AdamR28 Posted April 15, 2011 Report Share Posted April 15, 2011 http://www.sdplastics.com/nylon.html Water molecules produce polar bonds with the amide groups in the nylon molecules. Although small, water molecules take up space and displace the nylon molecules. This results in the nylon molecular matrix swelling. Dimensional changes of 0.7% can result. That would swell your piston from 13.90mm (new) up to 14.00mm, which is the same size as the cylinder and it therefore sticks. I have seen them as high as 14.02 before. However: The absorption of moisture by nylon is a completely reversible physical reaction. Drying in an oven will drive off all but a small percentage of the water molecules which can only be removed through dissolution of the nylon molecular matrix. When we see this problem here though, we usually just lathe the piston down to 13.95mm so the problem doesn't occur again. So there we have it - the reason water 'screws up' hydraulic rim brakes seems to be nothing to do with the seals Quote Link to comment Share on other sites More sharing options...
Krisboats Posted April 15, 2011 Report Share Posted April 15, 2011 I found this out the other day when looking at acrylic fish tanks and reading about how the acrylic swells over time as the water is absorbed. Wondered if the same might be happening in my magura and now i know. Cheers ads! Apparantly cell cast acrylic is supposed to be the best in terms of minimal water retention. Might be worth noting if ever anyone makes a water bleed specific trials brake or piston upgrades Quote Link to comment Share on other sites More sharing options...
Ben Swales Posted April 15, 2011 Report Share Posted April 15, 2011 That IS interesting (and geeky)! Worth knowing though, for sure! 1 Quote Link to comment Share on other sites More sharing options...
casualjoe Posted April 15, 2011 Report Share Posted April 15, 2011 This is nice to know and could open the door to someone making aluminium piston upgrades. Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted April 15, 2011 Author Report Share Posted April 15, 2011 This is nice to know and could open the door to someone making aluminium piston upgrades. My first thought too haha. Quote Link to comment Share on other sites More sharing options...
BradJohnson Posted April 15, 2011 Report Share Posted April 15, 2011 http://www.sdplastics.com/nylon.html That would swell your piston from 13.90mm (new) up to 14.00mm, which is the same size as the cylinder and it therefore sticks. I have seen them as high as 14.02 before. However: When we see this problem here though, we usually just lathe the piston down to 13.95mm so the problem doesn't occur again. So there we have it - the reason water 'screws up' hydraulic rim brakes seems to be nothing to do with the seals I had an arguement on here a few days ago, that water shouldnt be in your brakes, this is the exact reason why Quote Link to comment Share on other sites More sharing options...
Revolver Posted April 15, 2011 Report Share Posted April 15, 2011 I had an arguement on here a few days ago, that water shouldnt be in your brakes, this is the exact reason why Shush, it's not a 100% certainty. Some of us have used water bleeds for ages, most of those have only had to bleed once. I did have a sticky piston once on an old lever, the 04 style one. It was used and abused. I swapped the lever, no ball-ache whatsoever, and it's been fine since. Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted April 15, 2011 Author Report Share Posted April 15, 2011 I had an arguement on here a few days ago, that water shouldnt be in your brakes, this is the exact reason why But most arguments around it are 'it wrecks the seals', no? Quote Link to comment Share on other sites More sharing options...
forteh Posted April 15, 2011 Report Share Posted April 15, 2011 I had an arguement on here a few days ago, that water shouldnt be in your brakes, this is the exact reason why Youre argument was absolutely nothing to do with the swelling of nylon in water Ive known that nylon swells in water for the last ten years, just never occured to me that it would apply to maggies but of course it would. We use UHMWPE(Ultra High Molecular Weight Polyethylene - common brand names are perplas and cestilene) at work where we need a submerged or wet atmosphere bearing as it doesnt swell like nylon and has better self lubricating properties. Would make for a better piston replacement than aluminium because it wont scratch the bore, it can be a pig to machine to tight tolerances though because it is pretty soft and has a habit of deflecting rather than cutting unless its large section, it does cut like butter though Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted April 15, 2011 Report Share Posted April 15, 2011 Is this as in the piston in the lever or the brake cylinder? Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted April 15, 2011 Report Share Posted April 15, 2011 Has anyone thought/used Propylene glycol / water bleed? Propylene glycol is a lubricant, as vioscous as water, safe to seals (used as antifreeze in cars/computer water cooling systems) and lowers the freezing point of water. Everything you ever wanted right? Quote Link to comment Share on other sites More sharing options...
forteh Posted April 15, 2011 Report Share Posted April 15, 2011 Has anyone thought/used Propylene glycol / water bleed? Is what most people use Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted April 15, 2011 Report Share Posted April 15, 2011 Is what most people use I'll order some up for my next bleed Quote Link to comment Share on other sites More sharing options...
Sam Moss Posted April 15, 2011 Report Share Posted April 15, 2011 we usually just lathe the piston down to 13.95mm so the problem doesn't occur again. How do you get the piston out of the cylinder? Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted April 16, 2011 Author Report Share Posted April 16, 2011 I'll order some up for my next bleed No need, just walk into your local car shop and get some antifreeze The pistons are hard to get out of the slaves (and the process is generally irreversible), but as said it doesn't seem to happen down there. Quote Link to comment Share on other sites More sharing options...
Krisboats Posted April 16, 2011 Report Share Posted April 16, 2011 I had an arguement on here a few days ago, that water shouldnt be in your brakes, this is the exact reason why Yeah, you sure look like you have the mechanical skills to back up what you're saying. http://www.trials-forum.co.uk/topic/163809-crank-arm-fell-off/ Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted April 16, 2011 Report Share Posted April 16, 2011 Yeah, you sure look like you have the mechanical skills to back up what you're saying. http://www.trials-forum.co.uk/topic/163809-crank-arm-fell-off/ Game, Set and Match Quote Link to comment Share on other sites More sharing options...
forteh Posted April 16, 2011 Report Share Posted April 16, 2011 The pistons are hard to get out of the slaves (and the process is generally irreversible), but as said it doesn't seem to happen down there. Ive only ever suffered sticky pistons on the slaves, never on the master cylinder. I still blame the wiper seal being unlubricated in my instance Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted April 18, 2011 Report Share Posted April 18, 2011 Adam, is there any reason why echo slave cylinders are more common to leaking than magura's? Different diameter piston? Different seals? Also, whats the idea ratio for water/antifreeze? 50/50? Quote Link to comment Share on other sites More sharing options...
Revolver Posted April 19, 2011 Report Share Posted April 19, 2011 Adam, is there any reason why echo slave cylinders are more common to leaking than magura's? Different diameter piston? Different seals? Also, whats the idea ratio for water/antifreeze? 50/50? Magura has been making brakes for ages, deng has only made them for a few years. And, whatever it says on the bottle. Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted April 19, 2011 Report Share Posted April 19, 2011 Magura has been making brakes for ages, deng has only made them for a few years. And, whatever it says on the bottle. kinda didnt answer either of my questions Quote Link to comment Share on other sites More sharing options...
Mark W Posted April 19, 2011 Report Share Posted April 19, 2011 He did pretty much answer both of them. Just read the bottle of antifreeze you've got, it'll say on there. It doesn't matter massively either way in fairness, I've never been particularly accurate mixing mine and it's not been a problem. Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted April 19, 2011 Report Share Posted April 19, 2011 He did pretty much answer both of them. Just read the bottle of antifreeze you've got, it'll say on there. It doesn't matter massively either way in fairness, I've never been particularly accurate mixing mine and it's not been a problem. Well i wanted to know the REASON why echo slaves leak, i.e tolerances, seals ect. Revolver just said because Deng hasnt been manafacturing them for long. As with the antifreeze, the instructions are for car engines, not bike brakes Quote Link to comment Share on other sites More sharing options...
JD™ Posted April 19, 2011 Report Share Posted April 19, 2011 Well i wanted to know the REASON why echo slaves leak, i.e tolerances, seals ect. Revolver just said because Deng hasnt been manafacturing them for long. As with the antifreeze, the instructions are for car engines, not bike brakes So having your question answered twice isn't enough? Read the instructions on the antifreeze bottle you have, and it'll tell you how to mix it, if at all. Echo slaves leak because they've been around for less time, and as such have had less development time. And/or they suck. 3rd times a charm... Quote Link to comment Share on other sites More sharing options...
Mark W Posted April 19, 2011 Report Share Posted April 19, 2011 As with the antifreeze, the instructions are for car engines, not bike brakes If you can't work it out from that, I worry for you. Quote Link to comment Share on other sites More sharing options...
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