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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.
 

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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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Could be simple voodoo cure but I was told by a MV dealership to lock up the rears activating the ABS system and then bleed the brakes. Have not tried this yet.
 

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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....
 

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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.
Thanks for all the investigative effort.
 

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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.

479587



479589
 

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Discussion Starter #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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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.
 

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Discussion Starter #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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Well then perhaps this issue is simply one of dissimilar materials as Nissin had before. No, I haven't inspected the crimps as the importer and the Service Agent were working on the bike, but will.
 

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Probably, but it's still well within warranty and needs a new rear brake cylinder. I'll wait to hear what MV Italy come back with.
 

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Simon said very little, Dillon agreed that there was unusual erosion/corrosion. Just had another thought - what if the dissimilar metals are in the brake light switch and are the source of the bubbles, but this is causing a minute short which exits at the contact point between the piston and cylinder... ? Unless you dissect the switch, it would be hard to know.
 

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Discussion Starter #35
Again, switch off (winter storage)....no electrical source.
 

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Mate, two separate thoughts - your own quote " In dissimilar metals, no electricity needed. It simply creates its own through galvanic action" - so a reaction going on somewhere in the switch, fizzing quietly away on its own with the bike switched off. This could be the source of the 'air' whilst parked. The erosion damage in our case could be simply applying the brakes and triggering the brake light. I'll check tomorrow, but pictures I've found would indicate the the switch is a single wire - so an earth switch. Is it earthing through the piston? The marks sure point that way...
 

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Discussion Starter #37
For galvanic corrosion to occur, you need dissimilar metals and an electrolyte.

Water is an electrolyte. I don't believe brake fluid is. I'll look that up and report back.
 

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Discussion Starter #38
Attached is a study that was done early on in ABS brake systems research of corrosion issues:


Here is the conclusion section, that verifies brake fluid has such a low conductivity that is was difficult to do the tests. Modifiers of water and copper had to be introduced to have measurable results.

6.0 CONCLUSIONS
The hypothesis that the large surface area of copper in the brake lines corrodes slowly during
normal service resulting in the accumulation of copper ions in the brake fluid that can be
transported to other parts of the braking system and cause corrosion of ferrous alloys, once the
corrosion inhibitors become depleted, was evaluated by conducting exposure tests in brake fluids
artificially charged with copper ions. The results of the exposure tests are consistent with this
hypothesis. The largest copper particles observed during this work were about 8 μm in diameter
following only 5 hours of exposure. The results indicate that there is no physical reason why
longer exposures will not result in larger particles.
Electrochemical measurements were conducted to evaluate the difficulty of conducting
electrochemical measurements of corrosion rates in the ABS brake fluid environment. While the
low conductivity of these fluids is low enough to inhibit the application of the methods, it is
concluded that electrochemical measurements can be used to study the electrochemical properties of
metals in these fluids, measure corrosion rates, and evaluate the effect of changes in chemistry and
time on the corrosivity of these fluids, but the special methods and techniques developed for use in
low conductivity electrolytes need to be used to compensate for the errors that result from the low
conductivity of the electrolyte.
The analysis of the results of this work indicated that exposure tests conducted in sealed
containers of fresh brake fluids with 5% by volume water added prior to testing are not
representative of in-service corrosion conditions. Adding water prior to immersion of the coupons
will result in passivation of the copper coupons on immersion and excluding air during the
exposure test eliminates the oxidizer which can cause corrosion of copper. These two features of
the standard corrosion test should result in corrosion measurements that are lower than those that
can occur in-service.
 

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This is getting interesting. As a reminder of my B3 experience: a) bike brake ok for 1.5 years, then b) sudden total loss, plenty of fluid, c) had my Guzzi master mechanic diagnose-- he replaced faulty rear master cylinder and bled, d) brake lost pressure gradually over next two months, e) bike in for maintenance, had another bleed about a month ago--brake so far remains functional.

My guess/bet: something to do with MC failure? Cause either faulty Brembo components, or as diagnosed above some sort of electrical corrosion? Here in Houston, TX we have incredibly humid/wet climate-- is that part of the issue? The heat as cause theory, to me, makes unknown sense unless heat is swelling MC components? Aprilia forum seems to believe heat as cause.

It would be wonderful to have this rear brake problem resolved. Agree: its a major safety issue. MV corporate engineering needs to lean in on this problem-- help figure it out, and issue a recall other than bleed it constantly.
 

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The Nissin front brake master cylinder that was a global recall by Suzuki (even though some Kawasaki and Honda bikes had the same part and problem, and they didn't recall) had a plating QC problem on the master cylinder piston. The poor plating corroded allowing galvanic reaction with the spring creating gas that accumulated in the bore of the cylinder due to the side port to the reservoir.
Water in the fluid was a required element, as those bikes which had routine brake fluid changes per the maintenance schedule never had problems, and the majority of documented cases were in areas that experienced routine very high humidity levels.

On the MV, the gases could move up the brake hose on its way to the caliper and accumulate at the high point of the hose.
So is there an endemic problem with the piston plating, or some manufacture process that is causing damage to the piston, and related corrosion/galvanic action?

I don't think the normally open hydraulic brake light switch is the cause.....but an ammeter in series reading milliamps (or microamps) would quickly reveal any leakage there.
 
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