nukinfuts29

My '93 ZJ is giving me a weird brake issue. Sometimes they work fine, but more often then not they are spongy. And then today backing out of the garage they werent barely workiing at all, and now they are back to spongy.

When i come to a stop they go down sort of quickly, and when I'm at a stop they will slowly work down to the floor. Once the pedal is on the floor you can hear the brakes groaning, and it makes you wonder if they will even hold.

Sounds like low pressure right? Both the caps show full brake fluid when removed, this has been going on about a week and i keep checking the fluid with no changes. I can't imagine its a leak, since the fluid isn't going down.

The front brake pads were replaced about 1200-1500 miles ago and i have had zero problems until now. Tomorrow we have more bad weather coming in so hoping to get a fix on this today.

Any ideas?

jnicewan

If it has ABS it might be bypassing in the ABS control unit, if its not ABS it sounds like the master cylinder might be bypassing.

nukinfuts29

It's ABS. How can it be bypassed arent brakes closed loop systems?

jeepbus

There is no way they can bypas the ABS.You have a bad Master Cyl.Fluid is getting past the cups in the cyl bore.I would replace the Master cly and replace the fluid.

nukinfuts29

Awesome, not the issue but the definitive answer. Is it "safe' to baby it around town going to and from class for a few days?

At $65 + core and a 5 day wait maybe i will try and hunt down a decent used one.

Black00XJ

Your aged ZJ prob has some copper lines on it somewhere. Go toa Firestone or brake shop and ask to get the brakefluid tested. They will put a strip in your fluid and see if it tests possitive for copper in the system.

nukinfuts29

What would that indicate?

jeepbus

YOU CAN NOT HAVE COPPER LINES. First its against federal law 2 they don't make such a thing .Because the first time You applied the brake the line would explode. Copper is so soft it can not stand up to the pressure.

nukinfuts29

Yea thats what i thought, but who am i lol. Thanks again for the information, I'm going to buy a reman and swap it out this coming week.

Bustedback

The lesson here is, be careful of who you take advise from. Copper break lines? Really?

nukinfuts29

Yea i wasn't exactly jumping out of my chair to go hunt for copper lol

tiwvr1

I think the copper guy got confused. There is a test they can do to see how much copper is in your brake fluid, IDK where it comes from, but it is common on older vehicals. It isnt really a problem, but can cause a problem with corrosion. So when u replace that master, bleed all your fluid out till it is clear.

jnicewan

The brake lines arent made of copper but there is copper content in the metals used in the brake system (copper brazing). Copper is the metal that will corrode first in brake fluid and thats probably why they test for copper. Have you ever noticed old brake fluid having a greenish tint to it, thats copper.

Another major contamination to brake fluid is water. Brake fluid is hygroscopic, it will absorb moisture from air that gets in through the vented cap.

Not that I condone most of these places practices for generating revenue, basically because I cannot trust that they would do the brake fluid flush properly. I will say that brake fluid is probably one of the most neglected fluids as far a maintenance. I would at least try to flush and bleed the system out every 1-2 years or even during brake pad replacement.

You can also test your brake fluid with a Digital Multi Meter. Hook the negative lead to the neg battery post and stick the positive lead down into your brake fluid. Any reading over 0.30 volts is an indication that the fluid needs to be changed.

Bustedback

I seen an episode of Two Guys Garage that had some sort of test strips for the brake fluid. I've never felt the need to test brake fluid in the 25 years I've been spinning wrenches.

nukinfuts29

I cannot believe nobody stocks the master cylinder. There are probably 500 cherokee's within 15 miles of me this is insane