Having a strange brake issue on my 67 F100.

Installed a brake booster a few years ago. Recently the brakes are hit and miss. When I first start up and drive the brakes are super sensitive, lock up with little effort. Then sometimes I’ll go to hit the brakes and they barely engage. Sometimes I’ll have both feet pushing as hard as I can and the truck just keeps rolling, slowly, but still rolling.

I’ve checked for vacuum leaks on the booster. Everything seems alright. Any thoughts? Could the booster itself be bad? Sometimes pumping the pedal will give me momentary brakes. It’s sketchy.

 

At first the brake lock up I was thinking something on the shoes like brake fluid from a leaking wheel cyl.
I was also going to ask if they locked up first outing when damp / raining out? See the above line.

Then you said the pedal is really hard and 2 feet on the pedal it will not stop.
So I am thinking bad booster or master but ........................

When was the last time the wheels were pulled and the brakes checked?
I would also bet money (I dont bet) that all the rubber brake hoses on the truck are factory hoses?
And please dont say "they look good" unless you are supper man and can see the inside of the hoses.
They go bad from the inside out and if they will not let fluid pass you will not have any brakes.

If you have not looked the system over in a long time I would get new rubber hoses, wheel cyl & shoes and master as a start for the system rebuild.
May even go for springs kits for each wheel but if they look good then you might want to pass on them.
After all that and you have issues then replace the booster.

FYI
When I got my 81 F100 flare side I did a 4 year cab off frame rebuild when I got to the brakes I dont know how it stopped!
When I went to look at it 1 chamber was empty but the pedal felt good so went for a short drive.
When I got to the rear drum brakes someone put 2 long shoes on 1 said and the short on the other.
Self adjuster wire was wrapped around stuff on 1 side so not working.
Ebrake did not work, 1 cable broken other frozen.

I replaced everything but the metal lines as they looked good.
1 of the new wheel cyl leaked just sitting so I replace both again.
I used the booster & master from my parts truck, rollover so they had to be working right?
NOPE! When I got the truck on the road they were both bad and thing why the truck rolled.

2+ years latter I just replaced the master as I could not get a pedal after installing the right fitting Ebrake cables, booster still good.
I got to say I think that first master was bad as I never had a good pedal like I have now.

My take is rebuild the full brake system. You wont worry about it down the road, your life, others and the truck are not worth the risk.
Dave ----

 

So finally getting around to this….

replaced all hard lines

replaced all wheel cylinders

replaced all rubber lines

replaced shoes, springs and resurfaced drums

bled bled bled bled bled and bled some more.

Now I have no brakes really at all. Pedal very very soft and goes all way to firewall easy. I go an bleed and no air just fluid without bubbles.

Adjusted shoes. The way I did it was adjust until when I spin the wheel it stops on its own in one rotation.

Any ideas? After i replaced everything I gravity bled the system first and then did the good old pump pump pump hold method for a while.

 

Adding to the list....

Bled the MC tonight.. left it on the truck.. was able to see the bubbles from the drivers seat.... then also remembered that in my haste putting back together i didn't bother to look at the shoes... pulled rear.. both are same length... pulled front.. different.. had them backwards.. had long in front and short in rear.. flipped them...

Tomorrow I'll get one of the kids to help me re-bleed the brakes....

If all else fails at that point ill buy a new MC as everything else has been replaced.

Any specific tips on the star adjusters? Mine do not have auto adjusters. What I always was taught was to tighten them until they start to rub just barely and stop... was doing some reading and some adjust until fully locked up... bleed.. then back off 10 clicks....

 

My best suggestion is try different ways and just do what works best for you.
Because if you read 20 different posts on adjusting drum brakes, you’ll read at least 10 different ways of determining proper adjustment.

See if you can find a factory service manual page on the adjustment and see what they have to say about it.

 

By tightening the shoes until the wheel is completely locked centers the shoes in the drum. 10 notches back usually leaves a very small auditable drag which will clear up after driving the truck.

 

Thanks all for the feedback.

so I bled the master
rebled all cylinders
fully tightened star and then back 10clicks.

Brakes work! Now question. Should I be able to lock up the wheels? Because I can’t. I can stop but if I’m cruising along and apply fill brakes it brakes hard but doesn’t lock up any wheel.

 

Getting back to this, what exactly does that mean?
Front brake shoes and rear brake shoes? Or front and rear shoes of one brake or the other?
Are you saying that now that you fixed it, the drums in each corner have one short shoe in the front position and one long shoe in the rear position?
If so, then that’s good. If not then maybe that’s part of the issue with not locking up the rear.
What size tires?

 

Correct. Up front I had short shoe on back side of drum.

Rear they were same size. Was no short or long.

 

We’ve been seeing more and more often where boxes of shoes come all the same size instead of having a shorter primary and a longer secondary.
Did you check the other side to make sure that the different size wasn’t over there?

 

I did. They were same. Front's were fine.

I am still not ruling out that my MC is bad... remember what started all this was sometimes the brakes worked and sometimes the didnt. So I replaced everything but the MC so far.

 

First of all, if you buy a MC buy only a NEW one. Not a rebuilt. Considering as old as our trucks are, can you imagine how many times the MC have been honed out during the rebuilding process? Too many times creates the new inner cups not sealing right.
Second, if you have a good firm pedal and brakes working but not locking up, the problem is probably the friction material on the shoes you installed. Or glazed drums. As long as your truck stops hard and as quick as drum brakes can, I wouldn't worry about it. Think of it as anti-lock brakes you didn't pay for.