# Diaphragm/rubber seal not staying in master cylinder reservoir cap.



## Snappa (Mar 31, 2013)

Earlier today I did a changing of my brake fluid as suggested. It was very dark brown. After changing it everything turned out great, however I have one concern. During the process of taking the cap to the reservoir off and on while bleeding the brake system, I noticed the black circular rubber seal that's usually retained in the top of the cap itself would get seated and stuck in the fill hole of the reservoir. I would have to proceed to pick at it and pull it out from its edges. It would be seated in there very flush and even though. So my question is, is this normal and if so why didn't it do it before? What is the correct operation of this? I've only removed the cap maybe 2 or 3 times prior to this and don't recall this ever happening. The rubber seal would stay stuck in the cap itself .


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## brian v (Dec 25, 2011)

Take a pic of this seal and post it up snappa . And then we can see what you think should look normal ..


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## Aussie (Sep 16, 2012)

I have found on other vehicles I have owned that it is easier to put the rubber seal over the open top of the container opening and then put the cap over it.


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## Snappa (Mar 31, 2013)

I will post a pic for you guys.


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## Snappa (Mar 31, 2013)

Sorry it took a while to get these pics up, but is this okay/normal?







i took a series of photos showing the cap itself, the rubber seal that usually stays inside of it as well as how not now says inside that master cylinder when i remove the cap instead of staying inside the cap.


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## Robby (Mar 1, 2013)

The rubber bellows is supposed to be retained in the cap, so this looks odd already.
It appears, in pic #3 you are installing it in the reservour upsidedown as well.
So, it goes in the cap with the wording visable to you.

The reason the bellows was sticking in the reservour was because as you were bleeding the system and drawing the fluid down you were creating a vacuum in the reservour, pulling the bellows down.

The purpose of the bellows is to take the place of the fluid as it is drawn down as the brakes wear and in so doing, creates a situation that keeps the fluid in the reservour from foaming over bumps and at brake pedal release.

Hope my response wasn't too confusing.
Rob


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## Snappa (Mar 31, 2013)

Each time I try to put it I'm the cap, it does not stay in or even come close. I just reversed it and I don't get a tight fit in the reservoir or cap with wording visible to me and it in the cap


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## Robby (Mar 1, 2013)

Stop by your dealer (or a repair shop if you have no warranty) for a minute.....they'll either exchange the cap or reseat the seal.
Brake fluid must be sealed or it draws moisture a ruins the fluid.

Rob


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## Snappa (Mar 31, 2013)

And according to this stock photo of where it is being sold online, the orientation I have it in on pic number 3 would be correct. The part of the rubber seal that sticks outward is visibility when it is in the cap, meaning when the cap is placed on the master cylinder the side with the wording or indented side would be facing up as in my photo. I've noticed it also makes a very tight seal facing that was also. I was just wondering why it doesn't stay in the cap.


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