Brakes - Rear Drums, won't bleed

[khan0165]

Haven't posted in a few years, car's been in storage.
Problem initially started with a leak, I eliminated the leak, then began bleeding the brakes and noticed the rears are not engaging, and have gone unnoticed for quite some time. Reset the rear shoes, tried bleeding again, no bleeding from the rear.

I suspected the very old proportioning valve went bad, so I removed it, T'd the front lines together, and installed a Summit adjustable proportioning valve on the rear line. Then tried bleeding, same issue again. Some fluid drips out the rear, but no pressure loss from rear bleeder screw when bleeding.

Then opened all lines, cleaned or replaced bad ones, and tried again, same issue again.When bleeding, fluid only drips out slowly from rear, but no pressure loss from rear bleeder screw when bleeding. Brake pedal feels clunky on first half of travel, then firm on second half.

So then suspected bad master cylinder, and replaced with new one. Bench bleed use back-bleed method, installed on car, then tried again, same issue again. Now fluid squirts out from rear, but still no pressure loss felt on pedals. Brake pedal travel feels smoother with new master cylinder, but still no pressure loss felt when bleeding rears, front bleeding works fine.

In all attempts, fronts bleed okay and hold pressure. I drove car and test brakes with only front system, it works fine, but still no rear brakes engaged. If wheel cylinder is clogged, why does fluid squirt out the rear bleeder? If fluid squirts out rear bleeder, why no pressure loss on brake pedal?

What is going on?

Thanks for reading!

 

[ssn696]

There is a safety feature in the proportioning valve. You might need a helper to push in on the rubber button on the end of the valve to reposition it back to center if you let all the fluid drain out.

 

[khan0165]

Prop valve is out now, no sense in revisiting it... I have pressure all the way back to the wheel cylinders. How do I determine if the wheel cylinder is clogged inside. Are there any videos that show handy tricks on how to remove and reinstall the wheel cylinder clip/clamp?

 

[pontiacgp]

this is an F body but the same style wheel cylinder clip

 

[TURNA]

When you are bleeding the brakes do you have the E-Brake on?

 

[khan0165]

nice to see the old crew still around, site has changed a lot tho.

The e-brake has been eliminated. Just not understanding why bleeder squirts, but no pressure drop at the pedal.
Yes, I watched that Firebird video too, not sure I understand the exhaust adaptor. I figured I could just use a C-clamp with a 1-1/8" socket?
How do I remove the clip though?... just jam a fork screw driver behind the clip tabs, and pry the clip out?

 

[TURNA]

What is your bleeding procedure?

Pump the pedal 3-4 times slowly then crack the valve while keeping pressure on the pedal until pedal goes to floor, lock the valve and repeat.

If you think a wheel cylinder is bad.....

Do the above but crack the brake line that goes into the cylinder if there is a difference then you know the cylinder is bad

 

[pontiacgp]

new clips come with a new wheel cylinder so I pried mine out when I had the G body rear. I wasn't worried if I destroyed them

 

[CWPottenger]

I experienced this same issue on my car the other day with all new lines, master cylinder, and adjustable prop valve. I could get the front to bleed just fine after a quite a bit of time, but the backs just wouldn't do more then dribble. I finally had to go with a cheap vacuum bleeder setup and even that wasn't doing until I modified a bleeder screw so it could be in tight and still flow. Once I did that I ran the vacuum until I had solid flow out of each rear caliper and had gone through half a resevoir in the Master Cyl. Was a serious headache, but I have great brakes on all 4 corners. Like you I don't think my rears where working correctly for awhile even though I had a good pedal until the day I didn't, which is why the upgrade to all new parts.

 

[axisg]

Been a while Khan. Seen your car on Kijiji, too bad you are getting rid of it !

Have you confirmed the piston(s) are not seized or binding in the brake cylinder ? Some gentle pressure on the brake pedal with the drum off should confirm. I have seen them seize on one side and not the other which would drag and wear one shoe. It would be odd for both ( all 4 ) of them to be seized up though. Next would be to get a pressure gauge on the brake line where it splits and see whats going on. Maybe your new adjustable prop valve is not allowing enough pressure to the back ?