MKIII clunk in front suspension

The Buckeye Rider · Jul 3, 2024

On May 22, 2024 I posted about a noise in the front suspension with Lansdowne inserts.
After disassembling the front suspension for a thorough examination I found nothing amiss and the noise was still there.
Upon further investigation and trying this and that it was determined the noise was coming from the front fender. After several attempts to make the mounts correct it didn't get any better.
The rear stay is not OEM because of the aftermarket caliper and rotor and was installed under some stress. After bending the stay to bolt on without stress the noise was still there.
I removed the fender and the noise is gone.
I shimmed the stay away from the fender and the noise is still present.
Any ideas?
Ride On (quietly)
Dave

concours · Jul 3, 2024

The Buckeye Rider said:
On May 22, 2024 I posted about a noise in the front suspension with Lansdowne inserts.
After disassembling the front suspension for a thorough examination I found nothing amiss and the noise was still there.
Upon further investigation and trying this and that it was determined the noise was coming from the front fender. After several attempts to make the mounts correct it didn't get any better.
The rear stay is not OEM because of the aftermarket caliper and rotor and was installed under some stress. After bending the stay to bolt on without stress the noise was still there.
I removed the fender and the noise is gone.
I shimmed the stay away from the fender and the noise is still present.
Any ideas?
Ride On (quietly)
Dave

Mine does the same thing. A plastic shim at the bolt holes.

The Buckeye Rider · Jul 3, 2024

concours said:
Mine does the same thing. A plastic shim at the bolt holes.

Thanks concourse, could you be more specific? A shim at each contact area of the bolt holes of the stays and/or the bolts at the bottom of the fender. Did you shim the bracket that goes over the tire/fork brace?
Tell me what type of plastic. I'm so tired of fooling with this I just want it done and gone.
Thanks

concours · Jul 4, 2024

The Buckeye Rider said:
Thanks concourse, could you be more specific? A shim at each contact area of the bolt holes of the stays and/or the bolts at the bottom of the fender. Did you shim the bracket that goes over the tire/fork brace?
Tell me what type of plastic. I'm so tired of fooling with this I just want it done and gone.
Thanks

Between the fender & the stay, where the bolts are.
I have shim stock on hand, but you could cut them from a water bottle out of the bin.

DennisMo · Jul 7, 2024

I have a knock in my stock 1973 front suspension when it goes up or down (and is not hitting its limits.)
When I had it apart, I put new bushings and seals in thinking this would solve it but no luck.

I have been thinking that it could be the damper cups inside the inner tubes that are held with pins.
Maybe the pins have ovalled the holes in the damper cups?

Concours, I would love to find the problem but don't understand what mechanism is making the noise that the plastic shim is to correct?

Thanks
Dennis
Vancouver

Tornado · Jul 7, 2024

The Buckeye Rider said:
On May 22, 2024 I posted about a noise in the front suspension with Lansdowne inserts.
After disassembling the front suspension for a thorough examination I found nothing amiss and the noise was still there.
Upon further investigation and trying this and that it was determined the noise was coming from the front fender. After several attempts to make the mounts correct it didn't get any better.
The rear stay is not OEM because of the aftermarket caliper and rotor and was installed under some stress. After bending the stay to bolt on without stress the noise was still there.
I removed the fender and the noise is gone.
I shimmed the stay away from the fender and the noise is still present.
Any ideas?
Ride On (quietly)
Dave

Any chance a cable (tacho or speedo etc) is contacting mudguard on compression making the clunk?
Also, there is the headlamp bracket o-rings that can wear out or slip out of place when installing stancions, giving metal to metal clunks.

DennisMo · Jul 7, 2024

All Cables are clear. I pulled them away with zap straps to check
I have even isolated the rubber gaiters around the forks thinking maybe they inflated and caught the mudguard as the
forks compress.
I can make the noise even when bike is standing still by pressing the handlebars up and down.
I got a friend to do it and can't see any visual cause of the noise
If I do that standing still, I can't see how any noise would be made by the mudguard or its struts.

Dennis

concours · Jul 7, 2024

DennisMo said:
I have a knock in my stock 1973 front suspension when it goes up or down (and is not hitting its limits.)
When I had it apart, I put new bushings and seals in thinking this would solve it but no luck.

I have been thinking that it could be the damper cups inside the inner tubes that are held with pins.
Maybe the pins have ovalled the holes in the damper cups?

Concours, I would love to find the problem but don't understand what mechanism is making the noise that the plastic shim is to correct?

Thanks
Dennis
Vancouver

"Upon further investigation and trying this and that it was determined the noise was coming from the front fender. After several attempts to make the mounts correct it didn't get any better."

I could recreate the noise by open hand slapping the front of the fender.

o0norton0o · Jul 7, 2024

DennisMo said:
I have a knock in my stock 1973 front suspension when it goes up or down (and is not hitting its limits.)
When I had it apart, I put new bushings and seals in thinking this would solve it but no luck.

I have been thinking that it could be the damper cups inside the inner tubes that are held with pins.
Maybe the pins have ovalled the holes in the damper cups?

Concours, I would love to find the problem but don't understand what mechanism is making the noise that the plastic shim is to correct?

Thanks
Dennis
Vancouver

You need to pull it apart to look at the components. Then do a partial reassembly and see if you can isolate if the clunk is between the slider and the fork tube or something within the damper mechanism. As you said, the dampers are crude. My damper "cups" for lack of a better word were pretty sloppy when I inspected them. I modified modern dampers for my commando, but for people who are keeping the stock dampers, I always recommend buying Jim Schmit's damper upgrade parts. The tighter tolerances help the crude original design to work a bit better.

As was said in another recent fork thread, that the damper has no centering spacer on the damper rod, so the "knock" could be the spring snaking against the fork tube as it changes length and moves around inside the fork tube. You could add a 15mm OD x 10mm ID polycarbonate tube inside the spring to center it. OF course you have to leave the tube 6" shorter than the spring so it doesn't interfere with compression...

DennisMo · Jul 9, 2024

This is great. Thanks to all
I will take off the fender and test for noise. Even though the noise happens when the bike is stationary and I compress and release the forks. We must be methodical!

If that fails to reveal the cause, I will buy polycarbonate tubing and take off caps and slide down and test again.
If that fails, I will pull apart the forks .... again... this winter
Thanks
Dennis

o0norton0o · Jul 9, 2024

Dennis, the steering stem and bearings also might clunk if they have too much play. You should eliminate this as a possible cause, by putting the bike on the center stand with someone sitting on the seat so the front wheel is off the ground, then pull the front tire forward and backward to see if there's any movement of the yokes at the steering head. Just another thing to check that might clunk related to the front end

DennisMo · Jul 9, 2024

Another great idea for a check. Thanks.
I just now figured out why the fender could be the problem. Tell me if I am wrong!
If the forks are not perfectly parallel, they can stress the fender (causing twist) as they go up and down and that can result in a noise somewhere on the fender as something moves.
Maybe I will call you "Double O" Norton ....!
Dennis

The Buckeye Rider · Jul 11, 2024

DennisMo said:
Another great idea for a check. Thanks.
I just now figured out why the fender could be the problem. Tell me if I am wrong!
If the forks are not perfectly parallel, they can stress the fender (causing twist) as they go up and down and that can result in a noise somewhere on the fender as something moves.
Maybe I will call you "Double O" Norton ....!
Dennis

That's just brilliant! Now how to I determine if they are parallel? I'm thinking that taking the axle out could/would change the position of things. I've had the forks off several times dealing with this and have put them back together by the book.

On another note: per Concours suggestion I isolated the fender and stays at all contact points with plastic shims; no help. I removed the rear stay; no help. I re-isolated all contact points with neoprene washers; no help. When I take the fender off the noise goes away!

Or the fender isn't really the problem but just a transmitter/amplifier of an internal fork noise?

The noise seems to happen as the forks go downward into a hole but not in compression, if that makes any sense.

I'm at my wits end with this, I've had the fender off so many times I can do it in my sleep, and besides that the a/c in my workshop went out and it's bloody hot in there.

DennisMo · Jul 11, 2024

Hi Dave,

Mine make noise in both compression and extension and it is definitely not hitting the ends.

Where you pulled your forks apart, did you check the damper valves inside the damper tubes?
That they were not loose on their pins. I did not, so that remains a suspect on my side

Imagine if it turns out that the fender's design actually makes it a really vibration amplifier of noises in the forks!!

Dennis

DennisMo · Jul 11, 2024

And if the fender is the amplifier, the plastic/rubber shims would stop the resonance from passing through.
Dennis

Tornado · Jul 11, 2024

Heard a tip a long timme ago about centering the forks, eliminating twist. Ease off the lower yolk clamp bolts and the wheel clamp bolt (left side on mk2 commando). Also slacken mudguard mounting points, both at the stays and at the center bracket. This frees up everything for next step. Sitting astride the bike, on CS, push down on the tank with handlebars square to frame, to compress the forks...repeat a few times. Carefully get off bike without disturbing forks. Torque up lower yolk clamp bolts, mudguard stays/bracket and then the axle clamp bolt.

DennisMo · Jul 16, 2024

I think I found the problem clunk!
I took off the fender and the clunk noise went away when I rode the bike

HOWEVER, when I got back home, I pushed up and down on the forks with the engine off and the bike on the centre stand.
I could hear a click in the forks (which I could not hear before because the clunk noise was amplified by the fender.
The click was not the fork hitting the limit.

So this winter I will take apart the forks and look at the damping valves and pins. I suspect the pins and the holes they are in have worn which causes the click which is then amplified by the fender.

Dennis

MKIII clunk in front suspension

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