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M3 Track: Racing and DE Best mod for speed is learning to get the most out of what you currently have. Tracks and DE's is the place to start!


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Old Mon, Feb-10-2020, 02:44:29 PM   #1
Drewster
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Default Brake reservoir won't hold pressure?

I got my Motive pressure bleeder out for the first time, and in doing a pressure test I noticed the system would get to ~15 PSI fine, but after a few minutes the gauge would slooowly drop down.

Is this normal? I was worried there was a leak, but I looked around the car, didn't see any drips, no dripping under the reservoir or inside at the clutch master.

Figured I would ask here since folks bleed their brakes more regularly.
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Old Mon, Feb-10-2020, 03:49:12 PM   #2
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Default Re: Brake reservoir won't hold pressure?

Sounds normal. Mine leaks somewhere at the cap or the Motive hoses, not the car's system. It holds enough to bleed without any issue though.
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Old Mon, Feb-10-2020, 04:52:15 PM   #3
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Default Re: Brake reservoir won't hold pressure?

Normal


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Old Mon, Feb-10-2020, 06:32:00 PM   #4
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Default Re: Brake reservoir won't hold pressure?

Check the O ring in the cap. Mine developed a crack in the O ring and did the same.
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Old Mon, Feb-10-2020, 06:33:59 PM   #5
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Default Re: Brake reservoir won't hold pressure?

What they said. Nothing to fix.
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Old Mon, Feb-10-2020, 09:33:12 PM   #6
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Default Re: Brake reservoir won't hold pressure?

Quote:
Originally Posted by Fastboy View Post
Check the O ring in the cap. Mine developed a crack in the O ring and did the same.
The cap is supplied by Motiv in this scenario

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Originally Posted by aeronaut View Post
What they said. Nothing to fix.
Thanks for the reassurance, guys! I'm excited to see if bleeding the ABS feels any different on track
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Old Tue, Feb-11-2020, 04:15:55 PM   #7
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Default Re: Brake reservoir won't hold pressure?

Mine usually holds well (long enough to bleed without repumping), but I left some fluid in it for a little too long and found that the flapper on the bottom of the pump started to fail. Cheap replacement from Motiv though.
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Old Thu, Feb-13-2020, 09:04:37 AM   #8
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Default Re: Brake reservoir won't hold pressure?

I experienced the same issue and it ended up being the inline hose connector between the main unit and the line connecting the cap. Not sure what specific setup you have. Mine was purchased through ECS and I opted for the aluminum cap which was a separate piece with its own hose and threaded connector that attached to the main units hose. If your is similar try using some nylon tape to make a better seal.
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Old Thu, Feb-13-2020, 06:18:23 PM   #9
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Default Re: Brake reservoir won't hold pressure?

Quote:
Originally Posted by duracellttu View Post
I experienced the same issue and it ended up being the inline hose connector between the main unit and the line connecting the cap. Not sure what specific setup you have. Mine was purchased through ECS and I opted for the aluminum cap which was a separate piece with its own hose and threaded connector that attached to the main units hose. If your is similar try using some nylon tape to make a better seal.
Yup. I did this job last night and that turned out to be the issue. During the "pressure test" there wasn't any hissing or anything, but while bleeding it would slowly weep out of that NPT fitting. I gave it some ugga-duggas and it helped quite a bit

Bleeding the ABS was super easy. I was concerned about how much fluid the process takes so I got 2L of SRF.. turns out I didn't need that second liter, but live and learn. Excited to see if this helps brake feel on the limit
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Old Thu, Feb-13-2020, 06:59:05 PM   #10
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Default Re: Brake reservoir won't hold pressure?

Quote:
Originally Posted by Drewster View Post
I got my Motive pressure bleeder out for the first time, and in doing a pressure test I noticed the system would get to ~15 PSI fine, but after a few minutes the gauge would slooowly drop down.

Is this normal? I was worried there was a leak, but I looked around the car, didn't see any drips, no dripping under the reservoir or inside at the clutch master.

Figured I would ask here since folks bleed their brakes more regularly.
I had an issue with the cap not sealing. Are you sure your reservoir is seated fully into the master?
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Are you feeling loose in the rear end currently?
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Discussing Brake reservoir won't hold pressure? in the M3 Track: Racing and DE Forum - Best mod for speed is learning to get the most out of what you currently have. Tracks and DE's is the place to start! at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)