i have had horrible brakes on my truck for over a year now. they used to work, but then i blew a line, and they have never worked since. My foot generally goes most of the way to the floor before anything happens, but pumping them gives me somewhat of a pedal. In an attempt to fix the brakes i have done a new, not reman master cyl, new lines out of the master to the valve on the drivers front of the frame, new steel lines anywhere there are supposed to be steel lines, new rubber lines anywhere they exist, new front rotors and calipers, new rear shoes (3"), new wheel cyls, (bigger ones), new spring kits, new self adjusters, and as of last weekend, new rear drums b/c one drum had a bad gouge in it from an old pad digging in.

after putting the new drums on, i adjusted the brakes by jacking up the rear, and spinning the tire till it dragged a bit. i did not disconnect any lines during the drum replacement.

Now i have no brakes whatsoever. my foot goes all the way to the floor, and the truck keeps on rolling, pumping the pedal does nothing for me. the pedal makes a "airy" kind of noise. also, the "brake" light is on on the message center, even though the "black box" behind the ghlove box is disconnected. i cannot even count how many times the brakes have been bled over the last year. i have tried every method; one person on the pedal, one opening and closing the bleeder; open bleeder, put on hose, put hose in jar of fluid, pump pedal till no bubbles; long term gravity bleeding; air powered pressure bleeder,; hand-powered vaccuum bleeder, blah blah blah. i do not drip any fluid anywhere, and the reservior is always full. my truck is out of inspection now, and it definitly wouldnt pass like this, as even i would not attempt to drive it down the road how it is now.

anyone have any ideas as to where to look. i doubt any kind of garage would even look at it, considering the rwal is bypassed, and the truck is a mess to anyone but me. i have only driven the truck 1000 miles in the last year, as it is just unsafe to take down the road if i dont have a trailer with brakes hooked behind me. i, or anyone i know, has any idea where to go from here, and i am really getting sick of having a truck that is pretty much useless.

ok, done crying

 

hmmmmmmmmmmmm.... well it sounds like you have done everything, although i don't know what procedure you used to bleed the lines. i bled the furthest tire from the mastercylinder first in this order, back passenger tire, then back driverside tire, then front passenger tire and then front driver tire, i probably bled the brakes about 4 times until i saw brand new fluid coming out of all the tries and then i new that their wasn't any air in them. also you didn't mention it, but is your brake pedal stiff or real squishy? i had a vaccum leak on mine and it would stop unless you jammed it to the floor.


jason

 

my pedal is squishy to say the least

I can build a rock hard pedal in two pumps if the engine is not running, but when you start the truck, the pedal falls away rather quickly

 

Brake fluid wont compress, but air will. If the pedals soft or squishy as fury said, its got air in it. I have on a few occasions seen a booster cause simalar probs, they have a diaphram in them and a pin hole can give you headaches.

 

I have had auto parts stores sell me the wrong brake master, causing me a whole world of problems! The main things are master cylinder bore diameter and bore depth being balanced with the wheel cylinder bore. If too small a master bore is used with too large a wheel cylinder bore the master can't move enough fluid volume to actuate the brakes. If you've been given the wrong master it can also cause your pedal linkage adjustment to be incorrect.

In one of the threads here on this forum regarding 3" rear brakes there are at least three different rear wheel cylinder numbers listed. These are different numbers because they're different bores. Maybe yours are too large for the master to match the volume requirements?

Also there's another more accurate but more difficult way to adjust brakes. There can be play in the mechanical system and drums can be out of round, or shoes not properly arced to the correct diameter for brake drum circumference. When you adjust to slight drag you can be way off thanks to new shoes that haven't been run in yet.

The alternate method is to tighten adjusters down until drum is stopped from turning, then back off to a light drag. Do the same on the other side, backing off the same number of 'clicks' on the starwheel on both sides. This more closely simulates actual driving condition of drum and shoes.

Sometimes it's necessary to first mark the brake shoes with chalk and give the drum and wheel a spin and have somebody hit the brakes. Remove drum and see if shoes are making full or only partial contact with drum.

 

Does the pedal go down gradualy after pumping it up? Ive seen new MC's bad before...Had nothing but problems with my last two!

 

the pedal will stay rock hard w/the engine off, and not creep down until its started.

the wheel cylinders are one of the acceptable replacement/upgrades for our trucks.

appreciate the suggestions so far

 

how did you bleed the master? i killed a few of them trying to "bench bleed" it. finally i just mounted the last one to the truck to bleed it and it worked like a charm... i've still got a somewhat soft pedal, i need to replace the lines between the axle and the frame but i have been thinking of a lift and put it off. i am guessing there is a little bulging in those lines causeing a slightly lower pedal.

 

Micia thats a good point, i never bleed mine in a vice, i mount it and use the pedal to bleed it. The reason is the allowed movement isnt very much and if you bleed it in a vice and go 1/8 inch to far it tears seals, but on the truck the pedal cant over extend and tear them.

 

I had the same problem on my truck once after working on the rear brakes. I had replaced everything on the rear and had the pedal go nearly to the floor and had to pump them up to get a hard pedal. What I found I had to do was after I adjusted the star wheel adjusters(and thought I had the adjusted correctly) the shoes were not centered when I adjusted them out so they were hitting on the end, but not touching the center of that arch. What I found is that I had to pull forward and apply brakes, then pull backward and apply brakes. Then readjust the star wheel until they were adjusted out to the drum surface and also centered so the clearance gap was consistant and even all along the shoe lining surface. I did this 2 or 3 times before I got it just right. This fixed my problem, but I still hated the drum brake system and finally installed rear disk brakes using 03 RAm 3500 calipers and rotors. Now I don't have to pull the axle just to look at the pads. All I need to inpect them is a flashlight and a mechanics mirror, and all I need to do to replace the pads is pull the wheel and 2 caliper bolts. Of course the rear caliper conversion isn't the most cost effective thing to do...I like it better with the disk brakes on the rear of course, but an equal reason of putting them on there was to see if I could do it!!!!!!!!!

 

I went the oppsite way on my wheel cylinders 1" and got a lot better brakeing and less movement of paddle.

 

My '92 W350 won't stop on a dime but then it weights 6700#. I have good firm brakes. It took a few weekends and a lot of research on the internet, mostly right here, to get there. I started the same as you with the master cylinder, brake booster and bled the guts out of the system and still had soft petal. I dove into the rear brakes and did a complete overhaul and upgraded the wheel cylinders to the 1.1875 inch piston. I replaced everything except the drums. When I bled the brakes this time the truck was jacked up in the rear to the point that the master cylinder sat perfectly level. I had a buddy help do the bleed because with the rear anti lockup modulator valve I read here that one man brake bleeding doesn't work. I tend to agree. I've done it both ways. You must bleed all five points in order to get the best results. It's been over six months and even the automatic adjusters are still working.

 

thanks for the replies

the mc was bench bled, as per instructions, and was pumping solid fluid.

my rwal is bypassed, so bleeding that out is not part of the equation.

i usued to be able to "plug off" any one of the four brakes, ie put a male plug in one side of either of the two brake "T" (front or rear), and the brakes would work great, other than the obvious pulling to one side if i had a front line blocked.

 

EClancy- which method did youuse to bench bleed? I have run the little hoses back up into the reservoir, and had BAD results, even with no air coming through. I plug off the ports on the MC, push it til no more bubbles come up out of the little holes in the reservoir. I start out with about 3/4" of travel, then get down to about 1/16". THEN I hook up the hoses and run fluid into the reservoir. Good pedal every time. I dont know how you guys expect to stop the truck without bleeding the master cylinder. You may as well not do it at all.

ALso, I have talked to guys who have had the 1" wheel cylinders and actually got BETTER braking than with the 1-1/8" cylinders. REason being, I guess, it goes back to the ratio of the master cylinder bore vs the wheel cylinder bore. The 1-1/8" cylinders have to big a volume to fill before they push out, thus reducing your braking.

Daniel

 

dpuckett's last answer is absolutely correct!

They do make double-flare pipe plugs. It's possible to disconnect line to front or rear, one or the other, and plug the brake tee outlet. This might tell if the problem's from front or rear of system.

Larger wheel cylinders will do a couple of things. With the same amount of brake fluid moved by master cylinder per stroke:

They reduce felt pedal effort, not an issue with power assist.

They decrease the distance that shoes will travel at wheel[s].

They take more fluid volume to cause movement of shoes.

They give a greater hydrualic force ratio from master to wheel cylinder.

If the rear drums are rusty or out of round it's not possible to correctly adjust brakes by tightening to a slight drag.

You can get a junk/wrong master cylinder new-in-box regardless of who you buy it from. Add a junk/wrong master to improper bleeding and rusty or out of round rear drums plus oversized wheel cylinders and weak/bulging brake lines and you've got a very large compound problem.