Pad wear leading to spongy brake?

[foxM1223k3]

Yesterday on a particularly long, steep descent my rear brake lever started pulling to the bar. The brake was always functional, and after cooling it improved, but still felt very spongy compared to before.

When I got home I inspected the pads and they looked ok, total thickness was 3mm against the tektro replacement spec of 2.2mm


I therefore assumed I had some air to bleed so got everything ready and upon installing the piston block I noticed the lever was perfect again. I installed new pads and it feels back to normal without bleeding which suggests it was the pad, however a new pad measures 3.9mm so according to the spec my old pads were only just >50% worn?

Is it normal for brakes to start feeling spongy at a fairly low wear rate? When do others replace them?

I got approx 750km of riding out of this set, I like my rear brake so use it lots!

 

[Bndit]

Brakes are spongy because of air in the system, there`s no other reason. And only solution is to bleed them.

 

[salko]

Sometimes I used to wear the pads down to the metal plate and they were not spongy because of that. Brakes are designed to compensate for pad wear. Maybe your oil level in the system is too low, and when pads wear out, lever starts to push air bubbles into the hose and this will surely cause spongy brakes ... I would suggest you give them a nice bleed (replace complete oil when you're at it), maybe you also have a lot of moisture in the oil and when things heat up, air bubbles start to appear ...

 

[steve_sordy]

Long steep descent, dragging brakes heat up any moisture in the brake fluid and it turns to steam! Steam of course is a gas and will give you spongy brakes. When it cools down the steam turns back to water and the brakes go back to normal.

Bleed, with new fluid, not the new stuff that has been in the bottle for years. Brake fluid is hygroscopic (some are, can't remember which ones). So a full bleed with fresh fluid.

 

[RustyIron]

I installed new pads and it feels back to normal without bleeding

Proper brake maintenance involves cleaning everything, lubricating, bleeding, and installing new pads. Cutting corners is what leads to mediocre performance.

 

[foxM1223k3]

Sometimes I used to wear the pads down to the metal plate and they were not spongy because of that. Brakes are designed to compensate for pad wear. Maybe your oil level in the system is too low, and when pads wear out, lever starts to push air bubbles into the hose and this will surely cause spongy brakes ... I would suggest you give them a nice bleed (replace complete oil when you're at it), maybe you also have a lot of moisture in the oil and when things heat up, air bubbles start to appear ...

I think this might have been the root cause.

I put the original pads back in and retested, same spongy feel.

I then bled the brake and a load of air came out into the lever pot. The lever now feels normal with the worn pads so it seems like the fluid level was too low for the level of wear they reached after getting hot?

 

[salko]

I would say it was a combination of low level of oil and moisture in the oil. I'm glad you have managed to sort it out.

 

[G-Sport]

Sounds like you've sorted it, but always worth remembering to check disc wear as well as pad wear. I've had similar experience when the disc gets down to the minimum, putting new pads in offsets so can seem like a fix.

 

[Tom Sellers]

I placed (probably fake) XT levers on my (mineral oil) magura system to make it into a 'Shamgura' system. Still working well after 4 months. You just have to change the olive and nut on the compression fitting to mount the XT levers on your existing hydraulic lines. (Shimano BH90 olive, nut, and barbed insert designed for BH90 hoses). If you have a legacy Magura system that used DOT, then that may be more problematic.

 

[Tetley]

I had exactly this scenario with my Levo a few years ago - New pads worked well, but after a couple of rides the lever went back to the bars. I tried the traditional bleeding method of pumping loads of fluid through, but it didn't work. Only when I bought a proper reverse bleed kit, it was sorted out.

 

[sethimus]

Shamgura

that doesn't even make sense, those are called Shigura