Headset juddering under braking

jordan_217

I finally got round to cutting my steerer(s) last week, now that I'm happy with the bar height. I had to remove the expander bung to cut and it wasn't a type I'd seen before. It's this one:

http://www.ebay.com/itm/Trigon-7075-CNC ... 0991758841

It's only three parts, how hard can it be? Well, I couldn't get the bung back in the steerer initially. After some swearing, I walked away. I returned to my bike the morning after and fitted the bung first time. I then torqued everything up and checked for any obvious play by bracing the front wheel and shaking the bars. All seemed fine. However, I'm getting a bit of judder under front wheel braking, it's also noticeable on rough surfaces.

I've taken everything apart and repeated the process. Once the bung assembly is in place, it seems solid and isn't budging. The juddering persists. I'm a bit stumped as everything seems solid when I've finished. I have 3mm of gap between the top of the steerer and top of the stem. Any ideas/tips before I nip out and buy this type of bung instead?:

http://www.totalcycling.com/a-z/stems/s ... tAodWXQAjg

I cut the steerers on my other bikes at the same time, same process and they are absoultely fine. The only difference is they had the the expander bung from the second link above.

Yossie

All bearings seated in the right way round? Remember that the tops and bottoms of each race are different.

jordan_217

Yossie wrote:

All bearings seated in the right way round? Remember that the tops and bottoms of each race are different.

Thanks Yossie, yes I'm sure everything is the right way round. I'm a bit stumped to be honest. This would be the third time in a year that I've removed the whole stem/headset/fork assembly (for cleaning/greasing) and the only time I've had an issue is after I've removed/reinstalled that bung (I'm not convinced by that design too, TBH).

jomoj

some bungs just wont grip so it's hard to get the compression right and eventually they can slip.
These ones are good combined with a bit of carbon paste for extra grip

http://www.wiggle.co.uk/deda-expander-bung/

keef66

The bung that came with my Scott CR1 frame and fork was like that. Too loose and it wouldn't grip the inside of the carbon steerer tube sufficiently to allow it to be tightened. Marginally too tight and it wouldn't go into the steerer at all. Once I'd fathomed that out I managed to get it just right so it gripped the steerer enough to start tightening it once inserted. After the headset was preloaded to remove play and the stem clamped up, I removed the top cap and tightened the expander bung a little bit more just for luck. Still needed to remove a bit more play after the first shakedown ride, but it's been fine ever since.

Yossie

If its that shyte smash it with a hammer and throw it into next door's garden then order something that isn't rubbish.

patrickf

Did you cut the steerer short enough? I.e. have you got a good 3-5mm above the bung and the top of your stem (or the top of any spacers you have above the stem)?

This stung me with the CR1 as that has the same design bung, which sits on top of the steerer tube, not flush with the top so you have to take an extra mil or two off.

Thinking you might not be getting the bearings preloaded enough to take all the play out?

jordan_217

I got this sorted. Pretty much the same issue as keef66 posted above - if I tightened the bung too much then I couldn't get it into the steerer, if I loosened it a bit the bung wasn't getting enough grip of the steerer. I just couldn't find the sweetspot.

After lots of messing about, swearing and turing the bike upside down to retrieve the bung I paid a visit to my LBS and bought a M-Part expander as per my OP. Fitted within 5 mins, all torqued up and no problems whatsoever.

Thanks all!

@Yossie - someone smashed my next door neighbors shed window this week, the ba5tards