Changed my servo last week as was told by the RAC that it has failed. No feel in the pedal and had to pump to get it to brake. Today when driving with a replacement servo the same thing happened no feel in brake after driving for 20 minutes and had to pump the pedal to stop. Called RAC who suggested I call into the garage just down the road as he suspected air in the system and needed to bleed the brakes. Fella in the garage said the brake fluid was hot and suspect another reason for this happening. He couldnt fix it and advised driving home after allowing it to cool. Again after 20 minutes driving the brake went and suspect that the fluid had heated up again. Any ideas what caused this?, I have checked the hoses, but could the master cylinder be cooked?
Brake issues - hot brake fluid
- Thread starter Gar
- Start date
Help Support Early Bay Forum:
Sticking calipers or incorrectly adjusted brake shoes can cause the fluid to overheat, along with an incorrectly adjusted servo pushrod.?
A failed servo wont actually affect the brakes, it just means you'll lose the assistance in braking pressure and will need to use more leg work instead. Maybe the mechanic was referring to the master cylinder? A quick way to check this is to push down hard on the pedal whilst stationary and seeing if the pedal slowly sinks to the floor. But as above, it sounds more like something is causing the fluid to heat up and the brakes begin to fail. This problem will be exaggerated by old fluid that has absorbed moisture over time.
As above, friction = heat - which is then transferred to the brake fluid - if you have ever seen a rally car at night you may have seen the brake discs glowing red hot under extreme braking - these guys use a high boiling point brake fluid to minimize brake "fade". To find out which brake is sticking the best thing to do is drive your bus a mile or so from a cold start, ideally not braking very much - then stop - jump out and feel which wheel hub is hottest - be careful as they can get very hot - you may have one or more wheel that's hotter so this will help pinpoint the problem. If it's both rears is the handbrake releasing properly ? If all four are hot then it's more likely that the servo rod is incorrectly adjusted. Hope that helps
BJ1
Well-known member
Had this issue with repro servos on a couple of buses. It's related to the adjustable pushrod INSIDE the servo, not the adjustment outside. I did a 'how to' for Schofields which is now on their website here
http://www.alanhschofield.com/ourparts/prod_3804516-Brake-Servo-Unit-7174-211611905.html
These servos are excellent when the internal pushrod is adjusted correctly. If not, the front brakes will drag producing the heat that's causing your problem.
You also need to bleed the system using a pressurised bleeder. The usual pedal pumping method won't get all the air out from Varga m/cylinders with the servo attached.
http://www.alanhschofield.com/ourparts/prod_3804516-Brake-Servo-Unit-7174-211611905.html
These servos are excellent when the internal pushrod is adjusted correctly. If not, the front brakes will drag producing the heat that's causing your problem.
You also need to bleed the system using a pressurised bleeder. The usual pedal pumping method won't get all the air out from Varga m/cylinders with the servo attached.
