Very soft brakes after rebuild

[BanjoDude]

Hi guys,

Over the winter, I completely rebuilt the brakes on my '69 C-20. I kept it all stock, and replaced everything except the drums and the front shoes. Booster professionally rebuilt, new master, new hard lines, new hoses, new cylinders all around, and rear shoes (wheel seal had gone, soaking one side in oil from the rear end). I bled the lines with a vacuum bleeder.

I finally took it out to bed in the rears, and the pedal is really soft. It will stop the truck, but nowhere close to the braking power before I began this project. The pedal travels about halfway before I get any brake action. If I hold the pedal to the floor and hold it, the truck stops....eventually....and the brake warning light comes on until I release the pedal. I suppose now I know the warning circuit works... Before the rebuild, if I had held the pedal to the floor, it would have locked the rears pretty easily (also not ideal, but at least there was plenty of power). The rear drums are very warm as would be expected after bedding - not scorching hot by any means. I adjusted the rears to have a small bit of drag when installing the new pads. I checked under the truck for leaks at every connection and found one very small leak that was remedied by tightening the nut just a bit.

A few questions:

1) The booster came back from Booster Dewey with a note that said the pushrod was pre-adjusted. Should I pull the bolts and double-check that?

2) The brake light coming under heavy pedal would indicate that I'm missing power in one of the circuits, correct? The distribution block was completely seized, but I was able to free it up when I had it off the truck to repaint it. I found while converting the truck to LED that the PO had pulled the brake warning light socket out of the back of the dash and it was MIA - this might be why...

3) The master I got from NAPA looks a little different than the master that was on the truck. The bore is the same size, but the reservoir cover is completely different. Could this be the wrong master? I've attached before and after pics for reference.

In any event, I plan to bleed the brakes again tomorrow night.

What else should I look at? Any other advice?

Thanks in advance for your thoughts!

Wes

[Ol Blue K20]

Have you tried readjusted them? Sometimes takes a couple or three times. Adjusting doesn't center them. Using them does.

[BanjoDude]

Originally Posted by Ol Blue K20

Have you tried readjusted them? Sometimes takes a couple or three times. Adjusting doesn't center them. Using them does.

I have not. Thank you. Easy enough to do when I bleed tomorrow.

Does anyone have any input on the brake master differences?

[Sheepdip]

I would definitely check the booster pin to M/C clearance...."Pre-Adjusted" to what? I'm reading that you sourced your M/C elsewhere.

[HO455]

There's nothing we can do to help with the master cylinder differences. Both the old and your new one the castings come in different bore diameters You would need to measure the bore of the old and the new one to be sure they are the same diameter.

[howzzzit]

As stated above adjusting new shoes probably doesn't center them. I replaced my rear shoes and did the listen/feel when turning the drums by hand. After a few stops they didn't feel quite right. When I applied the parking brake it went 3/4 of the way to the floor because the shoes were misadjusted again. Bought a brake gauge which measures the inside of the drum and you slip the other side over the shoes. My shoes were way off. Adjusted them out to meet the gauge then backed them off enough to get the drum on again. Worked great and the parking brake works like it should. Maybe your problem. Can't say on the brake warning light. Good luck

[68Gold/white]

I have one of those gauges, also. The gauge can help save some time.

The adjustment is likely all you need to do. You can adjust them to being a little tight and it's OK. it centers the shoes and adjusting them to a useable position is not difficult.

Get all the air out and the light should go away...

[custom10nut]

I just installed the new CPP Disc Brake conversion kit on my 70.
During the process I had to convert the Drum/Drum Master Cylinder.and destroy block the the Disc Drum System.
We Go it all together, bled out the lines, and checked for leaks (none).
Then I experienced the same as you described.
Soft pedal and brake light on.
After asking for insight on here, I figured out that the Actuator Rod was too short for the new MC.
Luckily, the Rod that I have is adjustable (I don’t know if they all are or not)
It took me a little bit to get the adjustable end loose, without messing up the rod or the threads.
It took a couple test fits to get the length right (wasn't much, maybe 3/8 in?).
Jumped in for a check, and VOILA! I got pedal and no light!
Anyway, it sounds like you’re have the same issue.
Check your rod length.

[BanjoDude]

Thanks for all the suggestions, guys. I ordered a gauge and checked the booster rod adjustment - it was indeed perfectly adjusted as the sticker claimed.

I then went on and bled the brakes again. There was somehow a fair bit of air in the rear circuit still, so once that was gone, the brakes are back to normal stopping power with no brake light.

Still one strange thing - I don't get any real resistance or braking power until the pedal is about halfway down. Is that normal?

Lastly, it would appear from the service manual that the brakes are adjusted by going in reverse and hitting the brakes. Is that correct? I know you can also spin the adjusters with a flat tool - is there an advantage to manually adjusting them?

[HO455]

In theory the automatic adjustment will do a good job keeping them adjusted. However worn parts can cause them to not work.

I have also found that you have to brake hard to get the adjusters to work. Normal braking on pavement or hard braking on dirt doesn't seem to get the job done. I found moderately hard braking while backing down a hill on paved roads works well. Some times it takes several trys.

[BanjoDude]

Originally Posted by HO455

In theory the automatic adjustment will do a good job keeping them adjusted. However worn parts can cause them to not work.

I have also found that you have to brake hard to get the adjusters to work. Normal braking on pavement or hard braking on dirt doesn't seem to get the job done. I found moderately hard braking while backing down a hill on paved roads works well. Some times it takes several trys.

Thanks. I'll try that. Anyone have any input on the pedal travel question?

[Steeveedee]

It may take a pile of stops going backwards to get the brakes adjusted. I've only done that a couple of times due to the time involved. I'd creep up on the adjusters with a brake adjusting tool. Turn an adjuster until you just start to hear a scrape, and go step on the pedal to center the shoes. If you still get a light scrape, go to another wheel and adjust the same way. If you have no air in the system, the brake shoe clearance is right when the pedal moves about 3/8" when you step on the pedal. Shoes are cam-ground in order to fit the smallest diameter drum one may encounter when doing a brake job. It may take some time for the shoes to wear to the point where you have full contact of the shoe with the drum when braking. When working as a mechanic, I also "seasoned" the pads and shoes by driving the vehicle and making lots of slow speed stops. Hitting the brakes hard when the new shoes aren't in full contact is going to potentially cause the shoes to glaze over the high area and generate hard spots on the drums.