Stupid brakes question...

Author
Discussion

LennyM1984

Original Poster:

847 posts

82 months

Sunday 11th August 2024
quotequote all
You've been warned!

On a dual circuit brake system (no abs and in this case two separate master cylinders connected with a bias bar) if one circuit fails, the other circuit remains independent and can continue to operate.

However... When bleeding brakes, if you open a blender, you can pump the pedal (all the way to the floor) until all of the fluid in the reservoir has gone.

So... In the case of brake failure (let's say that a hose has ruptured) what is to stop the pedal going to the floor and all of the fluid pissing out? If this happened, would it not be the case that both circuits were just pumping air.

I know I'm being stupid here but I can't get my head around it

Kawasicki

13,762 posts

249 months

Sunday 11th August 2024
quotequote all
not a stupid question

There are two completely separate circuits. If you get a huge leak in one circuit it would no longer be able to provide braking power, and yes… if you kept pumping you would empty the reservoir. But an empty reservoir doesn’t stop the other circuit from functioning. The reservoir is there to keep the system filled with fluid as the pads wear and as temperature changes…

LennyM1984

Original Poster:

847 posts

82 months

Sunday 11th August 2024
quotequote all
Kawasicki said:
not a stupid question

There are two completely separate circuits. If you get a huge leak in one circuit it would no longer be able to provide braking power, and yes… if you kept pumping you would empty the reservoir. But an empty reservoir doesn’t stop the other circuit from functioning. The reservoir is there to keep the system filled with fluid as the pads wear and as temperature changes…
Thanks. I assume that the pedal would still go to the floor though, just that the pressure in the unaffected circuit would remain sufficient to hold the pads against the disc?

GreenV8S

30,784 posts

298 months

Sunday 11th August 2024
quotequote all
LennyM1984 said:
in this case two separate master cylinders connected with a bias bar
This setup is not common on production cars due to the cost and complexity, but if you have this setup it should be designed so the balance bar runs out of travel soon enough for the 'good' circuit to produce some braking.