Disappearing Brake fluid - can't find leak

[Cressida]

The brake fluid level in daughters old 92 Camry keeps needing to be topped off for past couple of months. I can't see any signs of brake fluid on the underside wheel or tire surfaces. No ABS on this car and both rear wheel cylinders have been replaced, but it's been 7 or 8 years now.

Reading, I learned that sometimes a master cylinder (MC) can be leaking fluid back into the brake booster. If that is the case should one be able to see any visible signs, like at the lower rear base of the MC where it connects to the booster? From what I can see that area is completely dry and I don't want to take off and replace the MC if that is not going to be the problem source.

 

[BrendanC]

pull the vacuum hose off the booster and inspect.

 

[FowVay]

I would pull the rear wheel drums and check that the wheel cylinders on either side are not leaking. That is the most likely place to start.

If that is clean then you can remove the master cylinder just slightly from the booster and check for fluid leakage. You don't need to unhook anything and you're just looking for fluid wetness. If it's leaking enough to require repetitive top-offs then you'll see it.

Here's a picture to give you an idea of what you loosen. Pull the master cylinder away from the booster only enough to check for fluid. There should be none.

 

[mk378]

If you do find that the master cylinder has been leaking into the booster, both have to be replaced. The brake fluid will ruin rubber parts inside the booster and cause it to suddenly stop working at some time in the future.

The newer design has a gap between the master cylinder and the booster so any leakage from the cylinder will obviously run down the outside of the booster. The older design, which is likely on a '92, has the cylinder sealed onto the booster.

 

[Chris142]

When the master on my jeep went bad it filled the booster up with brake fluid

 

[ChiTDI]

Fast pad wear will lower the fluid level.
Before tearing apart parts for non visible leaks, might want to check them.

 

[Jetronic]

I put a cable tie down the vacuum connection on the brake booster, if there's brake fluid there it'll be wet when you pull it out. But with that diagram Fowvay posted, that might not be feasible on a camry.

After 7-8 years the rear wheel cylinders could very well be done but it's a pretty bad leak if it requires several top offs. That would most certainly be visible on the drums.

 

[vavavroom]

Edit: Oops, wrong thread. I had two windows open.

 

[nascarnation]

Because brake fluid is nominally clear and thin, sometimes it can really be a tough thing to track down. Lots of good suggestions here and depending on the corrosion potential of your climate you may need to trace the length of all hard lines just to verify.

 

[Cressida]

Found it! First thanks to all the great suggestions. I used all of them starting with inspecting the brake booster vacuum line. It was dry so I went ahead and loosened the Master Cylinder enough as FowVay suggested and pulled it forward to see there was no fluid there on it's backside.

I next starting pulling individual wheels starting with the two in the rear. I figured it would have to show up here... but nothing. As it too often seems to go; the very last wheel that I pulled off was the left front. I didn't see anything at first glance and about ready to call it a day, but then some slight inboard wetness on the control arm caught my eye. I had to use a mirror to find a swollen and split in the brake hose on the back side of the strut. Looking at the strut from straight on you could not see it. I got a replacement line and got it on just before dark.

Despite putting down some papers to catch the dripping brake fluid when I pulled the line, I still made a big mess on the driveway. My wife assisted pumping the brakes while I did the final bleed at the caliper. The best thing... I was using her make-up mirror to find the leak and I got it cleaned up good enough and put back in the bathroom without her knowing. Unless she notices a faint smell of brake fluid still on it I think I'm good.