Fix for R12S rear brake

[Lentz]

Like most of you, I've been unhappy with the rear brake on the R12S and have been looking for a fix. I found a master cylinder off of a trials bike with a 9.5mm piston and the right bolt spacing. The 9.5mm piston provide a 34% increase in hydraulic leverage over the smallest Brembo, which is 11mm. The rear brake will now noticeably slow the motorcycle.

You have to drill out the threads in the M/C as this one is made for the bolts to thread into it rather than through it. I started with a .234 drill and went up in 1/64 increments until I got to .250 and didn't have any problem getting the hole straight. The aluminum was a bit gummy.

The second thing is that my BMW boot is permanently affixed to the MC on my bike. To fit the gas gas unit I had to take a boot off a brembo I had laying around and put it on the gas gas. By boot, I mean the rubber part that the push rod goes through. Maybe Kurvey girl or someone could get this part separately.

Here is the link. AJP Brake and Clutch Master Cylinders from AJPAmerica.com Make sure you get the pro model. BT280222010 Rear Brake master cylinder, DOT4 remote reservoir type. ( 9.5 mm bore ) OEM GASGAS Trial Pro model 2002~2010. I'm putting a picture at the end of the post.

If someone wants to put together a package deal, you can become a dealer for a $1000, which means that the MCs can be bought for about $85 instead of $105. So if 12 people sign up, you get 20% off. I thought the guy I talked to was kind of a dick about it though.

Now for the controversial part. BMW says to set the pedal up with .080-.120 clearance. I can't see any point in that because the M/C has a built in spring that pushes the piston up against the circlip in the M/C. So whether there is .010 clearance or a mile, it doesn't affect where the piston is when you are not on the brake.

I felt the lever has too much travel and I ground off the protrusion on the brake lever that serves as a stop and the set the clearance up (with out the lever spring on) to .035-.040. That's about .020 at the push rod and about .080 travel at the lever before the push rod touches the M/C piston. Altogether by tightening up the clearance and grinding off the stop, I took about .160 to .200 out of the travel (I'm sure enough to more than make up for the smaller piston).

I've driven about 35 miles with no problem and the push rod can't possibly get hot enough to take up the slack.

Ok so tell me I'm stupid.

[RIQUE]

Holy cow I just realized my 1200 has a rear break!

[Lentz]

I had this bookmarked in case any of you Limeys were interested and forgot to post it.

Splat Shop - GasGas Pro Rear Brake Mastercylinder

Pretty pricey though compared to the US and I'm assuming there is VAT on top of the 83 quid.

[Lentz]

Your MC boot may be detachable. It is on my R11S. Brembo makes them both ways and it may just depend on what's supplied with your bike. So if you are interested in doing the conversion, I wouldn't assume your boot is like mine (permanently attached).

I'm kind of surprised this thread hasn't generated more interest. People went nuts over buying a bearing kit for the brake lever and there were a couple of runs sold out of that product. It's the Werner kit I believe.

I couldn't see that fitting a needle bearing would do a whole lot more for braking force than keeping the stock bushing greased, although it would seem to be lower maintenance.

The different master cylinder really works.