Everything to do with a propshaft is about balance. There is a limit to how long a rotating shaft can be without some form of central support. That is why one needs to use the tailstock when machining bar in the lathe. Think about the effect of a front wheel/tyre that is out of balance. Chiswick machined the mating face of a flange to ensure firstly that it would be falt and therefore clamped evenly, but also to ensure it would be rotating in a true palne to its mating flange.

I used to have an Alfa 75, this had the transmission as a unit at the rear of the vehicle. The propshaft uses rubber couplings - 'Guibos' This was balanced as a complete assembly even the nuts bolts and washers had to be kept in the correct specific location.

I was asked today to investigate at the end of the rally season a rumble and vibration which occurs between two specific speeds. The speeds coincide with what I would assume to be the most common constant velocity the bus ran at between distant stops. I made a considerable improvement a couple of years ago to the vehicle by renewing the centre bearing. I suspect the true culprit will be the worm drive axle, however I shall start by removing the propshafts for thorough assesment. They will more than likely be either slightly bent or out of balance at certain rpm.

An interesting aspect there roy, that prop shafts can be in balance but out of balance at certain speeds.

I've seen some horrors abroad, an RM in Germany with a UJ so badly worn I fail to see how it could be driven for any length of time; and with the same owner a Bristol Lodekka with rubber bushes on the bearing housing that were non-existent. Luckily I found some shock absorber bushes that could be ground down to fit.

The RM prop shaft was only fit for scrap.

As an aside people sometimes ask if I can make their RM go faster. with the Cummins yes it is possible, but I wont do them as there's no guarantee of the condition of the porp shafts or UJs. Or the brakes for that matter. I wouldn't want to be held responsible for that lot vibrating through the entire drive train. It's not so bad on our bus where I can keep an eye on things and I know what may be wrong with it. Any vibration on the drive train can cause failures elsewhere.

My bus number (if any): RML2532