Do I need a new front brake master cylinder ?

[Gecko]

I had to change one of my front brake hoses the other day and when I was refilling the system and bleeding it I got the feeling that it's all a bit too spongy. I left the system open with the brake handle pulled in to allow the air bubbles to work their way out (about 5-6 hours) and bled the system as much as I could.
The brake lever still feels a bit spongy so it got me to wondering if after 104,000km that master cylinder might be tired. I can brake OK but I can also pull the handle right back to the handle bar grip if I want to and nothing I do seems to stop this. On the 1100 there are 4 positions I can dial in on the brake lever and 1 to 3 all still have it coming back to the handle bar ( if I really grab a hand full) position 4 is OK.
What are the symptons of a master cylinder on the way out ?

 

[the celt]

Take off lever and check for a leak at rubber boot where lever goes into
master cylinder, my one started to leak there but i still had full pressure
even with leak.

 

[nunesaf]

I had to change one of my front brake hoses the other day and when I was refilling the system and bleeding it I got the feeling that it's all a bit too spongy. I left the system open with the brake handle pulled in to allow the air bubbles to work their way out (about 5-6 hours) and bled the system as much as I could.
The brake lever still feels a bit spongy so it got me to wondering if after 104,000km that master cylinder might be tired. I can brake OK but I can also pull the handle right back to the handle bar grip if I want to and nothing I do seems to stop this. On the 1100 there are 4 positions I can dial in on the brake lever and 1 to 3 all still have it coming back to the handle bar ( if I really grab a hand full) position 4 is OK.
What are the symptons of a master cylinder on the way out ?

Hi,

I have a 1150 and half an year ago I had the same problem... until today. I changes the master cylinder piston (there is a repair kit available from BMW, but you have a 1100 so you can get it from Motobins), checked all the pistons from my calipers and yesterday I changed the hoses to braided lines (I had a hose split when leaving the ferry in Dover and drove to Leatherhead w/o front brakes ). Still spongy. So, I have to conclude (and correctly now) that I have air trapped in the ABS controller. I fell reluctant to take it to the dealer so I am inclined in following (and making the tool) the guide posted in the advrider forum.

Do you have ABS on your bike? That may very well be the source of the problem.

Cheers,

Afonso

 

[Stewart H]

I have had great success bleeding these brakes from the bottom up using a big plastic syringe, with the abs etc there may not be a clear path for the bubbles to get to the top of the system.

Stewart

 

[Noddy]

Get yourself a m/c seal and plunger overhaul kit. Fit it, easy job, bleed it, curse, swear and then bleed again. Then unbolt the calipers and just leave them hanging over night with a tight cable tie around the lever to let the air out.

Worked ok for me a few years back.

Still got your badge in your hat ?

 

[Gecko]

Still got your badge in your hat ?

Hell yes

 

[Gecko]

OK thanks folks. I'll get on and do some more fettling . Bottom filling the system may be the way then . It's a non-ABS bike by the way so relatively simple which is why I was thinking maybe the master cylinder might be on the way out. No signs of any leakage at the top end or at the Y- connector or where the new line has been fitted so it's either very stubborn air in there or the master cylinder.

 

[cookie]

if it only happened after fitting new hoses, it's not likely to be the master cylinder, just air trapped in the system. it should be quite straightforward to bleed if it's not ABS.

don't undo the nipple until you put pressure on the lever, and don't release the lever until you've tightened the nipple. do that for every stroke of the lever.

if all else fails, use a mityvac

 

[Keith Chapman]

Here is a thought, if the lever has different settings (1 - 4) to allow for short or long fingers reaching the lever, If you bleed the brakes with the setting on the narrowest it may not give full movement of the M/cylinder pulnger. Try bleeding again with the lever on the widest setting to give the plunger full travel.

 

[Tsiklonaut]

How worn are your break pads?

If they're extremely worn then breaks can give a bit "weak" feel too, since the pistons are reached too far out in calipers. Just replaced mine and much "fresher"/"stronger" feel of the breaks after the pads are run in and have the optimum bite (after 200km or so).

Master cyl can't "tire"! Simple system really. Only the pressure piston and seals can "tire" - normally starts to leak as Celt says. Mine did the same in Syria/Jordan trip, but I also had the full pressure - just topped up the oil level time-to-time. Got home, overhaul kit for R1100GS Magura front pressure cylinder costs around 50-60EUR from BMW dealer. I've overhauled mine - no leaks and works much better.

 

[Gecko]

if it only happened after fitting new hoses, it's not likely to be the master cylinder, just air trapped in the system. it should be quite straightforward to bleed if it's not ABS.

don't undo the nipple until you put pressure on the lever, and don't release the lever until you've tightened the nipple. do that for every stroke of the lever.

if all else fails, use a mityvac

Yup that's what I was doing - slow and steady and I was seeing the bubbles coming out for a while then it stopped and just gave clear clean brake fluid each squeeze of the lever - I flushed about 200ml of fluid through but it still let me pull the lever back to the bar grip when I squeezed hard.

 

[Gecko]

How worn are your break pads?

If they're extremely worn then breaks can give a bit "weak" feel too, since the pistons are reached too far out in calipers. Just replaced mine and much "fresher"/"stronger" feel of the breaks after the pads are run in and have the optimum bite (after 200km or so).

Master cyl can't "tire"! Simple system really. Only the pressure piston and seals can "tire" - normally starts to leak as Celt says. Mine did the same in Syria/Jordan trip, but I also had the full pressure - just topped up the oil level time-to-time. Got home, overhaul kit for R1100GS Magura front pressure cylinder costs around 50-60EUR from BMW dealer. I've overhauled mine - no leaks and works much better.

Brake pads are good - only been on for about 1500km and plenty of pad left. I'll check again to see if there is any leak at the top end. There was some signs of some fluid up there when I was bleeding the system but I put it down to a bit of spillage when the reservoir cover was off - maybe I need to check this closer. I've got Aserbis handguards fitted so it's not so easy to see - I'll take them off and have a closer look and then do what the Celt suggested and rmove the brake lever to be sure.
How's the new headlamps by the way ?

 

[Gecko]

Here is a thought, if the lever has different settings (1 - 4) to allow for short or long fingers reaching the lever, If you bleed the brakes with the setting on the narrowest it may not give full movement of the M/cylinder pulnger. Try bleeding again with the lever on the widest setting to give the plunger full travel.

Hmmm.... something worth trying - I was on position 2 so you might have a point with this. I'll try it on nr 4 and see if that helps. Ta very much for the idea.

 

[Tsiklonaut]

How's the new headlamps by the way ?

Hi Marc,

TT lights do fine, but I've just had first of my bulbs fried out and I've noticed the H4 lamps in the Honda CBR400 elements use different H4 mount than they are for sale in the petrol stations - bought one H4 bulb from there and it doesn't fit into Honda elements

So looks like H4 bulb isn't a common standard afterall as I first thought. Honda uses wierd 30/60W (low/high) H4 bulbs originally that came with the light elements and although they look very similar those bulbs have a bit different mounts than "regular" H4s avaiable commonly. So I reckon I need to find a suitable H4 bulb from some better equipped car bits shop etc. We'll see about that.

Good thing it's twin lamp so I have one light left till I find suitable bulb

 

[Stewart H]

If the bulbs look like H4s in other ways ie fitting the aperture in the reflector then perhaps a passing car might donate a suitable connector, you will probably need to replace that connector when you get your HID kit anyway

Stewart

 

[cookie]

Yup that's what I was doing - slow and steady and I was seeing the bubbles coming out for a while then it stopped and just gave clear clean brake fluid each squeeze of the lever - I flushed about 200ml of fluid through but it still let me pull the lever back to the bar grip when I squeezed hard.

i think i'd be looking at where air could get trapped then. banjo bolts for instance, can sometimes harbour a bubble. i've seen calipers needing removal and rotation before too.

or buy/borrow a mityvac, which will suck the fluid through faster than pumping & should take any air with it.
the gunson power bleeder thing is very effective too. cheap, but would need a custom reservoir cap knocking up. messy as feck too.

 

[(RIP) Kaister]

to test for a worn m/c - use brake hose clamp at the first section of rubber hose nearest to the cylinder.

99% of the time it'll be rock hard - which means its fine and you have air in the system or you need new caliper seals ( or a bulging pipe - rare )

if the lever is initially hard ( or completely soft ) then continues to pull back - then the cylinder seals have gone.