Brake Level moves from high to low
Got a 1998 Lexus GS400. Stock.
So I replaced my pads on all 4 calipers. I believe I may have over extended the caliper pistons though, as I was verifying the pistons moved freely. So here is my issue:
After changing my pads, I topped off my fluid to high. The next morning, I checked the fluid level and it was fine, still on high. I went to work, came home and noticed the fluid level was now on low. I checked all the calipers and saw no leaks or even a hint of one anywhere. So, I brought the level back to high and obviously noted concern and started monitoring it. The next morning, the fluid had overflown down the side and was beyond the high level. So, I removed some and brought the level back to exactly high. Went to work, came home it's on low again. So, hours later, the car had just been sitting there, the fluid level was back on high. The next morning, I opened the hood to watch what was happening as I started the car. I start the car and during the ABS motoring procedure that occurs for 20 seconds or so, I watched the brake fluid slowly go from high down to low. So that explains why after driving the fluid was on low. Hours later, the fluid moves back into the reservoir.
So, to sum it up: the fluid level moves from high to low in conjunction with the ABS motor procedure. After several hours, (e.g. overnight) something releases and the fluid flows back into the reservoir bringing the level back to high where it originally started. Some kind of delayed release or something obviously.
Now that I know this, I haven't filled the level up. The brakes work perfectly, and the level is at perfect high in the morn, and perfect low while driving. But, I know it never did the before and I know the level should not be moving like this.
So, my questions are:
1) has anyone else experienced this? If yes, your resolution?
2) master Lexus mechanics: can I rebuild the master cylinder or did something inside the ABS system tear and I'm sunk?
3) has anyone fixed it or do I need to replace the $2500 master cylinder?
Last edited by rogerroger; 01-06-14 at 10:56 PM.
Reason: adding some info