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No rear brake on my F4

6K views 27 replies 10 participants last post by  chad951 
#1 ·
I recently changed my rear brake to an aftermarket replacement and it seemed to be working fine. Then one day there is zero brake function. I bled the brake and managed to get good pressure, rode the bike and it was ok. Came back a few days later and again no brake. I mean zero pressure. I looked for signs of fluid but nothing so before I bleed it again anyone have any ideas.
 
#2 ·
Hmmm...Sealed system. No leaks. Where does the reservoir port into the master cylinder? Vertical or to one side? Bleed again and pay attention to volume of bubbles. A lot or just a tiny amount?

You didn't use a pneumatic bleeder did you? High line pressures will generate microscopic bubbles in the fluid which will join together after a short time to create mushy brakes. Most pneumatic bleeders call for less than 90 psi.
 
#4 ·
?

George;
Remove the caliper, hold it low with the line fitting at the high point, push the pistons all the way back in
Remount caliper

Now all the air is in the MC, now loosen or remove a bolt on the MC and rotate it so the pushrod end is highest
Push the lever repeatedly, slowly, the piston will expel all the air through the return port

Been doing it like this since I was a kid


Think like a bubble

:grin2:
 
#6 ·
If the piston seal is leaking by from the pressurized to the unpressurised side it will feel like no pressure.
 
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#7 ·
Yep....if no fluid leak and properly bled then the master cylinder cups are not sealing.
 
#9 ·
I took the master cylinder apart last night and am having trouble figuring out how air is removed from the piston cavities. Fluid goes in one side and is supposed to flow to the other cavity but there is no place for the air to escape or be bled off other than where it enters. I don't know, maybe I am missing something since I am not an engineer.
 
#10 · (Edited)
George...this explains everything, even if it is a car drum system described, the master cylinder piston works the same way.

 
#12 ·
George, in order to completely remove the fluid from a caliper, one must push the pistons completely into their recesses prior to bleeding. This expels as much of the old fluid as possible. If you want to experiment a bit, push the pistons in and then add the fluid to the caliper bleed valve while keeping the caliper lower than the master cylinder. Continue to add fluid until no bubbles expel from the master. In order to do this you need a rig to add the fluid. A syringe and tubing works, or you can use gravity...or you can use a vacuum bleeder at the master and suck the fluid through.

Personally, I use a vacuum bleeder that is air driven and suck the fluid from master to caliper.
 
#14 ·
What was the solution?
 
#16 ·
no it was more brake fluid. I put everything back into it's original configuration and took the cap off the reservoir which was empty. Started pumping the lever and had air bubbles. Kept pumping and more bubbles, then added more fluid then more pumping. You get the picture. The bubbles finally stopped and the pedal was firm. That usually happens- keep pumping and it gets firm :)
 
#17 ·
@number2: They should make a pill for that.

(For the record, Joe was right...more DOT 4!)
 
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#18 ·
No Rear Brake Pressure

How's it going MV family. I'm having the same problem with my 2013 F3 675; I had a little pressure last week but nothing now. I bleed the brakes, but I have no brake feel what so ever. I had a ton of air in my line while I was bleeding them and a lot of smaller bubbles also. I didn't use a pump to bleed my brakes, a friend of mine who's a motorcycle mechanic did it for me. We bleed at least a cup or more from the rear brake but still no pressure. I'm starting to think that my master cylinder is bad - has anyone rebuilt there master cylinder because as we all know its damn near impossible to find or get MV parts. What rebuild kit should I purchase, if there is one?
 
#20 · (Edited)
If you are in the US...

From this thread...

http://www.mvagusta.net/forum/#/topics/219434?page=4

You may want to contact
Ian (706) 867 0032 or (706) 429 4366

There is supposedly a warehouse now in Georgia. Maybe find what you need from there?

How's it going MV family. I'm having the same problem with my 2013 F3 675; I had a little pressure last week but nothing now. I bleed the brakes, but I have no brake feel what so ever. I had a ton of air in my line while I was bleeding them and a lot of smaller bubbles also. I didn't use a pump to bleed my brakes, a friend of mine who's a motorcycle mechanic did it for me. We bleed at least a cup or more from the rear brake but still no pressure. I'm starting to think that my master cylinder is bad - has anyone rebuilt there master cylinder because as we all know its damn near impossible to find or get MV parts. What rebuild kit should I purchase, if there is one?
 
#19 ·
@TheOne25 The master cylinder is an off the shelf part from Brembo (at least I think it's a Brembo). So a kit shouldn't be too hard to find.

You might try contacting other MV dealers around the country (there's on in Charlotte NC that's pretty good).

I think you will find basic parts availability is driven by dealer enthusiasm and care. Special parts/Cosmetic parts sometimes hard since MV makes them. Supplier made parts much easier to get. Some dealers just have crappy parts managers and staff with no interest in you or your bike.
 
#21 ·
?



Ed;
The rear M/C and caliper are Nissin....Hondas use them too

Basically Brembo doesn't sell internal parts (except for BMW and KTM)
As Fred Renz of Yoyodyne said "If you need a dust boot for your $1682.00 CNC racing caliper......it's $1682.00"
And Fred was a Brembo Distributor

:wink2:
 
#24 ·
I need the rear brake to work for two important reasons:

1. A traffic light I often stop at is on a steep slope. It's a looooooong traffic light too. It would be so nice to just step on that little brake and be able to sit up and stretch my back.
2. This should probably reason #1, but my bike is not road compliant if the brakes malfunction. Also I might void my insurance if I knowingly continue riding with a brake defect. Also wouldn't pass track day scrutineering...

Another thing - how do you guys know it's a heat issue?

I ask as I've just had my 2015 F4 stored for 3 months. Just before I stored it, the bike was serviced and I had the rear brake fluid changed and it was working fine. When I took it for a spin the other week - rear brake completely floppy and useless. I do have the whole exhaust heat wrapped too where the rear brake pump is.

Could air be getting in through other ways? Has anyone upgraded theirs or found a solid solution?
 
#25 · (Edited)
I had similar issues on my F3. Changed the brake fluid many times but heat caused one of the seals to allow air in. Replaced rear pump but still the brake faded after awhile. MV released a service bulletin for a different procedure to bleed rear brakes so my shop did that and used Motul brake fluid. Since then my rear brake has worked for the longest time since I had bike. The heat has discolored the brake fluid a lot but the brake still works. Try a new pump and use some really good race brake fluid. That cured my problem for now.

I still don't get why so many people think having no rear brake is OK. I use my rear brake often and for more reasons than the convince at stop lights. I guess everyone has their own riding style...
 
#26 ·
Angelo, did you ever heat shield the rear master? It is an inexpensive and simple process that helps immensely.
 
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