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Old 07-12-2007, 08:22 AM   #1
vermicious
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Default Aprilia Rear Brake Woes

Any other Aprilia owners out there suffering from pressure loss to the rear brake? I lose brake pressure steadily over a couple of thousand miles and have to bleed them dry in order to restore it. This is easy enough to do but gets to be a little obnoxious if you put real miles on the bike.

I love this bike and would really like to find a permanent solution to my solitary complaint with it. Any ideas?
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Old 07-12-2007, 09:06 AM   #2
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Default A hint from "The Aprilla Forum"

***TAKEN FROM "THE APRILLA FORUM"*** (I Googled "Aprilla Brake Problems btw).

"This issue of clutch hydraulic problems just won't go away. The front and rear brakes have also caused problems for many. Most, if not all, of these problems are caused by improper bleeding. Motorcycle hydraulic systems (brake and clutch) are notoriously difficult to bleed. On the clutch and front brake it is because of the vertical layout and the small volume of fluid displaced by the master cylinder. On the rear brake the volume displaced is even less and the caliper is usually generic, meaning not specifically designed for the aplication. This results in the bleeder being in the wrong position necessitating caliper removal and repositioning before effective bleeding can be achieved.

Using the old back yard method of pump and bleed, it is virtually impossible to properly bleed a motorcycle clutch or front brake. Vacuum systems like the Mityvac are a step in the right direction but are limited. The most effective way to bleed is with forced fluid injection.
Phoenix Systems is a company dedicated to providing tools and knowledge to the automotive indusrty for bleeding brake and other complicated hydraulic systems. They offer a variety of fluid injection tools that work better than any other manual system I have seen. They also offer technical knowledge which covers just about every difficulty you might encounter while bleeding complicated hydraulic systems. Please check their web site at Brake Bleeders, Brake Flushing by Phoenix Systems, LLC. All that being said, I have been using these same methods for over twenty years but with tools that are far less expensive. With a simple plastic medical syringe, of from 10 to 75 ML, you can use reverse fluid injection to effectively bleed any motorcycle brake or clutch in very little time.

Lets assume the system is clean and the slave cylinder is free of contamination; you do not want to force contaminated fluid from your calipers or clutch slave up into the master cylinder. Suck all the fluid out of the reservoir and wipe it clean. Take your clean syringe and fill it with new brake fluid. Attach it with a clear vinyl tube to the bleeder at the caliper or clutch slave. Open the bleeder and inject the fluid while watching the level in the reservoir. Stop when full. Close the bleeder. Suck out the reservoir and repeat as needed. This is basically all there is to it.

You can use this method on rear brakes but you still have to remove the caliper. Instead of positioning it with the bleeder up, as you would for normal bleeding, you must hold it with the brake hose port up. A better and easier method for the rear brake is explained further down the thread.

One last thing about bleeding our Mille clutches. Something that is being overlooked is that there is not actually a bleeder on the slave cylinder itself. It is part of the banjo bolt. Automotive clutch slave cylinders have the bleeder located at the top of the slave so that when bled the fluid is flushed through the cylinder. This does not happen with our system so it is possible to bleed and still have a pocket of air within the slave cylinder. It is however easy to remove it.

After bleeding as above and filling the reservoir, remove the three screws securing the slave cylinder. Remove the cylinder and hold it in its normal attitude then tip it slightly to the right (as if you were leaning the bike to the right). Allow the internal spring to slowly push the piston out 5 or 6 millimeters and push it back in forcefully. Take what ever precautions that you feel are necessary to prevent spilling fluid from the reservoir. Repeat this several times. Reinstall the cylinder and screws to proper torque. You may want to reverse inject one more time to be sure there are no bubbles in the banjo fittings and hose. THIS WORKS and it takes a lot less time than it did to type this. It is the very procedure described in the aprilia workshop manual.

It is also important to optimize the position of the master cylinder when doing this. Turning the bars to right full lock positions the MC in a more horizontal position allowing bubbles to find there way to the reservoir when you push the slave piston in. It might be necessary to loosen or remove the MC clamp to get the cylinder into the best position. Ideally you want the output end of the MC slightly lower than the fitting for the reservoir hose.

There are times, depending on the system layout, when it might be more advantageous to inject fluid into the master cylinder so fluid flows in the normal direction. To do this you must adapt your injection device to the master cylinder reservoir. With any difficult bleeding situation you must be keenly aware of internal passageways, banjo fittings and other possible high spots that might trap air.

It is also important not to over fill the brake fluid reservoirs. If you try to fill the reservoir all the way it can lead to brake drag. As the calipers warm up the fluid expands and is forced up to the reservoir. If the reservoir is completely full, pressure builds and is transmitted to the caliper pistons causing them to move toward the disc causing drag. As the brake gets hotter it drags more...

It is also a good idea to crack open the cap and reclose after the bike is fully hot, to vent any pressure. It is important to remember that this same thing can happen with the clutch fluid reservoir and cause the clutch to slip. Leave a little air space!

Please do not ride your bike if you are not absolutely certain that the brakes are working properly. If you monkey with the actuating rod on front (at the lever) or rear (at the pedal) brake be sure you have detectable free-play. If there is no free-play it can prevent fluid return to the reservoir and cause brake application and lock-up as system temperature rises."
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Old 07-12-2007, 03:05 PM   #3
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I've read all of this before and been in countless other forums discussing the topic but despite following the advice of so-called brake experts and having the line "professionally" bled the problem persists. I'm just looking for a more consistently reliable solution.
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Old 07-12-2007, 03:12 PM   #4
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I don't know much about these things but I was hoping for a kit that could effect a change in orientation such that bubbles were less likely to form WITHIN the brake itself. I've never experienced this issue with any other bike and I know of no one else that's experiencing it (outside of other Aprilia owners). I also have yet to hear of someone coming up with a long term solution. The forum you were quoting (if memory serves) suggests that the solution is bleeds every 3k miles or so but (in later response) finds that the frequency with which bleeds need to occur varies wildly even when executed by those experienced in brake work.
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Old 07-12-2007, 03:59 PM   #5
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Originally Posted by vermicious View Post
I'm just looking for a more consistently reliable solution.

Buy a Honda?
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Old 07-12-2007, 04:36 PM   #6
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Default Broken brakes

Quote:
Originally Posted by vermicious View Post
I've read all of this before and been in countless other forums discussing the topic but despite following the advice of so-called brake experts and having the line "professionally" bled the problem persists. I'm just looking for a more consistently reliable solution.
Seems there is a problem with Aprilla rear brakes, as when I google the issue, I get a couple dozen hits. After reading a few of the posts, looks like there might be some internal white teflon goodie that's meant to support the brake hose, that might be leaking air into the system.

You can lace up a nice Moto Guzzi Falcone drum if that doesn't work. Cables don't leak air. That's why I dig 'em.
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Old 07-12-2007, 04:40 PM   #7
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Buy a Honda?
bah... actually, I've owned a few Hondas and they're awesome bikes but I've never had the affinity for one that I have for my Tuono. *shrug*
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Old 07-14-2007, 08:08 AM   #8
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Motorcycles have rear brakes?..........
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Old 07-14-2007, 11:27 AM   #9
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Motorcycles have rear brakes?..........
It's that thing you use to stop in loose gravel, so's you don't dump yerself on yer arse.
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Old 07-18-2007, 09:32 AM   #10
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It's that thing you use to stop in loose gravel, so's you don't dump yerself on yer arse.
or to stretch your back when stopped on a hill
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