Could any of you guys help me with a brake problem or point me to a useful link? 77 F150, 351M, C6, NP205. My brake pedal seems to reach a point where I cannot push any farther despite the brakes being pretty weak. Pedal is not hitting the floor. Brakes have been "professionally" overhauled. New pads, rotors, shoes, drums, wheel cylinders, proportioning valve, master cylinder and booster. Engine is making acceptable vacuum and all lines are bled. Any ideas?

 

My best suggestion would be to take it back to the "professional" and tell him whats going on, and have him make his work right. If he is truly a professional, he will fix it, explain to you what was wrong, and not charge you for it.

--JB

 

What you didn't mention was calipers. Have the "pro" pull off the calipers and rebuild them. If they are like my '78's, which sat in the drive way for 5 years, the pistons were unable to move beyond a certain point. Everything seemed to look OK from the outside, bled nicely, opened nicely to put new pads on, no apparent leaks.... Inside was a mess!

In addition, there is a metering block below the master cylinder. This is an important component in front disk/rear drum to help compensate for the greater stopping force of disk vs. drums. Could be a lot of corrosion inside that puppy too.

What about the backing plates on the rear? The action of the shoes creates grooves in the backing plates - these grooves might prevent the shoes from fully pushing out on the drums.

What did the old brake fluid look like? Nasty dark brown sludgy stuff would drive me to remove and at least clean EVERYTHING in the lines. Contaminated brake fluid is bad, bad, bad.

What about stopping tests? Drive along a flat road and attempt emergency stops going both forward and backward. You should be able to lock up the front and back wheels in both directions. This test might help narrow down where too look.

 

I would also check the adjustment of the rear brake shoes. Almost no one adjusts them properly, due to the fact they have to be adjusted OFTEN. If you adjust them once, chances are they will need it again in a month or two. I don't know of any manufactuer that designed a proper self adjusting rear brake system (drums).

 

OK. Thanks for your help guys. Firstly, Colo79Ford, I like your idea but that's not really an option. The "professional" is a really nice guy but a lousy mechanic and he has already got enough of my money. I learned the hard way that you don't use 'friend of a friend' for work like this. But anyway!

Secondly, 78tinkerer, I forgot to add the reman calipers to the list of completely unnecessary parts replaced.

Thirdly, 77300i6, I have since replaced the rear shoes (MYSELF!!!) due to a wheel seal contaminating them and after adjusting them there was no discernable improvement. I appreciate you guys racking your brains on this but I am no closer to a solution. I have driven early 70's Ford pickups without a brake booster that had much better brakes than mine.

 

Is the proportioning valve set correctly?
Did he bench bleed the master cylinder before installing it?
Is the master cylinder a NEW one or a re-man? I had to replace my re-man twice!!
Did the WHOLE brake system get a good bleeding to replace the old fluid?
Did the springs in the rear drums get replaced?
Did ALL the contaminating brake fluid get removed from drums with BRAKLEEN or similar that does not leave deposits?

Far as I know, my haynes manual tells me that EVERYTIME the truck is moving backward the rear brakes will self-adjust. Now, when I drive, every time I take the truck out, I always reverse into my parking space so the brakes stay adjusted. I replaced everything in the brake system when I got the truck though. If there are any parts that are worn out, then the self adjusting aspect may not be working.

I have a friend that swears by GM stuff, and he is afraid to back into a parking space, he says it is quicker just to pull in to the spot to get into the store. Well, I pointed out to him that when you back into the spot before shopping, other drivers know you are backing in, you are adjusting your rear brakes, and you can leave quicker cause you can see someone come screaming fast at you in the parking lot and avoid the accident. He was not too pleased to hear that, and still does not back into ANY parking space in ANY vehicle he drives.

Point is, throw the truck in reverse at least once a week, and brakes will last a lot longer

 

At one point I had this problem. The problem ended up being that the rear diff axel seal was leaking and the fluid was traveling along the axel to the rear drums. They were contaminated with the diff. fluid.
Dak

 

Do these test.

How much fluid is coming out of each cylinder when you bleed the system?
The pressure should be consistent on the front and rear cylinders. if there is very little pressure, replace master cylinder.

How the pressure on the rear and the front when you bled that?
Are the rear brakes fully adjusted?

Are the rear caliper bleeder valves and brake line hose facing upwards. If brake lines are attaching to the caliper on the bottom of caliper, your caliper are installed wrong, your caliper should be installed on opposite sides (swap each caliper right to left) if brake lines are bolted at the bottom of caliper.

If the brake are not working properly, I would remove master cylinder (m/c), check the rod on the m/c for proper clearance (about 0.985 to 0.995 inch), the rod has an adjustment screw at the end and is measured from the tip of screw to the m/c. check the pressure on the M/C when you bench bled, if m/c is bad replace it.

 

OK, four-sixty-power, I don't know for sure if the proportioning valve is set correctly but that would be something to check. I am assuming the master cylinder was bench bled as it is pumping fluid evenly to all four wheels when you bleed the circuits. The master cylinder is a reman one but I honestly don't suspect it as there is no evidence of leakage at the booster. The whole system has been bled; I did that in an attempt to improve the brakes. All the brake hardware in the rear drums has been replaced. I am pretty sure the drums were de-greased before fitment; (they certainly were when I replaced the wheel seals and shoes). The truck gets a normal amount of reversing as I back out of my parking spot at my house, work etc daily.

dakonthemountain, thanks, but I have ruled out contaminated linings.

1975Ford, pressure is consistent, shoes are adjusted. I will certainly check caliper orientation and if necessary, master cylinder pushrod clearance. Thanks again. Keep sharing what you know!!!!

 

Sometimes, on master cylinders, the leak is internal, and does not leak out of the master cylinder.

 

I don't know if this will apply to you, but I changed out my master cylinder 20 years ago and had poor brakes from then on. Several master cylinders, pads, calipers, rear shoes, drums, proportioner valves, etc., and years later I decided to figure it out.

I pulled the booster apart and found that the push rod is adjustable. I turned it a few turns and wahlah full brake pedal. I drove it a few blocks and the brakes started locking up. I pulled it apart and backed the push rod off a turn and still full pedal with no lockup. I now have for the first time in years the brakes that the truck had when new.

I have over the last 25 years asked numerous people about my brake problem. Including several brake shops, and nobody knew that the push rod was adjustable. After I found the problem I went back to the same shops that worked on my brakes and asked them why they didn't adjust the push rod. They just stood there with stupid looks on their faces.

Just goes to show you that if you want it done right do it your self.

 

Good point on the pushrod. My truck has all new brakes, but the rear brakes are barely there; On ice, the wheels will spin, evben with full brake force. I have to pop into neutral before even TRYING park in the winter months. Then when I know the wheels aren't spinning, I move the lever to Park.
The self adjusters are working properly. All you have to do is try to remove the drums and feel that they still want to hold on a little, letting you know they are expanding with regular 'reverse' brake use.
I noticed limited pressure from the rear bleeders, both sides, so I am thinking prop valve or master cylinder pushrod... I wasn't aware that the factory proportioning valve was adjustable... Is it???
The pushrod is the easiest to try. Isn't it for adjusting front/rear brake bias? I definately have way too much front bias right now...
Any help on this would be greatly appreciated! '76 F150 Supercab Ranger XLT Trailer Special (with trailer brake kit plumbing removed completely from master cylinder)
Mark

 

The pushrod has nothing to do with the bias only the amount of brake pedal. It sounds like you definitely have a proportioner valve problem. The proportioner valve should self center when you push on the brakes. Normally the brake light will come on if the valve is not centered, but there could be a problem in the light circuit. My old chevy truck use to do it and I would smack it with a hammer and it would work ok for awhile. If I stepped on the brake and the rear end came around then I knew it was out of whack again. I am a little older now (40 years) and I would not do that again. I guess I had a spiritual guide watching out for me. If I was you I would get that thing fixed before it gets you into some serious trouble.

 

Well, it isn't a scary situation, and the truck still stops nice, but not with great grab. Just before I replaced the master cylinder due to failure, the pedal went to the floor while parked in my driveway. The brake light then came on, indicating a problem. So, I do know it is working properly. Once I installed the new master, I bled the lines and the brake light came off. I am hoping the factory proportioning valve is adjustable; I don't think so though, as I never recalled seeing an adjustment on it.
Pedal travel is normal. I always thought I read that the pushrod length helps control rear bias... Guess not.
If I buy an aftermarket PV, I may have to make new brake lines to it, no? I am hoping I don't have to go that far. I don't imagine the new PV will have the same locations for the outlet lines...
Mark

 

There is something that you might try. Back off the emergency brake cables until there is slack. Then adjust the rear shoes. I have seen people tighten the emergency brake cables up when the shoes were improperly adjusted. This will really mess thing up. If your light works and it went out when you pushed on the brake pedal then the proportioner valve is probably centered ok. You might check the flex hose between the differential and the frame. It might be ballooning and lowering the pressure getting to the wheel cylinders. I really think you have a rear shoe adjustment problem. I would back the emergency brake cables off until you have quite a bit of slack in them. Jack the truck up so that you can spin the rear tires freely, and take a brake spoon and start tightening the adjusting wheel on each brake. If you move the adjusting wheel more than 7 notches before the shoes start dragging on the drums then they are definitely not adjusted properly. I usually tighten them up until the drum wont move and then back them off 5 notches. Then stomp on the brake pedal hard and then recheck to make sure the drum spins without too much drag. After you are sure the shoes are adjusted properly then you can go back and retighten the emergency cables. (Not too tight)