Brake issues

Well, I searched and alot of the threads I came up with gave me the result I was expecting with a slightly different explaination of the problem. My brake pedal goes relatively far down and then catches and begins braking. Many threads said master cylinder.. which I thought could be my problem. I am not leaking at all. The difference I have is that all the threads said if pressure is applied, the pedal with gradually sink to the floor if the master cylinder is bad... I am getting nearly no braking till the pedal is quite far to the floor rather than a sinking pedal.. I had the brakes bled out properly and they worked great for quite a while, now in the past few days they seem to have become problematic all of a sudden. Any ideas other than master cylinder? or any possiblities or recomendations or whatnot?

Pads or adjustments? Umm new brake lines and or bleed it all out and throw some fresh fluid in? Other than the master you got me. Good luck.

You say you had good brakes before this problem raised its ugly head. Does that mean your brakes applied near the top of pedal travel? Also, was the pedal firm? And now, the pedal goes almost to the "floor" before your brakes apply? Does the front dip when you lay into the pedal? If you answere yes to all the preceding, I'd say something is amiss with your rear brake circuit. Try pinching off the rear flex hose and test for pedal action. If you have a firm pedal, it would indicate the rear brakes. You can test the fronts by clamping off both flex lines and again testing for pedal feel. Bad pedal no mater what hoses are clamped off would indicate a master cylinder. You recently bleed your brakes, right? If you did the pump them up, open the bleeder approach, pushing the master cylinder piston to the end of its travel, you could have damaged the piston cups on one or both pistons (moving the piston into areas it seldom goes), allowing internal leaking. If you take the hose pinching route, be careful not to damage the hose. Either use a clamp meant for pinching brake hoses, or at least put a shop rag arround the hose before applying vice grips.

Sounds good... now I have somethign to do tomorrow. If anyone can relate to this... it feels alot like when my rear brake line rusted through and I had no rear brakes. I just got back from a trip to NH and I didnt feel any more dipping of the front end than prior to the problem. The difference between now and when the rear line went is that now there is SOME pressure until it catches (with a blown rear line there was none) and now the pedal catches sooner than it did with a bad line. Dont know if that could clarify anything, could be the rear end, could be master, but I def dont think its front, they seem to be catching quite well when they do.

i would try bleeding all of the lines and put some fresh stuff in there.

The thing is recently I did bleed them, by recently I mean several months ago and all was fine and good until now. I will try that tomorrow, as well as everything else mentioned. One other thing thats confusing me is I believe yesterday my brake light (for e-brake) worked and I know that light also comes on when there is a problem with no pressure in the system. That light no longer comes on (ever since this problem got bad, it has seemed to get slightly worse over the past few days until I finally now have time to get to work on it, and its starting to get real bad) but now that light doesnt come on... not for the e-brake or anything. Could be a completely different electrical problem that just happened to arise at the same time as this, but I just noticed this and was curious about it...

It sounds like you have the same problem I have/had. I did an axle swap on my XJ and about a week later I had the same symptoms you have. When I went to bleed the rear brakes, nothing came out. My brake portioning valve was stuck in the front only position.

There's a threaded cap on the front of the valve that you have to remove along with the brake sensor on the top of the valve. Once you've removed those two items, take a small probe/pick and push the meter block as far back as you can gently and re-attached the previously removed items. Then bleed your brakes carefully.

That could be it. I did a rear axle swap over xmas break. Everything has worked fine till now, but still, that could be it if the symptoms are the same. Where is the brake portioning valve? Is that on the axle or master cylinder or where. With a quick search through the haynes repair manual i couldnt find it. I will def try bleeding out the rear brakes and if nothing comes out... you are my god for pointing that out.. haha, but anyway, yeah... where can I find this previously mentioned threaded cap and portioning valve?

correction, i just found the proportioning valve once I read a little more.. but still... just for clarification and to make sure I mess around with the right stuff... where is it?

If you follow lines that come out of your master cylinder, they immediately go into the brake proportioning valve. It's right beneath the master cylinder. The threaded cap is in the front and the sensor is on the top. You have to bleed the entire brake system once you take the front cap off.

Just a warning, there is a spring under that cap and parts will go flying it you're not careful.

lawsoncl said:

Just a warning, there is a spring under that cap and parts will go flying it you're not careful.

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Ooops! I forgot to tell him that!

one thing that i am in a rush and cant read through even my own posts.. but im not sure if i mentioned that the brakes build up pressure fine, as if nothign was wrong, when the car is not running, but once it is running is when the pressure is bad..

When the engine is off, your pushing through the power booster, so the pedal is always harder. As soon as you start the engine, you get "power brakes", that's why the pedal immediately falls. The test to see if a booster is working correctly is to pump the brakes with the engine off (this bleeds off any residual vacume in the booster), hold pedal pressure and start the engine. If the pedal falls, the booster is working.

themangeraaad said:

one thing that i am in a rush and cant read through even my own posts.. but im not sure if i mentioned that the brakes build up pressure fine, as if nothign was wrong, when the car is not running, but once it is running is when the pressure is bad..

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sounds like my problem. If you find out what fixes it could you post it here, thx.

xjbubba said:

If you did the pump them up, open the bleeder approach, pushing the master cylinder piston to the end of its travel, you could have damaged the piston cups on one or both pistons (moving the piston into areas it seldom goes), allowing internal leaking.

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Would that cause the exact problem?