Where Is the Brake Fluid Leaking?

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Robert Crain

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About two months or so ago, the dash light came on said low brake fluid. That's a new thing and sure enough, the reservoir was indeed a bit low. So yesterday, I got the message again and it was again a bit low. Today, I put the car up on jacks, pulled all four wheels to search for evidence of a leak and I saw nothing. I followed the lines back to the master cylinder-nothing. I can't find any evidence of a leak anywhere. Any ideas of where to look for my mystery leak location? Thanks for your input. Rob
 
If you really checked everywhere, including the ABS unit and don't see evidence of a fluid leak, then what is left is a leak from the master cylinder into the vacuum booster (from there, the fluid is consumed in the engine). Note that checking everywhere includes pulling the calipers off and looking in the dust boots.
AFAIK, there are no common brake fluid leaks on the LS. The only leak I have had was one of the rear calipers. It leaked enough to see it when disassembled, but not enough to notice a fluid drop.
 
Is it possible all of your brake pads are worn down completely and your fluid is in the calipers? This would only happen if you never top off the fluid though. Just a thought if you can't find a leak.
 
Joegr, can you talk more about your thoughts on the possibility of a leak from the master cylinder into the vacuum booster? Sounds interesting but am not familiar. No leaks around the ABS. Brakes still work great so no air getting into the system. I flushed out the old brake fluid last summer but incurred no problems until recently. Nothing else on the brake system has been touched. I will replace rear pads and rotors when some warmer weather comes around. Still snow on the ground here.
 
There's really not any more to say. I've seen it happen on other cars, but so far not the LS. You can unbolt the master cylinder from the booster (no need to disconnect any lines), and see if there is some fluid there.
As was said, are you sure it is a on-going leak, as opposed to pads getting thin?
 
My experience has been leaking at the seal for the parking brake arm on the back of the driver's side rear caliper. I have had the OEM and two reman leak from the same location. And only the driver's side. It appears to be worse if you use the parking brake.
 
XR$Ti, that's interesting and I use the parking brake a lot. Will a caliper rebuild kit include the needed seal to fix that problem if that is indeed where the leak is?
 
No idea -- around here it's easier to cross your fingers and get a reman.

But you should see it wet around that seal. Eventually mine got bad enough that I could see the wet trail down the back of the caliper and a tiny wet spot on the ground.
 
Robert Crain said:
XR$Ti, that's interesting and I use the parking brake a lot. ...
Click to expand...

Just as a different data point, I use the parking brake every single time, and I've never had it leak there on either of mine (04 with 220K when retired, 06 with 216K still going). This is, of course, not that say that some don't leak there. Anyway, you already said yours was not leaking there.
 
I indeed did not see any wet spots on any of the calipers but I found XR$Ti's comment to be a point worth noting since I will soon be replacing the rotors and pads soon. Worth a closer look when that time comes.
 
Yeah, I'm sure most never suffered my issue.

But I'm in what was the coldest capital city in the world this morning. My conspiracy theory is the road salt, brine, grime, and everything else nasty on the roads leads to corrosion and a leak -- and the driver's rear caliper is the most susceptible.

I would have written it off as bad luck or a defect, but when my reman leaked in the same spot, I figured it was more than coincidence (I thought I had a 2nd reman leak, but maybe it was just the one).

Not sure what the winters are like in New England, but I'm guessing one might see the occasional salt spray?

That said, if the leak was big enough to drop your fluid that low that fast, with no visible sign, then I vote for joegr's hypothesis.
 
We're right in the heart of the rust belt here in New Hampshire. Lots of salt used to keep the roads clear. I spend a lot of time at the quarter car wash during the winter. This brake issue isn't causing me to lose sleep yet, but you know how these things go, it won't fix itself.

The complexities of the Lincoln LS are fascinating to me. Wouldn't you just love to talk to a few of the engineers that designed this car?
 
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