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Discussion Starter #1
All,

Ok, my 2018 MV B3 Brutale RR Dragster showed a sudden failed rear brake. Took the bike into my local expert bike mechanic--Mike Haven at MPH here in Houston, TX. We have no MV dealer in Houston, TX. Gave him the recommended MV brake bleed service bulletin. His reaction: the MV bleed is temporary, what is cause... need a solution. Today he told me brake is fixed. Diagnosis: "Wear on seal cups. The bore looks great, so we put a piston and seal kit in it. Its a Nissin , japanese part, not brembo". He used this repair kit:


I will pick the bike up later this week, and update results -- will the rebuild permanently fix the rear brake B3 sudden fail issue? Mike's initial thought when I rode my MV in: well, lots of Brembo rear brakes on the big Guzzi bikes failed -- cause was Brembo master rear cylinder. Front brakes not a problem.

So there you go.
Perhaps MV needs to issue a recall?
 

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Thanks for updating with the (potential, and hopeful) fix! I wonder if new bikes will still have this problem...
 

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That Nissin rear master cylinder is very much the same as quite a few Japanese sport bikes. Maybe MV got some poor quality control on their purchase order production run??
 

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Discussion Starter #4
That Nissin rear master cylinder is very much the same as quite a few Japanese sport bikes. Maybe MV got some poor quality control on their purchase order production run??
Possibly... I will report how my Dragster RR brakes perform over time. Mike Haven is not a fan of Brembo rear brakes, and said he has seen many cases of this rear cylinder cup failure. Bad batch? Quite possibly.
Cant wait to have my Dragster back, I miss it.
 

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All,

Ok, my 2018 MV B3 Brutale RR Dragster showed a sudden failed rear brake. Took the bike into my local expert bike mechanic--Mike Haven at MPH here in Houston, TX. We have no MV dealer in Houston, TX. Gave him the recommended MV brake bleed service bulletin. His reaction: the MV bleed is temporary, what is cause... need a solution. Today he told me brake is fixed. Diagnosis: "Wear on seal cups. The bore looks great, so we put a piston and seal kit in it. Its a Nissin , japanese part, not brembo". He used this repair kit:


I will pick the bike up later this week, and update results -- will the rebuild permanently fix the rear brake B3 sudden fail issue? Mike's initial thought when I rode my MV in: well, lots of Brembo rear brakes on the big Guzzi bikes failed -- cause was Brembo master rear cylinder. Front brakes not a problem.

So there you go.
Perhaps MV needs to issue a recall?
Hope that your rear brake issue is solved with the rebuild kit. On my bike the rear master cylinder was replaced but I almost never use my rear brake on my f3, so it didn't fail from any wear and I also have a heat shield installed to protect it from the hot exhaust. Still the end result after some weeks of stand still is that the rear brake is gone again and the lever goes down to the end. Next week I will look into the issue and hoefully find what is wrong.
 

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I think that heat from the engine and exhaust has a bad effect on the rear master cylinder, hence the factory bikes are relocated and kits are available for this
 

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The myth about heat from the exhaust affecting the 3-cylinder platform keeps being perpetuated. It is untrue.

Here is why:

First picture is a the original 4-cylinder platform with the exhaust (red arrow) and catalytic converter running very near the rear brake master cylinder (Green Arrow).

475609


The second picture is the 3-cylinder platform with the exhaust (red arrow) run to the opposite side of the oil pan away from the rear brake master cylinder (green arrow).

475610


It is NOT heat from the exhaust that is causing the rear master cylinder to become air bound. And if your oil sump is THAT HOT, you will have other problems.
 

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And, just for giggles and being thorough, this is the heat shield/exhaust (green arrow) for the the Second Gen F4 running near and behind the rear brake master cylinder (red arrow).

475611
 

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@Tony F: How in the world did you come to that conclusion? Where I am going with this is what I said in the post...HEAT is not the issue.
 

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Discussion Starter #11
Silent of Service,

Much thanks, and I think you are likely correct. My bet is that the Brembo master cylinder cups are the issue. But I am not a technology/motorcycle mechanic. Rain again today, but Thursday is dry and clear and I will pick up my beloved Dragster and we will fly home. Weekend looks clear also: more miles. I plan a DIY oil change soon.
 

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Based on the experiences that have been described, and my own personal experience, there is an ingress point for air somewhere in the system.
 

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Discussion Starter #13
Rode the bike home, rear brake is a wonderful thing to have. Also had front brake and clutch flushed and new fluid.

I will report any following issues. Fingers crossed this does not happen for a long time.
IMG_8094.jpeg
 

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All,

Ok, my 2018 MV B3 Brutale RR Dragster showed a sudden failed rear brake. Took the bike into my local expert bike mechanic--Mike Haven at MPH here in Houston, TX. We have no MV dealer in Houston, TX. Gave him the recommended MV brake bleed service bulletin. His reaction: the MV bleed is temporary, what is cause... need a solution. Today he told me brake is fixed. Diagnosis: "Wear on seal cups. The bore looks great, so we put a piston and seal kit in it. Its a Nissin , japanese part, not brembo". He used this repair kit:


I will pick the bike up later this week, and update results -- will the rebuild permanently fix the rear brake B3 sudden fail issue? Mike's initial thought when I rode my MV in: well, lots of Brembo rear brakes on the big Guzzi bikes failed -- cause was Brembo master rear cylinder. Front brakes not a problem.

So there you go.
Perhaps MV needs to issue a recall?
Just had the same problem with by 2019 Brutale 800 RC. Took bike to dealer (Monkey Moto, Argyle TX). Nelson said the problem was crappy factory brake fluid combined with location of anti-lock pump being mounted too close to exhaust system. Which apparently causes the fluid to boil off??? They fixed it under warranty and advised me to monitor fluid level and keep replenished with top quality DOT 4. If I have any further issues will report. Thanks. And have a great day.
 

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Having done the MV rear bleed procedure awhile back on my '19 with temporary resluts I went at it again yesterday only to find my reservoir bone dry. I do recall checking it before. There may be something to that boiling off of fluid.
 

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Discussion Starter #16
My fluid reservoir was full-- interesting variations. Riding this weekend, the brakes will get a workout. I will report any changes. Maybe we can figure this out between several owners/bikes and mechanics. Much appreciated!
 
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