HMMWV Intermittent Brakes

[TexasJeffe]

First time on your site. I just purchased a 1990 Humvee from IronPlanet. Runs good but the brakes bleed down (not leaking fluid - just no brakes). It will brake fine when you first hit the pedal but if you hold the pedal down or hit it multiple times you lose all braking. It acts like a vacuum leak but possibly just need to replace the master cylinder. Any ideas?

 

[DatGuyC]

Yep sounds like a leaking master cylinder to me.

 

[Retiredwarhorses]

He says it's not leaking...one of 4 things, brakes need bleeding,hydroboost, mast cyl, bad proportioning....it's a pretty simple brake system,quite basic....