Think I F-ed my master cylinder

[OreoGaborio]

Pulling into the parkin garage the other day I used a bit of rear brake since the ramp is a little slick some times.... Usually my rear brake has decent stopping power despite the number of complaints voiced by Aprilia owners (Ya just gotta know how to bleed it right). This time it was a bit spongy so I push harder.... nothing... harder... nothing.... then........ "POP".


Now there's no resistance & no brake pressure until the pedal has been pushed down a good 3-4 inches. The lever has a LOT of travel before it engages and it's still pretty weak once it does finally engage.

No leaks, no external sign of failure. It's a Brembo rear brake system.... and me thinks it's gonna need a rebuild

[BMFR6]

should have bought jap.

[Crash Dummy Denno]

wheelie master who needs a rear brake?

[SSearchVT]

Check all the pivot points and linkages to see if there is a lot of play in any of them. Then watch the rear brake line while pressing the lever - The pop may have been the first sign of the line failing. Put your hand on it while someone else presses the lever and feel for expansion. Good luck...

[Awesome]

Like I told you at the track. You need room in the res for air, you have none. You popped it. I don't know about the internal workings but yes, rebuild or replace cause it's broken.

[OreoGaborio]

well it's got SOME air in there..... now?

& can ya blame me for askin a second opinion? I mean... you roadrace a motard, you're obviously confused.

[OreoGaborio]

bump to the top

Like I told you at the track. You need room in the res for air, you have none. You popped it. I don't know about the internal workings but yes, rebuild or replace cause it's broken.

turns out there WAS room for expansion inside the resevoir, it just didn't look like there was because the rubber piece in the top of the resevoir was taking up about 1/2 of the volume in the resevoir.

BTW, the line is a SS braided line. (stock)

I bled the system. The lever still travels a long way & has very little braking power once it does do something. Everything looks normal to my novice eye.

[schleppy]

Have you used one of those pump bleeders to "power" pull of the fluid through the system? Sometimes you need that extra bit of pull to get all that air out, then finish with a standard bleed.

If you haven't and need one let me know and I'll drop it off for ya. I have a Mityvac and I'm not far from you...

[OreoGaborio]

The aprilia rear brake system has a "trick" to bleading it and a Mityvac isn't necessary. I'm gonna bleed it again when I have a chance, but I seriously think there's an issue beyond air in the system.

Thanks for the offer though.

[butcher bergs]

Pete,
How sure are you that it's broken?

I ask only because the travel of the lever with my 929 is rather significant when compared to my FZ1. Both bikes stop very well, it's just that the Honda seems to have alot more travel before it really starts to bite.

I mean, are you down to the bar?

I'm not sure if you're aware of this but you can tie the lever to the bar and let it sit overnight. Turn the bars to the left when you do this....that should help get any remaining air bubbles out of the system. Not saying it will solve your problem but it might help.

[schleppy]

^ I don't know if there is a tie down trick with the rear brake.

[legalspeed]

Yes a rebuild. My rebuild kit came with spring, piston, gasket, a few washers ~ 24 dollars. Cheap and easy.

Is there fluid coming from the master? Make sure you check the inside bore, you may have scored it by continuing use while the piston was not properly guided by the gasket.

Hessoright has a lot of experience building many different bikes, I would trust him.

[CMG241]

wheelie master who needs a rear brake?

I had some on tell me I needed a steel braided rear brake line for my track bike (it came with one, still in original packaging though) - how much pressure am I going to put into rear braking?? Do I want the rear to lock up even faster? Its rare I ever touch it... the brake that is, not myself.

[loridin64]

I dont think that air is the issue. Its not just 'magically' going to get air in the system when you push it too hard.

Rebuild

[OreoGaborio]

I dont think that air is the issue. Its not just 'magically' going to get air in the system when you push it too hard.

Rebuild

i agree. it's not air in the system. something popped.

[Jim]

should have bought jap.

i was gonns say, should have bought a GSX-R

[brendanp]

Pressure is created by a close tolorence cylinder bore and good rubber on the piston plunger. I say rebuild kit with a good bleed and you'll be all set Pete..

[butcher bergs]

^ I don't know if there is a tie down trick with the rear brake.

There isn't.

I skimmed the thread and missed that part (apparently more than once).