Nasty clunk from underneath

[New Duke]

I'm getting a very nasty sounding metal clunk under the car driver side when I brake moderately and the car weight shifts forwards, or go over a sharp bump on the drivers side, or turn/reverse at left lock. Even reversing/turning at very low speeds.

Essentially whenever the car is forced to flex under load, it feels like something under the drivers side is shifting or releasing and goes 'CLUNK'. I can feel it as well as hear it. It's loud and causes pedestrians to "WTF?" and look towards the car. The sound/clunk normally comes from under the drivers footwell, but it can move, sometimes seeming to come from under the drivers seat, engine or wheel well. It's very disconcerting.

Bigpete has had the car up on the ramp and we've searched for the cause to no avail. The suspension, steering, brakes, engine mounts, exhaust and hangars have all been visually inspected. I've inspected the fuel tank strap too. But it seems like the kind of issue that takes braking/turning forces to surface.

We thought it may be due to a failed front lower arm rear bush. But after replacing the lower arm it still happens. I'd like to book a trackday but don't really want the car to pancake on me in a collision. That's how dramatic it feels when it clunks.

Any suggestions for things to check?

[ChrisHolmes]

Even though you have had the wheel off recently I suggest that you check the torque is correct.

Note: The Workshop Manual specifies a lug nut torque of 88-118 N.m (65-87 ft-lb), but for a field countermeasure against this noise, be sure to torque the lug nuts to 147 N.m (108 ft-lb). Revised wheel torque specs should be used anytime wheels are removed from the vehicle (wheel rotations etc..).

[ChrisHolmes]

plus there should be no paint or grease on either of the wheel/hub mating surfaces.
The job of the wheel studs and nuts is to clamp the clean metal-metal surfaces together.

Have you got wheel spacers?

[79398]

Loose nuts on wheel spacers can cause this.

[Cscameron]

Ask me how I know

[ChrisHolmes]

drop links, knackered bushes and loose bolts can cause this issue too. time to get spanner checking....

[350matt]

Check both bolts are present on the brake caliper sliding element

I lost one on mine and the whole caliper was swinging forward and hitting the inside of the wheel

[Neilparry]

Sounds to me to be a shock absorbers shaft snapped or broken up inside.
Worth changing the shock to eliminate it.


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[mrspiller]

Drop link


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[GreySilver Beast]

The first thing I thought of was drop Link and i'm no mechanic

[Neilparry]

Pete has already checked it out and the only non visible part to check would be the shock.


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[New Duke]

Thanks team, really appreciate the suggestions. Yeah wheels nuts, droplinks and brakes have all been taken off, checked and put back together by bigpete. It all had to come off anyway when the new lower arm went on. I've double checked those on my own ramp since too on every wheel, just in case the clunk is 'transmitted' from somewhere else. I've looked like a madman pulling/tugging on various bits underneath the car.

Sadly I don't have any spacers. Never any budget left over for cosmetics with all the repair/maintenance costs this car has.

Sounds to me to be a shock absorbers shaft snapped or broken up inside.
Worth changing the shock to eliminate it.

I really hope not but that looks like a good culprit thanks. It's PZ suspension from the group buy which was only fitted 3 years ago, so I'll be really annoyed if it's failed already and I have to change the whole suspension again. I can't just buy a replacement PZ damper, which fuels my existing regret in buying these.

From a Google search it doesn't seem like there's any definitive way to verify whether a damper has failed, other than signs of leaking or it not bouncing back (it passes both those tests and looks good and drives 'normally' except for the clunk). So I'd appreciate if anyone knows of a way to test it/rule it out, before replacement.

drop links, knackered bushes and loose bolts can cause this issue too. time to get spanner checking....

That's what led to changing the lower arm after spotting a warn bush. Pete and I ran out of things to check! His instinct was a cracked/failed exhaust, brakes or steering but those components all seem fine. At least the lower arm needed replacing anyway. No regrets

[dac69er]

Do you feel it through the steering wheel when it happens? If not, then it is less likely to be front suspension/steering related.

[79398]

Engine mount fixtures?

[v-rex]

When I had a clunk due to my lower left arm it was also accompanied by a pull to the left. When it was a drop link I figured it out by going up a drive and the clunk happened just as the front left went up. This doesn't sound like either of those but in case it's helpful

[ChrisHolmes]

It could be the ARB sticking in its bushes and then snapping free causing the clunk. Remove them, clean and lubricate with silicone grease. A quick way to check would’ve you liberally spray them with silicone lubricant spray or WD40.

[New Duke]

Thanks guys, these are really helpful suggestions.

Do you feel it through the steering wheel when it happens? If not, then it is less likely to be front suspension/steering related.

No I don't feel it through the steering wheel at all. I feel it through the car floor. If that makes any sense. You wouldn't know there was anything wrong from a handling perspective. The steering is smooth and both front wheels move up and down well. It just comes from underneath. To the extent that at first I thought the engine itself was lurching loose, a coil spring snapped or the chassis somehow cracked. It takes pretty extreme forces to make the clunk happen, like you get when when a car turns/twists or brakes at speed.

It feels like something underneath has been under tension, and that tension is being released with a clunk.

These suggestions give me more options to explore. The ARB next, engine fixtures (they look fine but worth a try), before I replace the suspension and remove body panels. Failing all that I'll give it a Viking burial and buy something else.

[Ken90s]

I've got the exact same issue on my R3, massive clunk when hitting the brake, it only happens once though until I reverse and hit the brake again, then it clunks once again. It has also started to clunk when I'm turning full lock once in a while.

Please update me when you figure it out!

[qwakers]

I've got the exact same issue on my R3, massive clunk when hitting the brake, it only happens once though until I reverse and hit the brake again, then it clunks once again. It has also started to clunk when I'm turning full lock once in a while.

Please update me when you figure it out!

That’s your pads moving in the calipers, annoying but not dangerous. Your anti rattle shims etc will be damaged or missing.

[casey]

I had something similar, which took ages to find. Turned out it was the nut on the end of the front ARB needed nipping up just slightly. Your issue does sounds more severe though, so could be a red herring.

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[ChrisHolmes]

Really clutching at straws now...

Could it be anything to do with the driver's seat?

I recall a strange clunk years back that was finally diagnosed to a pound coin jammed in the seat track, causing the seat to catch on one side and not lock properly.

That would have been a cloth seat as their runners have discrete locking positions fore/aft rather than the motors, but it could be something similar with "leather".

[dac69er]

I'm sure you have checked, but what about the cross braces under the car that bridge the exhaust/prop tunnel? Or the subframe bolts?