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2000 brake pedal soft

StylerG

StylerG

NAXJA Forum User
Location
Oklahoma City
have a 2000 with a recently replaced master cylinder due to soft brakes. Did a gravity bleed on the brakes, still soft so took it to a shop and they ran it through 2 vacuum bleeds and still got a soft pedal.
Ive got two opinions thus far and looking for some clarity. First opinion is i have a bad booster as well. In my mind my pedal going half way to the floor would not be symptoms of a bad brake booster as it seems i have plenty of boost to depress the pedal. Second opinion is that i have a bad check valve in my vacuum line to the booster. This also seems like it would cause a lack of pressure and not exactly my problem.

A bit of info on the jeep, new master as i said, chevy lines up front that arent that old, zj discs on back that arent that old and a prop valve from a zj. My brakes slow my jeep down but in no way stop it quickly-it would have to be slick outside for me to dream about locking them up. Jeep has 32's so im not running extreme tire size. Has a stainless line for the rear and i re-made the lines when i did the zj swap a bit ago. Problem has recently come up so i dont think its an issue with my actual setup.

Any ideas on this?
 
Engine off, pump the brake pedal four times and then hold pressure on it.

Start the engine--did the pedal feel like it dropped about an inch? If not, booster is bad.

I would expect a hard pedal if the booster check valve was bad.

Usually a "spongy" pedal indicates air in the lines, the brake drums are worn too thin (yes, I saw you have ZJ disks in the rear) or substandard brake lines/hoses.

I would try re-bleeding the brakes. You sound like you have experience, but did you bleed RT rear/LT rear/RT front/LT front?
 
thanks for the link and the suggestions. I did bleed in the correct order, and took it to the shop primarily to make sure the abs system was bled properly in case that was the issue and something i couldn't quite squeeze out with my procedures. The abs is disabled so dont ask how i got it back with the zj conversion, but it still flows through the system.

I looked on rockauto and for a 2000 i cant seem to find the booster vac line or check valve. Thinking i might replace those just as a precaution first. When our ice melts ill do a shakedown on the booster. I do know that i can pump the pedal with the jeep off and its firm, then when i start it drops about halfway to the floor. Its more than an inch but its not the firewall like some guys have stated.

Ill also check my pads/rotors for glazing and make sure the caliper pins are clean and working well-but neither of those would seem to point towards a spongy pedal to me.

Anything im missing on my to-do list here?
 
are your zj calipers upside down? i have zj rear discs. my buddyinstalled his calieprs on hte wrong side and couldnt figure out why his brakes were so soft.
mine is a little soft but the thing stops like crazy now. also, did you upgrade the prop valve insides from the zj?
have you thoroughly checked the lines for any leaks?
 
No, sounds like you are on track.

The only other things would possibly be swelling brake lines and you said yours are recent, or maybe some air trapped in the proportioning valve area.

Good luck. Post back what you find.

You must really be catching it according to the news.
 
Here's the correct way to bleed your brakes.
This was a "copy" & "past" from a Pirate4x4 thread. Credit goes to MrBlain.
Pasting was easier than typing it out:

"----Do a good bleed all the way around. It doesn't take much air in the system to reduce the effectiveness and lower your pedal height.

Use this process.

Open bleed screw, tell helper "down".

Have helper push hard and fast to the floor and let you know when it's there by saying "down".

When he says down, you close bleeder and say "up".

Helper lets pedal up at a moderate pace or about a slow 2 count and says "up" when it's at the top.

Repeat 3-5 times at each corner starting at the right rear and and then each successively closer corner to the master.----"

Note: No rapid pedal pumping before the "down" command; pumping can cause larger bubbles to coalesce into numerous smaller bubbles that are hard to remove.
Also, I've frequently had issues with air getting trapped in the proportioning valve. And, hopefully you properly bench led the new master cylinder BEFORE you installed it. Following MC install, you should crack the lines attached to the Prop valve, and expel any air in the lines running to the prop valve.
 
xjbubba said:
Here's the correct way to bleed your brakes.
This was a "copy" & "past" from a Pirate4x4 thread. Credit goes to MrBlain.
Pasting was easier than typing it out:

"----Do a good bleed all the way around. It doesn't take much air in the system to reduce the effectiveness and lower your pedal height.

Use this process.

Open bleed screw, tell helper "down".

Have helper push hard and fast to the floor and let you know when it's there by saying "down".

When he says down, you close bleeder and say "up".

Helper lets pedal up at a moderate pace or about a slow 2 count and says "up" when it's at the top.

Repeat 3-5 times at each corner starting at the right rear and and then each successively closer corner to the master.----"

Note: No rapid pedal pumping before the "down" command; pumping can cause larger bubbles to coalesce into numerous smaller bubbles that are hard to remove.
Also, I've frequently had issues with air getting trapped in the proportioning valve. And, hopefully you properly bench led the new master cylinder BEFORE you installed it. Following MC install, you should crack the lines attached to the Prop valve, and expel any air in the lines running to the prop valve.
Click to expand...

There is more than one way to bleed brakes, and this method is better in the summer:

Bleeding brakes: 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!) 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.

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 furthest 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 cylinder. 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.
"
 
blondejoncherokee said:
are your zj calipers upside down? i have zj rear discs. my buddyinstalled his calieprs on hte wrong side and couldnt figure out why his brakes were so soft.
mine is a little soft but the thing stops like crazy now. also, did you upgrade the prop valve insides from the zj?
have you thoroughly checked the lines for any leaks?
Click to expand...

yeah the calipers are the right way, ive double checked that. I appreciate the instructions on how to bleed brakes-even the best guys get air in the system every once in awhile but im confident that they are bled properly.

also i did use the zj prop valve when i did the swap.
 
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