Hello Marlin Crawlers,
I'm trying to help my Uncle with his Toy. It's an '85 2wd 1 ton. He had a rear wheel cylinder leak and replaced the cylinder. During the bleeding process it seems the master cylinder died (piston seal puked
), so I ordered one for him.
It's a reman, Aisin casting and appears to be an exact match. I bench bled it and it pushed fluid and bubbles as expected from both ports then cleared up and pushed only fluid, so I installed it. Then checked it again with the pedal before hooking up the lines.
Started bleeding the brakes and only the rear builds pressure (D rear, P rear, P front, D front and then prop valve). The pedal builds and holds pressure at about the half way point, enough that it feels like a mechanical stop. When you crack a rear wheel cylinder bleeder the pedal goes to the floor as it should. However the front doesn't build pressure and when cracking the bleeder it does not relieve the pressure from half way down. We've bled through the system several times and have fresh fluid and no bubbles. To get fluid through the front lines we had to open the bleeder, press and hold the pedal, close the bleeder and repeat. That's the only way I've been able to get fluid to flow through the fronts.
In 30 years of replacing/bleeding brakes I've never had that happen.
I checked/compared the actuator rod hole depth from old master and new, they are identical. I screwed the actuator rod all the way in (as short as possible) as well as spaced the master with a couple washers wondering if MAYBE the rod was not allowing the piston to return (preloaded piston). Nothing seems to make a difference.
So here I am, asking for thought and ideas. Bad Master? Some mystery about the prop valve I'm not privy to? Any thoughts are greatly appreciated.