Bleeding brakes!!
Discussion
So BMW S1000RR done this a gazzilion times changed brake fluid in the front brakes system.
But now slowly during a week the brake handle gets progressively more floppy. So I re-bleed from the nipple on top of the handlebar which lets out a big bubble of air and all is fine for another week.
So air is getting in. So far so good.
Normally this is easy to find because you wrap all joints in tissue paper and where the air is getting in brake fluid is getting out.
Only there is no brake fluid. Nothing. Absolutely no sign of a leak anywhere in the system from pistons to handlebar. Nothing under the ABS, nothing on any of the pipes. Actually not sure how its possible to get air in but no fluid out.
Anyone had this problem or got a solution to find where the air is getting in.
But now slowly during a week the brake handle gets progressively more floppy. So I re-bleed from the nipple on top of the handlebar which lets out a big bubble of air and all is fine for another week.
So air is getting in. So far so good.
Normally this is easy to find because you wrap all joints in tissue paper and where the air is getting in brake fluid is getting out.
Only there is no brake fluid. Nothing. Absolutely no sign of a leak anywhere in the system from pistons to handlebar. Nothing under the ABS, nothing on any of the pipes. Actually not sure how its possible to get air in but no fluid out.
Anyone had this problem or got a solution to find where the air is getting in.
julian64 said:
even so the suction is only when you release the handle. So when the handle is not being used surely you would expect to see a degree of leakage?
Air will get through when fluid won't IMEHowever I agree that if the lever was working fine when you left it and isn't when you come back (ie no usage) then I doubt it's the seals
I've had sucess cable tying the lever back when left - it allows any air to work it's way up
I need a clever PH way of isolating where the leak is coming from. Currently it could be coming from anywhere, so I've been through all the connections and done them up tight - no change
I don't want to take the whole ABS apart to find out its the nipple on the handlebar
There must be some clever way
I do have one idea from this thread if I tie the handle for a week with no loss of power that will confirm if its the low or high power side of the master cylinder?
I don't want to take the whole ABS apart to find out its the nipple on the handlebar
There must be some clever way
I do have one idea from this thread if I tie the handle for a week with no loss of power that will confirm if its the low or high power side of the master cylinder?
OutInTheShed said:
RTFM about bleeding the ABS.
ABS bled as per the manufacturers instructions using the STA+, as I said done this a gazillion times before with no problem as I've had this bike from new in 2010. New handlebar cylinder two years ago.Whatever is happening, I don't think its a lack of ability to do a routine brake fluid change.
If you are getting air in the master cylinder without getting any fluid leaks, then the ABS modulator is quite likely the source.
You can discount air leaking into the caliper, the fluid there is under a static head when the bike is standing.
Air can only leak in if the leak is under suction/partial vacuum.
How the master cylinder behaves when the bike is idle may depend on its orientation. On my bike, if the bike is on the centre stand, the feed tube from the reservoir is not above the point where it feeds the cylinder, which slopes upwards, so any air will migrate to the working end of the cylinder. To bleed it properly, I need to lean the bike, to get the last bit of air up into the reservoir.
On the back brake I find the best thing is to use a syringe to push fluid through the system from the caliper bleed nipple to the reservoir. It all depends where the lines run and what highpoints there are to trap air.
Master cylinders are basically not very complex and all work in much the same way.
ABS modulators less so....
You can discount air leaking into the caliper, the fluid there is under a static head when the bike is standing.
Air can only leak in if the leak is under suction/partial vacuum.
How the master cylinder behaves when the bike is idle may depend on its orientation. On my bike, if the bike is on the centre stand, the feed tube from the reservoir is not above the point where it feeds the cylinder, which slopes upwards, so any air will migrate to the working end of the cylinder. To bleed it properly, I need to lean the bike, to get the last bit of air up into the reservoir.
On the back brake I find the best thing is to use a syringe to push fluid through the system from the caliper bleed nipple to the reservoir. It all depends where the lines run and what highpoints there are to trap air.
Master cylinders are basically not very complex and all work in much the same way.
ABS modulators less so....
The only other bit of info is that the bikes been bled and worked fine. But since then I have bled from the top only and the bike engine hasn't moved.
I am thinking, possibly wrongly that if it was the modulator it would only let air in during an abs 'episode' not if the engine was stationary.
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.I guess taking the abs apart is the next step, and pretty resigned to it, but didn't want it in pieces only for someone on here to say there was something simple I could do to prove it.
I am thinking, possibly wrongly that if it was the modulator it would only let air in during an abs 'episode' not if the engine was stationary.
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.I guess taking the abs apart is the next step, and pretty resigned to it, but didn't want it in pieces only for someone on here to say there was something simple I could do to prove it.
Personally I would think long and hard before dismantling an ABS modulator.
I doubt it's 'letting air in'. I expect this air is somewhere in the system the whole time.
either in the modulator or outside the HP seal in the master cylinder perhaps?
Some systems you can usefully apply a little suction to a bleed nipple using a syringe, while the master cylinder is actuated. This can have the effect of expanding the air bubbles, so they are dislodged from where they are trapped.
Sometimes, you just need to wait a long time for the air to escape to the top where it can be bled.
Sometimes pushing fluid back up the system with a syringe or by pushing back caliper pistons works.
Sometimes pushing a lot of fluid through the system works.
I would be looking for different opinions on the best way to bleed/refill the exact modulator you have.
Generally I think the advice to never let air into a modulator to start with is as good as it gets, but I appreciate that's not so helpful.
Very possibly it's sorting itself out and you just need to be patient and bleed the MC a couple of times.
I doubt it's 'letting air in'. I expect this air is somewhere in the system the whole time.
either in the modulator or outside the HP seal in the master cylinder perhaps?
Some systems you can usefully apply a little suction to a bleed nipple using a syringe, while the master cylinder is actuated. This can have the effect of expanding the air bubbles, so they are dislodged from where they are trapped.
Sometimes, you just need to wait a long time for the air to escape to the top where it can be bled.
Sometimes pushing fluid back up the system with a syringe or by pushing back caliper pistons works.
Sometimes pushing a lot of fluid through the system works.
I would be looking for different opinions on the best way to bleed/refill the exact modulator you have.
Generally I think the advice to never let air into a modulator to start with is as good as it gets, but I appreciate that's not so helpful.
Very possibly it's sorting itself out and you just need to be patient and bleed the MC a couple of times.
OutInTheShed said:
Personally I would think long and hard before dismantling an ABS modulator.
I doubt it's 'letting air in'. I expect this air is somewhere in the system the whole time.
either in the modulator or outside the HP seal in the master cylinder perhaps?
Some systems you can usefully apply a little suction to a bleed nipple using a syringe, while the master cylinder is actuated. This can have the effect of expanding the air bubbles, so they are dislodged from where they are trapped.
Sometimes, you just need to wait a long time for the air to escape to the top where it can be bled.
Sometimes pushing fluid back up the system with a syringe or by pushing back caliper pistons works.
Sometimes pushing a lot of fluid through the system works.
I would be looking for different opinions on the best way to bleed/refill the exact modulator you have.
Generally I think the advice to never let air into a modulator to start with is as good as it gets, but I appreciate that's not so helpful.
Very possibly it's sorting itself out and you just need to be patient and bleed the MC a couple of times.
I think I'd agree with this. I will keep letting the air out and if that fails I'll pressure backfill fro mthe caliper. CheersI doubt it's 'letting air in'. I expect this air is somewhere in the system the whole time.
either in the modulator or outside the HP seal in the master cylinder perhaps?
Some systems you can usefully apply a little suction to a bleed nipple using a syringe, while the master cylinder is actuated. This can have the effect of expanding the air bubbles, so they are dislodged from where they are trapped.
Sometimes, you just need to wait a long time for the air to escape to the top where it can be bled.
Sometimes pushing fluid back up the system with a syringe or by pushing back caliper pistons works.
Sometimes pushing a lot of fluid through the system works.
I would be looking for different opinions on the best way to bleed/refill the exact modulator you have.
Generally I think the advice to never let air into a modulator to start with is as good as it gets, but I appreciate that's not so helpful.
Very possibly it's sorting itself out and you just need to be patient and bleed the MC a couple of times.
Just an update.
Have had the bike standing for nearly a month all told.
have bled the conventional way plus using the GS-911 tool to cycle the ABS
have used a pressure device at the callipers to push to the reservoir.
have used a vacuum device to suck from the reservoir to the callipers
have tied up the brake handle overnight to let the bubbles out (common youtubemethod)
All result in the same. perfect bike, which lasts for about a week and then slow fade of the brake until the handle comes all the way back and pretty much no braking left. same in both front and rear brake. When you them go to rebleed a nice bubble of air comes out.
No brake fluid anywhere, taken everything off to trace all the brake lines and no damage or leaks.
I guess the fact that it bleeds fine, and works for a week, means that bubble I get over a week later, is slowly developing somewhere.
Not sure how the abs modulator works, but unless anyone has any bright ideas I think that's what's coming apart next?
Have had the bike standing for nearly a month all told.
have bled the conventional way plus using the GS-911 tool to cycle the ABS
have used a pressure device at the callipers to push to the reservoir.
have used a vacuum device to suck from the reservoir to the callipers
have tied up the brake handle overnight to let the bubbles out (common youtubemethod)
All result in the same. perfect bike, which lasts for about a week and then slow fade of the brake until the handle comes all the way back and pretty much no braking left. same in both front and rear brake. When you them go to rebleed a nice bubble of air comes out.
No brake fluid anywhere, taken everything off to trace all the brake lines and no damage or leaks.
I guess the fact that it bleeds fine, and works for a week, means that bubble I get over a week later, is slowly developing somewhere.
Not sure how the abs modulator works, but unless anyone has any bright ideas I think that's what's coming apart next?
Do you need to do a full brake bleed to clear the bubble or is it sitting there at the master cylinder waiting for you to just pull the lever? Given that air will float to the top if it can then knowing where the bubble is may help in tracing through the system that is physically below that point to work out where the air leak is.
I wouldn't touch the ABS pump unless you're well versed in those devices.
If this was my bike, I'd start with replacing the master cylinder seals, remove and clean the brake pipes where they enter the master and callipers, make sure there is no corrosion and surfaces are clean, both front and back. See how that goes.
I agree it's probably not the calliper piston seals leaking and unless you've moved or disturbed the ABS pump, probably not that or the pipes to it.
One of my cars has an ABS pump high up under the scuttle area and if I allow the brake fluid to drain from it, I can easily go through 2 or 3 litres of brake fluid whilst a diagnostics machine cycles the ABS pump. Proper pita sitting in the car pumping the brake peddle whilst somebody opens the bleed value on each calliper whilst the pump cycles. Last time it needed doing twice and must have used over 4 litres of brake fluid.
If this was my bike, I'd start with replacing the master cylinder seals, remove and clean the brake pipes where they enter the master and callipers, make sure there is no corrosion and surfaces are clean, both front and back. See how that goes.
I agree it's probably not the calliper piston seals leaking and unless you've moved or disturbed the ABS pump, probably not that or the pipes to it.
One of my cars has an ABS pump high up under the scuttle area and if I allow the brake fluid to drain from it, I can easily go through 2 or 3 litres of brake fluid whilst a diagnostics machine cycles the ABS pump. Proper pita sitting in the car pumping the brake peddle whilst somebody opens the bleed value on each calliper whilst the pump cycles. Last time it needed doing twice and must have used over 4 litres of brake fluid.
If air is genuinely getting into the master cylinder and no fluid is coming out, yet the system works once bled, then:
Does the master cylinder 'work up hill' when the bike is on the stand?
I'm suspecting the air is leaking past the m/c pressure seal when the system is idle. Perhaps corrosion or wear in the bore.
I'd guess the fluid feed into the M/C is not exactly at the top so the air doesn't leave via the feed.
New master cylinder might be easiest, is there one which is seen as an 'upgrade' at a reasonable price?
Does the master cylinder 'work up hill' when the bike is on the stand?
I'm suspecting the air is leaking past the m/c pressure seal when the system is idle. Perhaps corrosion or wear in the bore.
I'd guess the fluid feed into the M/C is not exactly at the top so the air doesn't leave via the feed.
New master cylinder might be easiest, is there one which is seen as an 'upgrade' at a reasonable price?
The thing I'm not understanding is if it is the master cylinder seals why isn't there brake loss from minute one, why does it work fine for a week?
If air is getting into the master cylinder which is highly likely and therefore a progressive fade in performace after a week, and of course the subsequent bubble on bleeding. How is that manifesting through the master cylinder without showing a brake fluid leak.
reservoir to master cylinder downhill. I've disconnected twice to make everything a straight vertical drop from bleeding just to see if that was my problem I understand the recurrent warnings re the abs modulator and to be honest I'm trying to understand how this could be the culprit either as there is no vacuum in the system with the engine off over a week of standing in the garage.
However the length of time I've been waiting and just keep rebleeding thinking this is trapped air is ridiculous. I'm convinced its introduced air rather than trapped.
What I need are clear brake lines to see whether the bubbles are coming from
If air is getting into the master cylinder which is highly likely and therefore a progressive fade in performace after a week, and of course the subsequent bubble on bleeding. How is that manifesting through the master cylinder without showing a brake fluid leak.
reservoir to master cylinder downhill. I've disconnected twice to make everything a straight vertical drop from bleeding just to see if that was my problem I understand the recurrent warnings re the abs modulator and to be honest I'm trying to understand how this could be the culprit either as there is no vacuum in the system with the engine off over a week of standing in the garage.
However the length of time I've been waiting and just keep rebleeding thinking this is trapped air is ridiculous. I'm convinced its introduced air rather than trapped.
What I need are clear brake lines to see whether the bubbles are coming from
bgunn said:
Master cylinder seals.
This was your first answer and is correct. But the fact the seals were replaced is neither here nor there, the cylinder is probably scored. Go and pay BMW for a COMPLETE NEW master. It is a very high performance bike, so pay the high performance money and have brakes that work on your 200 bhp machine, preferably before you pile into the back of someone.
fred bloggs said:
This was your first answer and is correct. But the fact the seals were replaced is neither here nor there, the cylinder is probably scored.
Go and pay BMW for a COMPLETE NEW master. It is a very high performance bike, so pay the high performance money and have brakes that work on your 200 bhp machine, preferably before you pile into the back of someone.
Or get a better one that isn't going to have the same problem later on?Go and pay BMW for a COMPLETE NEW master. It is a very high performance bike, so pay the high performance money and have brakes that work on your 200 bhp machine, preferably before you pile into the back of someone.
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