Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) Clunking Over Bumps

2025 Plus Six. I have a clunking sound over bumps when the suspension has to work hard. It sounds like it is from the rear. It's a bit like a sound I had on my previous TR3A, which was due to the rear body to chassis mounts needing attention. Muted, not violent sound, but like something quite weighty is loose. A sound a bit like something heavy and unsecured knocking about in the boot.

Done so far:
- I have checked all underside bolts and under the circular vented rear cover (no spare wheel). Actually, several were not that tight and took half a turn. But it hasn't solved it.
- Wheels off and no noticeable play.
- My dealer test drove it, when I had it serviced. They told me it is fine, a normal Morgan noise over bumps.

Is that the case? If so, I can live with it. It drives fine and over 50mph is actually quite a compliant ride! But, it is niggling in the back of my mind that I should double check. Would welcome views from those with more Morgan (+6?) experience.

We have a 2020 Plus Six, I have been looking for a low level clonk from the rear when driving over potholes at low speed for the last 4 years. Each year I check everything in sight, from the suspension to exhaust.. We replaced the standard shock absorbers with the SSL touring option several years ago, this reduced about 50% of the noise but once your brain is adjusted to the noise you seem to notice it. I have found that after the yearly underseal spray with lanoguard the noise vastly reduces for roughly 50 miles, so I think its more likely a coilover spring compression noise as the spring works under a heavier load. The upper mounting bolt of the rear coilover unit connects to the body fairly close to the drivers side and there is not a lot of sound deadening in that area, so any mechanical noise is easily heard.

There are a couple of things to check though, make sure the hand brake cable is secured and not rubbing on the rear suspension wishbone when its under compression, also check that the rear inner plastic wing is fully secured, two of the studs that hold this in place are bonded/glued to the alloy, they can come loose and need rebonding. On the 2020/21 MY they are located at the lower front of the wing liner and on the outer rear of the wing, you will see they look like a stud rather than bolts that are used in the other locations ( this may still be the same on a 2025 MY). Lastly check the rear exhaust rubber hangers, we had one that had moved and rubbed against the main alloy bodywork.

Thanks Dave, that's really helpful. Will give the handbrake a check, I know the rear exhaust hanger and arch protectors are good and solid, but I'll double-check. I'll also work forward on the exhaust, just in case. More in hope than expectation. But it seems you have a similar noise, so may be just the way it is.

Good advice from Dave there. Had some rattling under the car early days, the rub plate under the car was full of shrapnel. As most of my driving is on A and B roads I routinely clean out sand chippings and crud. Just a thought...

My dad restored a TR3A in 1981-82. I had it off him in 2011. In all that time the front left rattled over bumps. Last year I found a bolt and washer trapped inside the front left spring cup. Fished them out with a magnet and no more rattle. 45 years, the hours spent tightening, removing and re-installing bits!

This is different. Not a rattle. More like a clunk. Bit like something heavy in the boot getting airborne and dropping back to the floor over the bumps, which is why I started by taking the spare wheel cover off, in case someone had stored the jack in there!

Behind the rear panel is the audio amp. Could that have come loose?

MartO,
I had exactly the same sound on my Plus Four 2025 immediately after its 1000 mile service, where they fixed the axle clonk (I think by greasing splines and tightening spinners) and the Nitron squeak - at all four corners. I erroneously thought the sound was e.g. a heavy tool accidentally left somewhere under a seat or under spare etc, being temporarily airborne over bumps. Nothing to be found. The heavy thump sound over bumps disappeared after about 100 miles and then the axle clonk returned after about 300.... The Nitrons remain squeak-free, after a further 2000 miles.
Guy

Well I asked AI most likely causes:- for what it's worth, the clunk seems t be a common problem across the CX range and SEEMS TO comes on with wear.......eg I never heard a clunk when I acquired my car, now 8 months on and a further 2200 miles mostly town driving and I get an increasingly more frequent occurance of a clunk

SO AI CAME UP WITH THIS, its a starting point......also see my post under P4 siuspension which also refers to the diff pinion bolt losing its factory torque settings.


Standard Drivetrain Backlash (Normal Characteristic)The BMW-sourced ZF 8-speed automatic gearbox and open differential have inherent design clearances (backlash) between the gear teeth to allow for thermal expansion.

The Cause:

In a heavy BMW car, rubber isolation bushings and thick sound-deadening absorb the mechanical take-up. In a raw, lightweight Morgan, you hear every millimeter of that free-play taking up slack as the gears mesh under load.

The Test:

With the car safely off, you can verify this by holding the differential's input flange still and minutely rotating a rear wheel back and forth. A tiny fraction of play is normal, but it should not feel entirely loose or sound violently metallic.

Worn Driveshaft U-Joints or CV JointsThe shafts transferring power from the transmission to the differential, and from the differential out to the wheels, rely on joints to flex.The Cause: If a Universal Joint (U-joint) or Constant Velocity (CV) joint develops play, it will create a hard click or clunk right as you take off

.The Fix:

Inspect the rubber boots on the half-shafts for tears or leaked grease. If the grease has escaped, the joint will wear rapidly and cause a clunk under load

Rubber Suspension and Subframe Bushings

The Cause: T

he differential and rear suspension are bolted to the chassis via rubber rubber mounts. If a bolt has worked slightly loose or a bushing has degraded prematurely, the torque of the BMW B58 engine will twist the mechanical assembly, causing it to physically slam against the frame.

The Fix:

Inspect the tightness of the rear suspension control arms and the differential mounting brackets to ensure nothing is shifting under load.

Our low level "clunk" seems to be suspension movement related.. only hear it when going over a pothole at low speeds, its the same when the car is hot or cold. Its always done it. The change to the SSL coilovers reduced the noise and after spraying the coil springs with the yearly application of lanoguard underseal the noise almost vanishes but returns after a few miles of driving, so with our car I think its the coilovers springs making the noise when they have a large deflection such as a pothole. Having said this I am still looking..

I did locate one new squeak/rattle from last year, it was odd as it sort of sounded from the rear but the cause was the mid level undertray as mentioned by aerotaff. It started after a grounding going into a Chateau in France during our 2300 mile road trip, we grounded going over the roads iron work in the centre of the entrance gate that held the bottom of the gates in place when closed ( learnt a lesson here, now get the passenger out going over these if fully loaded with luggage ).
On our return home I found that the middle of the undertray had been bent upward.. this in turn, allowed several areas on the edges of the tray that were not secured by the 10mm securing bolts to rattle aginst the body. The undertray is fairly thin sheet aluminium, so was easy to bend back flat, this then brought the unsecured areas of the tray back into a better contact with the body when it was bolted in place.. I also added thin self sticking neoprene to these areas to stop any future rattles, as its very easy to bend this tray.

dave

Weve had some real nasty scrapes in the plus 6 and sounds really bad but at a resent MOT the only sign of damage were some gouges on the undertray and a small dent in the exhaust. The undertray being so light in gauge thickness makes it sound worse than it really is. Regarding the wear and tear on the drive shafts etc long term I do think the six changes gear up and down way too early and the long term effect who knows.