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1969 brake master cylinder, drum/drum

1965 chevy c10 pickup, 1965 style power brake booster

Hi folks.

This has been the setup in my truck since I bought it, I have had to replace a few brake cylinders in that time.

This latest one though does not seem to want to work, so either I am bleeding it wrong or it is bad off of the shelf.

brake cylinder pic

This setup has the external valve thingy, before it goes down to the wheel cylinders.

I did the bench bleed before installation, no more bubbles. I mounted it up. I did the brake bleed, right rear, left rear, front right, front left around again.

Seems like it only has the rear brakes, which is why I was replacing it.

I did the crack all four bleeders at each wheel with a tube on them, submerged in brake fluid and slowly pumped the brakes... then closed them up.

Same deal.

Anyway... anything else to check or try again before I swap it out for another unit?

I am out of ideas at this point.

Thanks.

-Woog

What was this the reason you replaced the master cylinder in the first place?

Were the front and rear brakes working before you replaced the master cylinder?

MAke sure your rear brake hoses aren't collapsing.

The external valve thingy may be stuck closing off the front ,but that is just a guess.Looked on the net and 69 with drums that part is either a distribution block or a proportioning valve .Also the rear flex hose may collapse if they are old.

I would try bleeding the rear brakes again, this time with two people, (open bleeder then push pedal to floor, close bleeder then release pedal, repeat), so you can verify you have no air in the system before I did anything else.

When you leave it open while pumping, you may just be sucking the air back into the system when you let the pedal back up.

Ya, Phil has a point. Have someone else work the brake pedal while you work the bleeders one at a time starting with the right rear, then left rear, right front, left front.

Or get a Motive brake bleeder system, you won’t regret it….. pressure system works so much better than a 2nd person……

There is a floating piston in the combination valve that isolates one end of the vehicle in case of a pressure loss. Some people remove the electrical connector in the center of the valve and lock that piston into place with a screw device while bleeding. Anytime there's a pressure difference front/rear (including bleeding) that valve is prone to move.
Jerry

I took off the brake master cylinder because it was only grabbing the brakes in the rear(it never dived to the front and was harder/slower to stop), which every other time that happened in the 20 plus years I have owned this truck, that meant the MC was bad.

Thanks for the replies everyone.

I took the proportion valve off and took it apart as much as possible and cleaned it up, gave it a brake clean bath.

Re-assembled everything... went to bleed brakes, saw brake fluid shooting out of the brake line onto the exhaust manifold.

Hmnn, that seems like a problem.

So, new brake line, new brake union fitting in place... will double check it all tomorrow and trying bleeding the brakes again.

-Woogeroo

I finally got my new brake lines bent, cut, deburred, fitted, flared and installed without leaks.

I can drive my truck again, yay!

Thanks for all of the replies folks.

Merry Xmas.

-Woog

Looks good, Woog. Nice neat bends.

BTW, I cleaned up that url thing you reported. Happens occasionally.

Merry Christmas

Thanks kl, I wasn't sure what to do about that little issue

Thanks again for the replies folks.

Happy New Year.

-Woogeroo