Master Cylinder

vgames33 · #1 02-23-2008, 10:15 PM

After changing both rear calipers, pads, and rotors, I cannot get the pedal on my sister's Maxima to stay up. I can bleed everything, get a good pedal, let it sit, and then the pedal is low again. I've been told to change the master cylinder, but I'd like a second opinion since its not my money.

The car is a '92 Maxima SE with 4 wheel disk brakes and no ABS. The fluid is new in the entire system, and it has been through about 3 quarts of fluid since I started bleeding. The pedal is high but spongey with the car off. With the car running, the pedal is about 2/3 of the way to the floor and still spongey. It will sink after only a few minutes of sitting.

UncleBob · #2 02-23-2008, 11:02 PM

not very helpful, but you're describing a system with air in it

vgames33 · #3 02-23-2008, 11:18 PM

That's what I thought, but I've bled it for at least 2 straight hours. I have nothing but clean, fresh fluid from all four wheels.

The only peculiar thing that I noticed was that working the e-brake a few times seemed to have an effect on the pedal. Could there be air trapped in the e-brake assembly inside the calipers? Is there any special way to release it?

UncleBob · #4 02-24-2008, 12:09 AM

no, there won't be anything special about the ebrake. You are pushing the pistons out, on the rear calipers when you apply the ebrake, and that changes how the pedal feels

You have air in the system, and you method for bleading the system is missing an air pocket. could be air at the master cylinder, or you might have air trapped in the ABS pump, or proportioning valve, or some other spot that is unfriendly. Sometimes you have to get creative on bleading systems

As a general rule, the master cylinder is a favorite spot for problems, but that usually only happens after running a master dry

vgames33 · #5 02-24-2008, 12:55 AM

The master and proportioning valve are a single unit with no ABS. We bled the lines at the master 3x per line. The master has not been bled with one of those kits with the lines that run back into the reservoir, but there was no air visible at the lines. I will look for a bench bleed kit at the parts store and try to bleed the master again tomorrow.

Any "creative" methods that you have will be appreciated. I always have trouble with brake systems for some reason.

Moppie · #6 02-24-2008, 04:24 AM

Have you started with the wheel furtherest away from the m/c then worked your way back towards it?

i.e start with the rear wheel on the opposite side to the m/c and finish with the front wheel on the same side as the m/c.

Also make sure the nipple is fully closed before the pressure is taken off the brake peddle. It doesn't take much to such air back into the system.

G.A.S. · #7 02-24-2008, 07:13 AM

You stated that you are going to blead the master again..............
Did the fluid resivuar ever go empty?
If your bleading the master eather with a kit, Or you have blead it already, The master needs to be level.
Eather by jacking up the rear of the vehical or done in a vise

vgames33 · #8 02-24-2008, 11:51 AM

The master never went empty. We have bled with the rear end raised up and with it level (jacked up evenly), and the wheels in every order possible. I'm not sure if the master was ever completely level during bleeding (it sits at a slight angle on the booster).

vgames33 · #9 02-24-2008, 11:58 AM

It won't let me edit for some reason.

I wanted to add that the fluid that was in the system to begin with looked to be the original fluid, if that matters at all.

G.A.S. · #10 02-24-2008, 12:13 PM

Try this.
start the vehical, pump the peddel three four times, now hold it.
slowly start to let off the peddel. slowly. As your letting off you will still feel back pressure on the peddel pushing back at your foot. Now you lightly push back. feather the peddel with pressure and letting off just a little and re-applying pressure.
If the master is bad, the peddel will fall to the floor during this process.
Does the peddel go all the way to the floor?

vgames33 · #11 02-24-2008, 03:45 PM

Pretty close. When its running, the pedal will go about 2/3 of the way down, and then the rest of the travel is very springy. You can force it to the floor, but it gets pretty stiff after 2/3 travel.

UncleBob · #12 02-24-2008, 03:51 PM

if the master never went dry, then it has to be a problem with the rear brakes.

Could be defective calipers

vgames33 · #13 02-24-2008, 05:17 PM

How would I go about testing for a defective caliper? They both grab quite well (spinning the rotors by hand), and pump up within one pump after bleeding (pump, bleed, one dead pump, second pump will bite). Both sides act about the same, although the passenger side caliper looks like it moves around more when the pedal is applied.

I played with it a little more today. The rubber hoses do not swell up at all, the pedal will only pump up a little with the car off, none with the car running. If I press the pedal in quick sucession, it feels like I hit a wall after so much travel, but a slow pump will travel all the way to the floor. The master cylinder makes some noise, but there is no spray with the cap off.

bobss396 · #14 02-25-2008, 08:07 AM

With a 16 year old car and those symptoms, I'd get a master for it. When bleeding brakes, most people make the mistake of bottoming out the brake pedal. This pushes the master cylinder rubber cups past this ring of crud in the master bore and the cups wind up leaking.

Get a rebuilt or new master, bench bleed it, install it and bleed each caliper. I use this method of bench bleeding and it always works. I lock an ear of the master in a bench vise, fill it up with fluid and leave the cap off. I press two fingers over the brake line holes in the side and pump the master with a screwdriver. You'll see air bubbles come up through the fluid in the reservoirs, when the bubbles stop, the master is bled. Put the cap on and install it.

Also, as a wild thought, I've seen calipers installed on the WRONG sides of the car before. This puts the bleeder screw down instead of up.

Bob

j cAT · #15 02-25-2008, 07:06 PM

Quote:

Originally Posted by bobss396

With a 16 year old car and those symptoms, I'd get a master for it. When bleeding brakes, most people make the mistake of bottoming out the brake pedal. This pushes the master cylinder rubber cups past this ring of crud in the master bore and the cups wind up leaking.

Get a rebuilt or new master, bench bleed it, install it and bleed each caliper. I use this method of bench bleeding and it always works. I lock an ear of the master in a bench vise, fill it up with fluid and leave the cap off. I press two fingers over the brake line holes in the side and pump the master with a screwdriver. You'll see air bubbles come up through the fluid in the reservoirs, when the bubbles stop, the master is bled. Put the cap on and install it.

Also, as a wild thought, I've seen calipers installed on the WRONG sides of the car before. This puts the bleeder screw down instead of up.

Bob

I agree with bob replace master cylinder.... pedal to floor is master cylinder n/g.....why ? brake pedal pushed down too far damaging seals on master cylinder and don't forget bad,wrong or contaminated fluid... if pedal was spongy but did not go to floor I would say air.... this is bad master cylinder...

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