Slow brake fluid leak

[DJWUZJ]

Earlier this year I found that the brake light also comes on when brake fluid is low - not just when the e-brake is engaged. It re-occurred about 6 months (15k) later.

I added about 6-8oz of fluid to get it back to normal level (following correct protocol to measure) but now have the pesky task of figuring out where it's coming from.

Any one else have similar experiences and suggestions where to start looking?

Truck is an 03, with 154k.

 

[APKhaos]

Look for a leaky caliper. Probably losing fluid from a piston seal or two.
Seals can be replaced easily enough, or buy a recon caliper. I've got recons on the rear of mine and they've been rock solid for around $65 each.

 

[2001LC]

If a caliper your lucky and easy to see and fix as APKhaos said.

If you park in same spot regularly you should see some on ground, it will look like wet spot that doesn't dry. If not look at back side of wheel/tires for oil, inspect each caliper and brake line as you go.

If still can't find look behind brake peddle on and under carpet for oil. Then go into engine compartment looking at fire wall under master brake assemble, hopefully you didn't spill any brake fluid here when topping off. Work your way out from here checking all around master then follow brake lines

You may find this interesting: Toyota DOT 3 Brake Fluid....
Toyota 2005 - 2007 (not the series 100) had recall. This was due to master leaking when aftermarket brake fluid added to top off (Topping off should never be needed) Cause failure of seals due to probable chemical reaction. Toyota brake fluid that comes in vehicles made in Japan can not be imported into this Country, except in brake system. Don't top off Fluid or flush unless you must.

FWIW: Brake fluid should never need topping off, the fluid drops as pads wear. Once pads replace you'll see fluid rise to normal leave. If brake light comes on, brake should always be service ASAP.

 

[APKhaos]

There have been a few reports of rusted brake lines too, particularly in areas with high winter salt use on the roads. Its more likely that these will fail catastrophically when the line finally loses enough wall strength to hold brake line pressure, which is north of 1000psi on heavy braking. Doubtful that this is your slow leak problem though.

 

[YardPig]

Check rear caliper flex hoses, same problem and one of mine was split and leaking, top of backing plate caked with sandy moist brake fluid. Road grime is attracted to the oil and can mask the leak.

 

[AimCOtaco]

Could it have been low the last time the pads were replaced? As the pads wear the volume in the res moves to the calipers. If it stays up it may not be leaking.

I find that on most vehicles if I top the fluid over the life of the pads I will have to remove some fluid before installing new pads or the res can overflow. (I will often siphon out the reservoir and replace with fresh fluid when doing routine maint. to keep the fluid fresh and dry between flushes, hence my topping off habit) The volume change over a set of pads can be significant, just thought I'd throw that out there in case you don't have an actual leak to find.

 

[YardPig]

He has topped up his fluid before to the full line and the light is coming back on. Even if all pads were metal on metal with caliper pistons fully extended, this would not be enough to drain a reservoir of this size to the point of triggering the light. It is losing fluid somewhere and needs to be investigated.
I would climb underneath your rig with a flashlight and inspect the calipers(piston boot area's inner/outer) and flexible hoses, both at the banjo's, the flares and the hoses themselves connections front and rear. If your vehicle is clean underneath(rust wise) I would not suspect rusty brake lines, but it is possible.
Other possibility is the master is bypassing out the rear into the booster where you can not see it. You could inspect by removing the four bolts and pulling the master back just enough to inspect for dampness, there should be none.

 

[AimCOtaco]

... If it stays up it may not be leaking...

...just thought I'd throw that out there in case you don't have an actual leak to find.

Forgive me YardPig, I'm not trying to kill anyone just was not 100% clear on OP's description, OP is no dummy, he's not taking any safety chances.

Other possibility is the master is bypassing out the rear into the booster where you can not see it. You could inspect by removing the four bolts and pulling the master back just enough to inspect for dampness, there should be none.

The 100 does not have a vacuum booster so it's not set up as you describe, It would be prudent to look for seepage inside the cabin where the actuator is hidden by the bellows.

 

[YardPig]

Sorry for confusion of general removal of master to booster, although removal is truly the proper way to confirm of any leakage regardless of the setup.
I agree on checking the obvious before getting too in depth, although for the low level switch to be triggered back to back and the fluid level was topped up both times, the chance of it being from fluid transfer is not realistic. The leak should be obvious either as dampness near the leak or sandy silt stuck to the dampness.
We're all hear to help!