Why is brake master cylinder empty?

[fightingcec246]

I just returned from a extended stay way(12months) from home and had my truck in storage. Everything was fine with it, except when I checked my OEM master cylinder resevoir level - it was bone dry. I do not see any leaking around my brake lines to the drums. I am surprised as to this - I filled the resevoir back up, bled the brakes and "all is well" - or so I think. Is there anything I should be concerned for? It is puzzling that my resevoir was empty after the vehicle being in storage for 12 months. Is this normal? Or do I need to do more investigation and determine the culprit to the fluid loss. Thanks in advance.

[old cruiser]

just a thought. check firewall or floor possible leak at back of master cyl

[The Rocknrod]

Oh you "need" to investigate.

[mongocanfly]

X2....dont trust it..

[jayoldschool]

Leaking wheel cylinder (if there is no puddle on the floor). Get the drums off...

[PGSigns]

Since you need to work on it I would do the brake split and go to the dual pot master cylinder. Just so much safer if something happens like you have going on now.
Jimmy

[jocko]

Does your mc have the rubber gasket under the cap? Confirm whether wheel cylinders are leaking by removing the drum, can’t always tell just by looking for a puddle. I wouldn’t just replace the mc until you know why it drained. If you do replace it, then I concur with above comment about a dual res mc upgrade is a worthwhile upgrade for safety. Several threads on here for how to do that.

[fightingcec246]

Thanks to all. I found the "culprit". My left rear slave cylinder is the leaking cyclinder. I decided that I will replace the master cylinder and all four cylinders. I want to do the upgrade to dual master, but needed an expedient route to get my truck back on the road - its my daily driver. I looked up the conversion to dual master cylinders, looks pretty straight forward. Regards - joe

[fightingcec246]

It does have the rubber cap under the metal cap. What does that thing do anyways?

[jayoldschool]

Seals against air/moisture.

OP: glad you found the issue. I went through the same thing. Get the 67 truck master. Replumb the lines. FRONT port on the master to the front brakes, one line down to the splitter that you can reuse. REAR port to the rear line, use a connector, not a compression fitting!

[fightingcec246]

Thumbs up...