Soft Brake Pedal feel...

mr2fyre · #1 (**permalink**) 08-26-2003, 09:43 PM

Since i have gotten my jeep it has had a soft brake pedal. I have bled the system and still has the same pedal feel.

Basically the first half of the pedal movement is worthless. There isn't much resistance at all and certainly no stopping power. After i pass this point the pedal firms up and has the feel of a normal brake pedal and pretty good stopping power.

Anyone have any ideas,

John
88 Cherokee
91 Toyota MR2 Turbo

far_right · #2 (**permalink**) 08-26-2003, 09:51 PM

you might want to replace the master cyl

mr2fyre · #3 (**permalink**) 08-26-2003, 10:03 PM

Quote:

you might want to replace the master cyl

I know that is a destinct possibility.

I have also read some about rear brake adjusters not working right too, but i don't know if that would cause this. I am not too familiar with rear brake drums or the dual piston master cylinder.

I also read something about some special tool that you need to bleed the brake lines. I didn't have the tool nor could i crack the bolt in order to use the special tool. I bled without, but i am not sure if that makes a difference.

John
88 Cherokee
91 Toyota MR2 Turbo

XJNick · #4 (**permalink**) 08-27-2003, 08:54 PM

Hi, The brake bleeder tool is just to help prevent you from stripping the bleeder screws. It definately sounds like air in the lines, a weak master cylinder, break in the brake lines, etc.

Start by bleeding the brakes again. You MUST bleed all the brakes, not just one wheel. When you bleed the brakes, place a hose on the bleeder valve then into a jar with brake fluid in the bottom. Next step on the brakes, open the valve, when fluid stops coming out shut the valve, release the brakes, repeat until no air and only clean fluid comes out of the valves.

You also MUST bleed the brakes in the following order:
> Rear Right
> Rear Left
> Front Right
> Front Left

Hope that helps

-Nick

mr2fyre · #5 (**permalink**) 08-27-2003, 09:19 PM

I have done this bleeding process. It took me forever to get the red goo out of the lines and get some nice clear fluid coming out of all four ends.

I will replace the master cylinder if i can't find anything else wrong. But I don't want to jump the gun put a new MC in and then have it still happening.

I test drove 1 other 89 cherokee and it actually had the same feel for the brake pedal.

When i got this one i was hoping it was just in need of a bleed.

I am thinking i should look into the whole rear drums out of adjustment thing before moving on. Unfortunatly i know next to nothing about drum brakes. Guess i have to do some more reading out of the shop manual.

MudderChuck · #6 (**permalink**) 08-29-2003, 07:27 PM

On the rear brakes, there is a dust cover (rubber) over the ends of the wheel brake cylinder. Carefully pull out a bottom edge of the cover (fits in a groove over a lip) if a little brake fluid comes out, it´s time for new wheel brake cylinders.
You mentioned red goo, I can´t remeber seeing any red brake fluid lately. Is it possible somebody used Dextron (auto tranny fluid)?
When you push the brake pedal, do you hear a woosh sound. Could be your booster is leaking a bit.
Like mentioned before, the master cylinder could be the problem.
The threads on the adjusters, need to be greased every time the brakes are changed. Doesn´t take long for them to rust up and stop adjusting. Taking the brakes apart and greasing the adjusters, is best left to somebody that has done brakes before and with a good book handy. Replacing the wheel brake cylinders, can also turn into a major headache. As the bolts and brake line fitting, are usually frozen in there pretty solid and easy to break.
Many of the early XJ´s are a little soft, at the top of the pedal. I don´t really know if yours is excessive or not. If you have air, pumping the pedal, will usually raise the level at which the brakes start to work, at the pedal.

mr2fyre · #7 (**permalink**) 08-30-2003, 12:06 AM

Well i was just checking my oil and on the + side that hasn't gone down so much as i thought it was.

While i was under the hood i pulled the brake fluid resivor cap to check out how the fluid was doing and woudn't you know there was a nice red gooey mess in there again. I had it completely clear when i bled it 3 or 4 weeks ago. So I have to assume that there are some pretty rusty parts in there, and for now i will assume that that is what is causing my problems. I guess i will have to spend some more time trouble shooting to figure out exactly what is failing.

I performed all the tests the little book said to check the brake booster and they all passed, so i am not sure that is it either.

MudderChuck · #8 (**permalink**) 08-30-2003, 08:20 PM

If your fluid is turning rust colored, you probably have or had some contaminated brake fluid in there. It has a tendancy to pit the inside of the master cylinder and wheel brake cylinders. The brake cylinders are easy to check, like I discribed before. If they are passig fluid it´s usually pits in the inside wall of the cylinder.
If while holding a steady firm pressure on the pedal, and it begins to sink a bit (usually very little) this is an indication the master cylinder pistons are passing fluid to the other side of the piston (slight leakdown).
DOT 3 and some other brake fluids suck up water from the atmosphere in an open container. It´s also a good idea to make sure which brake fluid your vehicle requires. Some brake fluids don´t mix well, like DOT 5 and DOT 3. There are also some more exotic hydrolic fluids, that don´t mix at all, they turn to jello or cottage cheese if mixed.
Power bleeding a system, sometimes works wonders. Though it does require a special machine. The cost isn´t that much, might be an option if you suspect moisture inside of your brake system. The water has a tendancy to settle in the master cylinder and brake cylinders. The water/moisture) turns to steam, at normal operating temperatures.