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Hotmop

R1100RT Rear brake master cylinder rebuild kit. Alternate FOUND!

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Hotmop

This may be existing knowledge, but I could not find in searching so I figured I'd start a thread to help others in the future. 

 

The rear brakes on my RT failed on me. With @dirtrider help, we eventually diagnosed to the pressure seal being worn to a point where the piston would just pass thru the fluid in the cylinder. 

Facing the $150+ cost of BMW's 34312330456 replacement for what should be a $25 kit, I channeled this recurring parts frustration into some Google searching. 

 

Turns out there is a Ducati Brembo kit for a "12mm Front Brake / Clutch Master Cylinder". The pictures showed a piston that looked VERY similar to the BMW. Mike at Gotham Cycles was kind enough to open a kit and give me the measurements. It was close enough to risk $25. 

 

The kit is listed as Brembo 110436292 . 

 

It came in last night and my calipers say we have a dead-on match for all the parts that matter. The piston clearly has a shorter pin section but the ID diameter of the pressure seal and OD diameter of the o-ring sections are exactly the same. The spring is same except for the seat, but that should be easy to move over. The brass (?) washer under the pressure seal is identical.

 

I'm traveling for a week before I can get this installed and tested. I'll follow-up with results soon. 

 

- Matt

 

Comparison of usable parts from Ducati rebuild kit 

 

Clearly the BMW seal on the right is showing it's 20 years of wear. 

Close-up of Ducati and BMW rear master cylinder pressure seal

 

 

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GRIPPY
7 hours ago, Hotmop said:

This may be existing knowledge, but I could not find in searching so I figured I'd start a thread to help others in the future. 

 

The rear brakes on my RT failed on me. With @dirtrider help, we eventually diagnosed to the pressure seal being worn to a point where the piston would just pass thru the fluid in the cylinder. 

Facing the $150+ cost of BMW's 34312330456 replacement for what should be a $25 kit, I channeled this recurring parts frustration into some Google searching. 

 

Turns out there is a Ducati Brembo kit for a "12mm Front Brake / Clutch Master Cylinder". The pictures showed a piston that looked VERY similar to the BMW. Mike at Gotham Cycles was kind enough to open a kit and give me the measurements. It was close enough to risk $25. 

 

The kit is listed as Brembo 110436292 . 

 

It came in last night and my calipers say we have a dead-on match for all the parts that matter. The piston clearly has a shorter pin section but the ID diameter of the pressure seal and OD diameter of the o-ring sections are exactly the same. The spring is same except for the seat, but that should be easy to move over. The brass (?) washer under the pressure seal is identical.

 

I'm traveling for a week before I can get this installed and tested. I'll follow-up with results soon. 

 

- Matt

 

Comparison of usable parts from Ducati rebuild kit 

 

Clearly the BMW seal on the right is showing it's 20 years of wear. 

Close-up of Ducati and BMW rear master cylinder pressure seal

 

 

Good to know thanks.Looking for similar info on front master cylinder.

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GRIPPY
On 8/16/2019 at 10:23 PM, Hotmop said:

Wait, doesn't BeemerBoneyard still sell those? 

https://www.beemerboneyard.com/32722332037pk.html

 

Thanks,may be best bet, but with postage and duty(in Canada)it is still pricey.Would like just seals if possible.Next time I have it appart i will measure and see if local hydraulic place can source them.

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Selden
On 8/16/2019 at 10:23 PM, Hotmop said:

Wait, doesn't BeemerBoneyard still sell those? 

https://www.beemerboneyard.com/32722332037pk.html

 

 

That link is for a front master cylinder rebuild kit:

 

Quote

COMPLETE 20mm rebuild kit for the front brake brake master cylinder on all K100 4V, k1100 and R850/1100 bikes except the R1100S. 

 

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Hotmop

Because that’s what @GRIPPY asked for. 

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tvpierce
On 8/16/2019 at 2:09 PM, Hotmop said:

 

 

Nicely done.  I'd done similar research a few years ago and finally gave up.  

 

Thanks for posting!

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