Is my master cyl. bad?

[grs]

Replaced one rear cyl. The front bleed real easy. The rear has very little fluid coming out. Like none. If I leave the brakes alone for five or ten minutes then press on the pedal I can feel the drum tighten up. When I open the bleeder one time and close the bleeder then the drum won't tighten up. Has anyone ever had this problemo.?

[rs72z]

Originally Posted by grs

Replaced one rear cyl. The front bleed real easy. The rear has very little fluid coming out. Like none. If I leave the brakes alone for five or ten minutes then press on the pedal I can feel the drum tighten up. When I open the bleeder one time and close the bleeder then the drum won't tighten up. Has anyone ever had this problemo.?

You might need to adjust your rear shoes up tighter.

[Eyegore]

What year of truck do you have? On some there is a porportioning valve where it has to be clamped to allow proper bleeding of the rear wheels.

[grs]

Originally Posted by rs72z

You might need to adjust your rear shoes up tighter.

Thanks, but the shoes, and drums are new, and adjusted up real good.

[grs]

Originally Posted by Eyegore

What year of truck do you have? On some there is a porportioning valve where it has to be clamped to allow proper bleeding of the rear wheels.

My truck is a 1987 R-10. Where is the proportioning valve, and how do I clamp it?

[notyo_cheez]

Porportion valve is up front, mounted on the frame near the steering gear. Follow the lines downstream from the master cylinder and you'll find it. Never heard of having to clamp the lines at the valve and don't know how that's possible as they are made of steel.

Wheel cylinders should be replaced in pairs, just like pads for discs as they wear the same. Not sure why it won't bleed for you as I'm assuming the one you can't bleed isn't new...

If you suspect the master cylinder to be defective get a hose clamp tool and pinch off the rubber hose going to the rear cylinders, then press the brake pedal. If the pedal travels at all your master cylinder is bad.

[Eyegore]

It's not clamping the lines, there is a button that has to be pressed in and held during the bleeding process, I know I had to do it on my 77 K5 but I'm not sure on the newer one if its necessary.

[grs]

Originally Posted by notyo_cheez

Porportion valve is up front, mounted on the frame near the steering gear. Follow the lines downstream from the master cylinder and you'll find it. Never heard of having to clamp the lines at the valve and don't know how that's possible as they are made of steel.

Wheel cylinders should be replaced in pairs, just like pads for discs as they wear the same. Not sure why it won't bleed for you as I'm assuming the one you can't bleed isn't new...

If you suspect the master cylinder to be defective get a hose clamp tool and pinch off the rubber hose going to the rear cylinders, then press the brake pedal. If the pedal travels at all your master cylinder is bad.

I get know fluid out of both rear cylinders. The pedal won't even go down.

[grs]

Originally Posted by grs

Replaced one rear cyl. The front bleed real easy. The rear has very little fluid coming out. Like none. If I leave the brakes alone for five or ten minutes then press on the pedal I can feel the drum tighten up. When I open the bleeder one time and close the bleeder then the drum won't tighten up. Has anyone ever had this problemo.?

I put a bleeder tool on the rear brake part of the reservoir, Pushed down on the pedal, and no fluid came out of the master cyl. So the master cyl is bad. I will get one from Napa for $55.00. It comes with a lifetime warranty.

[toast]

hey i had the same problem, the proportioning valve is under the fan guard. (follow the lines down) and on the driver side of the valve there is a black rubber cap thing take it off and it looks like a air nipple or something. there is a lil pin in the center u have to press it down and hold to bleed the brakes. dont waste money on the tool it suck just get a c clamp on it. now my problem is the emergency brake. if i use it it wont release. so i cant get them to adjust good enough to lock up the rear tires.

[grs]

Originally Posted by toast

hey i had the same problem, the proportioning valve is under the fan guard. (follow the lines down) and on the driver side of the valve there is a black rubber cap thing take it off and it looks like a air nipple or something. there is a lil pin in the center u have to press it down and hold to bleed the brakes. dont waste money on the tool it suck just get a c clamp on it. now my problem is the emergency brake. if i use it it wont release. so i cant get them to adjust good enough to lock up the rear tires.

Thanks I will try to hold the pin down.

[hatzie]

Originally Posted by grs

Thanks I will try to hold the pin down.

It's probably the combination valve.
Try this.
http://www.classicperform.com/TechBo...t.htm#testprop