Disc brake issue, is it just the cold?

[ishaw]

I've not used my bike for a while but every now and again I give the brakes (magura mt6) a few cycles.

Over time I've noticed the front has developed more and more of lag before I get any feel but after a good few cycles it seems to get back to normal.

Today however this didn't happen. Pulling on the lever feels as thought there is no fluid in the system but there are no signs of a leak anywhere. Lever, pistons, hose joints are all dry as a bone.

Whats the score? It was working fine before the lack of use.

I remember one of the brakes was a potato get a good been on, but certain this was the rear as it had a dodgy connector so I replaced the hose. This one is still fine.

 

[d8mok]

Re:

My Maguras Trail (MT5) have never had that issue and it’s my winter bike so goes out when it’s cold.

 

[klunkrider]

Think weather can definitely affect them.

I remember when I was working in an lbs we'd get a flurry of customers bringing bikes in with brakes seized on in January (as some people get the bike out to burn off the christmas gluttony) and again in Spring (as the weather improved).

It was usually just a case of letting a little fluid out so seals must have swelled, or the fluid had absorbed some moisture or something? Opposite problem to what you have but definitely seemed like a weather thing.

 

[ishaw]

Re:

Cheers. I'll give them ableedwheni get time and see of that solves the problem. Just a bit strange as I could swear it was OK yesterday. I'd expect some evidence of an issue but nothing other than feeling like pulling air.

 

[ishaw]

Re:

Finally got time tonight to bleed the brake. Followed the recommended procedure. The only thing I did differently was I had the lever horizontal rather than slightly upward on the bar.

Bled the brake using a large allen key between the pistons. All seemed fine, got a strong action when the pistons hit the allen key.

Cleaned it all, popped the wheel.vack in, oriented the lever bake into the riding position. Pulled the lever a few times and it lost all strength, no power at all, barely any braking.

I used the same technique on the rear which is absolutely fine.

Clearly I'm doing something wrong but what?

I'm supposed to be taking the family on a ride over the weekend so need to sort this out.

Anyone got any tips, advice or help, or can spot what I'm doing wrong?

 

[drystonepaul]

Re:

Is the rotor worn?
If it's too thin then there won't be enough brake fluid in the system to actuate the pistons sufficiently.

Sounds like you have air in the system too still.
In my experience you really need a bleed block and a syringe at at the caliper to bleed Maguras properly.
A second syringe at the lever makes the bleed even more reliable.

 

[mdvineng]

Re:

Put something thicker than the disk between the pads and test.
If good it's a travel issue with thin discs.
If it's bad you could have either a m/c position issue or leaking seals on the m/c piston.

 

[ishaw]

Re:

There aren't any leaks anywhere, discs are brand new formula floating (limited a bit to choice as have centre lock wheels). When I do the initial bleed, there is the expected power, hold and feel at the lever. Basically once the wheel is put back in, I have to cycle the lever a few times before the oads (also new) touch the disc. Its after this that the brake has no power, just lightly touches the disc when pulled.

I'm wondering of the allen key I'm using is too wide, leaving a lot of space to be taken up once the bleed is done? I should have some of the travel spacers they use in the video guide, just odd the back is fine and I did it the same way that is failing up front.

 

[mdvineng]

Hydraulic calipers automatically adjust the pad position. Once the pads touch the discs with force, the caliper piston seals retract the piston when the m/c is released. You could have leak bypass in the m/c or if the reservoir is low from moving the pads into position, you won't have pressure due to no fluid left to replenish the m/c

 

[d8mok]

Re:

Magura discs are a different thickness to all other discs ........

Magura 2.0mm and all others 1.8mm