another brake ? : pedal to floor before stopping

[ConfederateTyrant]

I suggest pressing on the brake pedal while the Jeep is turned off and see how the pedal does then, pump it a couple of times to make sure it pressurizes. If the pedal goes all the way down, then you may have a master cylinder problem.

I had an issue similar to that with a 71 Chevrolet Custom 10, the pedal would hold, but gradually go to the floor before braking would pick back up. Replaced the master cylinder and the brakes hold almost instantly when hitting the pedal.

I can't see any other issues unless you are somehow getting air into the system via a loose bleeder screw.

 

[andyd]

does the car have rear drum brakes? will the pedal pump up? Maybe they need adjustment

 

[1 FMF]

it's all disc, no drums.
the pedal pumps up when the engine is off and holds. I highly doubt it's a master cylinder, or any hydraulic, problem.

how would you adjust brakes? I was under the impression that it's all self adjusting? But i'm not sure, which is why i'm asking.

 

[andyd]

if its all discs than there is no adjustment.

 

[ConfederateTyrant]

Have you spoken with the mechanic who did the original brake work?

 

[labman]

I can't explain why, but some rear disks do need adjusted. If you set your parking brake as often as the owners' manual says, it would keep them adjusted. The mechanism could be frozen by now. One hack for that is to tighten up the emergency brake cable. I said hack, not fix.

Could just be a hardware problem. Take the wheels off. Recruit a helper. Wives will work if you don't do it too often and let them sit in the car and push the pedal. Have the helper apply the brakes while you watch the calipers. The caliper and piston should barely move enough to see. If any of them move more than that, take it apart and clean up what ever sliding surfaces it has. Finish with a good coat of Sil-Glyde from NAPA.

And yes, if the pedal goes down with steady pressure and no leakage, the M/C is bad.

 

[GoldenRod]

Either your master cylinder is worn out or you have air in the lines. There is nothing else that can cause excessive pedal travel.

 

[1 FMF]

on wife's 2003 jeep grand cherokee, brakes had been done about 1-2 years ago. I know the front rotors were replaced with new, which was somewhere at 10k-20k miles. I'm sure all the pads too but I don't remember. And the system was bled. Work was done by reputable mechanic. Everything has been fine since, but recently the pedal has been going close to the floor before the brakes starting giving any real stopping power. What would cause this? After the brakes were done last, you put the brake pedal down 1" and your stopping. Jeep has 39k miles on it now. Brakes work fine, except for the pedal travel, no pulsation at all, and no pulling when stopping. Master cylinder is full.

 

[Dave H]

Exactly what Goldenrod and others have said. Either air in the line or a bad master cylinder. My wife's master cylinder went like that, and then abruptly she had NO braking. Luckily vehicles come with a manual parking brake which she used to stop her truck without an accident. In your case, unless someone has been opening your brake system (bleeder screws), I doubt air is in a line. Those parts should be too new for corrosion to make a hole. Plus you said your master cylinder is full, so a leak isn't likely it.
I'd get it checked ASAP. Brakes are just too darn important. With it being a 2003, is it still under warranty? If not, luckily master cylinders aren't hard to replace. I can't remember what my wife's cost for her '88 Nissan pickup, but it wasn't a whole lot. I'm not sure about a newer Jeep, though.

Dave

 

[labman]

quote:

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Originally posted by GoldenRod:
Either your master cylinder is worn out or you have air in the lines. There is nothing else that can cause excessive pedal travel.

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With hardware problems, you can have excessive travel in a disk system as I pointed out.

An oh, air in the line will give a distinct spongy feel to the pedal.

 

[The_Jeff]

ABS on this thing? Does this have a special procedure for bleeding?

You could have one of those ABS controllers that needs a scan tool to get air pockets out of the system.

 

[Tosh]

quote:

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Originally posted by 1 FMF:
I highly doubt it's a master cylinder, or any hydraulic, problem.

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I would like to scold you a little for rejecting the first two likely problem areas.

Two other causes not previously mentioned are a gas pocket of boiled brake fluid and a torn MC seal. It is possible that bleeding the brakes the old fashioned way of pushing the brake pedal to the floor could cause a burr to nick the seal. Small possibility, but not unheard of.
I think you should begin by replacing all the brake fluid by sucking it out at each caliper (and not pushing the brake pedal). Then report back.

 

[labman]

If the pedal pumps up to a firm pedal and holds, messing with the hydraulic system is a total waste of time. In the rare case of brake fluid vaporizing, it returns to a liquid when it cools. Some people are overly concerned with brake fluid problems.

As I mentioned, in the past, some rear disks depend on regular applications of the parking brake to adjust them. Don't know if that system was used on your Jeep or not. If the rear disks are out of adjustment, you can take the slack out by adjusting the cables. That is not the best way. Unless somebody more familiar with your Jeep posts, you will need to check a manual, or gasp, aruugh, take it to a shop. Some rear calipers are best done with a special tool.

 

[moribundman]

quote:

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In the rare case of brake fluid vaporizing, it returns to a liquid when it cools.

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Driving off the cliff with no brakes, I find much solace in your prediction.

 

[moribundman]

And there is this interesting article on the topic of brake fluid changes. According to it, Ford does now recommend regular brake fluid changes. Other car companies are also being mentioned.

 

[labman]

Why is it that so many of you see changing brake fluid as the solution to every problem? It really only solves the rare case of fluid vaporizing which typically only occurs under extreme abuse. Bleeding the brakes only cures air in the lines, which only occurs if the system is broken or leaks. Those that suggest messing with the fluid when you have a hard pedal, display a lack of knowledge of how brakes work.

If you have a soft, or no pedal, then look at the hydraulic system. Otherwise, quit distracting people from the real problem.

 

[moribundman]

quote:

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Why is it that so many of you see changing brake fluid as the solution to every problem?

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To my best knowledge nobody has ever claimed that changing the brake fluid was a cure for every problem. It's simply a standard preventive maintenance procedure among many other things.

quote:

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It really only solves the rare case of fluid vaporizing which typically only occurs under extreme abuse.

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I suppose you don't live in the mountains. I also reckon you don't ever have to brake hard.

 

[JHZR2]

oh boy, here we go again...

for my 2c, it is smart pr, and really costs nothing to do... on the other hand, many folks cant do it 100% right, and just introduce new issues...

JMH