Revolver Posted December 6, 2011 Report Share Posted December 6, 2011 RB levers are known for leaking. But that would make it lose pressure during use... Either it's holding air, your bleeds suck or the seals are bust. That's all I can think of. How could it pop the master piston out if the brake lever is holding it in there? Actually, that's right... So then what's the next weakest part of the brake? The hoses perhaps, or the cylinder itself. Quote Link to comment Share on other sites More sharing options...
J Trials 31 Posted December 6, 2011 Author Report Share Posted December 6, 2011 RB levers are known for leaking. But that would make it lose pressure during use... Either it's holding air, your bleeds suck or the seals are bust. That's all I can think of. Alright, yeah it worked perfect before and it wasn't even bled by me, it was bled by the person I bought it from, so I'll give a few things a try. How would you be able to figure out if it's holding air or if the seals are bad? Quote Link to comment Share on other sites More sharing options...
forteh Posted December 6, 2011 Report Share Posted December 6, 2011 It does seem to be bottoming out before the pads hit the rim if I have it barely screwed in, but I haven't given a full lookover yet. Does anyone know if it makes a difference when you bleed it if it's screwed out where it's not even in there or if it's just screwed in a little ways? Also what do you mean by having the bleed screw at the highest point? Yes, it's not clamped down to the bar because I had to loosen it to bleed it, I have been bleeding it with blood, but I may take it off and give a good bath bleed, was just using the blood because it's starting to get cold here and you know what that means. I have found that RBs can weep past the piston seals during use (they only have a pair of plain o-rings unlike magura who use an o-ring and a lip seal), however its never a massive leak and you wouldn't notice it normally; the problem is exacerbated if the bore of the cylinder is scored. When my lever was weeping badly (not leaking any noticeable amount) I would be constantly adjusting the TPA inwards to compensate for lost fluid, every couple of weeks or so I would have to top up the bleed and so on so forth. I've since had the cylinder honed and the seals renewed and its all as new again. Best thing to do is remove the lever blade pivot bolt, remove the lever and TPA adjuster and then remove the piston (you might need to undo the bleed screw, remove the ball bearing and poke the piston out using a 1.5mm allen key through the bleed hole). Check the o-rings for wear (a flat edge worn on the outside) or nicks in the rubber and scoring inside the cylinder. Seals are easier to sort out but scoring will need to be honed out properly. Reassembling the piston with a bit of silicone grease around the o-rings will help them stay lubed and seal better. Because the portion of piston outside of the seals (about 5-6mm length) isn't lubricated through normal action of the lever, the bore of the cylinder over this section can get quite badly scored with the ingress of dust and the movement of the piston. This is OK as long as the score marks don't impinge on the swept area of the seals. Greasing the outside end of the piston can help alleviate further scoring but will attract dust and potentially make the situation worse. The bleed screw needs to be at the highest point in the hydraulic system, with a normal magura this means you may need to rotate the lever so it points upwards during bleeding so as to not trap an air pocket in the cylinder; with the RB you can orientate the cylinder so it is always at the highest with your lever in its normal position. When bleeding, back the TPA out as much as you can, I try to make sure sure that the nylon piston is in such a position that the seals are only operating on the non scored section of the bore. Tapping the slaves, hoses and master cylinder with a small spanner whilst the bleed syringe is fitted will help all air bubbles move through the system up to the highest point. I use machine suds (milling machine coolant) in my brake and it works flawlessly, its a synthetic oil base that is water soluble, it does still freeze because I haven't got any antifreeze mixed in there but there's no reason why you couldn't; I'm just too old to be out riding bikes in sub zero temperatures these days It feels the same as water but has much better lubricating qualities Quote Link to comment Share on other sites More sharing options...
Mark W Posted December 6, 2011 Report Share Posted December 6, 2011 What would happen if the brake pads were really close to the rim though. Sure the pads would hit the rim then the frozen water would have to be forced somewhere... It'd be no different to you pulling the brake really hard, in so much as it just flexes your frame out. I've had mine freeze like that, and it didn't damage my brake at all. There's only a small amount of fluid in there so it can't really expand enough to do much damage. Quote Link to comment Share on other sites More sharing options...
J Trials 31 Posted December 7, 2011 Author Report Share Posted December 7, 2011 Alright, well I'm not too sure what it was really but I rebled it with a new jug of blood and it's working fine. Now to find some TNN clamps and booster and some pads. Thanks for the help guys, I used a lot of your tips so it all helped out considerably. I think it's safe to say that it didn't freeze or if it did it didn't bother anything. Quote Link to comment Share on other sites More sharing options...
dann2707 Posted December 7, 2011 Report Share Posted December 7, 2011 It'd be no different to you pulling the brake really hard, in so much as it just flexes your frame out. I've had mine freeze like that, and it didn't damage my brake at all. There's only a small amount of fluid in there so it can't really expand enough to do much damage. That makes sense. Quote Link to comment Share on other sites More sharing options...
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