Ok, so the problem with my 89. i have a little to no braking power and the pedle is low. We have bled the brakes tons of time's and we have replaced the MC , and both the rear cylinder's and still the same thing. What should i look at next. i know the flex lines are rubber! anyone think they could just be expanding to much and not giving any pressure? I'm seventeen and looking for a job. this is the jeep i learned to drive in year's ago and my dad has givin it to me and i need to fix it . it has been sitting in the yard long enough

 

How are the brake pads?

 

the front's were replaced when me and my brother inlaw began working on it. the rears still looked pretty good so we left em

 

sounds like a faulty master if no air coming out when bleeding.

 

No, its the same issue mine has had since I bought it. And now, I have met another person with the same problem. Both of us have replaced everything but the proportioning valves and boosters and we both still have low pedal and scary brakes. And I mean everything, hard lines, soft lines, pads, shoes, master cylinder, wheel cylinders, everything except the booster and proportioning valve. Try one of those or just do the upgrade to the grand cherokee master cylinder

 

well i havent tried lines yet. i guess thats next on the list, if that dont work i guess i will have no choice but to pul a booster and master outa a 97+ xj or grand. messing with this jeep has giving me a new hatred for working on braking system's.

 

do you have abs, and have you bench bleed the master?

 

Just my two cents worth: On another car I own (Alfa Romeo Spider) I had a very similar problem and it was the flex lines. What happens is that over time these become poreus from the inside out. So as you say they basically start to flex.

I appreciate/respect every bodies experiences, but I don't understand how the booster could lead to the problems you describe. No boost means you need to press harder on the brake pedal, but the brakes should still work just fine. You just need to press harder, nothing else. A wonky proportioning valve?? Not sure, maybe, but if you're able to bleed all four brakes just fine I wouldn't expect it to affect braking that much.

Back to basic; you say you have bled the system tonnes of times. Do you get a good steady stream of brake fluid out of each bleeding niple?? I have no experience with the brakes on my Jeep yet, but I do know that some systems are very sensitive on how you bleed them. The old "push the brake pedal" won't work well on some cars.

I have a very simple brake bleeding system that's pressurised and it allows you to really push out all old brake fluid and tralled air through the various systems. Better yet, are the vacuum systems.

I have an old Mercedes and the only way I can properly bleed the brakes is by using a vacuum system. Most mercedes owners I know use the "push the brake" or the pressurised system, but for some reason it won't work for my Mercedes. It's vacuum only!

Lastly, another experience; twice I have replaced a MC only to find out that the new MC was as bad as the old one.

I'm always very much in favour in troubleshooting as much as you can before starting to replace anything. Replacing without proper trouble shooting is a bit like hit or miss.

You might want to consider going to a garage where they can test your brakes, that might give you an indication of whether its' front or rear brakes or all. Might give some indication if your proportion valve is out of whack.

Depending on how you bleed your brakes, you might consider going to a garage and get them to bleed them for you.

If all fails, replace everything you haven't replace expect the booster. Only replace the booster if you brakes do work, but you need to press harder on the pedal.

Jeroen

 

no abs. and yes we bench bled it very well

 

i get a good stream of fluid out. and the last few times iv done it i havnt had any air come out.the next thing that i can figure is the flex line's are bad. and i cant realy to a pressure bleed cause of the way the master cylinder is designed. i do have another master that was working off of another xj my dad had so i may try that. but my next bet is the line's

 

I have the samr issue with my 88. Did the master . The pedal came back t really stiff but had to press the brakes really hard. So then I replaced the booster and bleed again and back to the same place I started. Im freakin lost too!

 

try using either a line crimp tool or a pair of vicegrips and clamp your rear hoses see if that helps if not, go to your fronts see if that helps. if not clamp all four pump the pedal up and keep constant pressure on the pedal if it bleeds down then your master is bad,they can be bad outta the box if they have sat on the shelf to long.if you clamp on the upper part of the soft line you will eliminate any kinda if line swelling. at least you can eliminate some of the guessing and replacing for no reason.also it is not your booster it will get a hard pedal when bad.

 

i replaced all the soft lines and hard lines and still have the messed up brake feeling. my booster tested good so i left it on instead of replacing it. i used a power bleeder to bleed mine and did the old fashioned way many times and still nothing. i even asked an old school mechanic to come check it out and he said htey should be fine as everything is correct but still nothing good.

you can replace your lines and hopefully it helps, but replacing mine did nothing

 

Is the problem when your just sitting there in park and you push the pedal? Is that when you don't like the feel?
Or is it when you are actually moving and you don't like how it seems to take forever for you to stop?

If it's the first then you do indeed have a problem in your brake's hydraulic system. You either have something being compressed (air) or something swelling from the pressure (rubber lines). If the brake fluid got contaminated, and believe me it does happen, the rubber used to hold the fluid in the system at the master cylinder or the slaves (caliper/wheel cylinder), and even the rubber lines, will start to swell from that contamination and will compress when force is applied.
The only cure is removal of all rubber parts and cleaning of the steel lines with an appropriate brake line cleaner. then replace all rubber containing parts.

If it's the second then that is a much simpler fix. Your brake pads and shoes WILL glaze over when they get really hot! Sometimes it's as simple as taking some 80 grit sandpaper and roughing up the surface. DON"T breath the dust!!! Other times the rotors and /or drums will need to be resurfaced if they have enough material left on them. You should do this when replacing pads or shoes anyways.

When I first became a mechanic back when dinasoars roamed, no brake job was complete until the drums were turned on a lathe. this left a nice new surface for the shoes to work on. Now it's just replace the shoes or pads and replace the rotors or drums if they are cracked or broken. Nothing is done to give them a new surface for the new pads to work on.

Scary!

 

this is so true. no one seems to do this anymore unless you specifically ask for it.