First line regarding brake bleeding in the BMW manual says:
"This description applies for brake filling and bleeding units with vacuum extraction"
Brakes again .......
- Thread starter ShakeyGS
- Start date
First line regarding brake bleeding in the BMW manual says:
"This description applies for brake filling and bleeding units with vacuum extraction"
Apologies for chipping in here - I am not a GS owner, but my motorcycle has a pretty complex braking system with linked brakes, proportional control valves, delay valves, secondary master cylinder and plenty of places where air likes to hide away.
Basically, you can go round the entire system with one way bleed valves or vacuum pumps and bleed it until no more bubbles come out of the bleed tube, and the brakes still feel spongey. As for pressure feeding, for my bike it is not advised due to the nature of the plumbing and the need to get rid of stale or contaminated fluid from all of the 'stagnant' areas. Pushing it against the flow doesn't work very well.
For vacuum bleeders, PTFE tape on the bleed valves threads is a must, but you can't completely stop the air from sucking past the threads. What you can do though, is get a good constant flow of fluid which leaves both hands free to help encourage the air traps to detach from the hose sides and the joints into the flow of fluid. Otherwise, quite large air bubbles will stay trapped. And they will not be where you might expect them to be.
Once happy the vacuum pump is not getting any more out, I go round with the one-way valve in a standard bleed tube, to be sure that no more tiny bubbles are in the system.
As for the air traps - I had a pretty good picture in my head of where these would be, and decided to write it up. I must have had a moment of inspiration, because I decided to check that what I had written was actually what happened inside the tube, and set up a simple experiment or two. One was blowing pressure into a container (by mouth) to force coloured water down the tube which had a join, and was taking a sinuous route to the waste container. The other was a simple n bend of clear tube, and I sucked the coloured water through from the other end. What I discovered, was not what I was expecting.
Watch the videos. Not that very large bubbles - not at the top of a bend, but in the vertical drops; in the bottom of a bend and attached to the joint in the tube - simply do not shift unless helped. Ditto, bubbles attached to the side of the tube. They need a flick with the finger, or a pretty sharp clout with a spanner.
Now I know what the bubbles do, I can chase them around the plumbing to the nearest bleed valve, and my brakes always feel rock solid.
Anyway, I think you might find them interesting. Note that in both videos, the fluid is flowing all of the time, although it looks to be stationary at times, it isn't.
Basically, you can go round the entire system with one way bleed valves or vacuum pumps and bleed it until no more bubbles come out of the bleed tube, and the brakes still feel spongey. As for pressure feeding, for my bike it is not advised due to the nature of the plumbing and the need to get rid of stale or contaminated fluid from all of the 'stagnant' areas. Pushing it against the flow doesn't work very well.
For vacuum bleeders, PTFE tape on the bleed valves threads is a must, but you can't completely stop the air from sucking past the threads. What you can do though, is get a good constant flow of fluid which leaves both hands free to help encourage the air traps to detach from the hose sides and the joints into the flow of fluid. Otherwise, quite large air bubbles will stay trapped. And they will not be where you might expect them to be.
Once happy the vacuum pump is not getting any more out, I go round with the one-way valve in a standard bleed tube, to be sure that no more tiny bubbles are in the system.
As for the air traps - I had a pretty good picture in my head of where these would be, and decided to write it up. I must have had a moment of inspiration, because I decided to check that what I had written was actually what happened inside the tube, and set up a simple experiment or two. One was blowing pressure into a container (by mouth) to force coloured water down the tube which had a join, and was taking a sinuous route to the waste container. The other was a simple n bend of clear tube, and I sucked the coloured water through from the other end. What I discovered, was not what I was expecting.
Watch the videos. Not that very large bubbles - not at the top of a bend, but in the vertical drops; in the bottom of a bend and attached to the joint in the tube - simply do not shift unless helped. Ditto, bubbles attached to the side of the tube. They need a flick with the finger, or a pretty sharp clout with a spanner.
Now I know what the bubbles do, I can chase them around the plumbing to the nearest bleed valve, and my brakes always feel rock solid.
Anyway, I think you might find them interesting. Note that in both videos, the fluid is flowing all of the time, although it looks to be stationary at times, it isn't.
I f you tried the experiment with tubing of the same I.D. as brake lines and used brake fluid the results would be rather different. Pipe diameter makes a big difference to fluid speed for a given flow rate and brake fluid does not have the suface tension of water and a different viscosity.
That’s right CPJS but whilst there is air in the system we’ll still have a wierd form of two phase flow and I think jfheath’s videos illustrate very nicely how easy it is to get air trapped in the system.
Update : it's definitely nothing to do with bleeding.
Use of front brake destroys the rear brake.
It's a linking issue.
You can test this yourself. Bleed. Get your rear pedal authority back. Go out and ride using only your rear brake. Rear brake does not go soft.
Then test using front brake. Immediately, rear brake fails.
Use of front brake destroys the rear brake.
It's a linking issue.
You can test this yourself. Bleed. Get your rear pedal authority back. Go out and ride using only your rear brake. Rear brake does not go soft.
Then test using front brake. Immediately, rear brake fails.
I think it shows what happens to water in an oversized pipe.
I think the best way to bleed the brakes would be with a positive pressure system fed via the reservoir with a replacement cover drilled with a tube attached to something like the gunnisons eezi bleed. The system could be bled with the bike running and the brakes being operated whilst a continuous flow of fluid being put through.
Of course non of this should be necessary, BMW have done nothing to address this in the 7 years of the LC GS.
I think the best way to bleed the brakes would be with a positive pressure system fed via the reservoir with a replacement cover drilled with a tube attached to something like the gunnisons eezi bleed. The system could be bled with the bike running and the brakes being operated whilst a continuous flow of fluid being put through.
Of course non of this should be necessary, BMW have done nothing to address this in the 7 years of the LC GS.
Today’s results / learnings
I learned a fair bit today.
1. The compressor driven vacuum bleeders are definitely the way to get results
2. PTFE tape on the bleed nipples is a MUST.
3. On the LC, the front right calliper bleed is already a non-return valve. If you completely remove the nipple nothing is lost from that side which is very helpful when you want to wrap PTFE tape around the nipple.
4. When everybody (and the procedure) tell you to retract the pads/pistons, DO IT
5. When someone gives you part numbers, it isn’t “looking a gift horse in the mouth” to check that they are right for your bike.
6. Ensure that the litre bottle of brake fluid you put on the floor doesn't get knocked over by the compressor hose moving as even if, like me, you’ve only bodged small holes in the foil, it makes a hell of a mess
7. When you buy a vacuum bleeder for nearly £40 because it’s a Sealey rather than a cheap ebay copy, it’s just possible (if you are me) that you’ve actaully bought two of them by mistake.
I was really surprised at how much air came out of the front brakes given that they’ve always been good
. I’m happy with my brakes now until I can get out and road test them.
I learned a fair bit today.
1. The compressor driven vacuum bleeders are definitely the way to get results
2. PTFE tape on the bleed nipples is a MUST.
3. On the LC, the front right calliper bleed is already a non-return valve. If you completely remove the nipple nothing is lost from that side which is very helpful when you want to wrap PTFE tape around the nipple.
4. When everybody (and the procedure) tell you to retract the pads/pistons, DO IT
5. When someone gives you part numbers, it isn’t “looking a gift horse in the mouth” to check that they are right for your bike.
6. Ensure that the litre bottle of brake fluid you put on the floor doesn't get knocked over by the compressor hose moving as even if, like me, you’ve only bodged small holes in the foil, it makes a hell of a mess
7. When you buy a vacuum bleeder for nearly £40 because it’s a Sealey rather than a cheap ebay copy, it’s just possible (if you are me) that you’ve actaully bought two of them by mistake.
I was really surprised at how much air came out of the front brakes given that they’ve always been good
. I’m happy with my brakes now until I can get out and road test them.Thanks, I'll look forward to seeing your demonstration !
If you think that it is irrelevant or wrong for the GS - please ask the moderators to delete it.
But - before I did the experiment with water, ink and wide pipes I used to find it difficult to get my brakes feeling solid.
And now I don't.
So it taught me something useful. I thought others might find it useful as well.
It's a discussion and I am glad you feel your experiment taught you something.
The wonderful thing about advice is, it is freely given and you don't have to take it.
This thread and it’s various contributions (all useful) put me in mind of the old saw about a group of blind people all feeling a different part of an elephant. Individually it’s a mystery but all together they finally reach a (could be Indian, could be African) useable solution.
Thanks all.
Thanks all.
I wouldn’t be as absolute and definitive as this post but I believe that there is a grain of truth in the assertion that use of the front brake lever does seem to have an effect on the travel of the rear brake pedal. The linked brakes are so good that I often find myself only using the front brake lever: I once made a point of only using the front brake on a short test ride and then looked at the brake application ratio - front/rear on my gs911. I found more rear than front-brake applications. It seems that applying the front brake lever applies the rear brake first, then as you increase the lever pressure, the front brakes are applied. This makes me wonder if the rear brake pedal hydraulic line is on a seldom activated separate circuit and if this has something to do with the feeling that it needs to be pumped a few times to get to pressure?
Alan R
If you apply the front brake then the rear, there is definately less rear lever travel than usual as some of the slack is taken up. On my bike I believe the rear pedal slack is not air, I think it is in the balancing valve of the linked system
As a footnote to this, the master cylinder's part number has never been updated in the many years since 2013.
The pressure modulator cum abs unit cum linking proportioning valve has been updated twice.
My suspicion is that BMW knows what is wrong but the cost of replacing pressure modulators is so high that they're not going to do anything.
The pressure modulator cum abs unit cum linking proportioning valve has been updated twice.
My suspicion is that BMW knows what is wrong but the cost of replacing pressure modulators is so high that they're not going to do anything.
Just been reading this over on Adriders. It seems to cure the soft back brake issues on the wetheads.
https://advrider.com/f/threads/r1200gs-gsa-lc-rear-brake-issue.1443368/#post-39965574
https://advrider.com/f/threads/r1200gs-gsa-lc-rear-brake-issue.1443368/#post-39965574
If the problem was moisture ingress it would get progessively worse, this does not happen on my bike. The after fluid replacement my brake are ok then degrade quickly to a particular amount of free play then no further, the take up point remains the same there after. My feeling is some form of mechanical 'slack' in the system.
I don’t quite see how that works either. I flushed with fresh fluid and still found some softness. The standard reservoir seems well sealed to me.
ianm00
Registered user
If you flushed with fresh fluid and bled the brakes well the brake pedal should be good. I find that with mine (2014 R1200GS) if I change fluid the brakes feel firm and as expected, however over a few thousand miles my rear brake travel keeps increasing until its virtually impossible to use when riding. Bleeding the rear brake seems to let quite a bit of air out and brings the pedal back to good operating point.
Not sure if the reservoir seal can let air in?
Ian
I just thought I would resurrect this thread to share something I learned yesterday.
My front brakes, although working well, have had excessive travel and play in the lever. I’ve been chasing those bubbles for ages with no joy.
Yesterday I went for my MoT (essential journey) and the tester picked this up. He didn’t fail the bike but he told me to get it sorted quickly. I told him everything I had done and he shared a little gem of knowledge with me. You’d expect that any air in the system would travel up to the master cylinder reservoir but he told me that he often finds air trapped in the banjo union. He squeezed the lever and cracked the banjo bolt. He did this twice but said he didn’t see any air come out but at least I could eliminate that from my search.
On the way home however, the front lever was nice and firm and I felt like I could do stoppies were I so inclined or skilled.
So I just thought I would share that nugget of sagacity in case it’s useful for someone
My front brakes, although working well, have had excessive travel and play in the lever. I’ve been chasing those bubbles for ages with no joy.
Yesterday I went for my MoT (essential journey
) and the tester picked this up. He didn’t fail the bike but he told me to get it sorted quickly. I told him everything I had done and he shared a little gem of knowledge with me. You’d expect that any air in the system would travel up to the master cylinder reservoir but he told me that he often finds air trapped in the banjo union. He squeezed the lever and cracked the banjo bolt. He did this twice but said he didn’t see any air come out but at least I could eliminate that from my search. On the way home however, the front lever was nice and firm and I felt like I could do stoppies were I so inclined or skilled.
So I just thought I would share that nugget of sagacity in case it’s useful for someone
Similar threads
