Changed rotor, now brakes are soft

[Mojoman]

I changed my rotor from its standard 160 to a 180 rotor (don't even get me going on how useless a large bicycle shop in my area was with selling me the wrong sized adapter! Evidently, unbeknown to the salesman, one size does not fit all!)

After fitting the new rotor and spacer, the brake feels spongy and I swear I can hear air when you press the lever. Am taking the bike in to have the brakes bled today (another shop, another story!) but I was wondering how can they get air in them if they were not opened and I do not see any mineral oil leaking out anywhere?

[andretraut]

Are you sure that the pads are not only in the bedding-in phase? Give it some time, and do some serious braking, and you should get it sorted out without the assistance of the bike shop. I have also recently changed rotors twice, and found the first couple of braking attempts to be poor and spongy, but as soon as the pads bed-in their performance increases. Good luck with your set-up!  

[Mojoman]

The pads have already done around 100km, do I need to buy another set of pads?

[AndreZA]

Does not make any sense. Are you sure the pads are touching the discs full on? The 100km you are talking about, is that with the new discs or the old? The pads need to "mate" with the discs again to get propper braking performance.

[Mojoman]

Pads do touch evenly (shone light into caliper and rotated the wheel), the pads have done 100km on the old rotor. I did have the fork out and did some other jobs while I was busy yesterday so I wondered if the air was not already in there but I managed to 'disturb' it by having the bike in many different positions (no work stand yet!). The lever comes all the way back to the handgrip.

[Mudsimus]

Are the rotors the same witdh? I thought they were all the same....but alas..they are not.

[parabola]

 

 

Are the rotors the same witdh? I thought they were all the same....but alas..they are not.

 

Definitely not something to overlook. I was using shimano XTR rotors with juicy 5's and they never felt quite right. Swopped them for avids when I changed hubs and the brakes sharpened up very noticably. the Shimano rotors are thicker than the G2 Avids.

 

Also bear in mind rotors like pads also need some time to bed in before they start working properly.

parabola2010-05-19 04:41:25

[SURFER]

Did you have the bike upside down.  heard of a guy transporting his  MTB upside down (back of DC bakkie).  Air moved from resevoir on handle bar to calipers.  Had to bleed brakes to remove air.

[Thug]

 

Are the rotors the same witdh? I thought they were all the same....but alas..they are not.

 

My initial thought as well!

 

[Mojoman]

Thanks for the replies. The original rotor is 1.88mm, the new one is 1.92mm. But I would have thought the calipers would have just pushed the piston out a bit more to make up for any width difference? I did have the bike upside down (not the first time mind you, I always turn upside down when fixing a flattie), I also had the bike on its side to remove the fork. To me if a closed system is kept closed and there are no leaks, how can air be introduced into the system?

[Mudsimus]

There is always air in the system. What brakes is it? Avids?

[Mojoman]

Tektro, Auriga Comps,  they actually work OK (or did!!) but I thought an upgrade on the front rotor would be a good idea as I ride a lot of hills in the area and hoped for an increase in stopping power.

[wac1]

I have the same brakes on my bike . When the bike is upside down the cyclinder sucks in air . All that you need to do is put the cyclinder at thee highest point and put a cable tie around the grip and lever and leave it like that over night . The next morning cut the cable tie and pump the brakes with the cyclinder still at the highest point . The air will all bleed out the cyclinder this way making the brakes much sharper . Tyring to bleed the small air bubbles down the pipe and out the caliper never works because as you release the leaver the air bubble travels up the pipe again . I tie a cable tie around both brake levers the night before a ravce to make sure the air is all out the system .

[Guest Big H]

Take the bike to Cycle Zone in Rustenburg..... I hear their service is awesome!!!!!!!

[Mojoman]

Haha!!Am off to buy the kit myself and let my own fingers do the work!

[TYGA]

wac1 haven't tried your advice but if it works it's you've def qualified for the tip-of-the-month mini-pump and socks gift set. Will be trying that this evening on a dodgy set of hydraulics with some very disturbing tendencies...the bike gets transported in all sorts of positions in the back of my bakkie and the front brake often softens up for no particular reason.