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R1100GS front brake issue


14TLC

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Hi Everyone.

 

Dealing with soft front brake on 1996 R1100GS without ABS. The bike had cracked front brake fluid reservoir and leaking brake fluid. The master cylinder was in bad shape and also there were stuck pistons on the right brake caliper wearing out the inner brake pad. The brake fluid was in bad condition also. I found one used complete front brake lever with reservoir and master cylinder in good condition. I decided to change the brake lines with new steel braided teflon brake lines. I also disassembled the brake calipers to clean them. Inside there was a lot of sticky black sludge, mixture of brake fluid, water and rubber from the old brake lines. The pistons and seals were in good condition. I decided to try them without replacing the seals. After cleaning and putting back together it was disappointing to experience a soft front brake with the expected brake force to be near the end of the lever travel.

With the old components the brake was much more harder and grabbing right away when you pull the lever. I also noticed that the screw for adjusting the position of the lever/master cylinder on the old brake lever is about 3mm towards the inside compared to the new inside. Attached are pictures from both levers. I now that this screw is factory adjusted and fixed with some glue. but is there any reason for adjusting this screw?

I have not removed the master cylinder for inspection yet but I assume that it is in much better shape than the old one. Any other potential cause for this issue?  Is it possible that the replacement brake lines have different inner cross section and thus changing the brake fluid volume? I have not ridden any other R1100GS so I don't know how the brakes should behave. But I know in general that BMW have very good brakes and this is far from it.

 

So , please let's here your thoughts.

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22 minutes ago, 14TLC said:

Hi Everyione.

 

Dealing with soft front brake on 1996 R1100GS without ABS. The bike had cracked front brake fluid reservoir and leaking brake fluid. The master cylinder was in bad shape and also there were stuck pistons on the right brake caliper wearing out the inner brake pad. The brake fluid was in bad condition also. I found one used complete front brake lever with reservoir and master cylinder in good condition. I decided to change the brake lines with new steel braided teflon brake lines. I also disassembled the brake calipers to clean them. Inside there was a lot of sticky black sludge, mixture of brake fluid, water and rubber from the old brake lines. The pistons and seals were in good condition. I decided to try them without replacing the seals. After cleaning and putting back together it was disappointing to experience a soft front brake with the expected brake force to be near the end of the lever travel.

With the old components the brake was much more harder and grabbing right away when you pull the lever. I also noticed that the screw for adjusting the position of the lever/master cylinder on the old brake lever is about 3mm towards the inside compared to the new inside. Attached are pictures from both levers. I now that this screw is factory adjusted and fixed with some glue. but is there any reason for adjusting this screw?

I have not removed the master cylinder for inspection yet but I assume that it is in much better shape than the old one. Any other potential cause for this issue?  Is it possible that the replacement brake lines have different inner cross section and thus changing the brake fluid volume? I have not ridden any other R1100GS so I don't know how the brakes should behave. But I know in general that BMW have very good brakes and this is far from it.

 

So , please let's here your thoughts.

 

 

 

Afternoon 14TLC  

 

Lot going on with this.

 

As for the brake line diameter difference effecting the soft lever condition?-- In a word 'NO' as the brakes are hydraulic so once all the air is out of the system then it is simply that what volume goes in at the master cylinder comes out the other end as the same volume.

 

On that lever-to-piston screw adjustment?-- That is factory set as it precisely controls the lever position to master cylinder piston operating position. If it is screwed in to far then the master cylinder piston won't (can't) return far enough to uncover the little take-up port in the bottom of the master cylinder reservoir & allow new or make-up  fluid into the piston bore.

 

If it is screwed out too far then it allows OK make-up fluid to enter but you end up with a lot of lever travel before brake pressure can build & move the caliper pistons   (you will have a firm lever but with a lot of pre-travel before braking starts). You can also end up running out of lever travel before the  piston travels full stroke.

 

With a soft lever feel that usually points to some air remaining in the hydraulic system, or soft piston seals, or ballooning of  the brake lines, or compliancy in between the caliper pistons & the brake rotors (ie something flexing in the brake pad area).

 

With a different master cylinder installation sometimes you can end up with air in the vertical brake hose leading from the master cylinder  or high in the very back of the master cylinder bore. Also try bleeding again with the handlebars turned all the way to the left then again turned all the way to the right (this can sometimes dislodge trapped air in the master cylinder area)

 

The brake fluid  goes DOWN as you bleed but some of the trapped air keeps trying to come back UP the hose so in some cases it never completely bleeds out to be air free. (try bleeding again with short lever strokes right at  the master cylinder bleed screw).

 

Last hope is to ride the bike a day or two THEN do a re-bleed as the riding usually frees up any  trapped air  so it migrates up into the master cylinder reservoir or into the calipers.    

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Hi dirtrider,

 

Is there any procedure for adjusting this screw. What I have here is two levers and on both of them it is clearly visible that the seal is broken and they have been adjusted or misadjusted. A don't have near me another R1100GS to check what is the factory setting, at least in what range.

 

There are no leaks or air in the system.

 

Maybe I will have to open and check the master cylinder after all, because I don't see any other reason for such soft brake when everything else is in good order

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33 minutes ago, dirtrider said:

 

Afternoon 14TLC  

 

Lot going on with this.

 

As for the brake line diameter difference effecting the soft lever condition?-- In a word 'NO' as the brakes are hydraulic so once all the air is out of the system then it is simply that what volume goes in at the master cylinder comes out the other end as the same volume.

 

On that lever-to-piston screw adjustment?-- That is factory set as it precisely controls the lever position to master cylinder piston operating position. If it is screwed in to far then the master cylinder piston won't (can't) return far enough to uncover the little take-up port in the bottom of the master cylinder reservoir & allow new or make-up  fluid into the piston bore.

 

If it is screwed out too far then it allows OK make-up fluid to enter but you end up with a lot of lever travel before brake pressure can build & move the caliper pistons   (you will have a firm lever but with a lot of pre-travel before braking starts). You can also end up running out of lever travel before the  piston travels full stroke.

 

With a soft lever feel that usually points to some air remaining in the hydraulic system, or soft piston seals, or ballooning of  the brake lines, or compliancy in between the caliper pistons & the brake rotors (ie something flexing in the brake pad area).

 

With a different master cylinder installation sometimes you can end up with air in the vertical brake hose leading from the master cylinder  or high in the very back of the master cylinder bore. Also try bleeding again with the handlebars turned all the way to the left then again turned all the way to the right (this can sometimes dislodge trapped air in the master cylinder area)

 

The brake fluid  goes DOWN as you bleed but some of the trapped air keeps trying to come back UP the hose so in some cases it never completely bleeds out to be air free. (try bleeding again with short lever strokes right at  the master cylinder bleed screw).

 

Last hope is to ride the bike a day or two THEN do a re-bleed as the riding usually frees up any  trapped air  so it migrates up into the master cylinder reservoir or into the calipers.    

Sorry, something went wrong with my PC and I did not see your complete replay before I replied back.

 

I tried bleeding the system several times. As I reassembled the brake calipers I pushed back the pistons all the way inside. In that position I filled the system with brake fluid and bleeding with vacuum extraction. After completely filling, I started expelling the remaining air with short lever strokes. When there was no air coming in the reservoir I repeated the procedure once again. Then I started slowly pumping the lever to extend the caliper pistons until the brake pads contacted the brake disks. After that I repeated the bleeding procedure once again with vacuum extraction and at the end I manually bled the system.

 

As you suggested I will ride the bike for several days and check again if there is any air left inside.

I am thinking to pull the lever all the way, tie it with zip tie  and to leave it that way overnight and see if any leaks will appear.

 

You mentioned master cylinder bleed screw. I don't see any bleed screw at the master cylinder.

 

 

 

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25 minutes ago, 14TLC said:

Sorry, something went wrong with my PC and I did not see your complete replay before I replied back.

 

I tried bleeding the system several times. As I reassembled the brake calipers I pushed back the pistons all the way inside. In that position I filled the system with brake fluid and bleeding with vacuum extraction. After completely filling, I started expelling the remaining air with short lever strokes. When there was no air coming in the reservoir I repeated the procedure once again. Then I started slowly pumping the lever to extend the caliper pistons until the brake pads contacted the brake disks. After that I repeated the bleeding procedure once again with vacuum extraction and at the end I manually bled the system.

 

As you suggested I will ride the bike for several days and check again if there is any air left inside.

I am thinking to pull the lever all the way, tie it with zip tie  and to leave it that way overnight and see if any leaks will appear.

 

You mentioned master cylinder bleed screw. I don't see any bleed screw at the master cylinder.

 

 

 

 

Evening  14TLC  

 

Some don't have upper bleed screws so on those you can bleed at the master cylinder attachment line banjo fitting.

 

You can try the zip tie as sometimes that will force the tiny little air bubbles in the system to compress then form together to make larger (easier to bleed out) air bubbles.

 

That lever screw can be adjusted close to correct but it is fiddly & takes some system understanding.

 

You have to make darn sure the the  master cylinder piston is ALL THE WAY OUT TIGHT TO IT'S OUT STOP, & stays there.  Then start with  the lever screw having some clearance to the piston with the lever at rest. Then turn the screw in until it just touches the piston, then back it out j-u-s-t a little (very little). You want to end up with the  screw almost touching the piston (as close as possible) without it  deflecting the piston (at all) with lever at normal unrestricted rest.

 

Basically you need to adjust to where the master cylinder  piston ALWAYS returns fully all the way out to it's stop but have the lever screw have  as little play as possible. (if  have an error in adjusting then have it on the loose side not the tight side as you ALWAYS want the piston to fully return to it's out stop.   

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I've had that problem every time I've changed brake lines on an oilhead. I ride it for a few days and it corrects itself.

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  • 3 weeks later...

Just to report. The zip tie trick solved part of the issue. After riding about 100 Km and braking with various pressure helped a lot. I bled the brakes once more and now everything is OK. Thank you everyone for your inputs.

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  • 3 weeks later...

Bump - maybe a small hijack.  Just putting '97 R1100RT back on the road for the season.  Dusting it off I find the front brake lever totally soft, and an obvious trail of leaked out brake fluid down the tupperware.  Reservoir totally dry and drop of fluid hanging on to the piston set screw shown by OP.  Seems like the Master seals have failed and the system (at the handle) has bled out.  Just started investigation today and only partially disassembled so far.  Are these generic o-rings / seals / other that I can cob together locally?  Or do I need an official rebuild kit?

 

I see a rebuild kit at Beemer Boneyard, and a warning that they soon to be unobtainium.  Should I grab that quickly, maybe twice?  

 

What else should I be aware of as I dig deeper?

Thanks in advance, Randy

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23 hours ago, TimberGuy said:

Bump - maybe a small hijack.  Just putting '97 R1100RT back on the road for the season.  Dusting it off I find the front brake lever totally soft, and an obvious trail of leaked out brake fluid down the tupperware.  Reservoir totally dry and drop of fluid hanging on to the piston set screw shown by OP.  Seems like the Master seals have failed and the system (at the handle) has bled out.  Just started investigation today and only partially disassembled so far.  Are these generic o-rings / seals / other that I can cob together locally?  Or do I need an official rebuild kit?

 

I see a rebuild kit at Beemer Boneyard, and a warning that they soon to be unobtainium.  Should I grab that quickly, maybe twice?  

 

What else should I be aware of as I dig deeper?

Thanks in advance, Randy

 

Evening TimberGuy

 

You might be able to find some piston cups to match up but they MUST be brake fluid compatible.

 

Probably better off using a rebuild kit  (especially since they are going to disappear shortly).

 

Can't advise much until you get it apart & report what you find.

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I've pulled apart the front master cylinder, the sealing rings look awful but the cylinder looks OK.  The rings are NOT simple regular o-rings at all!!  So no easy fix there I don't think.  

Have ordered the repair kit from BBoneyard and it is en route now.  Somehow I've got one extra small bolt hanging around I don't know where it goes but that should sort itself out during assembly.  

 

A few generic questions:

1) The whole front brake reservoir and master assembly is unsightly, the paint is pealed and crusty residue all over.  Would like to clean it up - seems pretty heroic to sand blast and repaint, and don't want to risk damaging cylinder or ports.  Any ideas on attacking that?  Should I just be happy with scraping with tiny wire brush and new paint?  Can I put the whole in parts washer for an hour to remove brake fluid residues without damaging cylinder?  Still rigidly attached to throttle assembly, do they separate easily?  

 

2) Should I in any way hone the front master brake cylinder?  It is pretty tiny and has a bottom so hard to clean.  Similarly, should I run a braided wire thru the tiny holes for reservoir and brake line to remove any crude?  

 

3) The front brake lever pivot bolt came out with a good coating of blue thread lock on it - should I remove & replace (sensible) or reuse as-is?  

 

4)  Anything special I should be aware of during assembly to assure a good seal for rings and minimize potential future failures?  

 

5) Is a failure of front brake master cylinder a common thing?  Is it possible this has worked fine since original ('97 model)?  I've ordered a second repair kit to have in my shop, is that nuts?  

 

Thanks in advance.  

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19 hours ago, TimberGuy said:

 

 

A few generic questions:

 

 

 

 

Morning

 

 

 

1) The whole front brake reservoir and master assembly is unsightly, the paint is pealed and crusty residue all over.  Would like to clean it up - seems pretty heroic to sand blast and repaint, and don't want to risk damaging cylinder or ports.  Any ideas on attacking that?  Should I just be happy with scraping with tiny wire brush and new paint?  Can I put the whole in parts washer for an hour to remove brake fluid residues without damaging cylinder?  Still rigidly attached to throttle assembly, do they separate easily?  -- Just painting usually won't last as even the brake fluid fumes will usually cause the paint to fail or bubble up. I have COMPLETELY plugged the bore, plugged line fitting, reinstalled cover then sand blasted the master cyl body, then powder coated (or heat-baked enamel paint)   & that usually lasts pretty good. (if regular paint isn't heat baked it will usually peel due to brake fluid)

 

2) Should I in any way hone the front master brake cylinder?  It is pretty tiny and has a bottom so hard to clean.  Similarly, should I run a braided wire thru the tiny holes for reservoir and brake line to remove any crude?  -- If the bore is still  good then do not hone as honing can roughen the bore enough to quickly wear the new rubber parts. Just scrub the bore real good with some a green Scotch Bright pad.

 

3) The front brake lever pivot bolt came out with a good coating of blue thread lock on it - should I remove & replace (sensible) or reuse as-is?   -- Use a little new blue lock tite.  

 

4)  Anything special I should be aware of during assembly to assure a good seal for rings and minimize potential future failures?  -- Not really, pretty straight forward.   

 

5) Is a failure of front brake master cylinder a common thing?  Is it possible this has worked fine since original ('97 model)?  I've ordered a second repair kit to have in my shop, is that nuts? -- Not real common but it does happen, more common after a long storage period or if fluid is not serviced regularly.    

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