The 120 has new tyres and wheels. All perfectly balanced with correct equipment.
At about 100 km/h the car is “shaking”. Can be felt in the steering wheel as well.
Where shall I begin to investigate?
Peder
really difficult to answer without having driven the car. However if it felt like its from the front check all the suspension and steering joints. The guy broad website mentions wen steering bees and give these symptoms so check the the adjustment on the worm is correct.
If its more general nd not from the front check the propshaft U/J’s
Just my thoughts.
Peder, you might want to check for a loose tire. I thought I had my wire wheels tight with its new tires, until I took her out and it vibrated like crazy. I had a wheel loose.
I had the same thing, 60mph. It was the Metalastik rubber bushings in the upper wishbones, part C3003. Some racing people go with polyurethane but I stick with the original rubber, more comfortable for a road car.
In my misspent youth I developed a similar problem with my Austin Healy 3000 above 80 mph after a brisk mountain road drive. Turned out that a half dozen spokes were broken off on the inside tier at the hub. The breaks were hard to see without a close inspection and there was no wobble at lower speeds.
A lot of potential for an unhappy ending that day!
Rob
If the only things different since the vibrations began are the new wheels and tyres, then I would focus on those items. Rotate the front wheels/tyres to the rear and see if the vibrations move from front to rear. If so, there may be a balance issue with a tyre, a wheel that is out of spec, or possibly a defect with one of the new tyres.
My disc wheeled XK120 had a vibration beginning around 62 mph and ending at around 65 mph. I balanced and rebalanced the tyres to no avail, and I even had all four brake drums rebalanced to no avail. It wasn’t until I had all four wheels and tyres analyzed on a Hunter Road Force machine that I learned that one of the disc wheels was out of spec. No amount of balancing would correct the vibration problem. A replacement wheel was the solution.
That would be my strategy too.
When a wire wheel is on the balancing machine it is under no load from the weight of the car, so if the spokes aren’t equally tensioned (or some are broken) the wheel may balance fine according to the readout, but once you put it on the car you have roughly 1/4 of the weight of the vehicle hanging on roughly 1/4 of the spokes (the uppermost quadrant): with a 72 spoke wheel 3 missing or loose spokes are enough to throw the balance off. You can put it on the balancer over and over again and it will always show true, and even acceptable runout.
One way to check this is to put the wheels on the car then ring out the spokes on the loaded quadrant as you slowly roll the car, the loose ones will make a different noise (as will the overloaded ones). The other thing you can try is fit a DI to the wing and check the runout at the rim while the wheel is in the loaded state.
I havle now tried with 2 sers of newtyres on new wheels, so itś not to do with the wheels…!
Check the horn, which supports the steering box/top wishbone,
where its welded to the main chassis. I have experience of this
weld cracking. Squirt some oil there, it might help you spot movement.
Peter B
I will check this but suspect the prop shaft. Easy to remove at the rear but very tight at the front…
I must admit that I never got around to removing the prop/drive shaft, but today I thought of the problem, and this thread, as I was driving the one owner 140 dhc from Wichita, Kansas. It has new wheels and tyres, perfectly balanced, it it has the same shakes/rattles at the ssme 60-65 mph. I feel it all over rather than just inthe steering wheel. This points to the prop/drive shaft in my opinion. I can live with it, as it’s not excesdive, but still anoying. I have other XKs which are super smooth up to 100 mph
I now need to remove the prop/drive shaft on a 120 and a 140 w/o OD.
I remember that I saw problems getting at the front 4 screws on the 120 when I ladt checked. How is it done?
Is it easier on the 140?
Must have been the cross members on the chassis that is in the way.
I need to have them rebalanced and check the UJs, to sort my vibrations starting at around 60mph
Peder