Brake Question

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  #1  
Old 02-13-11, 02:51 PM
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Brake Question

I'm doing brakes on a 2000 Chrysler Town & Country. I'm getting air in the brake system somewhere. I have thoroughly checked for leaks and haven't found any. I just replaced the master cylinder, properly bench bled, as well as bled both front tires.. again. I still have a soft spongy pedal and half the brakes I should have. Also when I was bleeding the drivers side I had lots of air at first, then barely had any pressure, unlike the other side which squirted out two feet.??? Does this mean I have a proportioning valve problem?
 
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Old 02-13-11, 03:37 PM
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1. proportioning valve system has nothing to do with this; it simply distributes hydraulic pressure between rear and front brakes. most of braking is done by front brakes, proportioning valve is attempting to compensate for this.
2. you made a major mistake bleeding brakes. bleeding begins with pass rear>driver rear>pass front> driver front. reason being, it is progressing from the farthest away from master cylinder to the closest one. as a result, you have plenty of bubbles trapped in the 2 longest lines.
3. you do not have to have air leak to get bubbles into the system; heat from braking slowly but steadily deteriorates brake fluid. when fluid overheats, some of it evaporates, causing bubbles inside the system. there can be various causes for this. dragging caliper, brake pads that sit on non-lubricated guides, caliper guides that have never been properly lubricated, hard braking habits, driving a lot downhill with brakes applied often to slow down. brake fluid is basically alcohol and castor oil, or any other oil that will not damage rubber components.
4. loose bleeder screws. i doubt though.

squirted out 2 feet? you had bleeder screw out completely? those have to be barely loosened, just enough to let fluid out. there's no "shooting out" of fluid....
 
  #3  
Old 02-13-11, 04:46 PM
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Sounds like air.
Could be a small leak.
Have an assistant and keep checking all the system leaks while someone pumps on the brakes. Dont take a very big leak to get air.
That 2000 has the proportion valve in a heck of a place on the left side near the rear tire. In front of it I think. ??? Sort of forget. But I know the position of it and the shape of it traps dirt and salt and it corrodes it until there can be a pinhole leak in it. On top of it. Hard to find the leak up there. Find the valve and get your fingers up there and feel if it is wet with fluid after all the pumping. Its aluminum and not very think. Ive played that game. Let me know if you see green brake fluid come from it
 
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Old 02-13-11, 07:19 PM
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Thank you for your replies. To give you more history; three years ago we bought this van that just had an abundance of work done to it, including the master Cly. All of the sudden the pedal would get spongy and you had to pump them to get any brakes. Still under warranty, I brought it back to where the work was done and they put a new master on it and bled the brakes.. It happened again. I took it back, they bled them all and said that there was just air in the front drivers side and that it may take a while to work out all the air, and that I may have to bleed that tire one or two more times. After that I have had to do it three times, and every time it has fixed the problem.. Until now.

I suppose I didn't think about bleeding the back ones after doing the master Cly. Makes sense because I opened both lines. My own stupidity. I will try bleeding them in the proper order tomorrow, as well as checking for leaks above the prop valve. I've never heard about green brake fluid, what causes this?

And as for squirting brake fluid two feet, that was an exaggeration, I usually crack the bleeder valve less than a quarter turn. There was just a substantial difference in pressure's. Like possibly a valve was stuck not allowing as much pressure??

Thanks, Josh
 
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Old 02-14-11, 09:11 PM
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The Solution

Today I bled the back brakes and released a lot of air out of the pass rear tire, and found no leaks on the prop valve. This seams to be the solution, the brakes are much better! Once again, thank you for your advice and quick responses.
 
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