2006 Silverado Brake Fuid Leak?

[Fishinguy40]

My truck seems to be losing brake fluid very slowly but I cannot find a leak anywhere. Vehicle has 52,ooo miles. A couple months ago I replaced the front pads and rear shoes. I was getting the service brake warning light. At that time I topped off the brake resevoir, as it was low. Low enough to make the light come on. I inspected the calipers, hoses, bleed screws, and drum pistons. I followed the lines from from the master cylinder to the anti-lock brake module and from there to each wheel assembly. I could not see evidence of a leak anywhere. There is a short run where I could not actually see the brake lines because they disappear up into the frame.

Yesterday when changing the oil I noticed the brake resevoir low again. Not low enough to make the light come on but lower than what I left it at a couple months ago. Again, no evidence of fluid anywhere to be found. Any ideas? Is there a common point of failure on these vehicles?

[westrush]

Well The Brake fluid well go down as the brakes wear down . But it could be the master its self leaking into the power booster or the brake line from the front to the back behind the gas tank they rust out

[Jeremy airjer W]

How far have you driven in the last couple of months?

Have you checked the rubber boots in between the caliper and the piston? I have run into quite a few lately that have had fluid leaking past the caliper pistons and collecting in the boots.

Otherwise another area of interest would be the back of the master cylinder and possibly collecting inside of the brake booster. If you don't see any evidence externally it may not be a bad idea to loosen the bolts that hold the master cylinder to the booster and see if there are any signs of brake fluid.

Lastly it may just be normal. As the brake pads wear the pistons move out further and further. More brake fluid is stored or needed in the caliper and it gets that fluid from the master cylinder reservoir.

[Fishinguy40]

I haven't driven that much in the last couple months, maybe only 2 or 3k. Resevoir was down a good inch. Also, when I did the brakes in August, and retracted the caliper pistons, the fluid level did not come up a whole lot and was still well below the max fill line.

I loosened the bolts that mount the master cylinder to the brake booster as suggested, no fluid.

How would you check the boots on the caliper? Aren't they sealed? Would you see them bulged? When I did the brakes in August, I don't recall any deformation or bulging of the boots that would indicate fluid but then I wasn't really looking for something like that. I will have to take another look. I'll also try to feel my way on top of the fuel tank for any leaks.