Juddering when braking

[danfoto]

My current pedelec has solid front forks and Tektro disc brakes. After about 150 miles from new, I'm getting very noticeable juddering when applying the front brake moderately hard. Light braking is OK, as is very hard braking as long as lever pressure's not applied gradually: if it is, we go through a sequence of no judder, judder then no judder as the pressure applied increases.

Am I correct in assuming that bicycle disc brakes still obey the laws of physics and that the cause of this has to be play in the headset bearings? I've checked carefully for a distorted disc, btw, and it's definitely not that. And there's no play at the caliper: it's rock solid to the fork leg.

 

[Fordulike]

I had similar issues with my Tektro hydraulic brakes a few weeks back. First thing to do is to clean the disc and pads with isopropyl alcohol. If that doesn't solve the issue, then you may need to replace the disc and pads, they're cheap enough. Then ensure you properly bed the new pads in by finding a steep hill and go down it half a dozen times, progressively coming to a stop each time.

The reason I have jumped to fit new a new disc and pads so quick, is that you'll tear your hair out trying to get them functioning properly, and sometimes it's just better to start afresh. If your current pads are contaminated, then they'll never brake right.

FYI, my issue was down to me fitting a Shimano disc, instead of the original Tektro. My caliper didn't want to play nice with that disc, so I swapped back to Tektro

 

[danfoto]

Thanks fordulike, that's jolly interesting. I can't imagine how the setup's got contaminated with what, but nevertheless it's no big deal to clean up as you suggest. Being so new it's still on the Tektro disc and pads, but funnily enough the dealer's suggestion for replacement pads when I need them is to fit Shimano!

Now I think about it, the back brake's exactly the same but it's working perfectly, so I guess that itself points to something weird at the front. I've tightened the steering head bearings to the point at which I'm sure there's no play, and although that's reduced the amplitude of the juddering, it hasn't cured it.

Off now to find the IPA ...

 

[vfr400]

Thanks fordulike, that's jolly interesting. I can't imagine how the setup's got contaminated with what, but nevertheless it's no big deal to clean up as you suggest. Being so new it's still on the Tektro disc and pads, but funnily enough the dealer's suggestion for replacement pads when I need them is to fit Shimano!

Now I think about it, the back brake's exactly the same but it's working perfectly, so I guess that itself points to something weird at the front. I've tightened the steering head bearings to the point at which I'm sure there's no play, and although that's reduced the amplitude of the juddering, it hasn't cured it.

Off now to find the IPA ...

Juddering is normally a sign of play in the headset. You can normally feel that by pushing the bike back and forth with the front brake on. If it's bad, you feel clunking. It's not so easy to detect if there's a small amount of play. The easiest way to feel it is to place your fingers over the join between the bottom of the head tube and the forks, then the top of the head tube and where the steerer tube exits while you rock it with the brake on.

 

[Fordulike]

Being so new it's still on the Tektro disc and pads, but funnily enough the dealer's suggestion for replacement pads when I need them is to fit Shimano!

Hee hee, it's a funny old game. I'm running Shimano resin pads with Tektro brake discs. Crazy that Shimano pads just don't like Shimano discs

As for juddering being play in the headset, maybe, maybe not. Mine was juddering because the pads were grabbing and releasing at regular points on the disc rotation. The brakes still worked, but it didn't provide a good riding experience.

 

[danfoto]

Juddering is normally a sign of play in the headset ...

Quite. But as I said above, there is no play in the headset. Hence my puzzlement ...

 

[GSV3MiaC]

Is the juddering tied to wheel rotation speed or something else? If it hics once per rev, then the disc is maybe suspect, damaged or contaminated at a particular point.. The simple option is to swap pads, then disc, and see what cures it. Not the cheapest option though.

 

[danfoto]

Is the juddering tied to wheel rotation speed or something else?

The jury's still out on that, mainly due to the difficulty I've had finding a stretch of road going downhill on which to do brake tests that has a halfway-decent surface on it! Testing in normal riding round town's been inconclusive so far on account of the influence of the substandard surfaces. However, I have a long ride planned for tomorrow which includes several long downhill sections which are still reasonably surfaced. Hopefully that will allow me to answer the question ...