How to "fix" Brake Fade

[Gubbins]

E-Bikes are heavy so brakes do a lot of work.. Today I totally ran out of brakes on a long steep hill, probably due to my going too fast. Back brake faded out first and then alarmingly the lever went soft as well so I was able to easily pull it in to the bars and pump it!! Thinking I had a leak and didnt want oil everywhere I used only the front only to pull up, Well, I couldnt pull up so heart in mouth made it to the bottom!! By this time rear had cooled down a bit and was back to normal, working fine and as it should.. Perplexed I am!!
I often get a bit of fade at the back, so just favour the front a bit more till the rear comes back, but never before has the lever gone.. Only to return! Is it a pad thing? Do different pads suffer fade differently? Has anyone experienced this lever issue before?

 

[KTM Bike Industries UK]

what brakes are they?

 

[D C]

E-Bikes are heavy so brakes do a lot of work.. Today I totally ran out of brakes on a long steep hill, probably due to my going too fast. Back brake faded out first and then alarmingly the lever went soft as well so I was able to easily pull it in to the bars and pump it!! Thinking I had a leak and didnt want oil everywhere I used only the front only to pull up, Well, I couldnt pull up so heart in mouth made it to the bottom!! By this time rear had cooled down a bit and was back to normal, working fine and as it should.. Perplexed I am!!
I often get a bit of fade at the back, so just favour the front a bit more till the rear comes back, but never before has the lever gone.. Only to return! Is it a pad thing? Do different pads suffer fade differently? Has anyone experienced this lever issue before?

I'm quite new to disc brakes on bikes but if it was a car I would say you would need to bleed and replace the brake fluid.

 

[RobF]

Sounds like the brakes overheated.

A different descending technique may help.

The classic way is to haul the bike down to slower than you want, let it go for as long as you dare, haul it down, and repeat.

This will not heat the brakes so much overall because they have a chance to cool a bit between applications.

Tinkering with the pads and bleeding the system may help, but I suspect the root of the problem is lack of overall braking grunt.

Scott probably fit the same brakes as they do to the unpowered version of your bike.

I expect most manufacturers do the same.

 

[Gubbins]

what brakes are they?

Shimano M615

 

[Gubbins]

Sounds like the brakes overheated.

A different descending technique may help.

The classic way is to haul the bike down to slower than you want, let it go for as long as you dare, haul it down, and repeat.

This will not heat the brakes so much overall because they have a chance to cool a bit between applications.

Tinkering with the pads and bleeding the system may help, but I suspect the root of the problem is lack of overall braking grunt.

Scott probably fit the same brakes as they do to the unpowered version of your bike.

I expect most manufacturers do the same.

Original brakes started leaking so LBS replaced under warranty. Originals were no longer available!
They are quite new, only done a few hundred miles since fitting.

 

[RobF]

Original brakes started leaking so LBS replaced under warranty. Originals were no longer available!
They are quite new, only done a few hundred miles since fitting.

Did you bed them in by doing several harsh stops?

If not, the pads may be glazed which won't be helping matters.

You could try some disc brake cleaner - Muc Off is as good as any.

Alternatively, you can now get pads with cooling fins.

But I think your best bet is to address your descending technique as per my earlier post.

 

[Gubbins]

Did you bed them in by doing several harsh stops?

If not, the pads may be glazed which won't be helping matters.

You could try some disc brake cleaner - Muc Off is as good as any.

Alternatively, you can now get pads with cooling fins.

But I think your best bet is to address your descending technique as per my earlier post.

Well. My descending method is to let it roll as fast as I dare and then......... I realise this is not the way to do it but it creates quite a buz. The brakes seem very efficient and the effort needed is really small just one finger on the levers will stop the bike really quickly. What I don't understand is the total lever failure, it just felt like how a burst pipe would feel. and now it's back to normal and working perfectly.

 

[KTM Bike Industries UK]

Take the cover off the reservoir, and pump the brake lever a lot... whilst tapping the calipers and flicking the hose - this will get any small air bubbles out of the system. If you can zip tie the lever to the bars and leave the bike over night.

I've been running shimano brakes for years, even the super cheap ones on my DH race bikes. They are awesome and very low maintenance. My DH Bike weighs more than our eBikes and is used in a lot harsher conditions.

pads should be ok. If they are fading, ie pulling to the bar, it'll be air in the system.

Doesn't need a bleed, just what I've said above.

 

[JohnCade]

The lazy man's brake bleeding method....

I used to do that with cars a lot. Rather than the hassle of bleeding just pump them up and wedge a piece of wood down on the pedal and up to the steering wheel. Left overnight and the brakes are free of air. Pressing down too hard will bugger up the seals of course if they're a bit old.

 

[Gubbins]

Take the cover off the reservoir, and pump the brake lever a lot... whilst tapping the calipers and flicking the hose - this will get any small air bubbles out of the system. If you can zip tie the lever to the bars and leave the bike over night.

I've been running shimano brakes for years, even the super cheap ones on my DH race bikes. They are awesome and very low maintenance. My DH Bike weighs more than our eBikes and is used in a lot harsher conditions.

pads should be ok. If they are fading, ie pulling to the bar, it'll be air in the system.

Doesn't need a bleed, just what I've said above.

Perhaps I am describing this badly..... Back in th old days when you had to replace steel brake lines on a car every few years I became quite adept at doing this, bleeding and generally resolving brake problems so I have some understanding of how they work. It is not possible to pump the lever up, the first pull does the job and any pumping makes no difference so can't be air in the pipes and when they fade it's just that, it's stops slowing me down.. I have to increase lever pressure to compensate for the fading and it never needs a second pull. Air in the system was what was wrong with the originals, and when they ran out of brake you just needed to pump them back up again, not so with these. So still confused. A total and sudden lever to the bars has to be bad news, but how can it repair itself 5 minutes later? Brake it fine now and no amount of pumping the lever makes any difference. If I took it to an engineer he would tell me there is nothing wrong with it.

 

[KTM Bike Industries UK]

There has to be some air in there somewhere, or a seal somewhere in the lever / caliper is failing and the fluid is getting in the the wrong part.

But honestly, don't worry about the logic... just try what I've suggested... I bet it sorted it out.

 

[RobF]

bleeding and generally resolving brake problems so I have some understanding of how they work.

You will know that water is most undesirable in a vehicle system.

You might not know that a lot of mountain bikers happily used water as the fluid in their brakes, and lots of other liquids.

I think the reason was at the time Magura was charging a fortune for a teaspoon of 'blood' fluid.

Don't ask me how water worked, but it did.

Moral of the story is that a bicycle is a unique contraption, and you need to be very wary of applying knowledge gained from other spheres.

 

[JohnCade]

You will know that water is most undesirable in a vehicle system.

You might not know that a lot of mountain bikers happily used water as the fluid in their brakes, and lots of other liquids.

I think the reason was at the time Magura was charging a fortune for a teaspoon of 'blood' fluid.

Don't ask me how water worked, but it did.


Moral of the story is that a bicycle is a unique contraption, and you need to be very wary of applying knowledge gained from other spheres.

Water will work fine as brake fluid it just rusts none stainless components. Plenty of MB bikers still use it.

I remember many decades ago having an old Ford Zephyr that was buggered and taking up space in my garage. Among other things it has zero brakes. So we put some water in it, pumped up the brakes and towed it down to the scrap yard. I took the driver's seat and the brakes worked fine for its one way trip.

 

[VictoryV]

You will know that water is most undesirable in a vehicle system.




.

Water may be incompressible like hydraulic oil, but it boils under high temperatures, even if it is pressurised by the hydraulic pressure you are applying through the lever. It may be that you have some water contamination, under high usage the steam would behave like air in the system, but when cooled it would become water so the brakes "heal" themsselves & appear normal. It is a safety thing i would change the oil. Remember oil floats on water so you cannot see if there is water in the reeservoir - but it will be the first fluid out of the bottom of the reservoir into the system

 

[Gubbins]

Water may be incompressible like hydraulic oil, but it boils under high temperatures, even if it is pressurised by the hydraulic pressure you are applying through the lever. It may be that you have some water contamination, under high usage the steam would behave like air in the system, but when cooled it would become water so the brakes "heal" themsselves & appear normal. It is a safety thing i would change the oil. Remember oil floats on water so you cannot see if there is water in the reeservoir - but it will be the first fluid out of the bottom of the reservoir into the system

This seems to make sense.. My first thoughts were boiling fluid, but, would it get that hot? And, how would it get back to normal? Good answer that satisfies my need to know why!.. A bleed kit needs to be purchased ..Cheers.

 

[VictoryV]

This seems to make sense.. My first thoughts were boiling fluid, but, would it get that hot? And, how would it get back to normal? Good answer that satisfies my need to know why!.. A bleed kit needs to be purchased ..Cheers.

You could drain the oil off into a clear container and let it settle, if there is water contamination then an oil / water boundary would become visible and u would know for sure.

 

[peerjay56]

Sounds like you have plenty of advice with what seems to be a hydraulic problem, but I would definitely advise cadence braking anyway (basically as Rob F suggested - braking in short bursts, gradually reducing speed) - not so sure about the 'speeding up as fast you dare' part though

 

[KTM Bike Industries UK]

Riding a slightly heavy eBike down a hill in the UK shouldn't cause the problem you're having Phil, the brakes are more than up to it... and a standard bleed doesn't often get the small bubbles out of the stange shapes inside Shimano calipers and levers.

Honestly, just try my tip... it costs nothing and will save you buying a bleed kit.

 

[EddiePJ]

Just to add to what KTM BI have said.

If you happen to spill or need additional fluid*, make sure that you use the correct grade and type to replace. Check the OE spec to find out which that you require.

* It's doubtful that you will ever require additional fluid.