Hydro boost leaking help!

[Trucksareforwork]

Ok folks, I’m working all around this 81 k3500 dually.

It has hydro boost brakes.

I am doing new brake lines and a new master cylinder. The brake fluid is just plain dirty.

I took the master cylinder off today. And behind it this is what I saw.

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Anybody know if this is leaking from the hydro boost or from the master cylinder? I’m assuming that slot on the bottom is the weep hole I see mentioned? That means the hydro boost is leaking.

Am I right or wrong?

 

[Blue Ox]

Based on the rust, unless you have water in your P/S fluid I'd go with the master is leaking.

 

[ali_c20]

^^^^^^^ This ^^^^^^^^
Master cylinder leaking.

 

[Trucksareforwork]

Good insight on the rust being from brake fluid. I didn’t think about that.

 

[Trucksareforwork]

I rebuilt the hydro boost after a little more sleuthing. The fluid was definitely coming from the hydro boost piston.

Wasn’t a difficult job, though I couldn’t replace the input piston seals because the input rod was permanently attached. Got it back together and leak tested on the truck. Much cleaner and no apparent leaks.

I’m replacing the master cylinder so should be in the clear on both fronts.

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