Rear Brake MOT scrape through
- Thread starter dazthephot
- Start date
Joined Apr 2012
207 Posts | 0+
Hmm so if I understand you correctly, dead brake is caused by Cavitation!! Lol
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Joined May 2008
379 Posts | 0+
Norfolk
oookay, since i wasnt sure wtf you were on about i looked up the definition of "cavitation" its pretty much "bubbles" which... guess what.. is caused by incorrect bleeding &or a leak to the FULLY SEALED SYSTEM
how do you propose there are bubbles (cavitation...) without air?
vapor bubbles from the fluid boiling?? (too much heat / incorrect fluid)..
what you said totally contradicts itself and i would really like to hear why you feel so strongly that you make it super massive bold text
how do you propose there are bubbles (cavitation...) without air?
vapor bubbles from the fluid boiling?? (too much heat / incorrect fluid)..
what you said totally contradicts itself and i would really like to hear why you feel so strongly that you make it super massive bold text
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Im a hydraulics specialist within my trade and I can tell you its not cavitation. As the fluid is not flowing in your brake system it's just a medium to transfer force, unless you happen to have ABS that is. Even then it would only suffer cavitation in the pump not the system itself. What's really the problem is either, incorrect bleeding of air or seals distorting with heat. By which I mean the MC is getting hot and its expanding.
If air is in there whichever way it gets there it will contain moisture which when heated via compression or direct heat will expand giving you a compressible bubble hence ***** brakes.
Just another thing I've not gone into the degradation on the fluid but its yet another problem to deal with lol.
If air is in there whichever way it gets there it will contain moisture which when heated via compression or direct heat will expand giving you a compressible bubble hence ***** brakes.
Just another thing I've not gone into the degradation on the fluid but its yet another problem to deal with lol.
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Joined May 2013
178 Posts | 0+
East Yorkshire
It which case it would appear on other bikes or after mods to the RSV, which it does not unless fault in the fluid system or poorly serviced.
Joined Apr 2012
207 Posts | 0+
So would a Mightyvac work better than using the traditional bleed method?
Or are we pissing into the wind because the MC is just going to keep expanding and letting air in past the seals?
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Or are we pissing into the wind because the MC is just going to keep expanding and letting air in past the seals?
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Joined May 2008
379 Posts | 0+
Norfolk
dunno what mightyvac is but i bought some cheapo syringe & tubing from fleabay and being able to move the fluid either direction is quite handy, to the point where traditional bleeding seems a total waste of time to me
high freq vibrations? what kinda nonsense is that.. whack some rubber washers or something on the MC mounts and i bet there will be no difference at all
i get the feeling we are just being trolled with this cavitation bs
high freq vibrations? what kinda nonsense is that.. whack some rubber washers or something on the MC mounts and i bet there will be no difference at all
i get the feeling we are just being trolled with this cavitation bs
Joined Apr 2012
207 Posts | 0+
Mightyvac is just a fancy vacuum pump mate. I bought it to bleed my car brakes after a caliper change. It is a sealed vacuum that draws the fluid into an inline container.
I have tried the reverse bleed method with a syringe and I found that it was a pain as I could never get the syringe tube completely empty of air.
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I have tried the reverse bleed method with a syringe and I found that it was a pain as I could never get the syringe tube completely empty of air.
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Joined May 2008
379 Posts | 0+
Norfolk
just hold the syringe up high and keep tapping the tube, hopefully you got clear tubing and you can see the pesky lil bubbles rise slowly to the top
sure its a pain in the backside to start with but its a very effective way of clearing bubbles out of the system i find
sure its a pain in the backside to start with but its a very effective way of clearing bubbles out of the system i find
Joined Apr 2012
207 Posts | 0+
I think the problem I had was that I only had one syringe. I needed another to empty the reservoir then a longer pipe on the syringe so I could top that up during the process.
Or I could just get a bigger syringe!
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Or I could just get a bigger syringe!
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Joined Jun 2009
350 Posts | 0+
Nope....you're not being trolled, and to save further confusion, or future accusation, this is my last post in this thread.
Cavitation is not bs...it IS a phenomenon that can affect any fluid given the right circumstances...usually vibration.
btw....a Mityvac is a vacuum brake bleeding tool.
Carry on.
Ps it normally turbulence lol mate I hate to say it but I can't help myself, honest I don't talk like I've got a peg on my nose lol. When fluid passes through a restriction either from or to if there is a step or edge in that flow it will start turbulence. In that turbulence will be bubbles which pop releasing high levels of energy which will damage the surface of the area, this is called CAVITATION :eatcorn
Joined Apr 2012
207 Posts | 0+
So, just to come back to this.
I have just bled the brake as per the workshop manual. The only extra bits I added were to take off the exhaust can to aid access and loosen the hose guard under the swing arm so I could get the calliper out and up onto the exhaust hanger.
The actual bleed was no more difficult than before. I did start with the Mightyvac but the vacuum pressure is too much for the bleed pipe bore, it sucks air passed the nipple making it harder to see where the bubbles are coming from. So I switched to the normal, open nipple, push brake lever down, close nipple then release and top up fluid. With the calliper now upright I did notice a couple of big air bubbles pop through.
I bled about 300ml of fluid through, put it all back together and I now have a solid back brake.
I won't be riding the bike until Thursday so I am hoping that the pressure will hold.
....I will let you know.
I have just bled the brake as per the workshop manual. The only extra bits I added were to take off the exhaust can to aid access and loosen the hose guard under the swing arm so I could get the calliper out and up onto the exhaust hanger.
The actual bleed was no more difficult than before. I did start with the Mightyvac but the vacuum pressure is too much for the bleed pipe bore, it sucks air passed the nipple making it harder to see where the bubbles are coming from. So I switched to the normal, open nipple, push brake lever down, close nipple then release and top up fluid. With the calliper now upright I did notice a couple of big air bubbles pop through.
I bled about 300ml of fluid through, put it all back together and I now have a solid back brake.
I won't be riding the bike until Thursday so I am hoping that the pressure will hold.
....I will let you know.
Joined Apr 2012
207 Posts | 0+
Rear brake holding!!!
Well, it's no game changer and there is still about 3 inches of travel on the pedal but the pressure is holding.
It means I can at least start on a hill without giving myself a hernia trying to hold the bike whilst letting the front brake off.
So I'm gunna start a new post about pedal travel length.
Well, it's no game changer and there is still about 3 inches of travel on the pedal but the pressure is holding.
It means I can at least start on a hill without giving myself a hernia trying to hold the bike whilst letting the front brake off.
So I'm gunna start a new post about pedal travel length.
Joined Jan 2012
44 Posts | 0+
Near Glasgow
Dazthephot, i was the same as yourself approx 2.5 to 3 inches of play before brake was activating after being bled to death, what i then done was adjusted very carefully the push rod that enters the brake master cylinder by extending it (turning a quarter of a turn at a time) always making sure i still had free play done this by putting bike on rear paddock stand and every time i extended the push rod made sure i could still push the brake lever at least 5mm before the pads started to bind on the rear disc, i know have a rear brake that works within 5mm of pedal travel and can be locked no problem within an inch of travel and no matter how often i use it it never fades and always has held its pressure, even on the longest of runs and on the warmest of days i have never experienced any binding or loss of feel
Joined Apr 2012
207 Posts | 0+
Thanks Colin, that's what I wondered about. It seems that the rod on mine is at its end or close to final turn before coming out.
Perhaps I should wind it back in towards the pedal first and then bleed again. Dunno?
In my eyes there should be no more than one inch from push to full brake pressure, at least that's how it is on others.
Perhaps I should wind it back in towards the pedal first and then bleed again. Dunno?
In my eyes there should be no more than one inch from push to full brake pressure, at least that's how it is on others.
