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Dodge Repair/'99 minivan: Brake pedal soft/not holding


QUESTION: It appears that the vacuum hose is ok. I have two questions now:

While checking today, I noticed that, while the engine is running and transmission in P, if I pump the brake pedal, the rpm will go up by 100-200 rpm and then drop to normal idle rpm. Is it normal?

The last remaining item is the internal link in the master cylinder. I want to ask how critical it is in terms of safety to get it fixed. Can I wait a month or so?

Thanks again.

ANSWER: Hi Shafique,
Did you check both ends of the vacuum hose? If so and you found nothing unusual then I would say that it is not usual for use of the brake unit to cause a change in idle speed. I would wonder if there may be a vacuum leak inside the power brake unit itself. So if you continue to have the soft brake you described and this change of idle speed I would consider replacing the power brake unit.
I am not clear what you mean by internal "link" so I presume you mean internal "leak", which I suggested was a possibility for the soft pedal without a brake warning light coming on. Now in light of what you told me about the idle speed being affected by use of the brake, I would instead lean toward replacing the power brake unit, and see if that solves the soft pedal and the variable idle speed observation.
But do look at the clamps at both ends of the vacuum hose and also look for any cracks in the hose along its length. Absent any unusual findings, I would check out the price and availability of a replacement power brake unit. The master 'leak' is less likely to exist    so don't do that yet.
Thanks for the ratings and nominations. Please consider doing both one more time.

---------- FOLLOW-UP ----------

QUESTION: Thanks again.
Now, if you remember, I was having a intermittent shut down problem. ( about a month ago. I was out of town for two weeks so was not able to see if that problem really went. However, it is not! The bare wires on camshaft sensor that I taped may be a cause but not the only cause. This time, I am suspecting some sort of air flow problem or may be a vacuum leak is causing both the brake and shut down problems, is it possible?

ANSWER: Hi Shafique,
It is possible, so the one item to check would be the exhaust gas recirculation valve which is mounted at the right rear of the engine, underneath the throttle body. It is mounted sideways with a round vacuum hose-operated top, the body of the valve which is attached to the intake manifold, and between those two parts is a flange hidden inside of which is the valve stem. You will notice that it has a slot in valve stem which allows you to move the stem back and forth against spring-action in one direction which closes the valve. If the stem gets gummed up the valve may hang up ajar which then can cause stalling when slowing down to a stop or even when trying to start. So take a spray solvent and apply it to the valve stem where it enters the body and then use the tip of a screwdriver to move the stem back and forth to assure that it closes tightly by the spring action.
I am not sure how that would relate to brake spplication impact on idling however unless there was some sort of other vacuum line leak and the brake action just pushed the limit. So take a look at all the vacuum hoses that are attached to the intake manifold to be sure none are cracked or loose.

---------- FOLLOW-UP ----------

QUESTION: I need to clarify two items:

1) A spray solvent means something like the carb/throttle body cleaner?
2) Power brake unit is the same as Brake booster, am I right?

Yes that is correct on both of those items.
Do you have a vacuum gauge? You can run a test on the power brake unit before replacing it.
First though do this: with engine off, press on the brake pedal and release, several times. Then press lightly on the pedal (15 to 25 lbs of effort and then start the engine. Pedal will fall slightly and then require less effort to apply the pedal. Is that the case?
If so, then if you have a vacuum gauge and a "T" fitting that will allow you to connect the vacuum hose to both the booster and the gauge will tell you how to do a vacuum leak test.
If not, then disconnect vacuum line from booster unit and attach vacuum gauge. With engine at warm idle check the vacuum gauge reading. If the reading is 12 psi or more, then the check valve (the place where the vacuum hose attached to the booster or the booster itself may be leaking.

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Roland Finston


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