Emptying rear brake reservoir but no leak

[utogitorogi]

Good day!

Has anybody experienced this? Bike got serviced at dealership. They changed fluid and pads. After some time noticed the rear brake is a bit off. Opened the reservoir and it's empty. So topped it off checked for signs of leak (there was none) and everything was back to usual. Then again after some time (no data on milage or time) it's emty again. They used Motul in the dealership. I used Prestone Synthetic. Bike is used often in heavy city traffic.

 

[Kiwicol]

Since the dealer did the service on it, take it back to them & have them fix it. Brake fluid isn't thinners, it doesn't evaporate, it's going somewhere, have them sort it at their cost.

 

[rick danger]

Good day!

Has anybody experienced this? Bike got serviced at dealership. They changed fluid and pads. After some time noticed the rear brake is a bit off. Opened the reservoir and it's empty. So topped it off checked for signs of leak (there was none) and everything was back to usual. Then again after some time (no data on milage or time) it's emty again. They used Motul in the dealership. I used Prestone Synthetic. Bike is used often in heavy city traffic.

Probably just leaks when you use the brake. So it flies off as you're riding. Maybe put a paper towel under the bike where the banjos are , and put pressure on the pedal over night.....or just bring it back as said.

 

[atomsplitter]

Sealed systems don't suffer evaporation and the combined brakes would be putting brake fluid in the reservoir on your handlebar to empty the rear reservoir (not possible). So you have a leak or it's magic.

 

[stingray]

They are not sealed systems. Air is allowed in and out as the brake fluid moves to the calipers and back or there would be vacuum lock. That's why you get moisture contamination in your master cylinders. The front and rear master cylinders are separate and never comingle. There is no linked braking.

 

[Gregger]

They are not sealed systems. Air is allowed in and out as the brake fluid moves to the calipers and back or there would be vacuum lock. That's why you get moisture contamination in your master cylinders. The front and rear master cylinders are separate and never comingle. There is no linked braking.

Actually, for practical purposes they are sealed by a rubber diaphram which sits between the fluid and the cover. As the brake pads wear the fluid in the master cylinder reservoir is used, displacing the outward movement of the caliper pistons as they compensate for the pad wear. The diaphram deforms preventing air from entering the reservoir. Air can get in between the diaphram and the master cylinder cap but not under it unless it's torn or installed improperly.

Since brake fluid is hygroscopic, it actively absorbs moisture. I try to purchase only what I need to bleed the system. Any extra is thrown out if I'm going to store it for any length of time. Apparently this stuff can absorb moisture through the smallest openings.

 

[Kiwicol]

A brake fluid tester lets you know if the fluid needs changing or not & also if the stuff you're about to put in is still ok. Cheap peace of mind, had one of these for years now.

 

[utogitorogi]

Thanks fellows for the inputs. Been thinking there should be leak somewhere too. Currently suffering from a back injury so can't bend over that much, but I had a kid follow the hose. Says it goes towards and hides inbetween a plate and underside of the engine. Thinking the leak should be there then the fluid gets evaporated by the engine heat so no traces.

 

[Kiwicol]

Have you checked under the rear master? If the banjo or something else on the master was leaking, it'd drip onto the road and you wouldn't see any leak. Could well beat the master cyl and only when you pressurise the system, ie press the brake - hard.

 

[utogitorogi]

Have you checked under the rear master? If the banjo or something else on the master was leaking, it'd drip onto the road and you wouldn't see any leak. Could well beat the master cyl and only when you pressurise the system, ie press the brake - hard.

yup, checked the master and caliper. Didn't see sign of leakage there, dust are dry.