need some brake love

just put new rotors and pads on the front of my 89 laredo (non-ABS) didn't break any lines but still bleed and got a little air out of them...

with the jeep off i get good peddle pressure. peddle gets stronger after each push and holds fine. but after starting the peddle sinks (which i read it's supposed to do) but sinks almost to the floor and won't build pressure . seems like there is only an inch or so of peddle before it bottoms out... the booster is new (2 months old)


is this normal?

Re: need some break love

Typical with either air in the system or a bypassing MC.

So, I would pull the rear wheels and roll the cups on the ends of the wheel cylinders to check for dampness. If any, replace the wheel cylinders. Adjust the rear brakes.

Also, did you change the MC when you replaced the booster? Take a look up under the dash and see if there is any dampness from the MC there.

Re-bleed the brake system (you shouldn't have gotten air if the hydraulic system hadn't been compromised). Start RR, LR, RF, LF, don't get over enthusiastic with the pedal.

Engine off, pump the pedal 4-5 times and hold pressure. Start the engine, should be a definite drop in the pedal, but not a great distance. If you are getting to the floor then the hydraulic system is compromised--air in the system or hydraulic fluid is bypassing the MC piston seals.

don't see any fluid on the firewall... the master was not changed with the booster.

i'll give the whole system a bleed and see if that helps. just seems backward that i get good pedal pressure with engine off but not with engine running.

thanks!

RedRoamer said:

don't see any fluid on the firewall... the master was not changed with the booster.

i'll give the whole system a bleed and see if that helps. just seems backward that i get good pedal pressure with engine off but not with engine running.

thanks!

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You seem to get good pedal pressure with engine off because there's no boost, and you probably just can't push hard enough to find the flaw in the system.

Usually a master cylinder that's worn out and bypassing internally will work at least sometimes if you stab it or pump it up, but sink slowly under moderate pressure. Try hitting the brake hard, as in a panic stop. If it is firm then, you're probably looking at a MC problem. If you can't pump it up at all, and it sinks the same amount every time, I'd be more inclined to think your problem is outside the MC, and a thorough bleed would be the first thing to try.

did you install calipers correctly

ehall said:

did you install calipers correctly

Click to expand...

OP said rotors and pads and that he didn't open the system, yet he got air when bleeding. Figured he didn't change the calipers/cylinders or any lines.

how were the original brakes when you first put them on? how did u bleed them?