docc Posted July 2 Share Posted July 2 When gravity bleeding (flushing), or using a vacuum pump, is the master cylinder chocked open? Link to comment Share on other sites More sharing options...
gstallons Posted July 2 Share Posted July 2 UHHHH , the master cylinder is in the relaxed position . As in no one is pulling/pushing on any lever or pedal . Don't forget DOT 4 fluid only ! 2 Link to comment Share on other sites More sharing options...
docc Posted July 2 Author Share Posted July 2 Thanks, gst! I have always done the press lever/pedal->open bleeder->close bleeder-> release lever/pedal->repeat/repeat/repeat. So, just open the bleeder and let the fluid drain into a catch can (or use the vacuum pump) while keeping fluid in the reservoir? 1 Link to comment Share on other sites More sharing options...
gstallons Posted July 2 Share Posted July 2 That is the easiest and most effective method , just keep the reservoir full . 2 1 Link to comment Share on other sites More sharing options...
docc Posted July 2 Author Share Posted July 2 The vacuum speeds up the process? Or is most desirable, otherwise? Link to comment Share on other sites More sharing options...
GuzziMoto Posted July 2 Share Posted July 2 I prefer speeding up the process with a vacuum pump. But my favorite way is to pressure bleed, where you force fluid into the reservoir and from there through the system. That pushes the fluid and any air present out the bleeder. Applying a vacuum to the system can in some cases suck air into the system, which is opposite to what you are trying to do. 1 1 Link to comment Share on other sites More sharing options...
Skip Posted July 2 Share Posted July 2 I always thought that the action of moving the master cylinder piston was always more desirable to agitate any lodged air pockets. IMO And yes very repetitive, but then I again I always just use a clump of rags. 1 Link to comment Share on other sites More sharing options...
GuzziMoto Posted July 2 Share Posted July 2 (edited) You can get one way valves that go at the bleeder, some of them are even a replacement for the bleeder with a one way valve built in. The ones I have used in the past were inexpensive one way valves from a tropical fish store that I throw away after I am done. They are not made to withstand brake fluid, so it tends to destroy them. But they last more then long enough to do the job. With a one way valve you can pump the master cylinder all you want, just make sure the reservoir doesn't run out of fluid. But it is easier then cracking the bleeder and tightening it, then cracking it, then tightening it. Edited July 3 by GuzziMoto 3 Link to comment Share on other sites More sharing options...
audiomick Posted July 2 Share Posted July 2 (edited) 52 minutes ago, GuzziMoto said: You can get one way valves that go at the bleeder, some of them are even a replacement for the bleeder with a one way valve built in. This would seem to be the leading brand of the bleeder replacement type here: https://www.stahlbus.de/index.php?language=en I've read about blokes putting them in time and time again, and they all seemed to be well pleased with them. Personally, I would prefer the solution that I saw in the workshop that I go to when I need help. The mechanic there uses an in-line valve downstream of the bleeder, i.e. hose on the bleeder like conventional "pump-open-close" bleeding, but there is a valve in the hose, so you just have to open the bleeder and keep pumping until the air is out. As has been mentioned, all you have to do is make sure to keep enough fluid in the reservoir to stop it sucking air in. The other thing that I picked up from watching him was to remove most of the fluid from the reservoir with a syringe before you start. That means you don't have to pump as much old fluid through the system before the new stuff comes through. Having said all that, I prefer to have mine done in the workshop. I hate doing it, and one always has some brake fluid left over that you can't store for more than about 6 weeks and that has to be disposed of properly. I'm happy to pay someone to do it for me. Edited July 2 by audiomick 2 Link to comment Share on other sites More sharing options...
docc Posted July 2 Author Share Posted July 2 I so appreciate all the replies! I knew I could count on you guys! Link to comment Share on other sites More sharing options...
LaGrasta Posted July 2 Share Posted July 2 I have been using one of these for a few decades, it's awesome. Mine is actually generic though. https://www.motionpro.com/product/08-0143 1 Link to comment Share on other sites More sharing options...
audiomick Posted July 2 Share Posted July 2 (edited) Yeah, that is pretty much exactly what I saw the mechanic using in the workshop. Thanks for the link. At that price, I might even buy one myself. PS: a different mechanic recommended "saturated silicon" tubing for brake bleeding. I got some, and I reckon he was dead right. The stuff is very flexible. When using the "pump-open-close" method, i.e. no valve in the line, the tip is to use a couple of yards of it, enough to go from the brakes up to the top of the frame/handlebars, and back down to a catch can on the floor, and hang it up in the middle on the handlebars or rear blinker of something as appropriate. Why so long? Firstly, the length allows the hose to twist enough to easily accomodate the turning of the nipple as it is cracked and closed. Secondly, the long way up allows you to very easily see if there are bubbles in the fluid or not. After swearing and sweating for years, that tip turned the job into something do-able. I still don't like doing it, but with those hoses it is almost bearable. The "saturated silicon" hoses I bought are now about 15 years old. I think I rinsed them out every time I used them, but am not sure. Anyway, they've had brake fluid through them a number of times, and are still transparent (slightly milky, as they were when they were new...) and soft and flexible. Edited July 2 by audiomick Link to comment Share on other sites More sharing options...
docc Posted July 2 Author Share Posted July 2 I just sourced Saint-Gobain Tygon tubing (F-4040-A) for a short length of reservoir hose. Looks like I should have gotten Tygon 2375 for this application . . . 1 Link to comment Share on other sites More sharing options...
Lucky Phil Posted July 2 Share Posted July 2 3 hours ago, audiomick said: This would seem to be the leading brand of the bleeder replacement type here: https://www.stahlbus.de/index.php?language=en I've read about blokes putting them in time and time again, and they all seemed to be well pleased with them. Personally, I would prefer the solution that I saw in the workshop that I go to when I need help. The mechanic there uses an in-line valve downstream of the bleeder, i.e. hose on the bleeder like conventional "pump-open-close" bleeding, but there is a valve in the hose, so you just have to open the bleeder and keep pumping until the air is out. As has been mentioned, all you have to do is make sure to keep enough fluid in the reservoir to stop it sucking air in. The other thing that I picked up from watching him was to remove most of the fluid from the reservoir with a syringe before you start. That means you don't have to pump as much old fluid through the system before the new stuff comes through. Having said all that, I prefer to have mine done in the workshop. I hate doing it, and one always has some brake fluid left over that you can't store for more than about 6 weeks and that has to be disposed of properly. I'm happy to pay someone to do it for me. Why? Phil Link to comment Share on other sites More sharing options...
audiomick Posted July 2 Share Posted July 2 1 minute ago, Lucky Phil said: Why? Phil Because brake fluid is hygroscopic, so you have to assume that an opened container of brake fluid has taken up too much water after about six weeks. No, I haven't tested that, but that is what I have been told by several professionals who earn their money by knowing about such things. Link to comment Share on other sites More sharing options...
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