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Bleeding front brake - problems after replacing seals and pistons


RoSPA_man

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Hi

I’ve just spent several frustrating hours trying to regain a firm front brake lever after servicing the calipers. I fitted new seals and pistons. That part was no problem, but the bleeding has been problematic.

 

I use one of those one-man bleed kits but I think it is a 2-man job actually in order to do it right.

 

In any event, while I have the brakes operating , the lever is really soggy.

 

I’ve given up for today and decided to think about it before re-attacking tomorrow.

 

The only conclusion I can come to is this. Because I FIRST refitted the pads and THEN started the bleeding, some air must still be trapped behind the pistons and can’t find a route to the bleed nipple – could that be possible?

 

I think I should jam the pistons back into the fully retracted position and THEN carry out the bleeding – or am I missing something obvious in the bleeding procedure – which I have done many times before. However, this is the first time I have done a bleed without a second pair of hands and after a complete caliper rebuild.

 

 

 

 

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Yes, the OEM procedure calls for removal of the pads and use of a fancy (read expensive) tool to push the pistons into the caliper and hold them there while the bleeding is completed.

 

You can use some small wooden blocks to hold the pistons in the calipers too... much cheaper than the fancy BMW tool.

 

I'm my experience while working at a dealership, this method works well and ensures that all the old fluid is flushed out of the calipers which in your case does not matter. Hope this helps.

 

 

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Afternoon RoSPA_man

 

What bike you working on? I see a 1200 in your profile but you are in the oilhead forum.

 

If you are working on a 1200 then you could be in for a fight. The New Gen I-ABS systems on the 1200’s are a real pain to get the air out of. Probably lots of air in the banjo fitting up by the master cylinder (you need to bleed it there) and air gets trapped in the ABS controller area as well as the upper front brake line from the ABS controller out to the junction block.

Turning the handlebars while bleeding helps as well as holding the brake lever down with a zip tie for a while to allow the air to move up the line a little and combine into large bubbles.

 

Plus as mentioned above if those caliper pistons are out a ways they can trap air behind them.

 

If air in the calipers you will have to bleed that out, if air in the upper lines and ABS controller it might work it’s up and out during riding. Remember the ABS won’t work worth a hoot until the air is out of the system.

 

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Afternoon RoSPA_man

 

What bike you working on? I see a 1200 in your profile but you are in the oilhead forum.

 

 

 

Hi Dirt Rider - thanks for all the info. I am in the hexhead forum...

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Afternoon RoSPA_man

 

Apparently I wasn’t, not sure what went wrong but I was in the oilhead forum when your post popped up. OR, maybe I’m just loosing it!

 

OK, then my 1200 brake info holds true. If you allowed the master cylinder to drain of fluid you will have to work at it to get the air out.

 

Even some dealers had a dickens of a time getting the air out of the front brake lines after the brake line recall was done. Seems lots of riders got their bikes back from the dealer with air in the front brakes. Mine came back from the BMW line recall with the front so soft I could easily pull the lever into the hand grip.

 

 

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I use a vacuum bleeder for the initial bleed and fluid flush. I push the pistons into the caliper, no need to block, vacuum bleed, finish up with a manual lever pump and bleed.

 

This procedure is noted in the manual for non whizzy brakes.

They note not to use a vacuum bleeder with whizzy brakes.

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I use a vacuum bleeder for the initial bleed and fluid flush. I push the pistons into the caliper, no need to block, vacuum bleed, finish up with a manual lever pump and bleed.

 

This procedure is noted in the manual for non whizzy brakes.

They note not to use a vacuum bleeder with whizzy brakes.

 

Hi New Blue/Dirt Rider

 

Well another few hours today and no farther along!

 

Today, I thoroughly retracted and jammed back all pistons. I bled from the top and bled from each caliper with my son working the lever, ran the balance of my 500ml through, but I still have the same, very soggy lever. It is partially firm, feels firmer as you are bleeding but when you tighten the bleed nipple, it gets less firm and will, with a little resistance come right into the handlebar grip.

 

This is really frustrating. There are no leaks. I've run a half litre of brake fluid through.

 

Possible causes are:

1. I can't see how it could matter, but yesterday I actually washed, blew compressed air through and then put the calipers into an Aga oven (pretty low heat). All this was done of course with seals and pistons removed. I heatyed them in the oven to dry them thoroughly - I can't think of any reason why that could affect anything but I mention it just in case- the calipers were hot but you could hold them in your hand - I'm sure that operating temperatures could be at least as high? Could I have melted any internal seals - I doubt it?

 

2. Seconsd possibility is that something else failed coincidentally during this work (or because of the work?) like the master cylinder. There is a a definite swooshing sound while you bleed, but I think that's normal? The only reason that might possibly fail is the repeated action of bleeding , but I think that is unlikely.

 

Otherwise, I'm stumped. What else to do? By the way, aren't the bleed nipples extremely unsatisfactory in that as soon as they are loosened off even a small turn, they leak out of the threads! Is there any way to eradicate that problem?

 

Thanks

Hugh

 

 

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RoSPA man

 

There are O rings between the caliper halves but I doubt they were damaged, if they were they would leak.

The bleed procedure is to bleed at the master cylinder, then the calipers, and again at the master to finish.

 

Don't worry about the slight fluid around the bleed nipples, if bled corectly they only see positive pressure. Adjust the thumb wheel so the lever is at the farthest position from the grip. Pump, crack the bleeder and tighten before the lever hits the grip, repeat.

 

The procedure is the same, other then the master, with the rear brake which you did after the clutch replacement.

 

When done go for a test ride using caution. my bike, as well as new bikes in the showroom will allow the lever to be pulled to the grip. It requires some effort but not much.

 

Off hand I can't think of anything else.

 

Hope it works out.

 

 

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Afternoon Hugh

 

You have nothing basically wrong with your brakes. I’m telling you that those New Gen I-ABS brakes are REAL pain to bleed once empty. Did I mention a real pain!

 

The vacuum bleeder won’t get the air out although it is a good start at getting fluid pulled through the system. That is what got my dealer in trouble as they thought the BMW vacuum bleeding was good enough (not so). Vacuum bleeding just doesn’t move the fluid quick enough to keep from having the fluid flow right under the trapped air pockets.

 

If you have the air out of the master cylinder banjo fitting area (just because it flows clean fluid there doesn’t mean no air trapped up high in that area) and the air is out of the calipers behind the pistons then you still have air trapped in the ABS controller as you have no means of cycling the internal valves at home, maybe some air trapped in the hydraulic circuitry for the rear linking and my guess in lots of air still in the front upper brake line.

 

Keep in mind that the front brake hoses runs down hill with high spots and air trapping areas and air wants to raise on the fluid but you are trying to push that air down and out with the brake fluid.

 

If I were at the point your are now if it has any front brakes at all I would ride that bike (carefully) then see if you can get it to ABS the front and rear wheel a few times on a gravel road. That will releases some of the air stuck in the ABC controller. It might also allow some of the air trapped in that front high brake line to migrate up the line and back into the master cyl reservoir.

 

 

Then after the ride bleed it again (don’t need to move much fluid, just get the newly appearing air out). Then ride it again and re-bleed again after riding.

 

Just moving massive amounts of fluid does no good as the fluid just flows under the trapped air pockets.

 

Cycling the front lever BRISKLY and allowing snap lever returns does help as well as elevating the front of the bike as much as you can while operating the brakes.

 

Also put the master cylinder cover back on and BRISKLY apply the front lever full stroke while turning the handlebars lock to lock then place the bike on the side stand and repeat. Allow the lever to snap back as quickly as possible between strokes. Some of your air will want to come back up and into the reservoir, allow it to as that is the natural way it wants to go.

 

I try my darndest now to never let those New Gen systems run dry as they are not fun to get the air out of.

 

You’ll get to a point that you start getting a decent firm lever then it will get better from there quickly.

 

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We'll have to disagree on the vacuum bleeding dirtrider.

It will work better then a pump and bleed if done correctly.

The air wants/has to go to the negative pressure created by the bleeder. The air will be pushed up, over, and under to get to it.

 

The problem with a pump and bleed is the lever stroke does not provide enough volume to get the air out. It will cycle back and fourth depending on the line routing.

 

You need to use a constant vacuum pull like a Vacula or similar, HF sells one for $25 that works well. A hand pump won't do it.

 

You can get some clear hose, coil it, hook one end to the vacuum bleeder, induce air, submerge in liquid and watch it. It will be pushed out. Or buy a crazy straw, silly straw? and drink your favorite beverage. Same thing.

 

You should do a hand bleed after to remove the air from the bleed nipple because air will be drawn in around the threads.

 

If the dealer induced air using a vacuum bleeder it would have been done incorrectly.

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Try pulling he lever to the handle and putting a bungie or ruber band around the handle to hold it in the full pulled position & leave it overnight. frequently the system will bleed it self if air is in the hoses. the only other thing I can suggest is get a brake fluid pump & pus the fluid from the caliper to the MC.

Also you can use teflon tape on the bleed screw to stop the threads from seeping.

 

Good Luck

 

 

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Afternoon New Blue

 

As long as you are happy using a vacuum bleeder.--- I’m definitely not, and so far neither is my dealer. My dealer has had issues getting the air out of the BMW New Gen systems using the BMW vacuum bleeder setup. They have ended up doing it the old way after the vacuum bleed on the problem air bound New Gen systems. With the number of other soft lever complaints on the New Gen systems after the brake line recall it sure sounds like a number of other dealers are having similar issues also and most use the BMW vacuum setup.

 

It sure sounds like RoSPA_man hasn’t had any luck with the vacuum method either.

 

I have done a “number” of empty system fill and bleeds on the New Gen systems and so far none have ended up air free using just my vacuum bleed set up and it has a high speed 110 volt electric vacuum pump on it.

 

It (the vacuum systems) work good for a simple maintenance bleed but I sure haven’t been happy using one on empty system air removal on the new BMW ABS systems.

 

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---- the only other thing I can suggest is get a brake fluid pump & pus the fluid from the caliper to the MC.

-----

 

 

 

Afternoon Jim

 

That is basically the way we do our brake test vehicles where I work. A 3 gallon pressure pot hooked to the brake bleed nipples or in some cases a drilled and tapped master cylinder cover with the pressure fluid forced through the system at high pressure high volumes from the top. We also use a laptop to cycle the ABS controller valves or plungers during the process to allow the air to be purged from that area.

 

Problem with pressurizing the calipers then forcing the fluid back up through the system is the possibility of a very big mess if it burps air and fluid as it blows all over everything. Not a big deal on our test vehicles but I sure wouldn’t want to do that to a nice bike.

 

At one time (before the new adaptable high tec learnable ABS systems) we would vacuum bleed from the bleed nipples then close them, then apply vacuum to the master cylinder reservoir top to form a low pressure in the reservoir as that would help the air migrate up and out the top. Not so much during the actual vacuum process but the air would come bubbling up as the vacuum was quickly removed. (I have done this on some bikes using a drilled hockey puck with a vacuum fitting installed but never tried it on the New Gen BMW systems). Painted plastic & clear plastic dash covers make me real nervous around Dot 3/4 brake fluid.

 

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All great responses- many thanks. I'm now waiting on fresh fluid to arrive, a new bleeder (just in case), I have the Teflon tape and some ideas from all the great advice. I'll be doing all the things suggested.

 

BTW, the Overnight cable-tie on the lever achieved no improvement. Will keep you posted

 

BW

Hugh

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kenthewrench

They're a bitch to bleed and very time consuming hence the 2.5hrs it pays while performing a service on one. Best advise I can give is to get a service manual and "strictly" follow the bleed procedures,otherwise your gonna be there for days. You've probably pumped the whole front system dry from the resevior to calipers. You have to do it "by the book" . Theres a sequence for the bleed procedure at the ABS unit(FOLLOW IT). Theres a step that requires you to install a BMW special tool on the ABS assy which is next to impossible to get so after removing the fill cap on unit I slowly pour fluid in while working the lever on my vac bleeder very slow with bleeder on caliper open. Sounds crazy but it works(this step is for bleeding front wheel circuit). You may have to bleed front pump circuit at unit if you drained too much(as it sounds). Good luck!!!!!!!!!

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----Theres a step that requires you to install a BMW special tool on the ABS assy which is next to impossible to get so after removing the fill cap on unit I slowly pour fluid in while working the lever on my vac bleeder very slow with bleeder on caliper open.

 

Afternoon Kent, you working on the post 08/2006 Gen (2) I-ABS here? Sounds more like you are talking about the older I-ABS (wizzy) brake system.

What special tool are you referring to here as my BMW service manual doesn’t show anything fitting on the Gen(2) ABS controller. Is this something new?

 

 

 

Just making sure we are all on the same page here as we are not working with the pre 08/2006 Wizzy brake system.

 

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Mmm... Never been 100% happy with my lever since the brakeline recall TBH. I did go check some showroom bikes and they were the same. It'll be interesting to hear what works for you Hugh.

Good luck

\v/

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Evening Hall Vince

 

Well if you aren’t happy with the lever feel take it back and have them re-bleed it. You rode the bike a while before the brake lines were done so you probably have a better feel for how it was before and after than the dealer ever would.

 

When I got my bike back from the dealer after the line recall the lever travel was spongy and the modulation was much worse than when I took it in. They tried to tell me all the BMW’s were like that (that’s nonsense).

 

Well, I said I have been the one riding this bike and it isn’t the same, I could easily pull the front lever clear to the grip with moderate hand pressure and the near lock-up lever modulation was not linear and felt vague. I did check a couple of new bikes sitting in the prep area but couldn’t tell much as those bikes were new and the pads weren’t seated in yet so that added a little compliancy to the static lever pull.

 

Long story short they did re-bleed the brake system (actually they did it twice) and it was better but still not like it was. It then re-bled it myself per my directions above and it was back to where it was before the line install. Where it’s at now I can’t pull the front brake lever to the bar on cold brakes without extreme force. Using moderate hand force it doesn’t even come close to the touching the grip.

 

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You need to use a constant vacuum pull like a Vacula or similar, HF sells one for $25 that works well. A hand pump won't do it.

 

 

 

I borrowed a Mity Vac to try but it is like a master cylinder in that it pulls instead of pushing. Are you saying that will not work or do you mean some other type of pump will not work?

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Did you ever try bleeding from the front calipers with the calipers off the forks, pistons spaced apart by blocks?

 

Allows you to rotate the calipers around to different orientations and get the air out that way if you have some trapped there.

 

 

 

 

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You need to use a constant vacuum pull like a Vacula or similar, HF sells one for $25 that works well. A hand pump won't do it.

 

 

 

I borrowed a Mity Vac to try but it is like a master cylinder in that it pulls instead of pushing. Are you saying that will not work or do you mean some other type of pump will not work?

 

Not sure what you mean about like a master cylinder, the master cylinder applies a poitive pressure a vacuum pump is negative (vacuum)

A mighty vac could work but the res is small and you have to keep pumping it. The type I was referencing is powered by air.

It's hooked to an air compressor. Sounds confusing but the air flow across the port creates a negative pressure in the bleeder res. and will cause atmospheric pressure to push the fluid out of the master cylinder.

In short it sucks the fluid/air out of the brake master and lines.

 

If the bleeder threads aren't sealed you will see air/fluid mix in the tube due to air entering around the threads. This is normal and is not getting in the brake system.

 

Try the mighty vac and you will see what I mean. Keep the cover off the master, start pumping the mighty vac, crack the bleeder (don't pump the brake lever) keep pumping the mv and be sure to keep the master res topped off. Tighten the bleeder while you're still pumping. I'll run a res fill quantity through each caliper bleeder (don't let the brake master res. go empty or you'll be back where you started) Finish with a couple manual lever pump and bleeds at each bleed nipple and call it a day. Hopefully.

It's a lot easier then I make it sound.

 

This is the one from HF http://www.harborfreight.com/brake-fluid-bleeder-92924.html

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Evening RoSPA_man

 

You can easily increase the effectiveness of your MityVac by building a simple large (sealed) catch container. That allows you to suck a large amount of fluid before the need to disconnect and drain, also allows viewing air bubble coming out with the fluid.

 

If the MityVac can’t maintain enough vacuum for what you are trying just use a mild mannered idling engine. That will produce more vacuum continuously than you can maintain by hand pumping a MityVac. Just keep the vacuum inlet into the jar up near the top so it doesn’t suck fluid into the vacuum inlet line.

 

 

VacJar.jpg

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Evening RoSPA_man

 

You can easily increase the effectiveness of your MityVac by building a simple large (sealed) catch container. That allows you to suck a large amount of fluid before the need to disconnect and drain, also allows viewing air bubble coming out with the fluid.

 

If the MityVac can’t maintain enough vacuum for what you are trying just use a mild mannered idling engine. That will produce more vacuum continuously than you can maintain by hand pumping a MityVac. Just keep the vacuum inlet into the jar up near the top so it doesn’t suck fluid into the vacuum inlet line.

 

 

VacJar.jpg

 

Sweet, add a 12V vacuum pump off a cruise control or climate control system, Hmmmmm just happen to have a few of those laying around.

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Did you ever try bleeding from the front calipers with the calipers off the forks, pistons spaced apart by blocks?

 

Allows you to rotate the calipers around to different orientations and get the air out that way if you have some trapped there.

 

 

 

 

Yep - they are off the forks and tied hanging

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Evening RoSPA_man

 

You can easily increase the effectiveness of your MityVac by building a simple large (sealed) catch container. That allows you to suck a large amount of fluid before the need to disconnect and drain, also allows viewing air bubble coming out with the fluid.

 

If the MityVac can’t maintain enough vacuum for what you are trying just use a mild mannered idling engine. That will produce more vacuum continuously than you can maintain by hand pumping a MityVac. Just keep the vacuum inlet into the jar up near the top so it doesn’t suck fluid into the vacuum inlet line.

 

 

VacJar.jpg

 

Sweet, add a 12V vacuum pump off a cruise control or climate control system, Hmmmmm just happen to have a few of those laying around.

 

Sweet indeed - I will first try the Mity Vac on its own (I'm an eternal optimist) and if that doesn't work, I'll make up DirtRider's excellent "contraption" :Cool:

I hope to get to it this evening and will keep you all up to date! Many thanks

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Morning RoSPA_man

 

Careful using JUST the MityVac on your brake system. Those things don’t like brake fluid pulled into them as it swells the piston rubber. More than a few MityVacs have been ruined by having brake fluid sucked into them. You’ll know it when you can’t pump the MityVac lever any more due to a swelled up piston.

 

That catch jar is a great way to protect your MityVac from errant fluid suck-in.

 

OR, if you wish you can use the pressure port on your MityVac instead of the vacuum side port and pressurize the container to force the fluid back into the system from the bottom up (make a pressure bleeder out of it). If the container and hoses are clean that also means you can re-use the fluid in the jar as it won’t be contaminated.

 

 

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Morning RoSPA_man

 

Careful using JUST the MityVac on your brake system. Those things don’t like brake fluid pulled into them as it swells the piston rubber. More than a few MityVacs have been ruined by having brake fluid sucked into them. You’ll know it when you can’t pump the MityVac lever any more due to a swelled up piston.

 

That catch jar is a great way to protect your MityVac from errant fluid suck-in.

 

OR, if you wish you can use the pressure port on your MityVac instead of the vacuum side port and pressurize the container to force the fluid back into the system from the bottom up (make a pressure bleeder out of it). If the container and hoses are clean that also means you can re-use the fluid in the jar as it won’t be contaminated.

 

 

 

Well – it works! Some combination of the Mity Vac and conventional bleeding did the trick. It was quite strange actually, because I had kinda given up on the session and decided to do the ABS trick so I reassembled everything and hey presto- a rock hard lever. I tested it thoroughly and even managed to get it to cycle on ABS on front circuit on dry asphalt. So I will ride for a few sessions and double-check. Thanks to everyone for all the help.

 

 

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Afternoon Hugh

 

Congratulations! Goes to show persistence pays off-- That is usually how those Gen-2 ABS systems go. Mushy and vague one minute then once it starts to get air free a firm lever in very short order.

 

You should be good to go now. Once the lever goes firm even if a little air left it will work it’s way up and out as you use the brakes.

 

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Hugh, Do you fancy doing another RT? Mines gotta spongey lever still. It would be good to show the dealer and mechy how they should feel! And ride with good modulation.

\v/

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Hugh, Do you fancy doing another RT? Mines gotta spongey lever still. It would be good to show the dealer and mechy how they should feel! And ride with good modulation.

\v/

 

A couple of thoughts Vince - Right now, it's about the last thing I want to touch for some time! It would also help if I knew precisely what I did! I think it was the vac. pump that did the trick but I basically just followed the advice on this thread and then it suddenly worked! So I'd be happy to help out (post-Ardennes)/I'm sure Roger Manning would be happy for you to borrow his MightVAc which I still have.

 

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  • 2 weeks later...
Hall Vince

Hello Hugh.

I know the feeling. I asked the question with a slight tongue in cheek.

 

It's been six months, since my brake recall. Maybe I'll just give it a manual bleed first, won't take long and you never know, may just help.

 

Happy Ardenning.

\v/

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