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2017 B3 Rear Brake

7K views 43 replies 18 participants last post by  Teeps 
#1 ·
Something I'm noticing recently, when on a hill my rear brake wont hold me when setting off. On a side road I wanted to see how much pressure it took to engage and I have to depress the lever quite a bit to feel ANY sort of braking. In fact my heel is off the peg and I have to push to rotate the lever almost 45 degrees to get any sort of bite. Is there an adjustment I can make to engage sooner in the rotation??
 
#3 ·
I have a 2016 Brutale and when I first got the bike the rear brake was almost useless. I tried to adjust the lever but that didn't work. I took it to the dealer for service under warranty and there was and air pocket in the line. Basically they removed the caliper pumped the brake and the air pocket worked its way to the reservoir.... problem solved. I was told this was somewhat common on the that bike.
 
#9 ·
Your 2015 800RR has ABS brakes and you need to bleed the ABS module.
 
#10 ·
When I moved on to my '18 Brutale the first thing I did was take it back as the rear brake seemed useless (having moved over from a Honda).

Turns out the rear brake just isn't very good. That said it will hold me on a hill, but requires a reasonable amount pressure to get half decent braking. I think the only thing it's really good for is trail braking!
 
#11 ·
This is a fallacy perpetuated by poor set up.
 
#12 ·
As SS says this is often down to poor set up. The system on my 821 Monster is nowhere near as good as the F3 (I’m not saying it is amazing, but it does work).

There is a correct procedure for bleeding the rear brake that involves bleeding the ABS unit and then removing the caliper and holding it up high at a 45 degree angle.

It’s also worth putting a bit of heat mat between the master cylinder and the engine and using a good fluid. Not all DOT4 / 5.1’s are equal.
 
#14 ·
Many bikes have the rear master close to a heat source due to the exhaust path. A simple insulating mat can have an excellent effect.
 
#17 ·
Hmm, rear brake on my 2018 Dragster RR is just "gone" today. Checked reservoir: empty. Did not find brake fluid leak so it must have happened on a ride. Guess I will find a local mechanic to refill, bleed and check for leak.
 
#21 ·
So there are three issues with the rear brake setup

1. The ABS unit is the highest point in the brake line (ie all the air bubbles that eventually form will find their way into the unit
2. The rear brake caliper needs to be turned a bit to make the air escape to the nipple
3. The routing and proximity to the engine cat / exhaust means the fluid will 'boil' (all fluid attracts water and the wet boiling point of the brake fluid is the important spec to look at)

Also see the attached tech info


1. Fit a speedbleeder at the ABS unit to make bleeding at the abs unit quick and easy (Speed Bleeder Bleeding Brakes Bleeding Motorcycle Brakes Automotive Bleeder Screw Brake Bleeder )
2. Follow the attached procedure to turn the caliper, cycle the abs unit
3. Use Castrol SRF Racing fluid - it has an extremely high wet boiling point ( https://www.ebay.com.au/p/1662080148?iid=163970221355)
 

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#22 · (Edited)
Much thanks all.. bike has about 3700 miles, hard to believe rear brake pad gone so fast? Then again, who knows?

I pulled the cover plate off the rear brake reservoir, shined a light: it is full of brake fluid-- so it has not leaked. Sounds like it needs a good air bleeding and or just new brake fluid. The bike will be in service 2 years next August.

I contacted two potential mechanics: my old MV dealer in Houston, and my old Guzzi dealer also in Houston. I hope one of them can fix this. If not there is one other possible mech in area.

+++++Or... can I bleed the air myself? Buy a bleeder and figure it out, do it right?+++++

It will get sorted. Hate riding with only front brakes, makes me slow down a lot.
 
#24 ·
My 2016 Turismo would make it about 6 months, then need bleeding. Which I could live with if it didn't require removal of half of the body work to access the ABS module.
Last month I fixed it for good.
Bypassed the ABS modulator, now the rear master cylinder is connected directly to the caliper.
I don't need no stinking ABS...

To stir things a bit...
I don't buy into the brake fluid boiling due to the proximity of brake lines to the engine or muffler. As the fluid will more likely
experience higher temperatures at the calipers during severe braking events.
Seen a similar problem, on cars. Air enters the brake line system due to faulty seals in the ABS module solenoid valves.

https://autocartimes.com/dot-3-vs-dot-4-vs-dot-5-brake-fluid/

From the link above:
Dot 4 Brake Fluid
Dot 4 brake fluid is preferred by many people because it can resist more heat in comparison to the weaker Dot 3 brake fluid. It is even formulated to be resistant to corrosion as well. The Dot 4 brake fluid’s ability to resist additional heat means that your braking system will be more reliable. For instance, if you tend to brake frequently as you drive in the city, then you will benefit more from Dot 4 brake fluid. In fact, any situation where you brake frequently will require Dot 4 fluid. Police vehicles and race cars even use Dot 4 because of its ability to resist heat so well.

The wet boiling point of Dot 4 brake fluid is 155°C and
the dry boiling point of the same fluid is 230°C.
Based on these figures, you can see that the Dot 4 brake fluid has a slightly higher boiling point in comparison to the Dot 3’s boiling points. That is why Dot 4 is more heat resistant.
 
#28 · (Edited)
Um 155C = 311F and 230C = 446F

Please use units so apples are weighted the same.

On the subject of Castrol SRF:

Text Blue Font Line Screenshot
 
#27 ·
It is not heat causing this.
 
#29 ·
I tend to think heat is not the issue also, but I am not an "expert" in fluid properties. Riding bike to my fav Houston tech this morning, with the MV service bulletin for guidance. Fingers crossed. If this becomes a frequent problem, well that's a problem for me. Bike warranty worthless in Houston. We shall see. My ability to focus bifocals is issue with doing brake bleeding myself.
Never had a bike do this: poof, no brake pressure. Is there a major design flaw? Bad master cylinder? Its not leaking, but it appears to be taking a lot of air.
 
#31 ·
Heat is a contributing factor.

Just like the ABS unit positioning that is the highest point.

The same poor rear brake scenario is on my Multistrada 1200. Different master cylinders and brake calipers but routing on the single sided swingarm / close proximity to the exhaust and the ABS unit being the highest point the same.



 
#32 ·
If heat is a contributing factor, riddle me this:

Bike in question is a low mileage 2015 B3 800RR ABS

Ride bike 150 miles, clean and maintain bike for storage, bleed brakes. Brakes are solid.

Same October day, wheel bike into enclosed ingested trailer for the winter.

In June, wheel bike out of said trailer.

...no rear brake.

Bleed rear brake and it’s solid again.
 
#33 ·
Poor ABS seals letting in air? 'Old' brake fluid used (I tend to not throw away a newly opened bottle if there is more than half left so i'm guilty of that). Not all air/water removed through ABS unit when last bled? Fluid 'extracts' water from air cavity in reservoir ?

You can't tell me heat has no impact in the whole poor rear brake saga. Maybe not in your case but with different higher boiling point fluids many have shown improvement

Also considering the difference between the front and rear brakes - my fronts stay awesome - ABS unit position is different, routing is different and far away from a heat source like the cat unit. Caliper position different when bleeding.
 
#34 ·
Therefore, your own statement blows the heat theory out of the water. Front brakes generate much more heat than rears. The touting of rear brake lines no longer is next to the exhaust. Especially on the B series...look at it.

I use new fluid from an unopened container. I do this a lot. It is not heat related.

I do feel it is rear brake circuit related.
 
#36 ·
Therefore, your own statement blows the heat theory out of the water. Front brakes generate much more heat than rears.
I am aware of different issue's causing brake fade, but purely regarding heat fade on an F4 and equivalent bikes and whilst I am certainly no expert, this is just my limited experience.
Doesn't exposure to heat over time count? ie my F4's front never gives me grief, but my rear was always a problem until I finally got the heat shielding right and went for a higher rated/boiling point fluid.

Heat exposure to the rear brake from the exhaust's central pipes is continual and quite hot, where as one would of thought that the front brakes during normal road use would not expose the fluid to the same equivalent of heat soak on a given ride?
 
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