Rubber cup inside clutch master cylinder - JeepForum.com
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post #1 of 16 Old 06-13-2021, 09:17 AM Thread Starter
YMFriday
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Rubber cup inside clutch master cylinder

So, I went to check the fluid level in my clutch master cylinder, and when I took the cap of there seems to be a rubber cup inside that looked to be popping up a little bit. I have the original Chrysler service manual & it tells you how to check the fluid level, but it makes no mention of that little rubber cup. I donít want to touch it and risk any sort of contamination unless I know for sure that I need to lift that out to check the level. But when I removed the cap, I didnít see any fluid at all. Do I need to move it to check the level?

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post #2 of 16 Old 06-13-2021, 12:42 PM
timatoe
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I'm confused by your description. The rubber is in the cap or the reservoir? There should be a rubber seal with a "bubble" type end on the cap and that's pretty common to be bulged out if the fluid is low. If it's in the reservoir, it's likely been sucked out of the cap. You're not going to contaminate anything unless your hands are covered in sand or something. You really shouldn't need to pull the cap to see the fluid level.

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post #3 of 16 Old 06-13-2021, 03:38 PM Thread Starter
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It’s in the cylinder. How would I check the level without removing the cap? It’s metal, not transparent plastic. Based on your answer, it sounds like I’ll need to remove it to check the level.
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post #4 of 16 Old 06-13-2021, 05:51 PM
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It should be rubber. Mine was missing and my local AutoZone had a Dorman product that dropped right in. I don't remember the part number.
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post #5 of 16 Old 06-15-2021, 12:56 AM
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A picture would probably help a lot.
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post #6 of 16 Old 06-15-2021, 04:57 AM
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There appears to be a part number in the center of the part. I think it's in the first picture.
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20210615_065344_1623754545625.jpg   20210615_065350_1623754562793.jpg  
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post #7 of 16 Old 06-15-2021, 05:11 AM
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Thats an insert that should be in the cap. Looks like it fell out. Pull it out and see if it will pop back up in the cap. If the gets sucked against the fluid port itll make your clutch act all kinds of crazy.
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post #8 of 16 Old 06-15-2021, 05:38 AM
JarheadAl
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Siva, you are correct. Mine doesn't snap into the cap, it's a little small but it works. I removed it to show the OP what he should looking for.
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post #9 of 16 Old 06-15-2021, 06:52 AM
Delta0
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I suspect it's a one way valve that restricts the amount of air getting into your M/c.
I believe it's bulge gets bigger and smaller as the temperature, and therefore the volume of juice in the reservoir, changes.

If you look closely, I expect you will find a small slit in the rubber.

As folks have said, that rubber dubry needs to be a tight fit in the cap.

Last edited by Delta0; 06-15-2021 at 07:08 AM.
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post #10 of 16 Old 06-16-2021, 11:10 AM
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Yes, this rubber bladder like device is an attempt to allow temperature based expansion and contraction of fluid while controlling the vapor space. The design is for keeping the air and humidity from passing moisture to the hygroscopic brake fluid
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post #11 of 16 Old 06-16-2021, 11:20 AM
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Quote:
Originally Posted by JarheadAl View Post
Siva, you are correct. Mine doesn't snap into the cap, it's a little small but it works. I removed it to show the OP what he should looking for.
I have two caps.
The one that came with the car, and one to use as a pressure bleed cap.

In both instances the caps fitted tightly enough to make getting them out challenging.

May I suggest you suck the old fluid out, and replace it it new fluid as soon as you can?

I'm concerned that the juice in the reservoir may be contaminated.

If it were mine, I change all the brake juice.
If you wish to know how to change all the brake juice, just ask.
I'm a bit more precious about changing juice than most Brits.

Last edited by Delta0; 06-17-2021 at 01:45 PM.
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post #12 of 16 Old 06-17-2021, 06:39 AM
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Quote:
Originally Posted by JarheadAl View Post
Siva, you are correct. Mine doesn't snap into the cap, it's a little small but it works. I removed it to show the OP what he should looking for.
Doah thats what I get for skimming and missing that you werent the OP.
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post #13 of 16 Old 06-19-2021, 06:50 PM
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Quote:
Originally Posted by Delta0 View Post
Quote:
Originally Posted by JarheadAl View Post
Siva, you are correct. Mine doesn't snap into the cap, it's a little small but it works. I removed it to show the OP what he should looking for.
I have two caps.
The one that came with the car, and one to use as a pressure bleed cap.

In both instances the caps fitted tightly enough to make getting them out challenging.

May I suggest you suck the old fluid out, and replace it it new fluid as soon as you can?

I'm concerned that the juice in the reservoir may be contaminated.

If it were mine, I change all the brake juice.
If you wish to know how to change all the brake juice, just ask.
I'm a bit more precious about changing juice than most Brits.
What are the signs of contaminated fluid?
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post #14 of 16 Old 06-20-2021, 01:37 PM
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Quote:
Originally Posted by JarheadAl View Post
What are the signs of contaminated fluid?
Swollen rubber seals is the only damage I've seen.

I doubt if your shrunken seal is from contamination.
However, I'd change fluid if it were mine.

I think I would take the reservoir and M/c out including the pipe to the ABS pump and flush those parts through very thoroughly at the very least.

Sorry
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post #15 of 16 Old 06-20-2021, 02:40 PM
JarheadAl
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Delta0,
Thanks for the info. My seal hasn't shrunk. It just is a tad too small. It won't snap into the cap but it doesseal the MC. I couldn't find the exact part I needed and this was the closest in size the parts store had.
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