motorbyclist
3rd December 2007, 00:11
today i had to put a new reservoir/master cylinder (single unit) on a dirtbike and did it "my way", and had it done in no time with no bubbles and little spillage.
meanwhile my mate was doing his bike after replacing the banjo copper washers and did it "his way" and after 15 minutes gave up.
i know my brother does it another way again!
how do you guys do it? i'm pretty sure my way is wrong, because it's too easy.
my way:
summary: use big syringe to squirt fluid from caliper up to reservoir - bubbles flow out naturally, different colour fluid to old stuff shows when you're done
detailed method with explanation below;
get a big syringe (approx 60-90ml, must be more than the surprisingly small volume of your brake line - standard equipment on a farm, pays to flush/rinse with fluid first) and an inch of clear, soft plastic tube (maybe 4mm id, fits and seals onto nipple on caliper perfectly). put the plastic tube on the end of syringe.
first i duct tape an ice-cream container so it's hanging under the reservoir, then move the bars/bike/reservoir so the brake line is all uphill - logic being the bubbles will flow out easily.
open the reservoir lid.
open the valve on the nipple on the caliper just to free her up and give a little squirt to clean out any grit in nipple that is already as clean as possible.
Fill syringe from bottle of fresh brake fluid, put the tube/syringe onto the nipple and open the valve - don't bother sucking the bubbles out.
make sure the syringe is held so fresh bubbles are not going to go into the brake line and then squeeze.
the brake fluid flows back up the brake line, carrying the bubbles with it, through the open valves on the master cylinder and into the reservoir, which then overflows into the ice-cream container. if you can watch it (i use a mirror) you can see any bubbles coming out, and if you're clever you're using a different colour brake fluid to your old stuff so when the new colour overflows the reservoir you know you're sweet.
close nipple valve, pull syringe off, then use syringe to suck excess from reservoir. put lid on reservoir, test brakes, and if all's good clean up. i recommend squirting everything with detergent and hosing off as i've run an experiment and can confidently say that brake fluid is an effective paint stripper
i'm concerned that if there's any crap in my nipple that i don't clean out (partly why i give a bit of a squirt before starting) i'll simply pump it up into my master cylinder valves - but i hasn't happened yet.
biggest spill i had was accidentally squirting the ceiling with my syringe and having fluid rain down on my other bikes:doh:
his way:
put long, clear tube on nipple valve and run into a receiver bottle/pan. open lid on reservoir and top up with fresh fluid.
now alternating between brake lever and nipple valve, manually pump the fluid through the system top down, against the natural flow of the bubbles, and watch bubbles flow through the tube into the receiver. remember to top up reservoir.
he pumped like this for 15 minutes and never saw an end to the bubbles, so gave up. apparently his way was "what the internet said" - he probably should have used a different colour fluid to see when he had flushed through
brother's way:
identical setup to my way, but instead of squirting the syringe he sucks the fluid down the system, and has to top up the reservoir. he had a lot of trouble with bubbles, wasted about 250ml of fluid and eventually gave up & got dad to do it - and i dunno how dad did it but it worked
SO, how do you guys do it?
i like my way as the bubbles run straight out, but i don't know what the risk of contamination is, and suspect my mate or my brother had the correct method executed poorly. although, if you keep a rubber cap on the caliper nipple i think my way is reasonably safe.... then again, the first thing i always do upon opening a reservoir is drop the lid, inside face down of course, onto some dust/grit/sand on the floor, so i probably get shit in the reservoir anyway<_<
meanwhile my mate was doing his bike after replacing the banjo copper washers and did it "his way" and after 15 minutes gave up.
i know my brother does it another way again!
how do you guys do it? i'm pretty sure my way is wrong, because it's too easy.
my way:
summary: use big syringe to squirt fluid from caliper up to reservoir - bubbles flow out naturally, different colour fluid to old stuff shows when you're done
detailed method with explanation below;
get a big syringe (approx 60-90ml, must be more than the surprisingly small volume of your brake line - standard equipment on a farm, pays to flush/rinse with fluid first) and an inch of clear, soft plastic tube (maybe 4mm id, fits and seals onto nipple on caliper perfectly). put the plastic tube on the end of syringe.
first i duct tape an ice-cream container so it's hanging under the reservoir, then move the bars/bike/reservoir so the brake line is all uphill - logic being the bubbles will flow out easily.
open the reservoir lid.
open the valve on the nipple on the caliper just to free her up and give a little squirt to clean out any grit in nipple that is already as clean as possible.
Fill syringe from bottle of fresh brake fluid, put the tube/syringe onto the nipple and open the valve - don't bother sucking the bubbles out.
make sure the syringe is held so fresh bubbles are not going to go into the brake line and then squeeze.
the brake fluid flows back up the brake line, carrying the bubbles with it, through the open valves on the master cylinder and into the reservoir, which then overflows into the ice-cream container. if you can watch it (i use a mirror) you can see any bubbles coming out, and if you're clever you're using a different colour brake fluid to your old stuff so when the new colour overflows the reservoir you know you're sweet.
close nipple valve, pull syringe off, then use syringe to suck excess from reservoir. put lid on reservoir, test brakes, and if all's good clean up. i recommend squirting everything with detergent and hosing off as i've run an experiment and can confidently say that brake fluid is an effective paint stripper
i'm concerned that if there's any crap in my nipple that i don't clean out (partly why i give a bit of a squirt before starting) i'll simply pump it up into my master cylinder valves - but i hasn't happened yet.
biggest spill i had was accidentally squirting the ceiling with my syringe and having fluid rain down on my other bikes:doh:
his way:
put long, clear tube on nipple valve and run into a receiver bottle/pan. open lid on reservoir and top up with fresh fluid.
now alternating between brake lever and nipple valve, manually pump the fluid through the system top down, against the natural flow of the bubbles, and watch bubbles flow through the tube into the receiver. remember to top up reservoir.
he pumped like this for 15 minutes and never saw an end to the bubbles, so gave up. apparently his way was "what the internet said" - he probably should have used a different colour fluid to see when he had flushed through
brother's way:
identical setup to my way, but instead of squirting the syringe he sucks the fluid down the system, and has to top up the reservoir. he had a lot of trouble with bubbles, wasted about 250ml of fluid and eventually gave up & got dad to do it - and i dunno how dad did it but it worked
SO, how do you guys do it?
i like my way as the bubbles run straight out, but i don't know what the risk of contamination is, and suspect my mate or my brother had the correct method executed poorly. although, if you keep a rubber cap on the caliper nipple i think my way is reasonably safe.... then again, the first thing i always do upon opening a reservoir is drop the lid, inside face down of course, onto some dust/grit/sand on the floor, so i probably get shit in the reservoir anyway<_<