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      11-09-2013, 09:37 AM   #11
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Originally Posted by Orb View Post
This is a good post in this section but needs some clarifications. If you replacing the check valve house assembly it will be a good idea to replace the seal. The method from “PhaseP” works well if you are creative in rigging up an installation tool for the seal.

There is nothing wrong with the seal design but a better design could have been used. The sealing takes place in the radial grove of the grommet and brake booster when the check valve is inserted in the seal. The compression of seal is about 30% so comments about the size problem excreta are not valid. The real sealing problem in this area is caused by containments on the sealing surface or poor surface finish on the brake booster with latter not being that common.

The most important step in replacing the seal is to clean the brake booster sealing surfaces with Isotropic alcohol and make sure you do a good job. The reason you need to do this is all seal material will leave a film on the sealing surface due to material loss which can causes leaks ( happens with any vacuum system). If you miss this step and you are likely to have problems.

There are two solutions to this problem. I would recommend using silicon grease (or vacuum grease). Apply a thin film (.05 – 0.1 mm thick) on grease inside the grommet sealing grove (3 surfaces), the lead-in chamfer of the seal to aid insertion, and the inside diameter of the seal where the hose barb is inserted. This is well know and typically done when working with any vacuum sealing system. The alternative is to use a silicon RTV sealant. Use only a thin film (0.05 mm thick) of RTV on the radial part of the seal grommet grove. Once the seal is inserted the silicon will spread on all sealing surfaces. If you use to much you risk getting pieces of the RTV getting sucked into vacuum pump. I would not recommend the RTV method unless there is no choice.

If you have replaced the check valve hose assembly and experience random hard brake pedal then you likely have a slow leak somewhere else in the system. The check valve in the brake booster is designed to holder higher vacuum than the rest of the system when the car is turned off. In other word, if you turn off the car then you should be holding about 28 hg in the brake booster and 16 hg past the check valve. If there is a leak past the check valve and the system leaks down to atmosphere pressure, then the check valve in brake booster will leak down significantly and you will have various degrees of a hard brake pedal. If you do have a slow leak in your system you will typically hear the waste gate rattle at start up that last more than 2 seconds since the vacuum has leaked done to atmosphere pressure and it take a while for the system build up a vacuum which can take 5-20 seconds. There should be no rattle of the waste gates at start up if the system is healthy.

To check for leaks you need a hand vacuum pump and gauge then you will be able to identify which component is the problem. Check all tubing individually for leaks. The list below is typical issues with this car:

• Two vacuum canisters. They should hold 30 hg more than hour when tested discretely.

• The two vacuum lines behind the oil filter housing will leak after time (replace every 3-4 years). Mine had a very slow leak.

• The waste gate pressure converters tend to leak randomly on pre 09 cars. Mine needed to replace although I had no issues with the car.

In my case, I had to replace 50% vacuum lines, check valve hose assembly + seal and the pressure coveters to fix the hard brake pedal problem.
Wow! Much of what you said just doesn’t make sense. Contaminants will not factor in as long as there is a tight seal. If contaminant build up is an issue here, it’s only because an under designed (loose fitting) grommet has allowed that kind of environment to exist. Your quick fix solution by applying grease or RTV sealant defeats your own argument. For this application, these products should not have to be used if the seal is tight. I’ve never had to do this on any of my other my other vehicles that I’ve owned through the years. Your suggestion of using these products is an admission that there is a problem with the rubber grommet. You also mentioned brake booster surface finish. The hard brake issue on these vehicles appears later on during ownership. A poor factory finish would have caused this problem to occur much sooner. You stated something about a 30% seal compression without any supporting data and then promptly used this to shoot down my argument. Not very compelling I have to say. Your compression figure is irrelevant especially if you haven’t taken sample measurements of any kind. The Test portion of the DIY performed on my vehicle proves that the slightest displacement of the grommet can break the vacuum within the housing. Unless the area of concern is remedied by a properly sized grommet being compressed by the barbed check valve forming a proper seal between its “radial” groove and the opening in the brake boost housing, this problem will continue to exist. I contend that the circumferential tolerance of the groove is just under which is minimally acceptable which is why only a few vehicles have experienced the leakage. Temperature variations over time, vibration and grommet shrinkage are more likely the factors which aid in initiating the problem, not contaminants or booster surface condition.

Again I have to call you out on your comments about leaks in other parts of the system that rely on a vacuum and how they can affect brake booster vacuum. Your arguments on this are basic nonsense. The check valve at the brake booster is designed to hold the 28hg no matter what happens in the event of vacuum loss in other parts of the system of lines otherwise the entire braking system would be compromised in the event of a catastrophic engine malfunction. A proper check valve (with proper rubber grommet) will continue to maintain the vacuum in the booster even with atmospheric pressure at sea level in the vacuum system lines.

I can’t imagine why someone would try to blame waste gate rattle for brake vacuum loss. IDK, maybe there’s some cryptic details that I’m missing in here.