I'm getting a 'knock' in the front forks on small, sharp bumps, e.g. the edge of a repair patch in the road. The knock is audible and I can feel it at the handlebars. I had one of these (1989 PC23) in 1990 and I don't remember any knocking then, so I assume it is down to 30k miles and 30 years of wear. To be fair, it's largely an irritation, doesn't seem to affect the handling and not noticeable once you wind it on.

So where's the wear? I've stripped, cleaned and rebuilt the forks. All parts, circlips etc. and present and correct. Didn't replace the bushes (bearings) and there is some play in them but they don't yet meet the workshop manual level for replacement (black coating worn away and copper base showing thru). I could replace them but I wouldn't expect much difference. And the steering bearings have been replaced and adjusted. The brake slider pins and the left-side mountings do have play in them but so does the rear and that's not rattling.

It doesn't feel like wear in the fork bushes, more like an internal damper component moving from one end of it's travel to another. It is more pronounced when I apply the brake a little approaching the bump. The stiffening up of the damping by the anti-dive would suggest it is indeed a damping component. Can't reproduce the effect just standing next to the bike and bouncing the forks, needs a sharp bump.

There are the valves at the bottom of the damper rod but these appear to operate as they should. And the damper rod is bolted to the slider so a knock down there would likely be softened by the fork spring.

Then there's a tube that sits inside the bottom of the stanchion. If that was slamming up and down it would definitely be noticed in the bars. That tube has some up and down movement in it. The parts list doesn't show it as a seperate item. Anybody know whether it is removal / replaceable / subject to wear?

So my question for you fine folks is - does anyone else have this knocking in their forks? And did you find a way to fix it?


[edit]
I should confirm that the knock was there before I rebuilt the forks and replaced the steering bearings. Disappointing that it had no effect

 

Well, somewhat shamefacedly I have to report that the knock was in the rear suspension.
The bearings in the connector between the frame and suspension link (so-called dog bone) are shot. Play at the bearing isn't much but translates to something significant at the rear wheel. Can only assume that the feel of the bumps thru the bars combined with the audible knock resonating thru the frame to convince me there was something amiss in the forks. Oh well, fixed now.

 

Thanks for the update, it is amazing how the rear of the bike can magically migrate to the front, I had a similar this with the rear suspension causing a head shake which was quite alarming.