Clunk goes the forks

I installed the Lansdowne damper kit about a month or two ago (after having it sit around for several). I also replaced the fork tubes, upper and lower bushes and used leak proof seals (purchased from OldBritts.) I used 15wt oil (but will change to 10 when I reassemble.) In other words about the only thing that wasn't binned was the lower fork sliders and the nut above the top bush. Everything went together well, and the dampers really made an improvement in all areas - they are really beautiful.

Here's the problem, there is a very noticeable "clunk" sound when I go over bumps. I should state that the clunk was there before all this, but I thought it was worn bushes and I had badly pitted tubes. I can't seem to replicate it when not moving and just trying to bounce around the front end. It also seems louder at low sppeds (like 5-10mph), but that could just be I can hear it better. I've tried to isolate the issue. At first, I thought it might be when the forks rebound and the sliders top out on the upper bush, but playing with the rebound damper valve made no difference. Further, I'm now almost positive that the sound happens on compression as well. I my initial thought was the sliders are worn and allowing the lower steel bush to bang around. That might still be the case, but I am at a loss of how to determine how they should fit. So I tore it down today and my attempt to get at this was to mount the slider/tube assemblies in a vice and try to move the fork tubes side to side. I really can't feel any play. I tried this at several points along the travel thinking there might be a more worn area in the mid range.

Some other notes, When I fit the upper bushes, they slid into the sliders easily- like finger pressure. I was expecting them to be more difficult. I measured the diameter of the fork tube diameter and the steel bush OD and they were spot on. Another clue, the clunk seems worse when the weather is warmer (i.e. the fork oil is a bit thinner....).

Any suggestions?

Just ordered the lansdown dampers for the same clunky reason, so im curious to know what you find.

Do you have a floating front disc brake, by any chance? Mine is a tad loose on its bobbins and makes a slight clunk going over bumps. I have also had this on a modern Suzuki. Also, if your brake pads are loose in the caliper, they will clunk over bumps. I took a tip from someone on this forum and put a dab of silicone on the sides of the pads. No more clunks. However, I have a Lockheed caliper, not the stock Norton item. While you are riding, apply the front brake and if the clunking stops, the noise is likely coming from the brake.

Checked your steering head bearings?

Then, on to the forks.

Are the bottom fork bushes securely held in by their circlips?

Are the screw-in seal holders firmly against the flanges of the top bushes?

Let us know how you get on.

Sorry for not posting the details - Its a '73 disk brake front end. The only mods are a drilled front rotor and the damper kit. My hope (if you can call it that) was the head bearings were bad/loose, but I replaced the head bearings a few years ago and just checked them and their torque. All seems correct there. Screw in bush holders are secure. I guess I need to open em up to check the lower bushes, but my recollection of the fit was tight. Thanks for the reply.

How about the same cause as on the stock bike? You are still using the dampener valve at the end of a too short rod to control the total stroke therefore when the springs assert themselves you get that clunk when the valve hits the inside of the Dampener tube cap. Same system better dampening.

Norbsa — I have the Lansdowne dampers and all I can say is that they eliminated the clunk on rebound that I used to get with the stock damper assemblies, but I had to play around with the damper valve positions. I noticed that even when the needles were slackened off completely, there was still a fair bit of a hydraulic cushion in both dampers that would appear to prevent 'topping out'. I remain to be corrected here. I am only going from my own experience with these dampers.

Napa — I still suggest it would be no harm to ride the bike to see if the clunking continues when the brake is lightly applied while going over bumps. At least you can then eliminate this from your troubleshooting list. The fact that you can't duplicate the clunk at a standstill and that you think the noise happens when the forks are compressing as well as on rebound would lead me to check this first.

My Landsdowne dampers are also very sensitive to changes in temperature, and need to be adjusted to suit. I had to change to a lighter grade of fork oil during the warmer months and vice versa.

daveh said:

I have the Lansdowne dampers and all I can say is that they eliminated the clunk on rebound that I used to get with the stock damper assemblies, but I had to play around with the damper valve positions. I noticed that even when the needles were slackened off completely, there was still a fair bit of a hydraulic cushion in both dampers that would appear to prevent 'topping out'. I remain to be corrected here. I am only going from my own experience with these dampers.

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I'm sure John engineered-out the topping out 'clunk' from his later version Lansdowne kits. My early Lansdowne damper kit can be made to top out when the forks are bounced if the rebound setting is slackened off far enough, however when set to the normal rebound setting the forks have never clunked at either end of their travel.

="daveh"My Landsdowne dampers are also very sensitive to changes in temperature, and need to be adjusted to suit. I had to change to a lighter grade of fork oil during the warmer months and vice versa.

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This is the first time I've heard a comment like this, how sensitive to temp are they because though the stock fork internals aren't necessarily the best and clunk over big bumps, I've never changed fork oil because of the weather/temp changes and none of my modern bikes with modern suspension require this sort of adjustment. unless you're talking drastic temp changes from summer to winter. (90 degrees to 20 degrees) and is this for street use? If this is the case I'm glad I found this out now.

Hi, If the "Clonk" was there before installing the dampers...its a sure fire thing the new dampers will not be the cause....the forks are ether sticking badly ore some thing as play in it, sloppy brake pads? or anchor points.

Your bush's are not clonking together,,they dont come together, Clonking at 5mph is nothing to do with damper assemblies,,head bearings?
Regards John lansdowne www.lansdowne-engineering.com

Later Lansdowne dampers are not prone to temp change's 5-20c is a exceptable range on SAE 10 grade,

britbike220 said:

="daveh"My Landsdowne dampers are also very sensitive to changes in temperature, and need to be adjusted to suit. I had to change to a lighter grade of fork oil during the warmer months and vice versa.

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This is the first time I've heard a comment like this, how sensitive to temp are they because though the stock fork internals aren't necessarily the best and clunk over big bumps, I've never changed fork oil because of the weather/temp changes and none of my modern bikes with modern suspension require this sort of adjustment. unless you're talking drastic temp changes from summer to winter. (90 degrees to 20 degrees) and is this for street use? If this is the case I'm glad I found this out now.

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Let's say a coldish day in winter of 40 F compared with summer 70 F. I have the earlier dampers and John has continued to improve them with each batch. I still think they are a definite improvement over the standard dampers and they are reasonably priced. I repeat what I said in another thread: I would not want to go back to the standard dampers.

Thanks John, I hadn't heard anything negative about this set up in all the posts I've read and thought it was odd, but none the less curious and did not intend to start a frenzied debate as on some threads, thanks again..

napanorton said:

there is a very noticeable "clunk" sound when I go over bumps. I should state that the clunk was there before all this, but I thought it was worn bushes and I had badly pitted tubes. I can't seem to replicate it when not moving and just trying to bounce around the front end.

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Could the source of the clunk be elsewhere, and perhaps not in the forks at all?

This is really simple stuff if you’re using the dampener valve against the dampener tube cap to stop the sliders from making their full stroke (as in the stock front end) than unless the valves are set right you’re going to get a clunk. Adjust the dampening. It’s nothing bad it just needs adjusting to my thinking.

norbsa48503 said:

This is really simple stuff if you’re using the dampener valve against the dampener tube cap to stop the sliders from making their full stroke (as in the stock front end) than unless the valves are set right you’re going to get a clunk. Adjust the dampening. It’s nothing bad it just needs adjusting to my thinking.

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But these are not standard Roadholder damper tubes and rods?

As John said, if the clonk was there before the Lansdowne kit was fitted-then it isn't likely to be the Lansdowne dampers causing the clonk-especially as the Lansdowne kits now have a proper built-in rebound buffer.

Guys - I don't really think the dampers have anything to do with it. The sound was there before I installed them. I was just adding that fact in case there is some interaction I was not paying attention to. I know it's hard to get good input if you don't include all the facts. I also wanted to point out that only 4 parts were reused - the busing top nuts and the sliders. The dampers allow adjustment and I was wondering if I just had it adjusted incorrectly.

As an update - I tore down the front end to check the yokes, head bearings, fork tube alignment, etc. I didn't open up the sliders, although I'm sure I'll have to at some point. I've been finding that you have to do the job about 4 times before you can say it's done. I also changed to 150 cc of 10wt fork oil per John at Lansdowne Eng. Took it out for a test spin - Drum roll please - it's exactly the same.

I'm really wondering if the ID of the sliders are worn, and allowing the steel bush to clank around. Any ideas how to either prove or disprove this theory (esp if I don't own a bore gauge...)

Only 4 times, I can't wait to get that handy at new Norton diddling. 150 ml is considered too low to function well in factory Roadholders, might ask if that is different in this kit.

I put like 190 in mine

Oil Amount........well the the damper require's a 10 mm "head" [3/8] above the upper-most hight of the rebound valve housing,

BUT....as the level is at its lowest when the machine is on it's centre stand ,and not in use...then the oil requirment is now un-important.

Levels as you all know increase and de-crease as the stanchion "takes up" the slider's internal space....in fact under hard braking 100 cc is enough!.

Only when you are wheeling [wheel of the ground] do you require 160cc... awaiting Hobots responce :lol:

Two much oil will increase the pnuematic effect, (stiffer action ) not enough will allow air to be sucked into the rebound side, resulting in no damping.

BMW Bob may have something to say about levels, he as reduced is to the min. Again air compression was his concern! and seal leakage.

200 kit users ...and quite a few forum members inc John Dunn the Norton Commando Tec adviser found the kit works well on 160cc.

The Holland Norton works fit the Lansdowne Kits ..Constant must be happy to install them, he as tested them well...i think he threw in a 1000 mile trip just to make sure :?:


All the best
John Lansdowne Eng

LAB, I am aware that John's kits are a cartridge set up and do not reuse the stock tubes. You miss my only point. The travel with this kit is controled by limiting slider travel by using the rod, tube and cap to stop the slider from using all the travel avialible between the bushings. So the valve controling rebound has the job of keeping this top out from clanging. Just that simple like it or not. There is nothing wrong with the kit in any way operator understanding is whats needed.
I think that if most people just did some testing with oil in and springs out to feel what the fluid is doing for the road feel the questions would go to a higher level.