Need help with troubleshooting a brake system problem....?

Question

I have a 1988 Dodge Dynasty 3.0L V6 that I have replaced every piece of the brake system on and yet it won't bleed correctly, and we can't find a leak. In December 2005, I was driving it and the pedel started to get mushier and mushier the cloder I got to home and by the time I got home, I almost wasn't able to stop when pulling into my parking stall. My husband, who is a mechanic, seen that the master cylinder was leaking and replaced it, then bench bled it, my brake pads and shoes also needed replacement, so we figured while it was parked to do that as well. Then after replacing the pads and shoes, we couldn't get it to bleed at the wheel, and I had a bleeder valve that was shot so we replaced that, then it was like dominoes, everything we replaced, we thought would be the last thing and then my car would work. So, altogether we replaced these things:
Master Cylinder
Brake Pads
Brake Shoes
Front Bleeder Valves
Front Calipers
Rear Wheel Cylinders
Brake Booster
ALL the lines

What else could it be? Could one of these parts be the problem, should I try taking something back and getting it from a diffferent store? HELP, we even bled them the way that the Haynes manual says to, by doing a criss cross pattern, with engine off, until no bubbles come out. No matter how long we work at it, when the car gets turned on, the pedal goes straight to the floor.

Answer 1

When you say you couldn't get it to bleed do you mean that no fluid comes out of the bleeder? Or, are you just not getting any bubbles or any appearance of air? In either case it is possible that you have a faulty master cylinder. Did you install a reman or a new one? Reman is usually good as I have probably installed about 500 + of them but I have had my share of defective ones. Just because you have no bubbles (if that's the case) coming from the bleeder doesn't mean anything. The master can be leaking internally which will not produce air, it just allows the pressurized fluid to escape and return to the system thus making no braking pressure. You will not be able to detect this while bench bleeding. One thing to remember is that I am pretty sure this is an aluminum master. If it is reman it could have scoring in the cylinder bore that was not detected therefore it was rebuilt and sent out as usual. About the only thing you can do is try another one. If it turns out that this is the problem you shouldn't have any problem with the warranty.
One the other hand. If you are not getting fluid out of the bleeders, as previously mentioned, it is possible that the proportioning valve is defective. That is kind of a rarity, you don't see it happen very often but it's not impossible. Good luck

Answer 2

Here are several things you can check.
Check to see if the vaccuum booster is holding vaccuum. Start car and let run a few minute to build pressure. Turn off motor and listen under hood for a vaccuum hiss. If nothing heard find the hose leading to booster and pull the connector out of the the booster. the connector is a one way valve that keeps vaccuum from leaking out. You should hear a hiss when taken out.
If that is ok replace the connector and then recheck all wheels to make sure all springs / retaining clips / ect. are still in place. A loose return spring or hold down clip can also cause the problem you described. ( I think that year Dynasty still had rear drum brakes.)
If that checks ok then most likley its air or other contaminents in the hydralic system. Since you had entire system open its a good idea to have the whole system pressure bleed at brake service shop. Make sure they run enough fluid throug to replace entire system volume.
Hope this helps.
FYI I worked on a Dynasty about that same year. Watch the fuel rail on the fuel injector system it tends to leak at joints between the two sides.
Hope this is helpful.

Answer 3

Do you know if your car has a vacuum brake booster? My GM truck had one, and it went bad twice. When this happens it's usually accompanied by a hissing sound as air makes it's way into the system. Over time the increasing loss of vacuum can even affect engine performance when braking.

As a last resort, even though you're proud of your husband's abilities, take it to a mechanic and get a second opinion. In the long run it will be better than throwing good money after bad.

Answer 4

what about the proportioning valve I don't know it is just an idea. Also maybe you could buy a cap or something to take off both rear wheel lines and cap them. After that try to use your brakes if they all of a sudden start to work then you will know that is something to do with the rear brakes. Keep me posted.

Answer 5

one of your wheels has the caliper hung up where the brake pads are actually stuck against the rotor put the front up in the air and see if you can turn the wheels by hand if you can then put the back up and check those one of the 4 will not turn by hand when doing the front make sure you put the tranny in neutral B.

Answer 6

If you have tried all that stuff....check under the dash,at the brake pedal...there is a rod..some are adjustable,some are not or it may be wore out.

Answer 7

if you did all of this and theres no fluid leakage then you have a faulty master cylinder and needs to be replaced again..

Answer 8

sound,s like you got a defective master cylinder............also check your proportioning valve..............try borrowing a power bleeder............you must have a lot of air in your system.