So I've got very frustrating brake issues. I'll start from the beginning.

I had a problem with brakes fading off at red lights. When I was stopped I would graddually start rolling backward. I assumed bad master cylinder.

I replaced the master cylinder and found I couldn't bleed the system well at all. Got a second master cylinder, same problem.

I noticed a rear wheel cylinder leaking so I replaced both rear wheel cylinders. Try and bleed system, rears bleed out and work great. Front passenger calliper will produce slight pressure then none. Driver side caliper will produce NO pressure. So I bled the Master Cylinder again, tried to vaccum bleed the fronts and pulled gobs of air and a pint of fluid through each bleeder but air would not stop. Still no pedal pressure.

One real odd thing I found, when I remove the bleeder screws completely from the calipers they do not drain any fluid.

I'm ready to put a For Sale Sign on my beloved truck i'm so mad!

Thanks in advance for any advice!

 

So as you bleed it, the air just keeps coming continuously? Does the person under the hood know what they are doing, keeping it topped up so it never draws air as you are bleeding the fluid through? The replacement master cylinder, was it new or from a wreckers? Also, have you looked around the master cylinder very closely for any leaks? Maybe where the reservoir mounts?

 

this has happened to me before, from some brain fade, and sound very much like something i have done before.

just asking have you ever had the front calipers off?
are the bleed nipples at the top of the calipers? or at the bottom?

if they are at the bottom it means that the calipers are on the wrong side and will never bleed properly, you will need to remove the calipers an install them with the bleed nipple at the top, which means changing them to the other side.

if this isnt your problem i will check tomorrow and help further if ican

 

The master cylinder is a reman. unit from Schucks. The resevoir does appear to loosley seal, however if I push on it, I can make fluid leak out. Is there something that can be done to remedy the seal between the resevoir and the master cylinder?

The resevoir was kept topped off during entire bleeding operation.

The calipers have the bleeder screw at the top.

 

Can you manually move the caliper pistons (screw driver between pad and disc, gently pry)? You could have sticking calipers. Try it with the bleeder open, all should move freely and spit fluid out.

How is the pedal? Stiff? Mushy?

 

did you bench bleed the master before installing it? try bleeding it out from the lines at the master. a little air could be trapped in there and that will make it hard to bleed out. have someone in the truck pumping the pedal, this works much better than those vacuum pumps to bleed it out

 

also possible that rubber brake hoses are f'd. Try all other suggestions first as they are basically free imho.

 

I haven't tired moving the calipers, however when I completely remove the bleeder, no fluid comes out! Seems fluid should seep out to me (rears do...). I think i'll replace the rubber brake lines tomorrow as they are only about 20 bucks a piece.

Bench bled the master and then i've been trying to bleed off air at the master fittings too.

A fella at work suggest a method to try checking pressure from the master cylinder out until I find the problem. I'll update as soon as I know something.

Keep the suggestions coming!

 

vacuum lines maybe?

 

You probably have seized front calipers (since they PARTIALLY hold, it's possible only one piston is sticking).

Before you spend any dough on the brake lines, try compressing the caliper pistons in (take the cap off of the master unless you want a brake fluid 'splosion). Since brake fluid is hydroscopic (fancy word for absorbs moisture), the pistons WILL rust in the caliper bores. Pistons should compress semi-easily, if they don't move (or move with a sudden "POP") they are seized. If there is enough rust in the calipers, you may not see any fluid seep out of the bleeder.

I've had the same issues on different vehicles I've bought. Changing the brake fluid is a maintenance issue most people don't think of.

 

Really appreciate the ideas, I will do some diagnostic work tomorrow night and post what I find. Starting to suspect the calipers as they are quit rusty. Taking tonight off so I don't get to angry!

 

Ok fellas, here is what I found...

Tried bleeding the lines at several points, won't get into the details cause they don't matter. In the end, I kept hearing air in the lines and/or master cylinder. It eventually became very apparent that I was getting airlock in the master cylinder but I couldn't figure out how to get the air out.

Turns out, the master cylinder comes with a large syringe with a rubber grommet that is about the same size as the holes that the fluid resevoir plugs into. I removed the resevoir and used the syringe to push fluid into the master cylinder and had a buddy open the bleeder screws on the front brakes one at a time. Pushing fluid through the lines from the top of the master. Put it all back together and the brakes worked!

They still feel a bit soft and if you press on them lightly, then stomp on em the pedal will go to the floor so I think there is a bit of air left in the lines.

MAIN POINT IS THAT FLUID MUST BE PUSHED THROUGH THE MASTER CYLINDER FROM THE RESEVOIR PORTS.

Hope this helps someone avoid all the trouble I went through!