Tyres, Brakes and Suspension » Rear brake failure

Hi, I have a 2017 R1200RS which had 50 miles on the clock when purchased in Feb 2022 and now has 1000 miles in June 2022. During this time the bike has been in and out of my local BMW dealer, under warranty, as the rear brake goes spongy after 30 or 40 miles and then bottoms out completely with no pressure. The brakes have been bled 3 times by the dealer and a new rear master cylinder was fitted last week. However, after a further 50 miles of testing, the brakes have disappeared again at the rear. The front brakes work fine. No idea if the linked system is working as I find it hard to tell and the bias is probably less than 20% anyway. No brake fluid leaks. They provided no spare bike last time. So I am getting mightily hacked off with BMW. Does anyone have any ideas before it goes back into the shop for probably another 5 weeks!!

A 5yo bike that only had 50 miles on it? I'm curious what the backstory is there.

Regardless, it obviously sat around for a long time and I'm wondering if the master cylinder has suffered for that.

No fluid loss = faulty master cylinder.

I wonder if a separate component can be causing the issue?

My Mazda pickup has a hydraulic clutch. The master cylinder isn’t mounted level, but at an angle. The first time I flushed it, I let some air get into the line…vastly affecting its function. I had to have a friend keep the clutch to the floor as I kept bleeding the system. When I did it myself, the object I used to keep the clutch depressed slipped and that’s how air got pulled into the system.

I say that because maybe air is in the system between the rear pedal and the master cylinder? It doesn’t make sense, but if the pedal acts like a pump and there’s fluid involved, maybe an air bubble keeps showing up.

First time I did the fluid on my RS, the rear was spongy. Next time, I flushed twice as much fluid through the system, and I was surprised how much air came out. I thought I did it correctly the first time…apparently I was wrong.

I know it took two bottles of dot4 when bleeding the neighbours R100RS until we realised the 'bubble trap' along the swing arm.

We took the caliper off the bike and hung it from the seat, old peice of tile between pads to mimmic the disc and bled the system in minutes.

The other 'old school' when having spongey front barkes was to wrap/cable tie the lever 'on' overnight and the extra compression often cleared the poor brake.

Looking at the system on the 2018 model, I wonder if you have an air bubble in the line going to the ABS modulator. As I recall, the ABS is always working…just not noticeably so.

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Thanks. I have asked them. They are willing. However, they are 200 miles away and there are no parts in the UK for oddball repairs. The Master cylinder took 5 weeks to be delivered! But that's not the solution as it failed again. Cheers.

Hi. That's what it could be. I noted in the Adventure Rider forum that they had a similar problem or a failed modulator. I have suggested this to BMW and sent the forum discussion. Let's see. Thanks.

BMW UK advised the dealer to go through a lengthy brake bleed process. The bike was in the shop for 4 days! Still failed. I was hoping the dealer had a good idea of how to properly bleed brakes. However, it's easy to see how they could have the apprentice do it with no supervision as it seems an easy enough process. I like the explanation though. I will use the details to chat with the dealer when I find a repair slot with them.

Edit
The other 'old school' when having spongey front barkes was to wrap/cable tie the lever 'on' overnight and the extra compression often cleared the poor brake.

You can try 'barking' to warn of possible impact when they fail but probably safer to get them working!

I know when I changed the clutch fluid the advice was 'bottom to top' forcing fluid from slave uphill to the master cylinder.

I guess in production bmw have to find the quickest, safest way and leaving each days bikes 'around' for a check is impossible.

Same with all new cars/bikes etc, easy in a producton line, slower at a workshop.

Hi. The initial buyer broke his back just after the bike was delivered. He continued to pay all the PCP off hoping he'd get back on board. In the end, he traded for a BMW scooter as he could no longer ride a leg-over bike. Sounds strange but there are lots of stories like that around. It could be the brake never worked properly from delivery and it has nothing to do with long-term storage. It took me a little while to notice as I don't often use the rear brake on its own. The linked system works well for all normal riding. The bike also looks brand new. Not a mark or sign of use anywhere. Clearly stored in a dry garage for the period. BMW was happy to provide the full warranty on sale to me. Seemed like a reasonable story and a reasonable deal. That's not my concern. I am hacked off at the poor service from BMW. It's now the end of June and they still have no idea what the problem is.

I see the logic there. The idea of running a workshop is to get bikes in and out quickly to get the cash through the door. Problems requiring extensive diagnostics are a pain. I understand that. However, the brake system is relatively simple apart from the ABS cluster of parts. And even with that group of parts, there must be tell-tale signs that would signify there was a problem in that area. I think their main problem in the UK at least is parts availability. It seems impossible for even relatively large dealers to get them. The days of parts storage went years ago with logistics chain improvements and almost just-in-time delivery. However now with logistics chains broken, parts are not being kept at dealers with the result we have to wait for weeks on simple parts. There are second-hand parts available but a dealer won't fit them under warranty.

Zitat von Guy im Beitrag #12

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Hi. The initial buyer broke his back just after the bike was delivered. He continued to pay all the PCP off hoping he'd get back on board. In the end, he traded for a BMW scooter as he could no longer ride a leg-over bike. Sounds strange but there are lots of stories like that around. It could be the brake never worked properly from delivery and it has nothing to do with long-term storage. It took me a little while to notice as I don't often use the rear brake on its own. The linked system works well for all normal riding. The bike also looks brand new. Not a mark or sign of use anywhere. Clearly stored in a dry garage for the period. BMW was happy to provide the full warranty on sale to me. Seemed like a reasonable story and a reasonable deal. That's not my concern. I am hacked off at the poor service from BMW. It's now the end of June and they still have no idea what the problem is.

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Does BMW say anything about vacuum bleeding?