Prop shaft geometry

[Ian Grace]

Clive Hamilton-Gould has been having back axle issues and during investigation has found that his rear axle has been mounted on the road springs with wedges - rather like the front axle. These wedges have the thick end forward.

My guess is that someone looked at the geometry of the rear coupling and realised that the prop shaft slopes down towards the rear axle from the gearbox, so wedged the axle to take some of the flex out of the rear coupling. But of course, that would not help the brake lever geometry with the levers below the brake cams.

I'm not sure why the axle was designed with the pinion dead level, rather than in line with the prop shaft. Surely this could have been done at the design stage, while preserving the brake geometry? The Minor's predecessors - the Bullnose and Flatnose cars - all had enclosed torque tubes that lined up with the pinion. They got away with this because the rear axles swiveled on the springs (although the Austin 7 didn't have this degree of refinement!). Any thoughts anyone?

[Simon]

The axis of the engine/gearbox unit and the diff unit should be parallel to prevent acceleration and dececeleration of the pinion as it rotates and the angle between the propshaft and the gearbox of pinion changes to ensure that pinion rotates at the same velocity as the engine. This is why constant velocity joints in the place of hardy spicer joints are used on front wheel drive cars. This is the basic reason. If anyone wants a better reasoned argument I will have to dig some old college mechanical notes.

Clive, if he has standard rear springs, could try removing the wedges.

[Ian Grace]

Hi Simon,

Thanks for this. I'll have to have a couple of stiff gins before it makes sense - surely everything rotates at the same speed (as long as the bolts are tight. )? Or are you talking about small rotational speed differences during a single prop shaft rotation?

I think Clive plans to toss the wedges - unless they are spare front ones!

[Simon]

Hi Ian,

Yes I am, but they must add up to some form of vibration when the propshaft assembly is rotating at 4000 rpm.

Simon

[Ian Grace]

Hi Simon,

This is interesting - so is it true that the gearbox and the back axle pinion have to be nominally parallel with each other (regardless of the slope of the prop shaft) to cancel out the vibrations caused by the angles they respectively make with the prop shaft between the two?

On the 7 and the larger Morrises with torque tubes, presumably their joints don't have the same problem - and is this true also for Hardy Spicers? I'm still struggling to understand how the rotational angle of the gearbox output shaft can differ - even a tiny bit - from the rotation angle of the prop shaft - even if the prop shaft slopes down towards the back axle - I would have thought that if the two respective shafts are angled with respect to each other by - say 5 degrees - then the whole geometry is symmetrical - 5 degrees either way you look at them ...

Is this what constant velocity joints are all about?

This is a real Christmas brain teaser - at least for me!

[Highlander]

Simon, The ball is in your court - we are all keeping awake waiting to hear your answer!!!!!!Highlander (I'm not bothered anyway)

[Simon]

Alister,

I am going to leave this one to 2010 or possibly later!!!!!!. Have you sourced and tried the "English" Whisky that is distilled in Norfolk yet??????

[Toby]

I'm scratching my head on this too, would be interested in the answer! I believe they make welsh whiskey too, saw it behind the bar in the virtual pub!

[tonym]

Whiskey with an e is Irish not Welsh. I suppose the Welsh version is with a leek!
I fancied the English single malt - well the wife does - but by the time I tried to get a bottle it was all sold. I gather the next lot to be released is in February - will have to get my order in quicker this time!
Has anybody actually tried the Welsh single malt???

[Highlander]

Wash your mouth out Paul!! Welsh Whisky v A Single Malt is like taking your Daughter to the Church in an Austin 7.!!! I am trying to get to Brooklands on the lst but yesterday I failed to do my Father Christmas 'act' in a vintage car. I have been doing it now for over 46 years - local childrens hospital, friends young children and now these same childrens children!!!s The problem is dischage at all times. I have put new fuses in the cut out and also the dynamo but still no joy so tomorrow the dynamo off and cleaned and a proper look at the brushes. I cannot thin k the cut out is at fault but I will look. - Any ideas? If the worst comes to the worst I could full charge the old, old battery, disconnect the dynamo and drive to Brooklands and back (not 20 miles). I only need a horn. May I wish everyone a very Happy and Healthy 2010. Alister, Highlander, Lofty Elf.

[Ian Grace]

Alister, your battery should easily provide ignition for that sort of distance - can you get some pictures while you are there?

[Toby]

Not sure how this has become a dynamo question check your little box on the dynamo, the terminals should only be connected with the curly wire around the outside, research shows that a dodge years ago was to connect these directly to each other to get top output and it appears to ruin the dynamo! Are you sure its not the regulator, it caused you problems at the windmill by sticking, there are some excellent previous dynamo topics on this site, use the search box in the top righthand corner to search the forum for them, it will pull up any use of the word you put in, eg dynamo, charging etc. Good luck, I'd lay off the whiskey before you start fixing it, a good test meter should have been in your stoccking this year