Hey! Its leaking from the rear brake amplifier, any troubleshooting tips and tricks, or just some tightning?

 

Thanks guys!

You probably need a rebuild kit available from Motorworks and I am sure other places also but the link shows the components.

Motorworks BMW Motorcycle Specialists - Shop - Spares and Accessories

Kjell.Martinn wrote:Its leaking from the rear brake amplifier, any troubleshooting tips and tricks, or just some tightning?

Around here that part is called a rear brake master cylinder. Tightening it is not an option. A repair kit might work if the cylinder is not worn out. You could consider replacing it with an inexpensive master cylinder that some riders here have done successfully. Here is a link to a thread about that.

I've never had any luck rebuild kits. The only fix that ever worked was to replace the original master cylinder with a Communist one for $13. It's in the thread that Laitch linked to.

The problem I have seen in these master cylinders is that water collects in them and corrodes the bore. Because the casting is so porous the corrosion goes deep and is almost impossible to correct. The communist master cylinders are so cheap it doesn't make sense to try to repair the old ones.

You can extend the life of your master cylinder by packing silicone grease into the boot. It will reduce the chance of water and road crap ingress.
Regards Martin.

MartinW wrote:You can extend the life of your master cylinder by packing silicone grease into the boot. 

I did that following Martin's suggestion. It gets renewed every couple of years. I wring out my moto on the worst municipal gravel roads in Vermont for six months out of the year—rills, ruts, moonscapes and mud. It's all so adorably rustic. The rear master cylinder hasn't been bothered by any of it for years. 

I love silicone grease it saves a lot of headaches. I haven't changed  fork seals in over 20+ years, just I pack silicone grease between the fork seal and the dust cover and change it every couple of years. I would change it more often if riding in dusty conditions. I also pack a bit in around the piston entry point on the front master cylinder.
Regards Martin.

I use the silicon grease in the forks ,never tried it in the brakes but what I do in the brakes is flush out the fluid every season .I had good luck with the rebuild kits.What I did there was really clean the bore then lightly hone it with 1500 wet /dry paper  and then cleaned it again with brake cleaning solvent a couple times .Gonna try the grease in the boots now.Never heard of using it there before .

yamaguzzi wrote:. . . what I do in the brakes is flush out the fluid every season . What I did there was really clean the bore then lightly hone it with 1500 wet /dry paper

When I salvaged the rear master cylinder on my moto, I used a Scotchbrite pad for polishing the bore. It worked well, too.

"...and then cleaned it again with brake cleaning solvent a couple times"


What is this brake cleaning solvent of which you speak?

Thank u guys! Thanks again Laitch for some very good help! I'll try to diasemble the master cylinder and maybe consider a repair kit, or follow the thread u showed me :-) Also great with som advice for maitance and making longer life of the Rear Master, great people with good advices! Thanks!

brickrider2 wrote:"...and then cleaned it again with brake cleaning solvent a couple times"


What is this brake cleaning solvent of which you speak?

I use this stuff pictured here

Another thing! The Rear Brake master cylinder started leaking after removing the caliper and gave air to the system? It will not fix itself when i assembel the caliper again and letting the air out again?

The master failed .It failed when you were in there messing around but that is not why it failed.It was shot before you ever messed around in there. it may not have been leaking at that point but it would have very soon and disturbing it just made it happen a little sooner .Looking for reasons for it's failure is like a dog chasing it's tail.The fact is you have two choices here.You can rebuild it or you can replace it.Getting the air out had nothing to do with the failure ,it just wore out.

I once used that very brake cleaner on a bike with a hydraulic clutch system.  Soon after the cleaning of the slave cylinder it started to cause problems. The brake lever would not return after using the brake.  I limped home and replaced the slave cylinder o-ring, which had swollen, preventing preventing the piston's return. The second time I had the cylinder apart I only used brake fluid to flush it.  The problem never returned.  
I urge caution when using brake cleaner.  It may well be that it is best restricted to use on drum brakes.

Another caution about using CRC brake cleaner is that if you have repainted anything on your bike with rattle can paint it may make a mess of the finish. No need to ask how I know this.

This product is for cleaning brake parts  like brake pads or shoes, metal parts like caliper pistons or wheel cylinder pistons , internal metal parts of wheel cylinders and calipers and master cylinders like the bores after a hone before coating them lightly with brake fluid for assembly.Just about any solvent will eat rattle can paint and lots of stuff will cause rubber to get flabby and swell. Carb cleaner will do the same thing.Using these chemicals requires caution and common sense .They have a specific use and are very good for their intended purpose .You can't just spray away you need to remove parts to work with this stuff or protect the surrounding  area somehow. As for the product,it's not the product that causes problems like bubbling paint or failing rubber it's the user

I have found and others here also mentioned it that when you are bleeding you use the full stroke of the master cylinder and gunk that has collected at the lower part has stuck to the wall and when the piston seal passes over it the seal is damaged. I always now clean the master cylinder before bleeding and so far (fingers crossed) I have not had a failure after bleeding.