Do you still have good brakes when the pedal gets hard?have great brakes when you push the peddle but after a couple seconds the peddle becomes hard?
And another crosses over to the dark side.Don't forget to check behind the seat, at oe time the Hydrovac vents were back there and a rag or coat or just stuff like rats nests would block them then the booster could not work.
I've heard of this happening before but have yet to see it. I heard one case where the deteriorated hose worked like a check valve and wouldn't allow the brakes to release!One other item to check is the rubber line between the cab & frame coming from the master cylinder to the booster.
Years ago we had same symptoms on the 1966 chevy C60. Hard peddle , brakes would halfway work .
We put a new booster on & nothing changed . Turned out the inner liner of the rubber line had separated inside itself stopping up the line and yet not leaking on the out side .
A vacuum hose won't "blow"... Implode maybe, but not blow. That's what makes vacuum leaks so hard to find. One way to find vacuum leaks is leave the engine idle and use small puffs of ether on suspect areas. Another possibility in the OP's case is the check valve between the intake and the vac reservoir isn't holding. It's all kinda coming back to me now.That's pretty much how it was in my case Steve . Rare when it happens but can happen .
You would think the brake hose would blow or at least leak if the inner liner fails and is stopping the flow . Made it tough to diagnose the problem .
We ended up with a new booster and a brake line hose
Sometimes I think you and I are the only ones in the choir.:bouncegrinYou're preaching to the choir there. I remember driving Chevy tandems at 50-52K with hydraulic brakes, first thing you did was get the coasting RPM as high as possible to get the vacuum to the max, at that point a tad bit of religious faith seemed to help too.
And yes, a serious pressure bleeder was needed for both air or vacuum systems. It's kinda funny, but I remember an old IH L-180 that dad had that seemed to have reverse hydrovac brakes... you would step on the pedal (that would screech on the floorboard) and it went all the way to the floor, as soon as it hit the floor you would have to let up as the hydrovac applied the brakes or she would toss you through the windshield.
Yeah RZ . Totally agree bro .A vacuum hose won't "blow"... Implode maybe, but not blow. That's what makes vacuum leaks so hard to find. One way to find vacuum leaks is leave the engine idle and use small puffs of ether on suspect areas. Another possibility in the OP's case is the check valve between the intake and the vac reservoir isn't holding. It's all kinda coming back to me now.