Brakes Jamming Problem

[shivam wankhede]

Hi all
I am a member of Axlr8r Formula Racing, IIT Delhi.
In our last test run, we faced the following issue with our braking system :
After a smooth run of around 6-7 Km, rear calipers got jammed while engaged to the discs which brought the vehicle to a complete halt, killing the engine. After releasing the pressure by opening one of the bleed nipples, pistons retracted only to jam again after 2-3 Km.
We are using two master cylinders, one for each front and rear circuit and dual piston brake calipers.
With only 10 days remaining until we ship our car for FS India, we are in a critical situation and need help in understanding as to why this is happening and possible solutions. We have thought of cleaning the whole system using compressed air for now.

[Pete Marsh]

Check the master cylinder has free play when the brake pedal is at rest.

The master MUST be allowed to fully return, to allow the reservoir port to open and allow the pressure to return.

Pete

[smokebreak]

What type of fluid are you using? Is it possible that it could have been mixed with another type of fluid? Any rubber hoses (steel braided are rubber) could be swelling internally either from age or fluid contamination. If there is or could have been a fluid contamination then all rubber parts need to be replaced (lines, internal caliper and master cylinder seals). Good Luck!

[Pranav Tumkur]

The only thing which I can think of is over designed rear brake calipers. And using a master cylinder of the same bore diameter for the front and rear is not recommended.

[Kevin Hayward]

The only thing which I can think of is over designed rear brake calipers. And using a master cylinder of the same bore diameter for the front and rear is not recommended.

Pranav, why would you think that? I am quite a fan of the same bore for front and rear, no good reason why you cant have it that way, and then you can use one spare part for both masters.

...

I would be with Pete. Check that your brake pedal is able to fully retract and that the master cylinder has no force on it in that position. It is an easy mistake to make. In order to keep the brakes on in a way that will overcome the engines you are likely to have one of the following:

- Pressure still in the lines, likely cause being a misadjusted master cylinder, driver unable to keep foot away from the pedal, a stuck pedal, or a master cylinder port blockage

- Mechanical interference if some sort. This can be checked by visual inspection.

- Jammed brake piston. Should be able to check this one manually.

Kev