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Discussion Starter #1
Hey everyone - I'm in need of some help. I posted this over on the chrysler forum, but haven't had a response yet. I have a '99 town & country with some annoying brake problems. Right now the problem is that the brake pedal goes straight to the floor. Based on experience with this vehicle, I know that if I bleed the system it will be fine for a period of time - may be a week, may be a few months. then the same thing will happen again - straight to the floor. So far, I've had the ABS pump replaced, master cylinder twice, calipers and rotors, drums and shoes, and a wheel cylinder. I'm at a loss as to what is happening, and the shop and dealer can't seem to get to the bottom of the problem. I've spent over $2,000 on this brake related issue over the past two years. I'm ready to torch the thing, but that would be wrong.

Last time it was in the shop, they said maybe its the rear proportioning valve. Does this sound plausible? The wife really wants her van back, and I want to be finished with it. Any advice would be greatly appreciated!

Doug
 

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Or even the rubber grommet on the brake booster for the vacume line.
 

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Discussion Starter #5
There are no obvious leaks. If it is leaking, it's at a rate that is so low it's almost impossible to notice. I'll put some cardboard under it jut to be sure. As for the booster, I don't know for sure, but won't it just make it harder to brake if it were bad?
 

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1st question - when you bleed the brakes, does air come out - ie: bubbles in the expelled fluid?
If so, then you have air entering the system somewhere, as obviously, that should not happen. If not, then you are not technically bleeding the system, and the problem is something else, that is sort of "repaired" by the pedal moving its full travel during the process.
That would tend to indicate the master cylinder is faulty, since no other parts are activated at that time.
Next issue, the ABS pump would not have a bearing on the braking system, since it is a pressure routing system only, and related to what the control unit tells it. Even if it fails, the system defaults to "normal" braking. The dealership can tell what is happening with the ABS with a DRBIII, and can activate all the valves and pump to determine if it is working correctly, and can tell if there are any faults in the controller that would have activated the system and caused a failure.
Basically, tere is nothing in the ABS portion of the system that can cause hydraulic pressure failure.
The only system parts that can cause that, are the master or wheel cylinders, and the physical brake lines.
So the first thing to check is the master cylinder.
place your foot on the brake pedal very lightly, with barely and weight or pressure.
The pedal should remain solid, and not move, even over a period of time, say 1 or 2 mins.
If it even slightly moves, the master cylinder has an internal leak, and should be replaced. You may need to try this several times, and at various brake pressures: press the brakes hard, to about 1/2 way, then keeping the pedal there, gently release the foot pressure, and see if the pedal drops. Try this in several spots in the travel.
The reason, is that there may be a bad spot in the cylinder bore, and you don't always press the pedal to that exact spot every time.
If you can press the pedal hard and maintain a hard pressure, but the pedal slowly goes down, and you tend to have a slight fluid loss over time, then you need to look for a leak in the rest of the system, such as rusted lines under the body, You only need a very tiny pin-hole to allow fluid to seep out, and possibly suck air in to have the failure of the brake circuit. Again, the question #1 is important, by looking at which wheel bleeder if any is showing bubbles. That narrows it to that line or wheel cylinder.

First places to start anyway.
 

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Discussion Starter #9
Thanks - i'll try bleeding them tomorrow. To be honest, I've been taking it to the shop because I've been so frustrated with it. The Dealer said the ABS pump was bad and needed to be replaced. They hit me for over $600 for parts and then labor on top of that. i think it came to $1,100 or close to that.

Your description of the master cylinder bore inconsistence makes a lot of sense. It doesn't seem like I'm losing any fluid, but I will try bleeding to see if there is air. if no air, then I'll replace the master cylinder.
 

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Thanks - i'll try bleeding them tomorrow. To be honest, I've been taking it to the shop because I've been so frustrated with it. The Dealer said the ABS pump was bad and needed to be replaced. They hit me for over $600 for parts and then labor on top of that. i think it came to $1,100 or close to that.

Your description of the master cylinder bore inconsistence makes a lot of sense. It doesn't seem like I'm losing any fluid, but I will try bleeding to see if there is air. if no air, then I'll replace the master cylinder.
try the light pressure first.
While they may have been correct that the pump and or controller were bad, that would not - in all probability - have any bearing on the loss of hydraulic pressure in itself. The only thing in the system that can change the pressure is the pump, and it is there to increase the overall pressure, not decrease it.
BTW there is no way that the proportioning valve could cause no peddle. It is purely there to limit the amount of pressure applied to the rear brakes, compared to the front for any given pressure applied.
It could not, in any way cause a total lack of hydraulic pressure, short of leaking.
One other small item, there are 3 master cylinders that could be on your van, and if the wrong one has been installed, it is possible to be causing a problem, according to the FSM I have.
It shouldn't cause a lack of hydraullic pressure, but it is remotely possible that using the wrong one depending on whether or not you have traction control could cause a problem.
 

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Discussion Starter #11
last master cylinder change I did ask for the one for traction control. My assumption is that they gave me the correct one - is there an obviouc difference between the three?

Light pedal pressure yeilded good results. The pedal stays in place - doesn't sink or fade. Interesting thing I noticed though - after the pressure test I applied the emergency brake. The pedal travels about 1/2 as far as when not applied. my theory at the moment is that the rear adjusters are not functioning properly. I'm going to manually adjust the rears (drum brakes) a little later this morning to see if it helps.

Thanks!
Doug
 
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