I've just about had it with a persistent vibration in my 1958 3.4 automatic Mk1. I recently rebuilt the differential, which is now perfect. I had replaced the centre bearing and universal joints as the driveshaft vibrated horrifically between 50-60mph, I also had the shaft balanced. The car is 1000 times better than what it was, however I still have an annoying vibration and thumping that comes in at 70mph and reaches its worst at 80mph after which it doesn't improve. The wheels aren't the culprit, as the vibration sticks around if I run the car without them on chassis stands. I have replaced the engine mounts, transmission mounts and the centre bearing mounts. I have mucked around endlessly with setting the alignment and the stabiliser - I can get the vibration to just about dissipate at 70mph, but it will randomly come back. We live in a country area, so we do a lot of long distance, high-speed driving. I love the car, but because of this vibration, I'm really struggling to enjoy it.

 

You've gone over the alignment of the prop shafts, but have you checked the angle of the diff? On manual cars? It should be somewhere between horizontal and slightly nose up - I guess automatics are similar. If it's off, there's a problem with the leaf spring location or the torque arm bushes are consumed.

What's the condition of dampers on the rear axle? Balancing is never absolutely perfect.There's always some small excitation at the resonant frequency which you'll feel if there's not enough damping.

You've fitted a lot of new parts. It's natural to assume they are all up to a satisfactory standard. Unfortunately, with classic car spares, it's often not the case.

Not long ago, someone was struggling with an auto prop shaft. It may be worth searching back to find the discussion.

 

I haven't checked the angle yet - I've purchased a digital readout and I'm going to calculate my angles from there I think. The pinion angle should be right as the control arm bushes and spring bushes are all fairly new (I put them in about 9,000 miles/two years ago). I haven't replaced the dampers, so that could be contributing to my problem if they're not perfect.

It's a very frustrating issue, as I drive the car a lot, I've done 3,000 miles in the last couple of months persisting with this annoying issue. It's getting to the stage where I'm not enjoying driving it because the vibration just always nags at me, which is sad, because I otherwise adore the car.

 

are both rear tires the same size?

 

Yes, tyres are brand new all round and the correct size. The vibration was persistent when running the car on stands without tyres. I have since found that the driveshaft was not adequately balanced when I had it done a few months ago.

 

That person may have been me.
I have recently been over to UK and had my wire wheels balanced by specialist. New set of Michellin tyres fitted. Still have vibration.
Propshaft balanced. so still looking for an answer. My only option is to remove and replace all the rubber I had fitted (by a garage) using certified parts.
I had an uprated sway bar fitted but this should not cause the problem.??
As above it spoils the car and the enjoyment.