No rear brakes 65 C10

[mrdave03]

Hi All, I had done a front disc brake conversion about 5 years ago on my 65 C10. (SBCC kit) I added an SBCC proportioning valve in the rear brake line at the time because they would lock on me. Everything was great till this week I noticed while tinkering on the rear and and my wife holding the brake. I had no rear brakes. So I tried to bleed but no fluid at all. Then I opened the proportioning valve all the way and was able to bleed just fine. I pulled the rear drums and adjusted the pads so there was slight drag on the drum when installed. Bled again.. and still no brakes. I didnt seem to be getting any more air. The emergency brake works fine. Could it be they need more adjustment? Or bad cylinders? Possibly bad proportion valve? It did flow fluid freely when all the way open. I left the proportion valve open thinking at least they should lock then decrease as needed. I'm stumped...the fronts work perfectly. Thanks for any advice.

[geezer#99]

Another member recently had similar symptoms and found mushy dirt inside the rear cylinders.
Pull the cylinders apart and have a look inside.
And it might help to flush the lines out too.

[MikeN]

This is quite common, and the culprit is the same 99% of the time. The short rubber brake line above the differential housing corrodes from the inside and becomes plugged. They have them at NAPA - generally under $20. Replace that line and I bet you'll have rear brakes again.

EDIT - I re-read your post and see that you did get fluid to the rears after tinkering with the prop valve. I can't imagine what is going on with your brakes, that's weird.

[jayoldschool]

^^^ exact thing happened to me on my 65. Bled brakes after replacing wheel cylinder, pedal went hard, couldn't get any fluid through. Replaced the rubber line, all good. Old line would not pass any air when I checked it.

[mrdave03]

Thank you all for the advice. I flushed the line to the rear and had good flow.. so left the flex hose alone.. but will probably change it over winter anyhow. What I found was both rear wheel cylinders were very corroded inside... the pistons were stuck. So rather than tinker I bought both new wheel cylinders (Raybestos) from Summit along with a better proportioning valve from Summit (Wilwood) and once all replaced and bled.. I have brakes... life is good My best guess is the old proportioning valve blocked flow and the cylinders went dry and froze up.

[MikeN]

Glad you got it fixed!