Help no BRAKES!

[Guest rsa2217]

I have a 95 Pathfinder xe with 177,000 on it. Brake pedal was getting soft so i replaced rear shoes, front pads, front calipers, and master cylinder. Now the pedal goes right to the floor. Bench bled the M/C the bled each wheel three times. Bled each wheel four times before replacing the master cylinder will no diference, that is why i replaced it with a reman. Any ideas to help me out.

The brake light and abs light was on berfore i changed the M/C now they are off but pedal goes to the floor.

[94extreme]

you sure the MC is good? otherwise i am stumped too..

[OR99.5Speed]

Do these trucks have a brake booster? I know that when they go out on BMWs the pedal feels soft most of the time.

 

Other than the MC I don't have any ideas.

[Guest rsa2217]

Yes it has a brake booster but it tested out ok. I guess the Reman M/C I got must be no good. No leaks from it and the pressure is just a tad better that the O.E. but the peddal still goes to the floor.

[glenn]

if you replaced the MC did you replace/adjust the pushrod? Do an internet search "master cylinder staging" You might find something helpful. Another consideration is whether there is a crack/ leak in one of the brake lines-if they're old and you manipulated them you could imagine that they could have been damaged and wouldn't hold pressure. just some thoughts --good luck ! ---glenn

[mws]

I found it was not easy to get both chambers in the MC to fully bleed on the bench.

A quick diagnostic check: One at a time, crack the brake lines loose (loosen about 1/2 to 1 turn) where they enter the M/C and have someone slowly depress the pedal.

 

- If air comes out around the threads: MC not fully bled

- Fluid comes out: Prob air in the lines or cylinders downstream, or the pads & shoes haven't pushed out all the way to make contact yet.

- Nothing comes out: Suspect MC

Edited January 9, 2006 by mws

[94extreme]

one note to the above.. have a pan or some rags below the mc to absorb the fluid which is highly corrosive.

 

[mws]

Good point.

If brake fluid is left on paint, it will soften and remove it.

[Vsicks Pathy]

I do not understand 'bench bleeding'. Can someone explain it to me?

[94extreme]

bench, as in work table... although what mws said is really bench bleading also.. basically manually plunging the pluger untill you have no more air coming out of the line terminals. (full reservoir)

[mws]

This is the phrase commonly used in the US for the process of priming the master cylinder with fluid.

If the cylinder is completely dry, it can be quite difficult to get it to fill. You can fill up the reservoir, but pushing the pedal back and forth will rarely get the MC itself to suck fluid in. Pushing the pedal just compresses the air, but not enough to push air down the line. So when the pedal is released, the full volume of air is still there and there is no vacuum to suck the fluid in. So it is best to get the master cylinder itself at least partially filled with fluid before installing.

 

Bench bleeding devices use a one way valve in a hose.

 

Myself, I just clamped the entire assembly in a vice, filled the reservoir, and pushed the cylinder in with a no 3 screwdriver. While pushing in, I left the output ports open to let the air out. While letting the piston back out, I plugged the ports with my finger tips so air couldn't get back in. This was enough to develop enough vacuum to start sucking fluid into the cylinders from the reservoir. I had to pump my Nissan MC at least 50 times to get all the air out of both cylinders - one (I think it was the rear?) was really stubborn. Most MC's prime within 10 or 20 pumps.

Edited January 9, 2006 by mws

[Precise1]

I bench bleed in the vehicle using the 'port finger pluugging' method and never really had issues... Maybe luck, maybe good fingers.

 

Ya rsa... you have air in the MC, or brake lines *bleed farthest first to closest last*, or the MC is garbage, or you have a blown line or a line that is bubbling (like the bubble gum) when you step on the brake... It sounds like you know how to check for these things. Check the lines first, then work backwards. Good luck and let us know whats up.

 

B

[Vsicks Pathy]

This is the phrase commonly used in the US for the process of priming the master cylinder with fluid.

If the cylinder is completely dry, it can be quite difficult to get it to fill. You can fill up the reservoir, but pushing the pedal back and forth will rarely get the MC itself to suck fluid in. Pushing the pedal just compresses the air, but not enough to push air down the line. So when the pedal is released, the full volume of air is still there and there is no vacuum to suck the fluid in. So it is best to get the master cylinder itself at least partially filled with fluid before installing.

 

Bench bleeding devices use a one way valve in a hose.

 

Myself, I just clamped the entire assembly in a vice, filled the reservoir, and pushed the cylinder in with a no 3 screwdriver. While pushing in, I left the output ports open to let the air out. While letting the piston back out, I plugged the ports with my finger tips so air couldn't get back in. This was enough to develop enough vacuum to start sucking fluid into the cylinders from the reservoir. I had to pump my Nissan MC at least 50 times to get all the air out of both cylinders - one (I think it was the rear?) was really stubborn. Most MC's prime within 10 or 20 pumps.

My Izuzu MC sh!t itself. Peddel going to the floor all of the time but it would stop you. Just the longer your foot was on the peddle the closer to the floor it got. Weird stuff.

When I replace the MC with a new one I bolted it straight on and filled it up. The lines have to be bled anyway and it causes a vacume when you open up the nipple. Perhaps I too have been lucky when doing that sort of work. Even on build ups I have never given a second thought to the MC taking in fluid.

But it was good to know what bench bleeding is. I have seen it mentioned a few times here but never got around to asking.

[mws]

My Izuzu MC sh!t itself. Peddel going to the floor all of the time but it would stop you. Just the longer your foot was on the peddle the closer to the floor it got. Weird stuff.

.

The sagging pedal syndrome? Yup, know that well. That's why I had to rebuild both MC's in my Pathy last year.

 

It indicates a leak somewhere. If it isn't leaking fluid out of a fitting or hose or cylinder under the car, it indicates a leak around the seal inside the MC. The fluid is passing around the seal from the high pressure side to the backside of the piston. And then it usually ends up seeping out between the M/C and vacuum booster and eating all the paint off the firewall and innner fender and frame rail (uh huh, it did...) or seeps along the pushrod and runs along the passenger side of the firewall and saturating the carpet and padding (as my clutch MC did last year).

 

Lucky for me, in both cases it was just worn out seals and the MC bores were not pitted at all. Which causes the same problems but costs a lot more to repair...

[Vsicks Pathy]

The sagging pedal syndrome? Yup, know that well. That's why I had to rebuild both MC's in my Pathy last year.

 

It indicates a leak somewhere. If it isn't leaking fluid out of a fitting or hose or cylinder under the car, it indicates a leak around the seal inside the MC. The fluid is passing around the seal from the high pressure side to the backside of the piston. And then it usually ends up seeping out between the M/C and vacuum booster and eating all the paint off the firewall and innner fender and frame rail (uh huh, it did...) or seeps along the pushrod and runs along the passenger side of the firewall and saturating the carpet and padding (as my clutch MC did last year).

 

Lucky for me, in both cases it was just worn out seals and the MC bores were not pitted at all. Which causes the same problems but costs a lot more to repair...

Yes, it was the old warn seal trick. I was going to put a kit through it but it was actually cheaper to get a new MC. A mate of mine had smashed his car and it had a brand new MC on it. I bought the whole car for $150 (smashed front and rear) took the MC of course and sold the rest for parts. I think from memory I made $800 odd on the car.