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Brake Level moves from high to low

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Old 01-06-14, 10:52 PM   #1
rogerroger
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Default Brake Level moves from high to low

Hi All,

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?

Thanks
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Last edited by rogerroger; 01-06-14 at 10:56 PM.. Reason: adding some info
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Old 01-06-14, 11:00 PM   #2
ttaylor993
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You didn't say anything about bleeding the brakes. Sounds like you may have some air incorporated into your break fluid.
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Old 01-07-14, 01:22 AM   #3
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If the brakes work correctly I wouldn't worry about it.
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Old 01-07-14, 05:32 PM   #4
rogerroger
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Quote:
Originally Posted by ttaylor993 View Post
You didn't say anything about bleeding the brakes. Sounds like you may have some air incorporated into your break fluid.
I didn't bleed the brakes. I only replaced the pads. If anything fluid would need to be removed after replacing pads if one keeps their fluid topped off.
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Old 01-07-14, 05:35 PM   #5
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Originally Posted by rgarjr View Post
If the brakes work correctly I wouldn't worry about it.
Generally I would agree and so far there have been no mishaps. However, there are times when the fluid would bounce around in the reservoir which could expose the valve underneath possibly letting air in (but hasn't happened yet). In any case, something is broke and I'm wondering if anyone has a resolution for it short of spending $3k or whatever it is for replacement parts.
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Old 01-07-14, 08:59 PM   #6
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The ABS master cylinder pretty much remains a mysterious item when it comes to remanufacturing/repairing, which is mostly why owners that have problems with them just replace the whole thing.
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Old 01-07-14, 08:59 PM
 
 
 
 
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