Brake help!

[RThree]

I have been getting my 72 Longhorn ready for C10 Intervention when i noticed some brake fluid leaking from my rear drum brakes. Opened them up and found that the Brake Cylinders were leaking on both sides. I ran down to the parts store and found a new set and got them installed.

This truck has Disc Brakes front and Drum rear and everything worked fine before i started this peddle might have been just a little squishy.

Since replacing the brake cylinders i have had a hell of a time bleeding them. I found out about the Metering valve and made sure that it was recenter and that the dummy light went out and then tried bleeding again. one side bleed pretty well, the other side still only a trickle but i thought i had it bleed. Started the truck and one step on the peddle it went right to the floor dummy brake light comes on and were back to square one.

When we are bleading it the top half of the peddle has near no resistance but the bottom half feels stiff.

what am i missing, the system remained full the whole time we may have got a couple air pockets but im pretty sure i bleed them out. i feel like this should be easy but im lost.

Please help the time crunch is real.

Thank you for reading any help is welcome.

[randy500]

Pressure bleeder takes all the hard work and guessing out if it, $65 on amazon

https://www.amazon.com/Motive-Produc...SH53AK195Q9YKM

[Wrenchbender Ret]

How old is the master cylinder. When you start pumping the pedal on an old master cyl. it goes into the part of the cyl. that has not been used for a long time. It is full of crud & corrosion & ruins the rubber cups. Its a good idea to replace or o-haul the mc any time you do major brake work.
The same goes for wheel cyls. when you replace shoes.
George

[PepperTreeGarage]

Are you pushing in the button on the proportioning valve while doing the bleed? This is the setup on our '72 C20. Good Luck.

[dmjlambert]

Perhaps you need a proportioning valve centering tool, the thing that keeps the valve centered while you are bleeding. I think you should get a similar amount of fluid out of both sides, the flow should be the same. Don't press the pedal all the way down during bleeding. Put your left foot under the pedal, or a block of wood like a 2x4 under there. I use a one-man bleed kit from O'Reilly Auto Parts, which is inexpensive. It is a little bottle (I wish it was bigger but the kit is cheap) with a tube that sticks down into it that prevents air from drawing back into he wheel cylinder. It has a magnet that lets you position the bottle on the fender higher than the wheel cylinder. I fill the bottle 2 or 3 times, and keep adding fresh fluid to the master cylinder during the process. Slow and steady pedal presses. Follow the directions on the bleed kit regarding where to place the bottle. Driver side rear bleed first, then passenger side rear.

If it has been a while since you bled the front brakes, go ahead and do those also. I filled the master cylinder from a big bottle of new fluid and kept on bleeding many one-man bleed kit bottles through the system the last time I did it, so I replaced all the fluid in the system and the fluid coming out of the bleed port was eventually the same color of the new fluid that was going into the master cylinder. The fluid gets old and absorbs water and changes color, especially in the tubing and wheel cylinders. The whole system needs a flush like that every couple of years, otherwise the master cylinder and wheel cylinders will start corroding. If you see a difference in color between the fluid you are bleeding out and the new fluid you are adding to the master cylinder, or if you have just not added fluid to the master cylinder as you go, you are not finished. I accumulate the used fluid that comes out of the wheel cylinders and put it back in the empty brake fluid bottle and mark it used, and take it to my county hazardous waste collection point. My 2 cents.

[dmjlambert]

PepperTreeGarage was writing his superior response at the same time I was writing up my little blurb. There it is, from the manual. I defer to advice given by those who know more than me.

[RThree]

Originally Posted by PepperTreeGarage

Are you pushing in the button on the proportioning valve while doing the bleed? This is the setup on our '72 C20. Good Luck.

Alright so i have heard of this proportioning valve centering tool and i have not been using one. My understanding is that this button on the front only keeps the proportioning valve from locking out the front brakes if they were to have a failure.

To get the valve re-centered i had to take off the rear brake line and push it back to center to get the dummy light off and i assumed i was good to go. i guess im incorrect?

[RThree]

Originally Posted by Wrenchbender Ret

How old is the master cylinder. When you start pumping the pedal on an old master cyl. it goes into the part of the cyl. that has not been used for a long time. It is full of crud & corrosion & ruins the rubber cups. Its a good idea to replace or o-haul the mc any time you do major brake work.
The same goes for wheel cyls. when you replace shoes.
George

It is the original equipment but ive been driving the truck for about a year now after it had been sitting for a couple years. it didnt have any brake problems untill i tried to fix the leaking drum cylinders. back brakes would lock up when i stomped on them and everything stopped fine.