Remove Metering Valve from Combo Valve?

[crakarjax]

I want to unscrew the metering valve portion of my combination valve (from a 1972 disc/drum truck, often erroneously called the proportioning or prop valve) but it doesn't look like it's got any hex portion to grab with a wrench. Anyone know the trick to disassemble this?

And on the subject, the same person might know... can I replace the brass flare seats in the valve? It looks like someone jammed a nut down on them at some point, causing a deformation.

[leftybass209]

Yes, it's removable, at least on mine it was. It was leaking so I replaced it with one I purchased from CPP.

[crakarjax]

Did you just use vice grips or something to unscrew it? Or maybe you are talking about removing and replacing the whole assembly...

[leftybass209]

Just the metering valve was replaced. It was hexagonal, underneath the rubber boot that covers the needle valve.

[crakarjax]

Yeah, so mine is just round and with no rubber boot -- I guess I'll try some vice grips later, just don't want to booger it up too much.

[crakarjax]

As I thought, I couldn't remove it and just boogered up the metal. I can't imagine how I'd get the thing out but the design seems different than most I've seen on here.

[leftybass209]

Combo valves aren't that expensive, you should just pick up a new one, or a good used one.

Why are you pulling the metering valve?

[crakarjax]

Just to clean it out really, I pulled the rest of the thing apart and cleaned it already... no idea what kind of gunk is in the metering portion. Actually I only *want* the metering valve to avoid nose-down under light braking(really the only thing it's for) so I might just skip the valve altogether. I've got an adjustable proportioning valve to use, and can just use a drum/drum distribution block for the brake warning light or nix the light altogether.

[leftybass209]

Hmm, nose down isn't what a metering valve is for. A metering valve holds off the pressure to the front brakes so the rear pressure can overcome the brake shoe return springs. You'll get nose dive from weight transfer during braking regardless if you have a metering valve or not, that's simply physics. The rear brakes are said to provide 30% of the braking, but in actuality, it's more like 10-15% for most brake applications.

[crakarjax]

Originally Posted by leftybass209

Hmm, nose down isn't what a metering valve is for. A metering valve holds off the pressure to the front brakes so the rear pressure can overcome the brake shoe return springs. You'll get nose dive from weight transfer during braking regardless if you have a metering valve or not, that's simply physics. The rear brakes are said to provide 30% of the braking, but in actuality, it's more like 10-15% for most brake applications.

The pressure will overcome the springs whether the fronts are applied or not!

See http://www.mpbrakes.com/techtalk/how...t-brake-valves