The brakes were not that firm before the rear brake job

CPELLA

MEMBER
2016 VOLKSWAGEN JETTA
1.4L
4 CYL
2WD
AUTOMATIC
53,000 MILES

I replaced the rear calipers, rotors, and brake pads. I bled the brakes by having someone press the brakes and me open and close the bleeder screw, then took it to a mechanic to bleed the lines. However, the brake pedal travels to the floor as in no pressure (like it did when I bled the lines). If I pump the brakes, there is some pressure, but the pedal travels to the floor again. I think there is either air in the master cylinder or the master cylinder is bad. Is there a way to bleed the master cylinder while it is on the car or should it be bench bled? Or is there way to test the master cylinder to see if it is bad? The brakes were not that firm before the rear brake job, so I am thinking it might be the master cylinder. Any thoughts?

6 Replies

KASEKENNY

MECHANIC
18,907 POSTS

I agree that this could be the master cylinder. The way to confirm this is blocking the ports of the master cylinder and press the brakes. If the pedal still goes to the floor then it is the master cylinder because everything else in the system is disconnected.

Clearly there could still be air in the lines but the fact that it seemed like it was starting before this replacement I would chase the master cylinder down before anything else.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

The only thing that gives me pause is the year of the vehicle. A master cylinder is rare to fail this early so we need to cap the lines and test it just to make sure.

Let me know what you find and we can go from there or if you have questions.

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Wednesday, June 3rd, 2020 AT 6:10 PM

CPELLA

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4 POSTS

Thanks for the answer! Would the brake master cylinder need to be bench bled before being put on the car? It looks like the reservoir would be in the way of a tap to tighten it to the car if it did need to be bench bled. Thank you again!

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Saturday, June 6th, 2020 AT 6:16 AM

DANNY L

MECHANIC
5,648 POSTS

Hello, I'm Danny.

Just to jump in here. Yes, it's always a great idea to bench bleed a master cylinder before installing. Usually the master cylinder when purchased will come with a paper instruction guide on how to do it with a screwdriver or punch on your work station or table. When it comes time to bleed brake calipers after installation just remember to start with the one farthest away and work forward. Right rear, left rear, right front, left front and always keep the master cylinder full of fluid to not suck any air back into the system. Keep us updated and let us know if you have any further questions about this. Hope this helps and thanks again for using 2CarPros.

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Saturday, June 6th, 2020 AT 11:37 PM

CPELLA

MEMBER
4 POSTS

Thanks for all the assistance! I replaced the master cylinder. Bench bled it before installing and bled all lines. The pedal was firm for a few times, but now it goes to the floor without much resistance. The old master cylinder did seem to not have much resistance as I tested it off the car. What would be the reason (or reasons) for the lack of firmness of the brake pedal?

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Sunday, June 21st, 2020 AT 11:37 AM

CPELLA

MEMBER
4 POSTS

More info: No leaks from what I can tell. I could not tell if it was leaking between the reservoir and the master cylinder though. It was low on brake fluid. Thank you for any assistance!