Need to pump brakes in order to get pressure - JeepForum.com

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post #1 of 43 Old 02-02-2010, 09:23 PM Thread Starter
97DCZJ
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Need to pump brakes in order to get pressure

So I'm having this wierd pressure problem with my brakes. If I start the jeep, and press on the brakes, they go all the way down, n then the brake light turns on. If I pump it, the light goes off and pressure builds up a little in the pedal. It still doesn't feel normal though. It also happens everytime I have to use the brakes. It'll keep pressure for a little but it'll do the same thing again after a little bit of driving. I was told to bleed the brakes because it seems like there's air in the lines. I'm doing this tomorrow. I feel it might be the either the brake booster, or maybe the master cylinder.


1997 Grand Cherokee Orvis: V8 5.2L, stock.
(Sold) 1998 Cherokee Sport: 4.0L I6, Stock.
(Sold) 1990 Cherokee: 4.0L I6, 4.5" Lift, 33" BFG's.
(Sold) 1997 Grand Cherokee Limited: V8 5.2L, 2" BB, 31" Dick Cepeks.
(Sold) 1999 Grand Cherokee Laredo:
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; V8 5.2L ,3.5" lift, 32" Tires
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post #2 of 43 Old 02-02-2010, 10:08 PM
jaytee
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It's the master cylinder, unless one of your calipers is leaking fluid. If the brakes were fine and then all of the sudden needed to be bled, it's because you have a leak somewhere. Master cylinder is a cheap and easy fix. Don't forget to bench bleed it first.

2004 GC Laredo
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post #3 of 43 Old 02-02-2010, 10:14 PM Thread Starter
97DCZJ
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Quote:
Originally Posted by jaytee View Post
It's the master cylinder, unless one of your calipers is leaking fluid. If the brakes were fine and then all of the sudden needed to be bled, it's because you have a leak somewhere. Master cylinder is a cheap and easy fix. Don't forget to bench bleed it first.
Well I'm not losing any fluid.
I thought the master cylinder would be the cause. And cheap/easy? I don't think so...
The cylinder I looked up, around 90 i believe, and not so easy. It looks as if the ABS module is in the way. It might not be, didn't really LOOK into yet.
And bench bleed? I have a feeling that has to do with a certain way of bleeding it if I'm replacing the master cylinder

1997 Grand Cherokee Orvis: V8 5.2L, stock.
(Sold) 1998 Cherokee Sport: 4.0L I6, Stock.
(Sold) 1990 Cherokee: 4.0L I6, 4.5" Lift, 33" BFG's.
(Sold) 1997 Grand Cherokee Limited: V8 5.2L, 2" BB, 31" Dick Cepeks.
(Sold) 1999 Grand Cherokee Laredo:
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; V8 4.7L, Stock.
(Sold) 1996 Grand Cherokee Laredo:
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; V8 5.2L ,3.5" lift, 32" Tires
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post #4 of 43 Old 02-02-2010, 10:23 PM
jaytee
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I personally have not put a MC in a ZJ, but 90 bucks isn't too bad as far as parts go for a "luxury SUV". I did just put one in my WJ. It wasn't too bad. If the ABS pump is in the way, well then you will need to move it, which isn't a big deal as you are opening the system anyway. Just be careful disconnecting the lines. I would shoot them all with some PB Blaster and let it soak for overnight. Bench bleeding is a simple matter of bleeding the MC on a bench before you install it. It is a simple procedure with some basic tools, rubber hose, brake fluid, etc. I believe many master cylinders come with instructions inside the box. Most of the parts stores have bench bleed kits with a little plastic bottle and some tubing, adapters, etc. They are cheap. Even if 90 bucks is not cheap, it sure as hell is less than paying 120 dollars an hour labor for some dude to do it for you.

2004 GC Laredo
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post #5 of 43 Old 02-02-2010, 10:24 PM
JS97ZJ
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Check around the calipers and brake lines for leaks. If you don't find any, your master cylinder is probably leaking internally. Air in the lines is usually caused by opening the lines at the calipers when servicing them, or air getting into the master cylinder because it ran to low. Having air in the lines will give you a spongy pedal and not a complete fade with a warning light.

In any event don't drive it until you fix it.
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post #6 of 43 Old 02-02-2010, 10:33 PM
JS97ZJ
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Damn I type slow.....
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post #7 of 43 Old 02-02-2010, 10:36 PM Thread Starter
97DCZJ
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Quote:
Originally Posted by jaytee View Post
I personally have not put a MC in a ZJ, but 90 bucks isn't too bad as far as parts go for a "luxury SUV". I did just put one in my WJ. It wasn't too bad. If the ABS pump is in the way, well then you will need to move it, which isn't a big deal as you are opening the system anyway. Just be careful disconnecting the lines. I would shoot them all with some PB Blaster and let it soak for overnight. Bench bleeding is a simple matter of bleeding the MC on a bench before you install it. It is a simple procedure with some basic tools, rubber hose, brake fluid, etc. I believe many master cylinders come with instructions inside the box. Most of the parts stores have bench bleed kits with a little plastic bottle and some tubing, adapters, etc. They are cheap. Even if 90 bucks is not cheap, it sure as hell is less than paying 120 dollars an hour labor for some dude to do it for you.
Alright I appreciate the info. thanks a lot!

Quote:
Originally Posted by JS97ZJ View Post
Check around the calipers and brake lines for leaks. If you don't find any, your master cylinder is probably leaking internally. Air in the lines is usually caused by opening the lines at the calipers when servicing them, or air getting into the master cylinder because it ran to low. Having air in the lines will give you a spongy pedal and not a complete fade with a warning light.

In any event don't drive it until you fix it.
The light goes away after I pump it.
So you believe it's a bad MC?

1997 Grand Cherokee Orvis: V8 5.2L, stock.
(Sold) 1998 Cherokee Sport: 4.0L I6, Stock.
(Sold) 1990 Cherokee: 4.0L I6, 4.5" Lift, 33" BFG's.
(Sold) 1997 Grand Cherokee Limited: V8 5.2L, 2" BB, 31" Dick Cepeks.
(Sold) 1999 Grand Cherokee Laredo:
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; V8 4.7L, Stock.
(Sold) 1996 Grand Cherokee Laredo:
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; V8 5.2L ,3.5" lift, 32" Tires
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post #8 of 43 Old 02-03-2010, 12:33 AM
ZJ5point2GCL
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if your doing an MC make sure you buy a line wrench, just using an open end can / will cause you allot of issues, so its not worth risking
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post #9 of 43 Old 02-03-2010, 12:36 AM
ZJ5point2GCL
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Quote:
Originally Posted by 96DCZJ View Post
Well I'm not losing any fluid.
I thought the master cylinder would be the cause. And cheap/easy? I don't think so...
The cylinder I looked up, around 90 i believe, and not so easy. It looks as if the ABS module is in the way. It might not be, didn't really LOOK into yet.
And bench bleed? I have a feeling that has to do with a certain way of bleeding it if I'm replacing the master cylinder

the master cylinder has pretty good access, nothing in the way, it will take longer to bleed them than install the new MC
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post #10 of 43 Old 02-03-2010, 12:41 AM
Planetcat
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Check the booster while you have everything apart. I think I had the same symptoms like 5 years ago on my 96 XJ and it ended up being the brake booster and not the MC. The booster had lots of fluid in it and I picked up a remanufactured one from napa parts for something like $80. It would have been a quick install had I not tatered one of the rear lines and had to replace it. Bleeding the brakes will take longer than all the other parts combined. It's a fast fix.

2010 WK Laredo 5.7L, 2004 WJ 4.7L (totaled), 1959 CJ-5, 1996 XJ (sold), 1989 YJ Wrangler 4.2L (Sold)
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post #11 of 43 Old 02-03-2010, 12:44 AM
BigE3
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Have you tried bleeding your brakes before you dump money somewhere you may not need too. I used to have to flush the fluid after every race because the fluid would break down. And since you're from LI with a jacked up jeep with big tires in stop and go traffic. That right there can cause you fluid failure and give you sponge foot.

Thats up to you before you jump into everything else. Its your money.

I like my Jeep, just like my women. 'Loose and Flexible'
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post #12 of 43 Old 02-03-2010, 06:24 AM Thread Starter
97DCZJ
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Quote:
Originally Posted by BigE3 View Post
Have you tried bleeding your brakes before you dump money somewhere you may not need too. I used to have to flush the fluid after every race because the fluid would break down. And since you're from LI with a jacked up jeep with big tires in stop and go traffic. That right there can cause you fluid failure and give you sponge foot.

Thats up to you before you jump into everything else. Its your money.
did you read the OP?
i said how im bleeding them today before i go and spend money.
and its not spongy, it just goes all the way down at first then pressure builds up after i pump it

1997 Grand Cherokee Orvis: V8 5.2L, stock.
(Sold) 1998 Cherokee Sport: 4.0L I6, Stock.
(Sold) 1990 Cherokee: 4.0L I6, 4.5" Lift, 33" BFG's.
(Sold) 1997 Grand Cherokee Limited: V8 5.2L, 2" BB, 31" Dick Cepeks.
(Sold) 1999 Grand Cherokee Laredo:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
; V8 4.7L, Stock.
(Sold) 1996 Grand Cherokee Laredo:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
; V8 5.2L ,3.5" lift, 32" Tires
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post #13 of 43 Old 02-03-2010, 08:51 AM
vdub
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Could be a vacuum leak.

Does your heat go to defrost when your accelerating or putting load on your jeep? Also does your cruise conrol work?
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post #14 of 43 Old 02-03-2010, 10:06 AM
JrMechanic
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Quote:
Originally Posted by vdub View Post
Could be a vacuum leak.

Does your heat go to defrost when your accelerating or putting load on your jeep? Also does your cruise conrol work?
If it were a vacuum leak, the pedal would be stiff. Not go to the floor.

Bleeding your brakes will be a waste of time. The brakes in your ZJ (or any vehicle) are a sealed system. Air doesn't just get introduced. Have you checked the fluid level? Are you positive you aren't losing fluid? If so, then yes it's the master cylinder.

The new MC will come with a bench bleeding kit and instructions.

Want to swap an NP242 or NP231 into your ZJ? Here's how:

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post #15 of 43 Old 02-03-2010, 10:09 AM
vdub
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Quote:
Originally Posted by JrMechanic View Post
If it were a vacuum leak, the pedal would be stiff. Not go to the floor.

Bleeding your brakes will be a waste of time. The brakes in your ZJ (or any vehicle) are a sealed system. Air doesn't just get introduced. Have you checked the fluid level? Are you positive you aren't losing fluid? If so, then yes it's the master cylinder.

The new MC will come with a bench bleeding kit and instructions.

Not from what i have heard. There was a poster on here a while back on here that had a soft brake pedal that would go all the way to the floor. He also had the same symptoms of a vacuum leak and found the leaks and fixed them. this also fixed his soft brake pedal.

If the MC was bad the pedal would not gain pressure by pumping it. it would keep going to the floor regardless of if you pump it or not.
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