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Brake Problems Help?

Nova Wake

NAXJA Forum User
OK now, i had my front brakes done about 6 months ago and up 2 about two weeks ago i have had no problems. Now sometimes my brake pedal goes 2 the floor and then other times its fine and right were it should be. And then today i had to hit my brakes hard and the interior BRAKE light came on and will not go off, most of the day today my brakes seemed fine, occasionally it would feel like it went closer to the floor than it should but im lost, do i have air in my lines? i checked my fluid level and it seemed fine even added a little.

Also when taking it out of 4wd i have to first go into neutral then reverse and then drive or i get a pop noise when it disengadges when im driving, ive had other vehicles do that but dnt remember what the problem was.

I have a 95 cherokee sport. auto. 181,000miles
 
OK now, i had my front brakes done about 6 months ago and up 2 about two weeks ago i have had no problems. Now sometimes my brake pedal goes 2 the floor and then other times its fine and right were it should be. And then today i had to hit my brakes hard and the interior BRAKE light came on and will not go off, most of the day today my brakes seemed fine, occasionally it would feel like it went closer to the floor than it should but im lost, do i have air in my lines? i checked my fluid level and it seemed fine even added a little.

Adjust the rear brakes first. If that doesnt help, replace the master cylinder.
 
X2 - My rear adjustment was built with the wrong length cable in it so self adjustment doesn't work. Try to adjust it manually through backing plate. If stroke on rear cylinders is too long (due to not adjusted), it will use up the fluid that the master is pushing (and also needs to send to the front). But the test for the master cylinder is to pump it up and press down hard. If it keeps going down to the floor slowly, it is leaking out at a wheel cylinder (which you will eventually see from underneath on a tire), a rusted out break line, or pushing back around the piston inside the master cylinder.
 
I guess a better question I should have asked, how do you know it's not air in the lines ?
(I'm not second guessing you, I'm just tryin to learn a bit)
 
How would air get in the lines if the MC was full of fluid from the beginning? Unless his nieghbor cracked the lines to fawk with him.

If there was any holes in ANY of the lines, air wouldnt get in, it would leak out. If there was air in the lines, it would be like that all the time, not just every now and then.
 
i agree with the Master Cylinder. what happens is the brake pedal is never pushed all the way down during normal driving. so when the brakes where done the pedal will easily go right to the floor and all the crud that has accumulated cylinder scraps over the seals ripping them ever so slightly.

i found this the hard way after bleeding my brakes.
 
i agree with the Master Cylinder. what happens is the brake pedal is never pushed all the way down during normal driving. so when the brakes where done the pedal will easily go right to the floor and all the crud that has accumulated cylinder scraps over the seals ripping them ever so slightly.

i found this the hard way after bleeding my brakes.

That's why you don't bleed them that way. (and I'm not calling you stupid cause I did em that way for MANY years too). Called the kids or the old lady out and told em "pump it up and hold it down", and opened up the bleeder until the pedal went way down. There is a way easier way, but it takes longer. I use it whenever I replace brake cylinders or calipers, but mostly it's just to change the brake fluid, which I do whenever I change shoes or pads. Ideally you change brake fluid at least every other year. If you worked on old cars and saw rusty pistons, you'd know why, but people also say that old brake fluid boils and won't stop you right.

The best way is the GRAVITY method. The only problem is it takes a lot of beer and you don't want to drive right after. (CAUTION: YOU MUST BE 21 TO BLEED YOUR BRAKES THIS WAY!)

1.) Get the car in a position where you can open up the bleeders. I always like to break them loose with a 6 point socket being careful not to break them off. If you can, spray them with breakaway or similar a day before.)
2) Starting with the bleeder futhest away from the master (pass. rear), open it about 1 turn. You can put a little hose and cup on it if you want to keep the old fluid from running all over. Make SURE to keep the master cylinder topped off with fluid and DON"T let it get down to where air gets back into the master cyl. Let it flow this way until the fluid comes out of the bleeder clean. This will take at least 2 cups or so of brake fluid. Using gravity alone, you can drink 2 beers while topping off the master cylinder for the first corner. (CAUTION: Do not store brake fluid in beer cans or put beer into master cyinder. Drinking a little brake fluid however will probably not kill you. Beer in your brake lines might.) Snug up bleeder good when you're done.
3.) Proceed to drivers rear and repeat. It won't take as long because the long brake line has already been purged of the old fluid. So you have to drink your beer faster.
4.) Pass front. Drink even faster.
5.) Drivers front. Etc.

Patience can be substituted for beers, but that's no fun.

This prevents the rubber pieces from going any further than they are used to and self destructing.
:cheers:
 
i agree with the Master Cylinder. what happens is the brake pedal is never pushed all the way down during normal driving. so when the brakes where done the pedal will easily go right to the floor and all the crud that has accumulated cylinder scraps over the seals ripping them ever so slightly.

i found this the hard way after bleeding my brakes.


Makes perfect sense.

And on to a different, but similar topic - that's why you may not want to change to synthetic motor oil on a super high mileage vehicle - it will often "wash" the crud/buildup off the seals (depending on the compatibility / detergents in the oils in use)
 
you instantly know it's the master cylinder?
Pretty much. The intermittent pedal dropping is symptomatic.

The cups in the master cylinder piston are designed to expand outward under pressure. When they wear, fluid can leak past them, causing a low pedal, but if the cup expands enough to seal when you first apply the brake, it will continue to hold, and the brakes will seem all right. If it fails to seal initially, it will drop. Often a bad master cylinder will drop under light application but still work fine if you hit the brake hard.

First you should as noted, make sure the rear brake is adjusted, because that can also cause a low pedal. It would have to be very far out to cause your brake warning light to come on, and would not likely be intermittent.

A radically worn out front wheel bearing cal also cause an intermittently low pedal, because when the disk wobbles it pushes the caliper piston in too far, but this will usually be accompanied by obvious other noises and poor steering, and should not result in your brake warning light coming on.

And of course you should make sure there are no leaks, but it's pretty obvious that if the level is not going down in the reservoir then it isn't leaking out.

A quick master cylinder test (after ensuring that there are no external leaks): start the engine, and press on the pedal, starting very gently, and pushing steadily but not too firmly. If the pedal sinks slowly to the floor you have a bad master cylinder.
 
Bad wheel bearings could push the pads away from the rotors due to excessive runout, and require pumping to get back. But if you can sit with the vehicle stopped, pump up the brakes, and then feel the pedal go down to the floor, it is leaking somewhere you would eventually be able to see (and the flid level would go down) like a brake line, wheel cylinder or caliper, or it is bypassing the bad master cylinder (fluid won't go down, but usually looks nasty). Pump it and hold it down hard until you can tell for sure. Better to break it when your standing still instead of when a little kid runs out in front of you.

Master cyls can be rebuilt (did quite a few of the single system ones). You need to hone the cylinder and replace the rubbers. It's not worth it, especially with the dual systems like they all are now.
 
With the price of a new/reman one, its not worth it to buy all the small parts, and do it yourself. Ive tried a few times, but without much luck(worked for a few months, but gave up again).
Agreed. If the bore is worn or scored, it won't last unless it's honed well, requiring that you find and use the hone, and add another step to the already finicky need for scrupulous cleanliness. Get a new or reputable rebuilt one, unless you're doing it for adventure, education or hobby.
 
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