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Thread: Recurring Clutch and Rear Brake Issues

  1. #1
    apriliaforum expert kzmille's Avatar
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    Recurring Clutch and Brake Issues

    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 http://www.brakebleeder.com/. 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.

    If you have an 04 or later RSVR or other model with the OEM Brembo radial clutch master cylinder the position decriptions above do not apply and you will need to do some additional bleeding/Purging to bleed out the master cylinder itself through the bleeder there. You can do this in either of two ways.

    1st) Put a length of your vinyl tubing on the bleeder at the MC, open the bleeder, pull the lever to the grip, close the bleeder, release the lever. Repeat several times till there is no air.

    2nd way) Attach your syringe, full of fluid, to the bleeder on the slave cylinder. With another length of tubing on the bleeder on the MC, open both bleeders and inject the fluid up through the system. Obviously with both methods you'll want the loose end of the tubing from the MC bleeder in some kind of container.

    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!

    **** 9-12-07 **** If you have your OEM slave apart, reassemble with liberal amounts of silicone O-ring lubricant and you will put an end to the blackening fluid. The discoloration is from the rubber seal wearing at a high rate due to lack of adequate lubrication. I have the original slave and seal on my 01 Mille and the fluid has remained crystal clear since doing this. The lubricant can be found at any dive shop.

    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. If any of this is not clear let me know and I'd be glad to talk you through it.

    **** Update - Clutch Slave Lube And Bleed - 3-31-10 ***

    Lubing the seals with silicone paste is highly recommended (by me anyway) no matter which type of fluid you plan to use. The best way to bleed the clutch system (in my opinion) is to inject fluid into the system at the slave cylinder bleeder and force any and all air upward to the reservoir. To have success with this you must first ensure there is no air in the slave cylinder (method explained in the article above) and take measures to optimize the flow path in a continuously upward path from slave to reservoir. You can also do the whole thing just using the slave cylinder itself as your injector and never even crack a bleeder. This is how I now do it.

    Here is the basic idea. Clean the slave cylinder and all internal parts. Install a new seal if needed. There is no need to loosen the hose at the slave so that connection and the one at the MC should be tight. All bleeders closed and reservoir cap removed. Cover the reservoir with a clean cloth to avoid spills. Optimize the flow path by turning the bars full right and even leaning the bike to the right a bit or unbolting the master cylinder so the banjo fitting is at the low point. You want a continuously upward path from slave to reservoir. Look into the slave and note the position of the fluid exit port, you will need to know this later. Lube the entire bore, piston OD, and seal with the silicone paste. Hold the the slave cylinder with the open bore facing up and fill with fluid. It's a good idea to have a catch pan below. Insert the piston making sure the seal enters correctly. Try and avoid trapping any air as the last bit of the lip enters. Once the seal is fully seated push the piston in just slightly and then tip the cylinder so the exit port is at the highest point of the cylinder, hose leading up. Firmly press the piston fully into the slave watching the reservoir as you go.

    At this point some of the fluid from the slave should be in the reservoir. Can't remember how full it gets. With the piston fully pressed into the slave you can top up the reservoir a bit so you don't let it run out. Now let the internal spring push the piston out. if it needs some help pull the lever but don't push it out too far. Repeat this cycling back and forth a few times. Each time you force the piston in hold the cylinder in the optimum position. Put some waterproof grease on the pushrod seal and bolt the slave back on. It's really easy once you get used to it. I try and lube mine once a year with a fluid change.

    This procedure as written is for the early master cylinder. If you have a radial master you will have to do some additional bleeding at the master.


    Here is a Service Bulletin on the rear brake from aprilia 13-07-2007:
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    Last edited by kzmille; 09-19-2014 at 01:22 AM.

  2. #2
    apriliaforum expert Chuck B's Avatar
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    Good post!
    Chuck B
    Arizona

  3. #3
    apriliaforum newb
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    This is great stuff, I am not sure my dealer would go that far (I have two left hands only, sorry).

    I will tell you what happened to me. My dealer had trouble to bleed the rear break. He did a lot you described here but it still would not work.

    One summer day I was riding about 80KMH and engaged the rear brake very frequently to get the brake oil moving. After about 15 to 20 minutes (!) the air apparently got out (to the reservoir) because the rear brake suddenly engaged heavily (watch out). Since then I have had no problems with the rear break, and that has been 6 months now.

    Just luck I guess.

    Gerrit
    Gerrit

  4. #4
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    Question one question

    Does the evo slave have a bleeder on the slave or same on the banjo bolt only?

  5. #5
    apriliaforum expert kzmille's Avatar
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    Adjusting The Master Cylinder

    **** Update - Adjusting the 98-03 Mille, Falco, and Tuono clutch master cylinder ****

    Though normally not necessary, the master cylinder can be adjusted. There is a small rod in the lever assemble that pushes on the master cylinder piston. This rod is threaded and so adjustable. It is locked in place by a set screw in the underside of the barrel. The set screw was originally installed with thread locking compound. A heat gun should be sued to heat it some before you try to loosen the set screw.

    Before messing with this ensure the system is thoroughly bled of all air. In this state the end of the clutch lever will normally travel 10-12mm before you start feeling the clutch. If you have this amount of free lever movement there is probably not much to be gained from messing with the adjustment. If you get the adjustment too tight fluid will not be able to travel to and from the reservoir and the clutch will slip when the engine comes up to temperature. If you are going to alter this adjustment you need to ensure that fluid can flow to the reservoir. The only effective way I know of to do this is to unbolt the slave from the engine. Normally the piston will start to move out of the slave but fear not, it will not be forced all the way out. You can push it back in and restrain it. As you push it in fluid flows up to the reservoir. Adjust the threaded rod to the maximum length that still allows the slave piston to be pushed in by hand and be pushed back out somewhat by the internal spring.
    Last edited by kzmille; 08-17-2014 at 09:05 PM.

  6. #6
    apriliaforum expert kzmille's Avatar
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    The Aprilia Rear Brake

    Because the rear brake problem keeps coming up, I decided to see if I could get to the bottom of the problem. As I have said before, to the consternation of some, I believe most of these problems are the result of improper bleeding. Let me say at the outset, in thirty five years as a mechanic I have never seen a hydraulic system that allowed outside air into the system without leaking fluid. I know that some believe that the problems with the clutch on the 04's might be caused by the rubber boot gulping air and forcing it into the system. Although it seems unlikely I can understand the reasoning behind it and it is certainly easy to test by poking a clear hole in the boot with a hot wire.

    Back to the rear brake. I have an 01 Mille and the rear brake has always been rock solid. I have changed the fluid but because I have never had any air in the system, I thought I might not be getting the full picture. Recently I removed the master cylinder and completely disassembled it, opened the bleeder on the caliper and drained all the fluid from the caliper and hose. I also forced the pistons into the caliper to remove all the fluid. The master cylinder was unremarkable but well designed. The white bushing in the picture is teflon and necks down at one end to act as a seal around the piston to prevent any contamination from entering. It seems unlikely that air could be forced past this seal by the boot.

    As some of you may know, I favor the use of a fluid injector to bleed brakes but decided not to use it so that I could try and find a simple procedure that can be easily explained and followed and produce consistent results. I spent a few years working in a specialty brake shop and although we had a very nice power bleeder we would usually bleed most cars with the universal pump and bleed method. Some cars just could not be bled this way and for those we used the power bleeder. I found that there were some cars that were in between; difficult to bleed without the power bleeder, but it could be done. Working on these difficult cars I made the following observations. (1) Pumping the pedal with the bleeder closed did very little except turn bubbles into smaller bubbles. (2) The slower you proceeded the less successful you were in forcing bubbles down hill. Understanding these two things I came up with a new method that I use to this day.

    With an assistant at the pedal and starting with the bleeder closest to the master cylinder I open the bleeder and put a finger over the end. The assistant then pumps the pedal vigorously until I get clean fluid. I then have him hold the pedal down while I close the bleeder. This is effectively doing the same thing as a Speed Bleeder. Speed helps flush the bubbles out without giving them time to retreat up hill. This is then repeated on each cylinder in the system. Obviously on a bike this won't work because no one wants to spray brake fluid all over their wheels and everything. On a car I have a water hose handy and rinse everything down immediately. Effective but I have modified this method for obvious environmental concerns. A length of vinyl tubing on the bleeder extends things into a container where you can still use a finger over the end of the tubing as a check valve..

    So, on the Mille you need a piece of vinyl tubing that fits the bleeder. Put one end on the bleeder after your box end wrench and run the other end into a jar. Fill the reservoir. Remember, speed is good and only push the pedal down when the bleeder is open. Open the bleeder. Push the pedal all the way down. Close the bleeder. Let the pedal up. Open the bleeder. Pedal down. Close bleeder. Pedal up. Open bleeder. Pedal down. Close bleeder. Pedal up. Repeat this as quickly and smoothly as you can till the reservoir is almost empty and top up. Continue until you see no bubbles.

    8-5-17 In addition to the method above I have also put a finger over the end of the open bleeder to act as a check valve and just pumped rapidly to get a good flow and prevent it sucking back as the pedal is released. The pressure bleeder mentioned in the first post comes with inline check valves that do the same thing.

    Before you can proceed as stated above you must position the caliper correctly. I found that to really get all the air out you need to hold the caliper in two different positions as pictured below. The first is to flush the air out of the gallery in the caliper that distributes fluid from the banjo fitting to both sides of the caliper and the second flushes the air out of the piston bores. You also need to be sure there no high spots in the brake hose where bubbles will collect. It may not be absolutely necessary but it is helpful if you unbolt the hose retainer plastic from the underside of the swing arm to free the hose. I bled mine with both pistons pushed all the way into the caliper. I didn't even have anything in between the pads but it's probably better to put something in there. Mine crept out a little but not much because you never push the pedal with the bleeder closed. Bleeding my bike this way I was able to get a solid pedal after filling the reservoir only seven times.

    I really hope this can help some of you and forgive me, I really am not interested in disparaging anyones abilities. I'm just trying to share some things I learned the hard way.

    May 14, 2006

    Sometimes if the system has been completely open, such as after replacing the supply line and the pressure line or replacing the MC, the MC may need to be primed with the pressure line removed.

    Place a large pan or cookie sheet under the MC as this can get messy. Protect all painted surfaces including the wheel. Remove the wheel if you have to. It doesn't hurt to have a hose or spray bottle of water handy just in case.

    Remove the banjo bolt securing the pressure line. Fill the reservoir. You're going to use your finger like a check valve. Put your finger over the MC outlet. Push the pedal all the way down allowing any pressure you feel past your finger. Close the opening and let the pedal up. If you feel any suction keep a tight seal till it dissipates. Pedal down, releasing pressure. Pedal up and again keep a tight seal till the suction dissipates. Pretty quickly you will start to get fluid flowing. Repeat till you get a full stroke with no bubbles. Hold the pedal down somehow and reattach the pressure line and tighten.

    You can now start bleeding the system as described in the article.
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    Last edited by kzmille; 08-05-2017 at 11:51 PM.

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    apriliaforum expert kzmille's Avatar
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    Position 1

    The first position is to flush the air out of the gallery in the caliper that distributes fluid from the banjo fitting to both sides of the caliper.
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    apriliaforum expert kzmille's Avatar
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    Position 2

    The second position flushes the air out of the piston bores.
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    apriliaforum expert 2pist's Avatar
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    kZ, you are the god of hydraulics The link to that site was quite informative. My mityvac has a pressure port as well as a vacuum port. This post gave me an idea on modifying the catch tank on ye old mityvac to a pressure tank. Not as sophisticated as the pheonix injector but I think it will do the job.

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    I have used the syringe method so that you force the plunger out as you pump and bleed that way you can see the point when the fluid goes from old n dirty to fresh and clean. but I prefer the reverse fill way for expelling trapped air. Great thread. Thanx.

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    apriliaforum expert hagasn's Avatar
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    rear brake?

    i will bleed brakes this weekend (again). nice write up. thank in advance.

  12. #12
    apriliaforum expert hagasn's Avatar
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    brakes

    hello, along with changing my sparkplugs (goodtimes), a friend and i bled my rear brakes last night. kzmille i told my friend that we might have to go through the bleeding process 5 to 7 times and move the caliper into 2 different postions. he to say the least was doubtful about this method. only after moving the caliper into the 2nd postion, as you suggested, did we notice a TOTAL CHANGE IN BRAKE FEEL thank you kzmille! my brakes have never felt this good!

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    apriliaforum Member l8-apex's Avatar
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    Bingo!

    I've bled many brakes over the years and never had any problems. Since my rear brake did not really feel 'spongy' to me, it seemed more that it was an excessive pedal travel issue with these brakes. I was convinced that the master cylinder diameter was too small.

    Tonight I gave it another try. As soon as I got the caliper into 'position two'; BURP... a couple of LARGE bubbles came out and my brake was transformed. This is definately the answer to our rear brake issues.

    THANK YOU KZMILLE!
    Last edited by l8-apex; 04-10-2006 at 01:35 PM.

  14. #14
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    Same old, same old....................................

    THANK YOU KZMILLE!
    I echo that sentiment. My '07 Tuono R arrived sans rear brake, so evidently the folks at the Aprilia factory STILL haven't learned how to properly bleed their own system. Either that, or they ran out of brake fluid - and substituted olive oil.

    I followed kzmille's instructions.........and wound up running three resevoirs of fluid through the system in each of the recommended caliper positions. The first go-through in each position produced the most air bubbles, then diminishing, untill by the third go-through (in each position) only fluid was being pumped. The rear brake works quite well now, hopefully it stays that way.

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    apriliaforum expert SoulDaddy's Avatar
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    Ah, ... so the reason my front wheel will not spin freely is due to an excess amount of fluid in the res since I recently flushed it and replaced pads.

    Outstanding. Thanks for the insight and wisdom.

    And I'll look forward to an actual rear brake soon, too!

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