BRAKE PROBLEM

[StephanieG]

Hi...bought 1985 T25 camper a few weeks ago. Everything was good, then yesterday after about 60miles I noticed it was squeeking on the nearside when I touched the brakes. Then about 10miles from home I went to brake and the pedal went all the way down and didn't appear to slow down at all. By pumping the brake pedal I managed to get home safely! I checked the brake fluid and there's plenty in there. Does anyone have any idea whats happened? or how to fix it?

[andyb]

front or back brake? could be caliper on front. fraid youll need to strip em down and check.

[StephanieG]

Thank you...Think its the back, and as I limped home I'm sure the offside started squeaking too! would that cause the pedal to go soft?

[mrdp]

If the caliper is squeeking it could be rubbing and this will cause heat on discs and pads that can transfer to the fluid. maybe the fluid got very hot and caused brake fade which reduces the efficency of the brakes.Probably take out both sets of pads and generally clean the caliper and make sure the pistons slide properly ie that they're not siezed. Also check that there are not fluid leaks both front and back ( Squeeze the gaitors/dust seals to be sure, as fluid can collect in these)Hope this helps

[kevtherev]

cheap pads cause squealing brakes
lack of brake gease on the reverse of the pad
seized piston in the caliper, (again squeal)
the lack of pedal is the master cylinder seal failure.
After twenty years the fluid is shagged.. time to replace it

[StephanieG]

Lovely...thanks for you help

[California Dreamin]

The technical explaination for this phenomenon is called 'vapour lock' this is where some of the heat generated by the brakes is conducted (transfered) via the brake pads and pistons to the brake fluid. DOT 4 brake fluid has a minimum (dry) boiling point of 230 degrees C. Once the temperature reaches or exceeds this the fluid boils.
Basic science dictates that fluids don't compress where as gasses do.
Boiling fluid produces gas bubbles that no longer transfer the fluid pressure to operate the pistons/brake pads...effectively the brake pedal goes to the floor as the gas in the fluid compresses.

Your symptoms certainly sound like vapour lock, possibly due to a partially seizing brake caliper (fairly common for these aging buses) creating the excess heat that leads to the fluid boiling.

Also: DOT 4 brake fluid has an undesireable property, it is 'hygroscopic'. It basically absorbs water from the air around it (even when contained in a sealed system), and because water boils at 100C, any contamination of the brake fluid by water lowers the 'brake fluids' boiling point.(which as we have discovered is not a good thing).
Therefore, brake fluid MUST be changed every two years irrespective of mileage, to minimise water contamination.
FYI: Just 3% water contamination lowers brake fluid boiling point by 100 degrees......!!! water contamination also leads to corroded internal brake components.
Martin