R1100RT Rear brake master cylinder rebuild kit. Alternate FOUND!

[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

 

 

 

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

 

 

[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

 

 

 

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

 

 

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

[Hotmop]

Wait, doesn't BeemerBoneyard still sell those? 

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

 

[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.

[AndyS]

1 hour ago, GRIPPY said:

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.

 

How about Motorworks in the UK?

https://www.motorworks.co.uk/vlive/Shop/Parts.php?T=5&NU=15&M=30&Ct=HA&SbCt=BA_15_30_HA_40

[GRIPPY]

13 hours ago, AndyS said:

 

How about Motorworks in the UK?

https://www.motorworks.co.uk/vlive/Shop/Parts.php?T=5&NU=15&M=30&Ct=HA&SbCt=BA_15_30_HA_40

Good to see alternative suppliers thanks.

[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. 

 

[Hotmop]

Because that’s what @GRIPPY asked for. 

[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!

[TexanF250]

Before I get started, I do realize this thread is over a year old. 

 

Back in the spring I came out of the local Home Depot to find the front brakes on my 1999 R1100RT had locked up.  Bought a wrench to pop the bleeder loose and rode it home (3 miles or so) with no front brake.  Decided to do a full brake overhaul on the bike.  Finally getting cool enough to do it (summer - Houston, TX).

 

Thus far I have:

 

- Removed and rebuilt the front brake master cylinder

- Removed and rebuilt both front brake calipers

- Removed and rebuilt the rear brake caliper

- Removed and replaced the OEM BMW rubber brake lines with Galfer SS braided lines

 

Like others, I was having trouble locating a rebuild kit for the rear master cylinder and then I found this thread.  I purchased the Ducati/Brembo kit from Gotham Cycles.  Like the OP (Hotmop) I was willing to gamble the $25 if it would save me $75+.  After all, it is a Brembo kit.  Not Like I'm trying substitute inferior or suspect parts into the brake system.

 

The rear master cylinder is on the workbench along with the rebuild kit.  Ready to go.

 

Questions:

 

Thought I'd ask how yours (OP - Hotmop) turned out before I move on.  Did it work out or would I be better off buying a new MC?

 

Also, did you replace the master cylinder reservoir and line?  I found the reservoir at Motorworks in the UK but mine seems to be fine.

 

What did you use for hose clamps on the rubber line between the reservoir and the master cylinder since the originals are not re-usable?

 

Thanks in advance.  Appreciate any feedback or experience others may have had as well.

[TexanF250]

Well, since I did not receive a reply, I will answer my own questions in the event it may help someone in the future.

 

Questions:

 

Thought I'd ask how yours (OP - Hotmop) turned out before I move on.  Did it work out or would I be better off buying a new MC?

Mine worked out fine.  If I had to do it over again, I would buy the kit and rebuild again vs. cost of a new master cylinder.  Very straightforward job.  Much less expensive.  Brakes are back in service and work great.

 

Also, did you replace the master cylinder reservoir and line?  I found the reservoir at Motorworks in the UK but mine seems to be fine.

I re-used the reservoir but did replace the reservoir line with something I found at the local O'Reilly's auto parts store.  Works fine. 

 

What did you use for hose clamps on the rubber line between the reservoir and the master cylinder since the originals are not re-usable?

Used a standard non-worm gear type hose clamp to replace the factory one-use clamp.

 

Thanks in advance.  Appreciate any feedback or experience others may have had as well.

[Hotmop]

@TexanF250 Terribly sorry I didn't get a reply out first time around. Your experiences is same as mine. Everything worked out fine. I had used my existing reservoir and had a re-usable clamp on it.

 

Cheap and easy rebuild and the brakes have been 100% solid ever since.

[Brodiepunker18]

On 8/16/2019 at 1:09 PM, 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

 

 

 

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

 

 

 

i don’t mean to resurrect such an old thread but when you used this kit for the rebuild, did you use the new piston with the shorter pin? Or did you reuse the bmw piston? 
 

I’m doing my whole brake system and this is something I need to know.
 

Thanks,

Eric

[dirtrider]

1 hour ago, Brodiepunker18 said:

 

i don’t mean to resurrect such an old thread but when you used this kit for the rebuild, did you use the new piston with the shorter pin? Or did you reuse the bmw piston? 
 

I’m doing my whole brake system and this is something I need to know.
 

Thanks,

Eric

Afternoon Eric

 

Hotmop hasn't posted here since September 22, 2020 so you might try messaging him.

 

That piston travel limiter is probably in your master cylinder for a reason so you might want to think about re-using your original piston.  

 

If you decide to try the short limiter piston then you might assemble the master cylinder with JUST the short limiter piston (no rings or cup, just the spring. Then hook the pedal up & slowly cycle the foot pedal looking for proper push rod tracking & a non-critical working angle at full stroke.  

 

The short limiter piston will obviously work as long as you have a good air-free normal foot-lever stroke as the hydraulic pressure build up will limit piston travel. Where the problems can occur is during bleeding or IF for some reason the piston travel goes long, like air in the system, or a pad kick-back event. 

 

 

[Brodiepunker18]

@dirtrider

 

ill probably just reuse the original piston for the reasons you mentioned…just was wondering if they had or not since it wasn’t clarified in any of the posts.

 

thank you

[lymington_bob]

I have a 2011 R1200GS with a leaking rear master cylinder. The BMW replacement is extremely expensive. The cylinder has an internal diameter of 14mm. Anyone know an alternative to the BMW? I have found a Ducati one that externally is identical but is 13mm. Any thoughts as to whether this would work? Any advise would be appreciated. Thanks Bob (UK)

[dirtrider]

24 minutes ago, lymington_bob said:

I have a 2011 R1200GS with a leaking rear master cylinder. The BMW replacement is extremely expensive. The cylinder has an internal diameter of 14mm. Anyone know an alternative to the BMW? I have found a Ducati one that externally is identical but is 13mm. Any thoughts as to whether this would work? Any advise would be appreciated. Thanks Bob (UK)

Morning   lymington_bob

 

You are posting your camhead brake question in an oilhead thread so way different ABS  braking systems. 

 

You need to post your camhead brake question in the camhead forum so this  thread doesn't get hijacked then become confusing to future readers and become very confusing to future 1100 brake system searches.