Leaking brake fluide

[The Grebe]

My nephew has an older S-10 pick up he pounds around in....he is losing brake fluide and he said he has looked and looked and he can't find where it is leaking underneath and he can't smell anything....any ideas?

[Eric Wettschreck]

I had one. Check the proportioning valve.

I had a slow leak, hard to find. Finally found it at the proportioning (sp) valve.

[Macgyver55]

If all the lines, calipers and wheel cylinders look dry, check the rear of the master cylinder where it attaches to the brake booster.

[98prosport]

fluid can leak past the rear of the master, then be sucked into the engine thru the vacuum hose, and be consumed by the engine.

[FishLocker]

Had an International with that same problem. Turned out the O-ring on the plunger was leaking. Since the seal on the firewall was good, it leaked into the carpet inside the cab. Try running your finger around the carpeting just below the plunger or push rod that goes through the firewall...you may find it there.

[Jeremy airjer W]

It might be hard for brake fluid to make its way to the firewall with the booster in between the master cylinder and the firewall.

[1968]

If it's old enough, it could be a steel line rusting out. Only 25 feet or so to inspect. Check every inch front and back. Between the gas tank and frame rail is usually the first spot to go. If it's mid 90's or older it could be getting close to a total reline.

A slow leak in a wheel cylinder(s) can be hard to spot without pulling drums as the fluid combines with dust, turning to sticky mud.

Also, unbolt the master cylinder to check for leakage in to the booster.

[The Grebe]

Thanks to everyone, I relayed the info to my nephew...it's got to be one of these things? Maybe he needs thicker glasses?