I am currently trying to sort my clutch, the biting point of which gets closer and closer to the bars as the engine gets hotter. I have been reading up on this problem and have seen quite a few references to a "spongy clutch lever". Now I can see how you can tell when you have a spongy brake, but how on earth do you tell if your clutch lever has a spongy feel to it? Just wondering.
Spongy clutch lever?
- Thread starter Burny
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Tom Mac 04a
Site Supporter
same thing as with brakes...if it feels spongy, then replace the DOT4 fluid and bleed the system....should fix all.
The clutch should start to engage off the handlebar about 1 inch and over the next inch fully engage, freeplay all the way out pulling in is about 1/4-1/2" ( depends on load,rpms, etc )
The clutch should start to engage off the handlebar about 1 inch and over the next inch fully engage, freeplay all the way out pulling in is about 1/4-1/2" ( depends on load,rpms, etc )
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After battling with this for several years, bleeding and filling, bleeding and filling, I finally drained ALL of the fluid out, and filled it with fresh DOT4. Since then, no more problems! I was told that unlike conventional DOT3 fluid, DOT4 absorbs moisture over time, which diminishes it's effectiveness, and left in long enough, it turns to "Jelly"
tnbill
Site Supporter
Don’t know where you heard this but both absorb water. Castrol marketed a dot4 as LMA or low moisture absorption.
Andrew Shadow
Site Supporter
DOT 3 and DOT 4 both absorb moisture. DOT 4 actually absorbs moisture more quickly than DOT 3 does. Its main advantage over DOT 3 is that it has higher dry and wet boiling points, making it better suited to higher brake temperature operations.
Since you bled the system several times over a short period of a few years moisture was not the problem, it would have been flushed out with the old fluid. More likely is that there was either a blockage or an air bubble stuck some where, and draining and refilling dislodged it and flushed it out. Either way, good that you resolved it.
Since you bled the system several times over a short period of a few years moisture was not the problem, it would have been flushed out with the old fluid. More likely is that there was either a blockage or an air bubble stuck some where, and draining and refilling dislodged it and flushed it out. Either way, good that you resolved it.
bdalameda
PaleoCyclist
Something also to check is the pivot bolt and hole in the lever. There are known to wear and cause issues.
tnbill
Site Supporter
From an article by bendix dot 4 has a slower rate of absorbsion
tnbill
Site Supporter
But it still should be changed out at the recommended intervals.and more often if you live in a swamp.
Mine does that, too. The water becomes compressible when it gets hot enough to vaporize, and there's too much play.
If it gets hot enough, the clutch will not release, and the engine will stall. Ask both of my old mirror covers how I know.
I'm going to replace the fluid as soon as I get my hip replacement done, so I'll be ready for the summer and fall riding.
If you live IN a swamp, riding motorcycles is hard. Air boats are preferred. Watch out for the gators1
Andrew Shadow
Site Supporter
Boiling point of brake fluid is tested with a water concentration of 3.7%. DOT 4 fluid will absorb that 3.7% water amount 20% faster than a DOT 3 Fluid. It has a higher dry and wet boiling point and also resists the effects of moisture in the fluid better than DOT 3 fluid does, making it preferable if maintenance is done..
Mophead
Site Supporter
And to make that bleeding so easy I highly suggest Speed Bleeders.
Easier than the vacuum-and-jar method?
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Even with speed bleeders, the return stroke of the lever results in some negative pressure, which will allow bubbles to stretch and stay put in the lines. It is always worthwhile to leave the bleed valve closed, pump the lever a few times and hold it in on the last stroke. This seals off the master cylinder - so that fluid cannot flow back - and then open the valve to allow the pressure to force the fluid out of the valve. Close the valve before the fluid stops flowing.
Repeat.
You may think that the bleeder valve stops the reverse flow, but when the lever is released, fluid can go back into the reservoir through the compensation port. It can do this because the air bubbles that you are trying to get rid of are squeezed when you pull in the lever, and expand when you release it. The expansion pushes the fluid in both directions. Result is that bubbles can simply hover in the lines one step forward, one step back.
Repeat.
You may think that the bleeder valve stops the reverse flow, but when the lever is released, fluid can go back into the reservoir through the compensation port. It can do this because the air bubbles that you are trying to get rid of are squeezed when you pull in the lever, and expand when you release it. The expansion pushes the fluid in both directions. Result is that bubbles can simply hover in the lines one step forward, one step back.
I doubt it, but different strokes for different folks.
Andrew Shadow
Site Supporter
Question for you John (@jfheath);
I understand how a speed bleeder works, but I have never used one. I have also never used any check valve when bleeding brakes, such as the often mentioned Motion Pro.
Having no experience with them to draw on, and therefore not knowing what pressures they open and close at, I am asking the below based on the theoretical.
For discussion purposes, let us exclude the issue of air ingress around the threads of the bleeder screws when they are in the open position, be they the traditional or the check valve type.
Using a traditional bleeder screw, the brake lever is applied and held so that pressure is built up in the system before the bleeder screw is opened. The bleeder screw is opened, fluid flows out and the pressure drops. It is closed before the pressure has been completely dissipated. Closing the bleeder screw prevents any air ingress through it. This would be one cycle.
During this process, the brake lever is held in the applied position while the bleeder screw is cycled. This keeps the piston in the master cylinder in a position that blocks the compensation port throughout this process.
If the speed bleeder is functioning properly, it causes pressure to be built up in the system until it reaches a level where the spring in it is overcome and it allows fluid to flow. As the fluid exits, the pressure in the system drops. Long before complete dissipation, the spring overcomes the fluid pressure and closes the valve to prevent air ingress through it. This would be one cycle.
During this process, the brake lever is held in the applied position throughout this entire cycle just as with a traditional bleeder screw. This method also keeps the piston in the master cylinder in the applied position throughout this cycle. This is the same scenario as what happens by opening and closing a traditional bleeder screw, only it happens automatically without user intervention.
They both are;
- forcing pressure to be built up in the system.
- maintaining that pressure throughout the entire cycle.
- maintaining the brake lever in the applied position throughout the entire cycle.
- allowing fluid to exit through the bleeder screw.
- preventing air ingress through the bleeder screw.
What is the difference between manually opening the bleeder screw versus it happening automatically?
The only difference would seem to be that the traditional bleeder screw must be manually manipulated to achieve the above, whereas the speed bleeder opens and closes automatically without user intervention.
The result is the same is it not?
If there is a difference and your theory is correct, this would mean that the speed bleeder's only advantage is that they are easier to use, but they are less effective.
If that is the case, then all of the check valve type bleeders would be subject to the same deficiency, including the Motion Pro check valve that is much touted on this forum as a God send.
I understand how a speed bleeder works, but I have never used one. I have also never used any check valve when bleeding brakes, such as the often mentioned Motion Pro.
Having no experience with them to draw on, and therefore not knowing what pressures they open and close at, I am asking the below based on the theoretical.
For discussion purposes, let us exclude the issue of air ingress around the threads of the bleeder screws when they are in the open position, be they the traditional or the check valve type.
Using a traditional bleeder screw, the brake lever is applied and held so that pressure is built up in the system before the bleeder screw is opened. The bleeder screw is opened, fluid flows out and the pressure drops. It is closed before the pressure has been completely dissipated. Closing the bleeder screw prevents any air ingress through it. This would be one cycle.
During this process, the brake lever is held in the applied position while the bleeder screw is cycled. This keeps the piston in the master cylinder in a position that blocks the compensation port throughout this process.
If the speed bleeder is functioning properly, it causes pressure to be built up in the system until it reaches a level where the spring in it is overcome and it allows fluid to flow. As the fluid exits, the pressure in the system drops. Long before complete dissipation, the spring overcomes the fluid pressure and closes the valve to prevent air ingress through it. This would be one cycle.
During this process, the brake lever is held in the applied position throughout this entire cycle just as with a traditional bleeder screw. This method also keeps the piston in the master cylinder in the applied position throughout this cycle. This is the same scenario as what happens by opening and closing a traditional bleeder screw, only it happens automatically without user intervention.
They both are;
- forcing pressure to be built up in the system.
- maintaining that pressure throughout the entire cycle.
- maintaining the brake lever in the applied position throughout the entire cycle.
- allowing fluid to exit through the bleeder screw.
- preventing air ingress through the bleeder screw.
What is the difference between manually opening the bleeder screw versus it happening automatically?
The only difference would seem to be that the traditional bleeder screw must be manually manipulated to achieve the above, whereas the speed bleeder opens and closes automatically without user intervention.
The result is the same is it not?
If there is a difference and your theory is correct, this would mean that the speed bleeder's only advantage is that they are easier to use, but they are less effective.
If that is the case, then all of the check valve type bleeders would be subject to the same deficiency, including the Motion Pro check valve that is much touted on this forum as a God send.
- Joined
- Mar 18, 2006
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- 70
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- 000679
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- 2570
I use the in-line type that us basically an aluminium cylinder, with a ball bearing and a spring inside. I've taken them apart to clean them on a few occasions. It isn't possible to blow into them to break the seal. Not a very scientific test.
I understand your argument and agree with the theory, but it isn't what I've observed. There must be some resistance in the non return valve, but it isn't that obvious at the lever / pedal when pumping - the valve gives way very easily. You can increase the resistance / pressure by not opening the bleed valve as far, of course. But the pressure is released the instant the spring gives way - so you can't hold the pressure - although by keeping the lever held in, you can stop the fluid returning through the compensation port. That effect would be marginal, as the air bubbles wouldn't have been compressed much, so they wouldn't be expanding much either when the lever is released.
I imagine that the compression of air bubbles is important. If you close the bleed valve you can pump up the pressure in the line and hold it. The fluid cannot be compressed of course, but there is flex in the brake line walls and any air bubbles in there get squeezed and become smaller - which helps to detach them from the side of the brake lines. I believe that it is this behaviour that improves braking performance if the lever pressure is held overnight.
The big advantage for me is that when the bleed line with the bleeder is attached, there is no back flow of fluid into the bleed valve when you stop pumping. So say if you are working at the PCV bleed valve or the rear outer, you can leave the bleed valve open with the tube in place and go round exercising the brake pedal and the SMC to get fresh fluid flushing out the system, without worrying about closing the valve.
The in-line bleed valves work well for me, but my 'finish off routine' involves the pump, pump, pump, hold, open, bleed, close technique. I find it helps to tighten up the feel at the lever. I think this is particularly important with the clutch, as with the bleed valve open and the non-return bleed valve fitted, squeezing the lever is not enough to push the clutch slave cylinder piston in, so that mechanism may not get cleaned with the new fluid.
I don't know. I used to think that the inline non-return bleed valve was enough, but then I came across the pumping up technique in the Honda common service manual and so (with the non return valve still attached, I tried it. I observed an improvement in the feel at the lever / pedal. This is my attempt to explain it.
I've never used the permanently fitted non-return bleed valves, so I don't know how much pressure is required before the valve opens up.
I understand your argument and agree with the theory, but it isn't what I've observed. There must be some resistance in the non return valve, but it isn't that obvious at the lever / pedal when pumping - the valve gives way very easily. You can increase the resistance / pressure by not opening the bleed valve as far, of course. But the pressure is released the instant the spring gives way - so you can't hold the pressure - although by keeping the lever held in, you can stop the fluid returning through the compensation port. That effect would be marginal, as the air bubbles wouldn't have been compressed much, so they wouldn't be expanding much either when the lever is released.
I imagine that the compression of air bubbles is important. If you close the bleed valve you can pump up the pressure in the line and hold it. The fluid cannot be compressed of course, but there is flex in the brake line walls and any air bubbles in there get squeezed and become smaller - which helps to detach them from the side of the brake lines. I believe that it is this behaviour that improves braking performance if the lever pressure is held overnight.
The big advantage for me is that when the bleed line with the bleeder is attached, there is no back flow of fluid into the bleed valve when you stop pumping. So say if you are working at the PCV bleed valve or the rear outer, you can leave the bleed valve open with the tube in place and go round exercising the brake pedal and the SMC to get fresh fluid flushing out the system, without worrying about closing the valve.
The in-line bleed valves work well for me, but my 'finish off routine' involves the pump, pump, pump, hold, open, bleed, close technique. I find it helps to tighten up the feel at the lever. I think this is particularly important with the clutch, as with the bleed valve open and the non-return bleed valve fitted, squeezing the lever is not enough to push the clutch slave cylinder piston in, so that mechanism may not get cleaned with the new fluid.
I don't know. I used to think that the inline non-return bleed valve was enough, but then I came across the pumping up technique in the Honda common service manual and so (with the non return valve still attached, I tried it. I observed an improvement in the feel at the lever / pedal. This is my attempt to explain it.
I've never used the permanently fitted non-return bleed valves, so I don't know how much pressure is required before the valve opens up.
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It does seem a proper faff, doesn't it. I don't mean to be flippant but we all must remember when all we had was a misfitting piece of tube and an empty jam jar.
How many cars and bikes must we all have bled the brakes on, probably with fluid that's been on the shelf way too long. I think it's fair to say we don't see vehicles flying off the road at every bend because the brakes failed and most of the vehicles out there aren't pampered like our ST's.
I use one of the one way aluminium bodied check valve thingymabobs, not sure it helps much to be honest but I bought it so I use it.
Is it important to keep fresh fluid in there, you know it is. But if a quick bleed and change of fluid doesn't cure your issues, which was the original question, you have other issues. At that stage any new fangled bleeder apparatus will not help.
Upt'North.
How many cars and bikes must we all have bled the brakes on, probably with fluid that's been on the shelf way too long. I think it's fair to say we don't see vehicles flying off the road at every bend because the brakes failed and most of the vehicles out there aren't pampered like our ST's.
I use one of the one way aluminium bodied check valve thingymabobs, not sure it helps much to be honest but I bought it so I use it.
Is it important to keep fresh fluid in there, you know it is. But if a quick bleed and change of fluid doesn't cure your issues, which was the original question, you have other issues. At that stage any new fangled bleeder apparatus will not help.
Upt'North.
Mophead
Site Supporter
Much easier. I have the Harbor Freight vacuum thingy and it won't be used anymore.