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Andrew Rey Babia Posted on Dec 01, 2015
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Low pressure on the rear side of the brake system

But the front side have high pressure.. is there a clogge in the system?

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Juan Castro

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  • Contributor 29 Answers
  • Posted on Dec 01, 2015
Juan Castro
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Hi Andrew,
As Ted previously said, you might want to take it to a brake shop if you're not comfortable with your brake repair knowledge.
However, if that's not the case; your car has a single piston rear brake caliper. First make sure that there are no leaks in the system. If you have never flushed your system, this would be a good time to do it any see if there are leaks anywhere. If there are no leaks, then your master cylinder could be the most likely problem. You can find one for $59.79 to $89.70 at rockauto (depending of whether you have dynamic stability control or not).
If you don't have a brake vacuum pump, I got mine at Harbor Freight for $39.99 (hopefully there's one near you) or you can order it online from them. MITYVAC - Item#39522

Good Luck

Testimonial: "thank you for your advice sir but i have another question sir that maybe you could answer. The brakes in front have good pressure but what i don't understand is why does the brakes in rear wont have enough pressure to function properly where there's no leak found."

  • Ted Maxwell Dec 02, 2015

    Hi Andrew:
    This is fun!
    Juan and I could have a great project with you.
    - There are two possible causes for the lack of desired performance of your rear brakes.
    - A "pressure" problem would originate at the master cylinder and be caused by a failed piston seal or low fluid.
    - A system with air in the cylinders or lines would feel "spongy" and the affected brakes would not receive the desired pressure.
    - A problem at the wheel would be associated with the slave cylinder and the brake pads.
    We would need to confirm that the slave cylinders are functioning properly, not restricted by grime or rust, and that the pads and disk have not been compromised in any manner. A problem with a slave cylinder is usually associated with brake fluid leakage.
    Please reply by comment to this post. No need to call me Sir, I'm 72 and if you call me Sir I start to feel old.
    Cheers.

  • Juan Castro Dec 02, 2015

    You're absolutely right Ted.
    Andrew should really start by changing the master cylinder and go from there.

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Ted Maxwell

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  • BMW Master 3,519 Answers
  • Posted on Dec 01, 2015
Ted Maxwell
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Hi Andrew:
Some brake systems have a double piston on the master cylinder. This is a safety feature that prevents total failure in the event that a component stops working.
I would recommend that you take it to a certified brake repair shop. Brake maintenance can be tricky, and if not done correctly can lead to nasty unwanted situations where your vehicle won't stop when you want it to.

Testimonial: "thank you for the help sir Ted!"

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