Leaking Brake Fluid

[Our Gee]

Just spent an hour trying to find any info / part number / price etc for a Front Brake Fluid Reservoir Filler Cap Seal. I believe this part is also referred to as "Bellows". I can't find any info on either the Rainbow or Max BMW parts fiche. I will call the dealer on Monday but in the meantime any info appreciated.
2013 Twincam.

[RTs4me]

Have a look at the 'Steering' section of the parts fiche. This section seems to cover the handlebars and associated assemblies attached to them.


I think that the part you are looking for is described as a 'boot'.


Part 5 in this diagram:
http://www.rainbowbmw.com/BMWETK/Produc ... 202500.php

[Our Gee]

Good on yer, just about the only section I didn't look at. Thank,s a lot.

[pwbike]

I had a bit of a weep/leak on mine, the metal cover needed to be oilstoned flat and then it sealed OK.

[Our Gee]

That's interesting, having had a good look at mine it would appear that the gasket (rubber seal bellows) is supposed to locate in a narrow recessed groove at the edge of the cover. I can,t see how "oil stoneing" the cover flat would help. Looking carefully I noticed that at the rear edge of the cover there are two "slots" about a millimetre deep which the gasket seems to partially seal. Are these slots to allow "venting" ? and are they the cause of leaks ?.

[pwbike]

I haven't removed the cover to see how the seal is arranged.
At a service I showed the workshop that it was weeping and they said they'd have a look at it.
On the service invoice it just showed that they'd removed the cover and flattened the mating face on an oilstone.
It hasn't weeped since.
I'd assumed it may have been distorted from a previous overtightening, or was somehow not machined correctly from the factory.
But it's possible that they meant the top mating face of the reservoir body, rather than the lid.

[David.]

As the brake fluid level in the reservoir falls due to brake pad wear, the boot (seal/gasket) must be able to vent, otherwise the vacuum below the seal would cause it to become distorted. Provided that the brake fluid is not above the max. level, it shouldn't leak. If the brake fluid is changed or topped up as the pads wear, the action of pushing the pistons back in the calipers when cleaning or replacing the pads could result in the fluid level rising too high and leaking.

[Our Gee]

That's probably the reason why mine has "weeped". Pushing pistons back during caliper service. Should have thought of that !!.

[simbo]

The rubber boot is under the cap to allow for the movement in fluid from use and wear on the pads, it also acts as a seal to prevent moisture getting in the fluid from the atmosphere. Mine was past its sell by date on my 2011 and weeping and the fluid in the reservoir was showing signs of contamination from moisture (white sludgy build up) so I replaced the boot and changed the fluid.

[David.]

If the brake fluid is changed or topped up as the pads wear, the action of pushing the pistons back in the calipers when cleaning or replacing the pads could result in the fluid level rising too high and leaking.

My RT recently had the brake fluid changed at a BMW Dealer. With the handlebars in a position where the reservoir is horizontal, the fluid level was between the min & max levels. Cleaning the calipers & pushing the pistons back (almost flush with the caliper face) resulted in the fluid level rising to the max level. Because the bike will be stored with the handlebars on full lock, the brake lever was pumped to reduce the fluid level. The front wheel is still free to rotate & further pumping of the brake lever will be required prior to hitting the road next year.

[Sullivj]

Mine was overfilled by the dealer, which made it weep.


I took some out with a syringe - problem solved.

[David.]

Looks like BMW Dealers do like to overfill the brake fluid reservoirs. Checked the rear brake fluid reservoir level prior to cleaning the rear caliper. The level was more than the max., probably why I found a load of blue roll stuffed around the reservoir under the seat when I got home after the brake fluid service/change. As above, reduced the level by using a syringe, prior to pushing the pistons back during the cleaning process. The foot lever was pumped to bring the pistons towards the pads, but not too close, allowing the wheel to rotate freely. This leaves room for the pistons to move when commissioning the bike for use next year.

[David.]

Noticed a slight weep from the front brake fluid reservoir, might have been due to the high ambient temperature when out last Saturday.

As a precaution, have ordered a new rubber boot, £12.49 inc. free P&P from my local BMW dealer.

[David.]

The new rubber boot arrived today, great service from Cooper BMW Sunderland.

The old rubber boot was distorted & had brake fluid on top of it beneath the cover. Hopefully, the replacement will stop the leak.

[simbo]

The new rubber boot arrived today, great service from Cooper BMW Sunderland.

The old rubber boot was distorted & had brake fluid on top of it beneath the cover. Hopefully, the replacement will stop the leak.

That'll be condensation under the aluminium cover, the rubber boot stops that entering the brake fluid.