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I replaced the following:

  • Front brake: a brand new Magura MT4 (pre-bled) brake with brand new pads installed

  • Front rotor: replaced it with a brand new Magura HC Storm 203mm rotor

I used the correct adapter (160mm PM to 203mm from Shimano) for mounting the caliper to my fork (Shimano part number SM-MS-f203P/P).

I cleaned the rotor with brake cleaner (Würth brake cleaner and a clean rag) before installing the disc. I only handled the disc/pads with clean gloves on and tried not to touch the braking surfaces..

Note: The "reach adjustment" screw is screwed all the way in, meaning the lever is as far away from the bars as it possibly can be. I don't think I should be able to press the lever this close to the handlebars using only one finger, please see photos below.

The brake lever feels a bit spongy even though it's brand new. When I press the lever with 2 fingers I can easily press it against my ring finger, which is then clamped in between the lever and grip.

The brake lever in neutral position looks like this:

enter image description here

The brake pads touch the disc when the lever is at approximately this position:

enter image description here

With one finger pressing very hard this is the furthest I can push in the brake lever. towards the bars:

enter image description here

Are Magura brakes supposed to be this spongy?

I tested it out whilst riding just now and even with the brake lever approx 3mm from the grip (pressing very hard with two fingers) I barely slow down. For comparison on dry tarmac I can currently slow down approx 2 to 3 times as fast with the rear brake - which indicates how bad the front brake is working.

When trying to brake hard (by pressing hard with 2 fingers on the lever) I can hear some noise from the disc brake and the handlebars vibrate a bit but the deceleration is very, very underwhelming (especially for 203mm rotor).

I tried with two different brake pad sets: the original set that came with the Magura brake and some aftermarket pads made by BBB. No noticeable difference in performance.

After the first test I also cleaned the rotor with lots of methylated spirits (it was suggested online this was a good cleaner), I though perhaps somehow the brake cleaner had made my braking performance worse so I wanted to try and clean it off. After cleaning with methylated spirits still the same. I also replaced the pads after the first test after having cleaned the disc with methylated spirits in case the brake cleaner had somehow messed up my brake pads.

Whilst testing I braked approx 40 times as hard as I could (not able to lift rear wheel or coming close to doing so.) No difference in performance before and after.

I vibrated the brake line with a funnel on the reservoir port of the brake lever in order to get potentially trapped air bubbles out (even though this shouldn't be needed since this is a brand new brake), this made no difference to the 'sponginess' of the brake lever. It felt the same before and after (I made sure to elevate the lever well above the caliper whilst doing so).

I don't think the brake is defective but perhaps it could be. I've read that some Magura levers tend to be quite spongy. Before buying the MT4 I bought a (also brand new) Magura MT5, this one felt even more like a sponge (Bob). That lever I could easily press against my grip with 2 fingers with not a lot of effort. I exchanged that brake for the currently installed MT4 since I believed the MT5 was meant to be a lot more firm and therefore must have been defective.

Here is a photo of how much I could press the brake lever towards the bar (with quite a lot of force from that one finger) on the Magura MT5 brake:

enter image description here

My questions:

  • What could be wrong / what could be causing this issue?

  • What could I try to improve braking performance?

  • Should I choose a different disc with different hole pattern in order to get more braking power? Or is the pattern I currently have on my 203mm disc just fine?

  • Are there any tests I can perform to see if the problem lies with the brake (if so which part of the brake) or with the rotor or with something else?

  • Should I clean the rotor better? If so how/with what?

  • Will the braking performance improve with more braking? do the brake pads/discs need some time to be 'bedded in' ? If so what would be the fasted way to achieve this (bedding in)? And how long should it take approximately?

Disc rotor: Magura Storm HC 203mm

Pads: The ones that came with the MT4 brake

enter image description here

Note: There appears to be a lot of brake dust on the caliper for just approx 20km of riding (I did a little trip to test the brake properly), is this normal? If not what might be causing the excessive (?) brake dust?

Thank you!

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    How many hard stops did you do? Bedding in brake pads takes roughly 20~50 hard stops, and gentle braking between times makes it take longer. – Criggie Feb 2 at 1:53
  • @criggie I tried to do approx 30-40 hard stops (as hard as I could) but since the braking performance is so bad I can't really do hard stops... I will try some more today and see if it improves.. – Maarten -Monica for president Feb 2 at 10:14
  • @criggie as mentioned it probably takes me 6-8 seconds to come to a complete stop from 40kph braking as hard as i can with the front brake :/ so I wouldn't consider that a hard stop.. I could perhaps try removing the rotor and putting it in a bath of methylated spirits, trying to clean it even better, even though I don't suspect this to be the/an issue considering the circumstances. – Maarten -Monica for president Feb 2 at 10:24
  • @criggie I just did some more brake tests..approximately 40 times from average 45 km/h and the braking performance did not change, still very weak. Brake pads are still quite cold, only about 45 celcius(the backing plate temperature that is) (i did the brake tests in quick succession, approximately in 4-5 minutes riding time), this might indicate the brake pressure isn't sufficient... what do you think? – Maarten -Monica for president Feb 2 at 16:25
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    Bedding in will not work well if you have air in the lines - sounds like another bleed is required still. – Criggie Feb 2 at 18:15
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It sounds like air is trapped in the system and you should do a rebleed. Just start over, follow the manufacturer instructions carefully, take your time and be very careful to get ALL of the bubbles out. I don't see any evidence that anything is wrong with the brake or the rotor or anything else.

Yeah, new pads do need to be bedded in, but when you say the lever is spongy and you barely slow down with the lever 3mm from the bar, that's not because of the pads or anything else... that's because of air in the system.

| improve this answer | |
  • Thank you for your suggestions! I did try to get potentially trapped air out by tapping the brake line/pumping the lever and it appeared as if there was no air left trapped in the system (no bubbles were coming out) as is to be expected with a brand new brake. Also I can put quite a bit of force on the lever (I'm not able to get the lever to touch the grip with a lot of force from 2 fingers). Even though the lever does feel a bit spongy wouldn't you expect the braking performance to be quite good still (if the rotor and pads are in good condition)? – Maarten -Monica for president Feb 2 at 10:17
  • Since there is quite a lot of resistance on the brake lever (even though it does only occur when the lever is quite close to the bar/grip) wouldn't you expect the force being exerted on the lever and indirectly on the oil/caliper pistons to be sufficient regardless of sponginess? Or perhaps I am missing/ misunderstanding something? – Maarten -Monica for president Feb 2 at 10:19
  • Think about what is happening when there is air in the system. The reason that brakes are hydraulic is that fluid can't be compressed, which enables all of your lever force to be transmitted to the calipers. When there is air in the line, and you are squeezing the lever hard, some of that force is compressing the air instead. Some force does still go to the calipers, but less than there should be. That's what is causing the weak braking, and the air is what's causing the sponginess. – alexantd Feb 2 at 16:46
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    In my experience, sometimes after a bleed I feel like I did everything right, but the brake is just not performing the way it should, and then I do it all over and the problem is solved. Air bubbles are pesky little things. – alexantd Feb 2 at 16:50
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I already had trouble after Magura brakes bleeding. The point is that you need the adequate bleed kit, with a bottle plugged in the bleed prt at the lever. And important : with the syringe at the caliper, you first push the fluid into the system, and also pull (hence the bottle, making sure the fluid come back from the bottle, not air)). I could remove lots of bubbles during this pull phase. Some Youtube tuto show that.

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  • @Maarten -Monica for president Check out some reviews of Magura MT line of brakes posted on MTBR.com. Frequent criticism is that they're tough/tricky to bleed and factory bleed is poor. Also the lever throw is quite long in many peoples opinion, which I note here because you discuss it in your question. – Jeff Feb 28 at 17:20

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