RX-Fanatic

Hi, my 2004 RX330's brake warnig light came on recently and I noticed that the brake fluid reservoir went from MAX to MIN within a few weeks. Hence, I brought it in to Midas for a brake inspection where they found nothing. They pulled the calipers apart and checked the main culprits but found no leaks and no issues. I was reallly hoping that would be the end of this, but then after driving for less than a week after the inspection, I checked the brake fluid reservoir again and it is now near the MIN again.

Something is definitely going on here in my opinion. The brakes do not feel spongy and there is no drop in the pedal to indicate that the master cylinder is leaking. I know that some drop in fluid levels is normal as the pads wear down, but my pads are still good and the rate of fluid drop is much too rapid to be excused by that. Any experts out there want to suggest something?

Unfortunately, my warranty ended at Lexus so I'm on my own for this....

Thanks in advance...

salimshah

Your intuition is right ... the fluid has to go some-where [it does not evaporate] and one can understand slight drop to compensate for the wear of caliper.

You really ought to carry bottle of brake fluid and check level before driving off [for safety reason].

Trace any pool of liquid ... the brake fluid should be clear and slick to touch with a oily odor. Look for drips around master cylinder, ABS and at each slave cylinder.

So start the engine and with RX in park, Apply and hold the brake down. Keep the pressure for a minute. I would expect the bottom position of the pedal to drop [with the amount of fluid you are loosing].

Once you know the source of leak, It will be evident how to fix it.

Salim

Bear60

When the outside temperature drops and brake fluid shrinks and the level goes down. There may not be a leak in the system. Use DOT 3 brake fluid and fill the master cylinder to the MAX level (not above) and then check it once a week or so.
Very common to have happen at this time of the year.

RX-Fanatic

Well, just got my diagnosis from my Lexus dealership... The master cylinder and brake booster needs to be replaced...

Well, it's going to be an expensive XMAS for me I guess...

Grumpa72

As a shade tree mechanic, I have a hard time understanding how BOTH the MC and booster went bad at the same time. What did they say was wrong with them?

I would suspect the MC simply because they do wear out. While I haven't looked at the Lexus MC yet, every other vehicle that I have owned, has a MC that is relatively easy to replace. Have you thought about doing this yourself or letting one of the independent shops that specialize in foreign/Japanese cars do the work?

salimshah

One of the problems with repair these days, is that the repair facility usually will opt to replace the whole assembly instead of spending more time to actually replace the failing part.

I am not saying that this procedure is bad ... as it may save the customer the additional diagnoses time and less labor to replace. The customer gets some additional new parts and would be less likely to return unhappy.


If you were a DIY and or have min to low labor charge, you may prefer a more precise repair and even an incremental repair.

So RXFanatic, did they find the fluid leaking inside the booster? The fluid has to go somewhere. May be that is why they are recommending booster change as well.

Salim

Lex2000TL

I actually suspected that it will be a problem with master cylinder, but did not have chance to write in the post.
What happened is that your master cylinder leaked “internally” into booster and that is why you did not see brake fluid anywhere. This is not too uncommon, unfortunately. Master cylinders either leak internally, between chambers, or toward brake pedal, right where the booster is in all cars.
Why would they want to replace master cylinder and the booster altogether? I think that they speculate that brake fluid may deteriorate the rubber diaphragm in the booster, as this diaphragm is not designed to work with oily substances. Unfortunately, there is no way to confirm if there is damage there, as booster is sealed unit, I think.
If it is not too late and your car does not have too many miles over warranty or too much time over it, you may want to ask your dealer for "assistance" in repair. Quite often manufacturers like Lexus and other top brands will offer some relieve. However, you will need to negotiate nicely.

RX-Fanatic

I believe they said the fluid was leaking from the master cylinder in to the brake vacuum booster. That is why they need to replace both...

johncdoyle

That is actually a fairly common problem that ends up baffling people. The brake fluid leaks out of the rear seal in the master cylinder and into the booster. Once in the booster, engine vacuum sucks it into the engine and it is burned in the combustion process. That's why you didn't see any leak. The car was consuming the evidence! Sounds like they found the culprit in the end, though. Good luck.

RX-Fanatic

Question... If the engine vacuum sucks it into the engine and burns it off, can this attribute to a puff of white/gray/blue (can't really tell) smoke that I get when I start my vehicle up in the mornings? This only happens after I leave the vehicle over night after being driven??? I was assuming an issue with the engine (ie. seal, valves, pistons), but hopefully it is not.

I haven't looked for it after I've had the master cylinder and brake booster replaced recently - hopefully it is the same problem and hence resolved as well after this...

Lex2000TL

It can, but it seems like it is sign of more serious problem with engine oil leaking through valve guides. If that is the case, you will need to replace valve seals (rubber or neoprene, not sure). That may require lifting engine heads, big job.

salimshah

You can start by observing which fluid/oil you are loosing...

Salim