• This topic has 45 replies, 17 voices, and was last updated 3 years ago by igm.
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  • Hydraulic brake woes
  • Bushwacked
    Free Member

    I’ve been using Magura MT5’s for a few years now and love them, however in the last year I’ve found that every 2-3 months the brakes suddenly lose their power and start to pull closer to the bars before engaging. This usually means they need a bleed so, out comes the bleed kit and off we go.

    However last time this happened the fluid was clear. On todays ride the brakes have gone so I need to bleed but it’s only 3 months since I did it last time.

    Could this be the hose has failed? It does have a kink in it and looks worn so might be letting air in.

    Anyone got any ideas?

    paton
    Free Member

    Are the pads too worn?
    Is there any obvious oil leaks?

    Do the levers have Pressure Point adjustment?
    see page 20
    https://www.magura.com/media/922405/mt_2017_en.pdf

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    thols2
    Full Member

    It does have a kink in it and looks worn so might be letting air in.

    It would leak fluid if it had a hole.

    It sounds to me like you just need to reset the pistons rather than to bleed the brakes every few months.

    Bushwacked
    Free Member

    Thanks for the input. Good to get more thoughts on this as I’m not sure what is happening.

    Pads are new and hardly worn. I can’t see any noticeable fluid leak.

    When you say “reset the pistons” you mean just push them back into the caliper housing and pump them a few times to let them settle?

    Bushwacked
    Free Member

    Having a think about it – I’m wondering if the bleed screw is worn and letting air in – this might be the weak link in the system

    thols2
    Full Member

    When you say “reset the pistons” you mean just push them back into the caliper housing and pump them a few times to let them settle?

    Yes. Check that the pistons aren’t stuck in the seals and can move freely, then push them back in and pump the brakes to reset them.

    Bushwacked
    Free Member

    Yeah, all moving OK.

    I should mention it’s only ever the back brake. Front is always good, in fact in 3 years only had to bleed it properly once. The rear is always a problem.

    Pump the brakes a few times and they come back to life, but leave for a few seconds and they go all spongey. I’m thinking air in the line but can’t work out where from apart from the EBT screw or the hose has a really small leak that I don’t notice but under pressure (braking) air is getting in and is compromising the system.

    luke0912
    Free Member

    I have had a few mt5 levers develop a leak from the master cylinder, the pin that operates the master cylinder just seems to attract a lot of dust to begin with then you might see an odd drop. Magura have a leak guarantee I think it’s five years they have replaced quite a few of mine.

    jonba
    Free Member

    Not that it really helps but your brakes are broken. You shouldn’t need to bleed that much.

    Not familiar with the brakes so this is general. It should be easy to check the lines. It is harder to check the calipers and lever. I had something similar with Shimano calipers, the infamous seal issue. Tissue paper in the caliper picked up the tiny amount of fluid. But there was the squeel/loss of power which also gave it away.

    Are the brakes serviceable. I’d consider a seal change or overhaul. It sounds like something is leaking, letting fluid out or air in.

    pdw
    Free Member

    If pumping fixes it, then it pretty much has to be air.

    Not familiar with these brakes, but I’d probably suspect the reservoir bladder or lever bleed port first. If you’ve got enough of a leak downstream of the master cylinder to let air in, then I’d expect it to be gushing fluid out under braking pressure, but if think the kink in the hose is leaking, wrap it in tissue, apply the brakes with an elastic band and then leave it overnight.

    spicer
    Free Member

    The fluid being clear or dirty isn’t anything to do with it- they’re letting air in from somewhere. Air compresses when you pull the leaver, hence the lever pulling back.

    Bushwacked
    Free Member

    Thanks – I’ve sent an email to Magura to discuss with them.

    I’m wondering if it might be the master cylinder now although it looks dry.

    I have just left the bike on it’s back wheel to let the air get to the top of the hose (as much as possible) and noticed the lever is working as good as ever in this position. Not sure what that means but if I can’t resolve it I may have to manual everywhere.

    frogstomp
    Full Member

    I have just left the bike on it’s back wheel to let the air get to the top of the hose (as much as possible) and noticed the lever is working as good as ever in this position. Not sure what that means but if I can’t resolve it I may have to manual everywhere.

    Also, strap the lever closed to pressurise the system and help extract the air. Once you’ve left it like this for a while (e.g. overnight) then bleed at the lever end. Maybe also try unbolting the caliper and rotate it around in case there is an air pocket.

    pdw
    Free Member

    Not sure what that means

    It confirms that you definitely have air in it. The air that was in the line making the brakes squidgy is now in the reservoir.

    I’m wondering if it might be the master cylinder now although it looks dry.

    If the reservoir is leaking then there may not be much/any fluid coming out as it’s not under pressure, but it may let air in which then makes its way into the lines.

    strap the lever closed to pressurise the system and help extract the air.

    How does pressurising the system help extract air?

    tjagain
    Full Member

    sounds to me like a failed seal in the master cylinder. they can draw air in on return if this happens

    thols2
    Full Member

    How does pressurising the system help extract air?

    I think what happens is that air gets into the master cylinder reservoir and then into the master cylinder when you turn the bike upside down. By pressurizing it, you compress the air bubble and then it pops out of the master cylinder and back into the reservoir again when you release the pressure.

    In this case, I think TJ might be right, it could be air getting drawn into the master cylinder on return.

    frogstomp
    Full Member

    How does pressurising the system help extract air?

    The theories / reasons behind it seems to be a whole can of worms.. my thoughts are that holding the lever pushes the maximum amount of fluid into the system which then causes any pockets of air to be absorbed into the fluid (having nowhere else to go). The air then works its way from the denser, higher pressure fluid to the (marginally?) lower pressure of the reservoir. Just a guess, and happy to be corrected, but there seems little consensus on t’internet…

    sounds to me like a failed seal in the master cylinder. they can draw air in on return if this happens

    But wouldn’t this just be drawing air into the reservoir, which would be at the top of the system and have no effect (the reservoir always has some air in it)?

    thols2
    Full Member

    my thoughts are that holding the lever pushes the maximum amount of fluid into the system which then causes any pockets of air to be absorbed into the fluid (having nowhere else to go). The air then works its way from the denser, higher pressure fluid to the (marginally?) lower pressure of the reservoir. Just a guess, and happy to be corrected, but there seems little consensus on t’internet…

    No, that’s not how it works. The air can’t be “absorbed” by the fluid. The reservoir is not pressurized at all. When you apply the brakes, the master cylinder piston moves until the port to the reservoir is closed. Once that is closed, the system becomes pressurized, but the reservoir is now closed off and remains at atmospheric pressure. The fluid is basically incompressible so the density will not change to any significant degree due to pressure.

    But wouldn’t this just be drawing air into the reservoir, which would be at the top of the system and have no effect (the reservoir always has some air in it)?

    No. It would draw air into the master cylinder. By squeezing the lever hard and holding it for a few seconds, then releasing it, you can often get air bubbles to pop out of the master cylinder and back into the reservoir. The reservoir should not have air in it. It has an expandable bladder on top to prevent air mixing with the fluid.

    pickle
    Free Member

    I had MT5s for a while as they came on a Radon Swoop I bought, they were superb once bedded in and were really powerful. That was until they needed bleeding, once they’d been bled I just couldn’t get them to work properly. a few times they would feel perfect until about 20 minutes into a ride then they’d pull back to the bars.

    I honestly think there’s a design fault in the bleed screw at the caliper, it’s not a nipple (chuckle) and you have to remove the whole thing to get the bleed kit fitted. Obviously when you remove the bleed kit air gets in before you can screw in the bleed screw.

    pdw
    Free Member

    By pressurizing it, you compress the air bubble and then it pops out of the master cylinder and back into the reservoir again when you release the pressure.

    Not sure I buy that. The air bubble isn’t going to expand back to more than its original size when you release the lever, and compressing the air bubble will actually make it more dense and less likely to float up.

    I suppose it’s possible that when you apply the brakes it pushes the bubble down a little from wherever it’s stuck. If you then wait with brake held, it floats back to where it was before, then releasing it pulls it up and hopefully into the reservoir.

    Whenever I’ve had badly bled brakes, I’ve always found that just flicking the lever a few times is enough to get the air back out of the line.

    tjagain
    Full Member

    How does pressurising the system help extract air?

    My opinion – what it does is reset the seals so they are in the optimal position hence the better lever feel

    You might also get the effect of a bubble rising to the top of the line then being drawn into the reservoir when the lever is released

    muggomagic
    Full Member

    Wondering if it’s a brake bleed issue as it sounds similar to the issue a mate of mine was having. He was certain it was something wrong with the brakes but was told that the issues he had was consistent with air in the system and as there were no signs of leaks that it was likely to be that he hadn’t bled it properly. He ended up buying some of those Pro SRAM syringes and said that made the difference and is now convinced the syringes he had were pulling in air when you have to pull on the lever syringe.

    militantmandy
    Free Member

    I too am struggling with my MT5s. Just cannot get the rear brake to bleed properly. No matter what I do, the lever is soft and pulls to the bar. It’s maddening! Such good brakes, but this is nearly enough to make me look for something else.

    igm
    Full Member

    I’ve already got my coat and I’m heading for the door as we speak but…

    every 2-3 months

    …ouch.

    As a Hope-ista I feel annoyed if they “need” attention more often than once every few years. They tend to get bled when I feel like it. And it’s an easy process.

    militantmandy
    Free Member

    Has anyone got any recommendations for good quality syringes for bleeding? The one that came with my Epic Bleed Solutions kit is knackered, which I think may be contributing to my problems.

    nickc
    Full Member

    what’s the routing of the hose like to the back brake? I’ve found that my best rear brake bleeds are where the caliper is at the lowest point (obviously) but sometimes that’s half way up the chain stay, It’s sometimes worthwhile unbolting the caliper from the frame and either unclipping or (snip through the zip-ties) on the chain stays to let it dangle on the end of the hose to encourage the air to move back to the master cylinder, and make the hose routing as straight as possible

    Scienceofficer
    Free Member

    This really does sound like a bleeding issue.

    It’s way harder to get all the air out of a back brake. Its probably twice as long and is nearer to horizontal than vertical, meaning that air buoyancy can’t really help like it does with a near vertical front brake. Where possible I either remove my back brake, or hang the bike as close to vertical as I can when bleeding.

    Given how narrow the bore of the hose is, pressurising the system can help dislodge air that is stuck in the bore or trapped on the edges of internal surfaces. It does this by compressing the bubbles which means they are more likely to become dislodged. Sure, they may get a bit denser because of your thumb pressure on a syringe, but since liquids are incompressible and your single meaty appendage is pretty weak, there will still be plenty of bouyancy for the objective. I’d only do that as finishing actions though, after the main bleed.

    nickc
    Full Member

    He ended up buying some of those Pro SRAM syringes

    personally, I’m not a fan of the “syringe at each end push and pulling” method of “bleeding” brakes. For me, lid off (or reservoir of fluid screwed in) and then: Open bleed screw, pull lever, close bleed screw, release lever…good old fashioned stylee. Always a better and more consistent bleed (for me at least) that way

    muggomagic
    Full Member

    I’ve not had Maguras myself but I had SRAM codes which used the 2 syringes. I’m not sure you could have bled them like that as you need to pressurise the system. With the bleeding edge thing they were super easy to bleed though so never had any problems with them (until the pads got over 50% worn, but that’s another story)

    thols2
    Full Member

    nickc’s method above is generally effective if you have brakes where you can add fluid at the reservoir. Some brakes (Hayes HFX, for example) make it difficult or impossible to do this so you have to bleed them from the bottom up. Also, pumping the lever with the bleeder open lets the master cylinder piston travel the full length of the cylinder, which it normally doesn’t do. IF the brakes are old, this can be bad for the seals because you can get corrosion and debris in that part of the cylinder. I tend to use this as a last resort.

    What I’ve found with rear brakes is that you need to either position the bike so that the hose runs vertically from the caliper to the lever or remove the brakes from the bike completely and hang them with the hose vertical and the lever at the top. With the bleed port at the lever open and at the highest point, open the bleeder on the caliper and let some fluid drain by gravity, with the caliper aligned so that the bleeder is at the highest point. This should clear any air from the caliper. Then you can attach a syringe and pump fresh fluid in from the bottom until fluid comes out of the master cylinder without any air bubbles. If this doesn’t work, then use nickc’s method to force out any remaining air bubbles.

    militantmandy
    Free Member

    I’ve taken the brake off the frame and had it hanging from bar to floor. Then bleed as:

    Attached full syringe to caliper
    Attach empty syringe to lever
    Push fluid from bottom up
    Flap lever a bit
    Pull back
    Repeat a couple of times

    Put it all back together, pump lever, discover lever comes to bar, cry.

    Scienceofficer
    Free Member

    In which case, perhaps the master cylinder seals have failed.

    nickc
    Full Member

     this can be bad for the seals because you can get corrosion and debris in that part of the cylinder.

    Ah, that’s a very good point, never thought of that.

    pdw
    Free Member

    Put it all back together, pump lever, discover lever comes to bar, cry.

    When you’re pushing the fluid through, give it a sharp shove rather than a gentle push. This can help dislodge air bubbles. When done, close the caliper port then gently push fluid in from the top to make sure the reservoir is full.

    If you close the caliper bleed port when bleeding, do you get a firm lever feel?

    igm
    Full Member

    Reverse bleed works a treat on Hope. Keep stuffing good fluid into the calliper and sucking it out of the master cylinder until you have clean fluid and no bubbles coming out.
    Might work on others.

    I know it’s not Hope’s recommended method, but I like it.

    dyna-ti
    Full Member

    I think what happens is that air gets into the master cylinder reservoir and then into the master cylinder when you turn the bike upside down

    For any air to get from the master cylinder reservoir into the rest of the brake it would first need to get past the seals on the lever piston, (if upside down)
    Try tightening everything. Take off the hoses, clean the seating, tighten any hose/fitting connections and refit.
    Also I’ve in the past noticed that on earlier hope brakes(the mini mono lever, the underside of the top cap can be a bit sharp, and if you tighten that down it can actually cut into the diaphragm. Check to see theres no damage on the diaphragm as air would be drawn in there as you release the lever.

    thols2
    Full Member

    For any air to get from the master cylinder reservoir into the rest of the brake it would first need to get past the seals on the lever piston, (if upside down)

    No. When the brake is not applied, the transfer port from the reservoir is open and fluid or air can transfer into the master cylinder – that’s the reason the transfer port is there. When you apply the brake, the master cylinder piston and seal move and close off the transfer port. If you clamp the levers so the brakes are applied, it’s no problem to turn the bike upside down. However, if you turn the bike upside down with the brakes not applied and there is air in the reservoir, it can get into the master cylinder. Generally, pumping the brakes will cause it to pop back out into the reservoir. This is one cause of the wandering bit point problems.

    Bushwacked
    Free Member

    Thanks everyone. I left the bike to “stand” overnight and then topped up the fluid at the lever – now seems to be back to normal – so might have just been a little air getting in somewhere.

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