master cylinder rebuild kit leaking

[mgordon]

Just had a rebuild kit installed by a BMW shop about 4 months ago. Today i noticed brake fluid all over the plastic after a long start/stop ride, mostly highway. How long are these seals supposed to last? It's been about 2k miles. Is there a warranty on the parts?

[deilenberger]

Just had a rebuild kit installed by a BMW shop about 4 months ago. Today i noticed brake fluid all over the plastic after a long start/stop ride, mostly highway. How long are these seals supposed to last? It's been about 2k miles. Is there a warranty on the parts?I'm surprised a shop would do a cylinder rebuild.. chances are fairly good that the rebuild will fail just like yours did - and they end up eating the labor to do it again. BMW parts are warrantied for 1 year or 2 years depending on what the part is. Will they cover a rebuild kit where success is highly dependent on the parts being reused and the skill of the rebuilder?

Dunno... If it was me - I'd be asking the question at the shop that did the rebuild.

And get the fluid off the paint - it will eat it up real quick.

[AntonLargiader]

I'm surprised a dealer would do that also; by 'BMW shop' I assume you mean dealer?

That said, I use these kits pretty frequently and AFAIK have not had one leak. You need to be really careful with the cleaning and installation. For a bike with a custom or otherwise very nice paint job (Legends bike, etc.) I would replace the MC rather than rebuild it, due to the risk.

If it's leaking at 4 months & 2000 miles, it was never right.

[mgordon]

thanks, Anton. The shop is claiming that there is no guarantee with the rebuilds, and that the cylinder must be replaced, due to age/wear. They said to drop by and they'll have a look, but at what? To see that it leaks, duh. They are an independent BMW repair shop, not a dealer. But i have been dealing with them for 15 years.

[lazywizard02]

On my 96RT the rebuild process was not at all difficult. There are several things that could affect the leak. Typical are the barrel, cylinder, will show pits as a result of water inclusion over a long time. Brake fluid is hygroscopic which attracts water.

You can buy a brake hone for a few bucks and even finish it on the bike i believe. Run the hone with some brake fluid to wet it and polish the barrel with a few strokes at a time. A smooth barrrel may still show "stains" from earlier pits and be good enough for rebuilding. You don't want to take large amonts off.

The seals themselves can be either nicked or placed on incorrectly. Such as when you roll the o-ring on the piston, you don't want to produce a curl on it. You could even find they used the wrong kit. But dealers seldom make mistakes, right?

Buy a new kit and follw the manual's instructions. You can do it in an afternoon. Be careful, as noted, to not let the volume of brake fluid fall low and require a purge of the ABS. Worst case is you get the dealer to purge it or find a thread with a technique. I had no difficulty there or bleeding the system.

[AntonLargiader]

On my 96RT the rebuild process was not at all difficult... ... when you roll the o-ring on the piston...

The BMW kit comes with the lip seal already on the new piston. There is no O-ring. I have a write-up on this procedure on my website.

[warredon]

Anton, last fall my front master cylinder started leaking badly on my K1. I had only had the bike for about three weeks and it is my first K bike. I've been riding airheads since the 70's and had no clue about the K series.

I read your very well written article on the master cylinder repair, it appeared to be the same cylinder that my K1 has. I bought my piston kit from Beemer Boneyard. Your write up made the job easy for me, and it has not leaked yet in the seven months since. Thanks! I also added Speedbleeders at that time before changing the fluid.

[mgordon]

Cleaned up the master cyliinder dust seal/cover last night. I rode about 75 miles today and it's totally bone dry now. Wierd. I'm still going to pursue it with the shop, as i've barely put 1000k on the bike.

[mgordon]

It's not leaking:clap

Water is getting in under the MC plastic cover when it rains, which makes it look like the dust seal is leaking brake fluid, but it's only water pooling! What a relief!!!