Brake problem, need help from experts

[Sander23]

Last week I had a crash and snapped off my whole brakelever from my back brake
Have magura mt4 brakes.
Got a new one with 2 finger lever, changed to a 1 finger lever.
installed it and did a full bleed with the caliper loose from the frame, also got new brake rotors and brakepads.

Went for a ride today and noticed that my rear brake have nearly any stopping power. It's so bad that when I drive 25 km/h and use my rear brake on its own it won't even lock my back wheel or make the bike slip.

What's left that I can do to get the brake working better?

 

[Jackware]

Try bleeding again, depending on how the hose is routed some people seem to struggle to get all the air out.

 

[Sander23]

I've done the bleed twice as the first one failed

 

[Stihldog]

Magura brakes can be difficult to bleed.
After the initial install and bleed the brake action may seem fine. Go for the first ride and they fail.
I’ve installed several sets of MT7’s and have noticed that a mini-bleed is necessary after a short ride. Likely the shaking motion has dislodged more bubbles or air which is locked in the system. After that they work great. Unless it’s something else (poor alignment, stuck caliper, etc).

 

[Stihldog]

I've done the bleed twice as the first one failed

Make sure that there is no pinch points in the hydraulic line at all. Use the proper size hose provided by Magura. Don’t over tighten the olive.

 

[Stihldog]

Ok, I’m not familiar with the MT4’s and you only changed the lever. But you did bleed the system from the calliper. You may have accidentally introduced air into the system. The Magura bleed kit is not very good. It can introduce air at the calliper and go un-noticed at first. During the push-pull watch for micro bubbles coming from the calliper, you may be adding air to the system.
I use a good quality syringe, threaded adapters and properly sized clear hose for the full system bleed.
I then use a funnel with proper threaded adapter at the master cylinder. Add a bit of royal blood and rotate the master cylinder until no more bubbles appear after you pull the lever. Flicking the lever may dislodge more trapped air in the master cylinder. Close the system and pump the lever again. If it still feels spongy…do it again or go for a quick bumpy ride and do the mini bleed again. Trapped air in the system sucks and for some reason Magura brakes seem very sensitive …I don’t know why?
Anyways, I’m not an expert but this is my experience with Magura brakes.

 

[Sander23]

Make sure that there is no pinch points in the hydraulic line at all. Use the proper size hose provided by Magura. Don’t over tighten the olive.

Ok, I’m not familiar with the MT4’s and you only changed the lever. But you did bleed the system from the calliper. You may have accidentally introduced air into the system. The Magura bleed kit is not very good. It can introduce air at the calliper and go un-noticed at first. During the push-pull watch for micro bubbles coming from the calliper, you may be adding air to the system.
I use a good quality syringe, threaded adapters and properly sized clear hose for the full system bleed.
I then use a funnel with proper threaded adapter at the master cylinder. Add a bit of royal blood and rotate the master cylinder until no more bubbles appear after you pull the lever. Flicking the lever may dislodge more trapped air in the master cylinder. Close the system and pump the lever again. If it still feels spongy…do it again or go for a quick bumpy ride and do the mini bleed again. Trapped air in the system sucks and for some reason Magura brakes seem very sensitive …I don’t know why?
Anyways, I’m not an expert but this is my experience with Magura brakes.

No I had to replace the the brake master on its own, it came with 2 finger lever but I gmchanged it to a 1 finger lever. Used the original brake hose

I own a bleed kit from aliexpress wich has all the adapters

 

[Mikerb]

So everyone seems to be talking a bout bleeding the brakes but if you had pressure at the lever and you have checked that the caliper pistons push the pads onto the rotor I would have thought the problem is associated with the brake pad to rotor interface. So thoroughly clean the new rotor with IPA and maybe even use some emery paper on the braking surface. Then do some running in for the new pads ( something you do not mention as having done). The running in process consists of using the brakes to transfer a sacrifice layer of the pad onto the rotor. To do that you need to brake quite hard from a moderate speed but only for a few seconds...........and repeat several times. The idea is to brake quite hard but avoid generating any heat in the rotor which will defeat the running in process. The grip between pads and rotor should noticeably improve progressively with each application of the brake. It can take 5 or 10 minutes of repeating this process if you using sintered pads........other pads should be quicker.

 

[apac]

Agree with above. you Don't mention bedding in the pads and discs.

 

[Mikerb]

...and a new rotor probably has a surface coating from the manufacture process which you do not want...hence the need to at least clean it...personally I would rub the braking surface with wet and dry ( at an angle outward from the centre at all points)

 

[RustyIron]

the problem is associated with the brake pad to rotor interface.

^^^What he said.^^^

I"ll add that whenever I change pads or rotors, braking is abysmal at first. After several braking runs in the street, things become noticeably better. But braking never becomes GREAT until one or two REAL downhill runs on the trails.

 

[All4Fun]

I'll run MT5 here, had the same experience after an upgrade to Jagwire hose and new disc and pads on the back.
After bleeding the lever feels hard, but with a test run bad performance, again bleeding, and yes.. a little bit air came out, but still bad performance .
Did clean the disc and sanding, no use....

In the end i ended up with the bike hanging in an angle with the hose only in a rising line, and tapped everywhere from the lowest point of on the hose/ frame, flicking the lever, each time i could fill with another drop of fluid, did this several times after i couldn't fill anymore... it seems there was still air in the system .
But now it's rock hard, you can feel exactly the point where the pads grip the disc and you can apply brake force...

So.. in the end it was the bleeding that did the trick for me, i did read bleeding Magura was hard, but now i know it for sure....

 

[Sander23]

So I did bed it the brakes ,5+ times each brake.
Good speed with long brakes.
These are magura 7.p performance pads

Did a lever bleed haven't seen any bubbles come out. This time I left the brake pads in and sqeezed a couple times and tried the brakes again. The brake lever feels alot stronger now, but still no stopping power on the rear brake. Cannot make the back wheel lock and slip.


I did the front brake the same way except the bleeding and it's pretty powerfull.


I guess I have to do the bed in again?

 

[Woodyboy]

Try pouring some clean water over the pads and bed in as mentioned. It instantly fixed a similar issue I was having.

 

[apac]

Very lightly rub down the pads with some fine sandpaper. Be careful you only take off the glazing and dont take too much off the pad. Also then rub down the discs so the contamination cannot go back on the pad. Use isopropyl/alcohol spray to clean.

 

[Stihldog]

The importance of brake pads and rotors can’t be overstated and posters have made very good suggestions for maintenance or repairs.
After the many possible scenarios of brake issues that I have come across, the pinched hydraulic line was the most difficult to find. A kinked or bent hydraulic line can be obvious and can result in poor brake performance. A pinched hydraulic line is possible and harder to detect. Likely areas for this is where the hydraulic line passes through the frame(s), motor area or battery compartment.

The Magura hydraulic line may be slightly larger in diameter than the original line. In my case I followed the same path, as the original line, through the battery compartment. The pinched Magura line was not even noticeable but I repositioned it anyways. Problem solved! The repositioned line likely returned to the correct roundness and the rear brakes worked properly.
I don’t know if this could be an issue with the OP but it happened once to me after several Magura brake installations.

 

[Mikerb]

The importance of brake pads and rotors can’t be overstated and posters have made very good suggestions for maintenance or repairs.
After the many possible scenarios of brake issues that I have come across, the pinched hydraulic line was the most difficult to find. A kinked or bent hydraulic line can be obvious and can result in poor brake performance. A pinched hydraulic line is possible and harder to detect. Likely areas for this is where the hydraulic line passes through the frame(s), motor area or battery compartment.

The Magura hydraulic line may be slightly larger in diameter than the original line. In my case I followed the same path, as the original line, through the battery compartment. The pinched Magura line was not even noticeable but I repositioned it anyways. Problem solved! The repositioned line likely returned to the correct roundness and the rear brakes worked properly.
I don’t know if this could be an issue with the OP but it happened once to me after several Magura brake installations.

Spot on! and adequately describes the difference between a bleed issue and either poor pad/rotor interface or a hydraulic hose blockage/kink. Poor bleed leads to excess lever travel. Poor rotor/pad interface/ seized pistons/hydraulic hose blockage would mostly result in a firm lever but no ( or weak) resultant braking.

 

[Rotwilder]

When I first bought my ebike I was always cleaning and spraying Muc products all over it. My brakes suffered badly, although I was always careful to avoid overspray. I have learned to spray onto a cloth to apply products now; this avoids noisy, failing brakes completely! I periodically remove the brake pads and wash them under the tap with fairy liquid-they come up like new! I’ve used just one rear set of brake pads in just under 22000 miles.

 

[steve_sordy]

These are magura 7.p performance pads
View attachment 76949

Bloody hell! I have NEVER seen pads that black and shiny before!! Are they a special type, made of carbon fibre or something? Those would be a write off on my bike. They look as though they have been oil-polluted.

 

[Mikerb]

Bloody hell! I have NEVER seen pads that black and shiny before!! Are they a special type, made of carbon fibre or something? Those would be a write off on my bike. They look as though they have been oil-polluted.

well they are certainly not sintered.........more like cindered!!

 

[Sander23]

Bloody hell! I have NEVER seen pads that black and shiny before!! Are they a special type, made of carbon fibre or something? Those would be a write off on my bike. They look as though they have been oil-polluted.

Semi metal pads and I don't come close to the pads with oil or sprays

 

[1oldfart]

I went out to test a new bike, it was freshly mounted out of the box. There was 1% braking power.
I simply repeated accelerating than braking like 12 times and it cleared the discs from a
protection film and progressively the power improved without doing anyting but braking.