Hi guys, Over the past few months I noticed that the effectiveness of the rear brake pedal had decreased to the stage where the pedal would travel its full range without slowing the bike at all. My MOT was close so I asked the garage to look at it. When I collected the bike they informed me that they had bled the rear brake and the effect was very noticeable. The pedal now barely moved at all before slowing the bike. However within 4 months of use the same problem had occurred: full travel with zero braking action, so I decided to bleed it myself. I bought a hand vacuum kit and Dot 4 fluid and just tried it myself. No matter how many times I closed the valve, topped-up the cylinder, pumped some vacuum pressure, opened the valve.....etc etc, the fluid NEVER ran through without loads of air in it. In all the videos I have watched, eventually they had fluid flowing through the tube without air, and I never had this. Do you think this is indicative of a larger problem? That somewhere there is a leak letting air into the system? Married with the fact that a successful bleed led to zero pressure within a few months suggests an issue. Thoughts please? Thanks as always. Martin
Hi martin have you tried the old school method with just abit of tube over nipple,apply pressure crack off until lever is down then lock off nipple then repeat. I have no luck using vacuum kits.
Agree with @Lifeofriley. Sometimes I just have to revert to the old method. Also how old is the replacement fluid you are using, and how have you stored it?
Just re-tried using the manual method and found it worked much much better. Successfully bled now. I expect the loss of pressure will still occur but for the interim, it’s sorted. Thanks guys
When I fitted my rear sets I had to install a pressure switch for the brake light, thus having to bleed it. After a few attempts I was getting nowhere, so I decided to unbolt the calliper and raised it above the level of the master cylinder letting the air travel up the pipe. With the calliper still in the same position I gave it another go, and after a few pumps ot the master cylinder it was job done. Do you know if the garage flushed out all of the old brake fluid? I’m assuming non ABS.
The problem you will be having with the vacuum bleeder is that it is pulling air in from around the bleed nipple thread as this doesn’t make an air tight seal, the bleed nipple only seals at the base when tightened. A good tip I’ve had is when you are at a point to bleed again take the bleed nipple all the way out and smear a small amount of gas jointing paste around the thread being careful not to get it at the sealing surface of the nipple. I did this with mine and now have no problem using my vacuum bleeder. I always remove the caliper and have it higher than the master cylinder to get the bubbles rising and just when you think you have all the air out give the master cylinder a few gentle taps with a rubber mallet, tap the banjo connections and finally a gentle tap of the caliper and you will see some more air, these bubbles generally get trapped around the back of the caliper pistons Check the new brake pressure before re fitting, put an old brake pad in between the brake pads so as not then needing to force the pistons back to refit over the disc Same procedure for the fronts This is the way I do it and have solid brakes every time
When you are doing the front's, what threadlock do you use if any, on the caliper mounting bolts? I'm guessing you dont replace the bolts every time as indicated in the service manual.
Hitch, Mine is a track bike only so the caliper are on and off all the time so I don’t use anything. On my road bike I use blue thread lock but only the smallest amount, when you do remove the caliper bolts the next time make sure to clean out all the dry thread lock before applying more. If you don’t remove it over time it will build up and it will make the bolt feel like it is cross threading, I have had a bolt snap before, not a caliper bolt, they go really tight on the old thread lock What ever you do do not use the red thread lock, this sets hard and you’ll have a great time trying to remove them after
If you do have problems with something threadlocked heat is the best thing and it has to be above 100 deg, use blow torch, lick finger quickly touch bolt if it hisses it is warm enough , do not think you can man it out half the time it will shear, ps dont burn your finger, better still get someone else to touch it
check out the post about brake nipple leaking. I too took the plunge & bought a vaccum kit and posted my comments on using it. The sir bubbles are very worrying at first specially as you get zero fluid out!! As gas mentioned, you need to put some sealant on the threat to staop air being sucked though. I used teflon tape. gas's is also a good alternative. The user manual also mentions grease
