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3-Cylinder Platform Rear Brake Issues

60K views 339 replies 64 participants last post by  bioluminescence 
#1 ·
There are numerous accounts of air in the rear brake system of several models of the 3-Cylinder bikes.
I was perusing a Ducati Forum and ran across the following issue with the crimping on certain ABS equipped Ducati bikes.
As this issue pertains to a very similar, if not the same, equipment on the MV bikes, I thought it might be of interest and might be the actual problem.

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#6 ·
@Panchomeneguzi ... if you look across brands, you will see that most rear calipers are in that orientation.
 
#8 ·
Mine is fine since bleeding the shit out of it (no specialprocedure, just as normal and I didn't remove anything) when it was a month old, and I hang a 5 litre tub (of PVA glue if it makes any difference) each time it's parked up in man cave. I took it out the other day, first time in months and rear brake worked a treat, anti lock kicks in and slows bike more than I always remember when using it alone.

I know it's not acceptable on a premium product but I don't mind. Hanging the weight off and plugging in the charger is all part of the locking up process now.

Just my 2p's worth.
 
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#11 · (Edited)
MV have issued a new "MV Agusta internal service bulletin that MV dealers and service agents are following" with a new bleed procedure for the rear brake. It seems that the process has been carried out on some bikes with the process being filmed and sent to MV. The MV NZ rep advises that it is an internal document so cant be shared. But he is sorry. Surely someone will leak it!

The source of this was a discussion on the MV New Zealand facebook page where a few owners of 3 cylinder bikes were expressing frustration but the discussion has since disappeared from the page.
 
#12 ·
@Tony F: How "new"?

There has been this Tech Bulletin since last summer:
 

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#14 ·
Let's see it!!!!
 
#18 ·
Hi there and thanks. It's actually my eldest Son's bike and I've taken up trying to resolve the issue on his behalf. Yes we work with Simon here in New Zealand and he is being supportive in terms of getting the brakes bled under warranty, especially since the Dealer and Service Agents in Auckland have either folded (Red Baron) or relinquished or lost the franchise (Cyclespot). Our nearest Service Agent is now halfway down the North Island, or there are two in the South Island. As an engineer and based on our experience with the bike from new, I'm not at all convinced that the new bleeding procedure (which supersedes Service Bulletin #189) will offer anything other than a temporary benefit. I'm also unconvinced that the issue is related to heat soak, given that I looked at a brand new machine in the showroom at Cyclespot which had not been ridden, had 0kms on the clock and had exactly the same issue - namely no rear brake. It would have left with a solid brake pedal from the factory, yet somehow in transit and sitting it was now so full of air as to not operate. This is a serious safety issue, the bike would not pass our local WOF inspection and therefore would not be covered by insurance should an accident occur. I'm particularly keen to hear from anybody else with this issue on the ABS 3 cylinder platform - preferably off forum at this stage. Please feel free to PM me as I collate things. Thanks.

Cheers, Richard
 
#19 ·
There have been a lot of members raising the issue on this forum Richard, hopefully some will contact you.

Was the new bleed procedure carried out on your son's bike?

A suspension specialist I deal with told me he had a spate of premature fork seal failures which he ultimately put down to a shelf life issue with the rubber deteriorating over time. He is now managing stockturn more closely and says the problem has gone away. Its hard to envisage this type of issue causing such widespread brake problems unless MV has been working through a huge stock pile of M/Cs. But mildly interesting.
 
#20 ·
Hi Tony, no we haven't been subjected to the new bleed procedure yet. I don't think that it's a rubber deterioration issue. Our bike went into Cyclespot at 3000 or so KM's to have the issue investigated. They basically pushed the bike out into the weather each day for 2 months until a set of master cylinder seals arrived, which apparently they hadn't ordered... It was only at that point that they stripped the bike and pronounced that the master cylinder was stuffed (the diagnosis I had delivered the bike with after having the system bled by a service agent 4 weeks before). If it were a seal issue they would have fitted seals, but no they ordered a complete new replacement cylinder. You would only replace the cylinder if the bore was scored or corroded. My money is on the latter but unfortunately I didn't think to ask to see the faulty component. I have another MV owner delivering me a supposed new M/C in a few days time (need to cross check the part numbers) and I'm going to offer to pay for Dillon from TR20 to strip the master cylinder from our bike to inspect it, before anybody attempts the new bleeding procedure.
 
#21 ·
Folks, we have the local importer and one of the Authorised Service Agents making a house call tomorrow to carry out the new brake bleeding procedure as per the latest service bulletin.

However, I'm paying the Service Agent to first strip and inspect the rear master cylinder before any bleeding is attempted.

I've made something of a breakthrough today in my investigations which very much supports the theory I've been working on.

I should have more to share tomorrow.
 
#22 ·
I will let you know my experience. I have 2016 TV800 that had same rear break problems like everybody else. My dealer would bleed the breaks and they would work for few weeks and then fail again. Then I decided to push him to add insulation to the rear break cylinder to protect it from the heat coming from the rear exhaust. We did that and again I had this problem in few weeks. After that I went to a different service where they finaly managed to completly beed the system and change the brake fluid 100%. This was more then a year ago and my rear break is working fine. Right now I am not sure if this last bleeding changed the situation or was it a combination of heat shield + bleeding. In 10 days I will be visiting this service again and then I will ask them what they think is the problem. I am sure they did not change the brake cylinder or something like this...


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#24 ·
You can only get air trapped inside the ABS pump out by cycling the pump, either by manual activation (hard braking) or by use of diagnostic software.
Any air left in the pump will eventually cause soft pedal/lever. But this rear brake problem on the MV 3 cylinder bikes seems to be on both ABS and non-ABS bikes....
 
#26 ·
Ok, I think we have the smoking gun in our case. Had a house call from the Importer and local Authorised Service Agent today to perform the new brake bleed. However, I made them pull the master cylinder to bits and inspect first. Some pretty serious corrosion on both the bore and the piston. I believe that this corrosion is the source of the 'air' in the system. Logically if you have you own onboard bubble factory, you can bleed it all you like, but it's going to gradually go soft again.

Now that we know that it is corrosion, where is the corrosion coming from?

The corrosion appears to be at the point of greatest contact between the piston and the bore - the outside edge where the pushrod is doing the propelling.

I now have another theory and that the issue is perhaps not a galvanic reaction between dissimilar materials - but the effect is similar. What if it's arcing between two electrical contacts?

On the other end of the cylinder you have a power source, namely the hydraulic brake light switch. If there were some current leakage on the +ve side of this, it might be trying to earth through the hydraulic fluid (which is conductive) and exit stage left through the nearest point of contact. This would seem to be the outside edge of the piston where there is perhaps side pressure form the pushrod and less support of the piston by the seals. The erosion seen is in fact the result of minute arcing and presumably the arcing creates a tiny stream of gas bubbles, which then makes the pedal go soft.

I need a big drink now... Brain hurts.

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#27 ·
In order for your theory to be viable, the voltage must be transmitted to the offended area at all times. Were that the case, the you would be able to check for voltage, or current draw, from the push rod to ground.....
My opinion is that this is unlikely, but not impossible. You could have a very tiny insulation leakage.

Do you have a diagram of the inner working of the switch contacts?
 
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#28 ·
Agree ignition on and the +ve side of the switch would be live. If you look at the pattern of 'arc' marks on the piston, the forward line is slightly curved almost as though the piston is being pushed fractionally off centre to the point where it make contact with the bore. I'm sure that somebody who knew there way around a multimeter might be able to confirm or disprove. A dodgy brake light switch might explain why the fault seems somewhat random between similar bikes.
 
#29 ·
IMHO, this is a highly unlikely scenario and the reasoning is simply thus: On my bike, as a test case, the bike was stored for six months with the key off and freshly bled. When the bike was removed from storage, the rear brake was in need of a good bleed. No electrical input should have been present for electrolysis to occur.

Did you look at the crimps on the rear brake lines as per the Ducati reference? Are they of similar design?

With air, comes moisture, with moisture and air, comes corrosion. In dissimilar metals, no electricity needed. It simply creates its own through galvanic action.
 
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