ago, the brakes started acting wierd. When you depress them, there is a grindy feeling and they don’t brake at the rate they should. (It takes twice as long to brake as normally would.) This happens approximately once out of every 20 brake depressions.

We took the car into the shop and they polished the rotors. That did nothing. We took it in to a different location (Goodyear) and they told us we definitely needed new rotors and pads, which I had them do. The car worked perfectly for about a week, and then started doing the grinding when you depress the brakes, this time it happened about once for every 40-50 times.

We took it back and they polished the (brand new) rotors, this didn’t seem to help. About a week after this, the VSC Check Engine Light came on (Vertical Stability Control), which, when we read the manual, said this had to do with brakes/suspension, etc. So we thought this was the problem and took it in to the Lexus dealer in Hawaii. The Lexus dealer replaced an 02 sensor in the engine, and said the brakes were fine.

The car still does the grinding about every 40-50 braking depressions. Basically you get normal resistance and normal braking, and then every 50th time, the resistance to the brake pedal goes out, and it starts grinding. You have to slam on the brakes to get it to stop in the normal distance that a regular depression would get you. So far two different auto shops and the Hawaii Lexus dealer have told us the car is fine, nobody knows why it is doing this. HELP!

Has anyone checked the master cylinder for proper operation / no leaks?

What you are probably feeling is the ABS system kicking in. If these braking events are normal moderate to gentle braking events on dry roads then you have a problem with the ABS system - which seems likely given the warning light. That warning light means that there are error codes stored in the computer and those error codes need to be read in order to have a place to start with diagnosis.

(Of course, if these grinding brake events are on very hard stops, especially where conditioned might produce some loss of traction, then your ABS system is just doing its job).

I’m thinking along similar lines, @cigroller. That comment in the last paragraph about “resistance to the brake pedal goes out” makes me think the MC might have a bad seal, and the ABS module is getting upset at the lack of pressure.

Do you know what anti-lock brakes feel like when they activate? If you do, are you saying this “grindy” feeling is different from that? If you don’t, can you find a slippery road, slam on the brakes (with no one around you, of course), and see if that’s the same thing you’re experiencing on dry roads?