Propshalft UJ's and rear diff... Seven Special GN312

[goodwoodweirdo]

Hello chaps,

I'm a complete novice regarding sevens and are trying to work out whats std / date correct on my special - firstly to understand a little about the build and to avoid ordering the wrong parts  

My cars is Oct 1930 would it be fitted with a UJ Prop shaft from new ? after a little googling I understood the UJ's where only introduced later.

Whats the most desirable rear axle for a special, I appreciate you'd want different diffs for hill climbs or track use ? I need to work out what I have 

Same with the front suspension the leaf looks very flat, anyway to tell if its altered ?

The various books I have are handy but assume you know what you have haa haaa

cheers
Matt

[Howard Wright]

Hi Matt

Some pictures would be useful!

The "correct" prop for a 31 would most probably be a shaft with a fabric coupling at the gearbox end and a Carden block at the pinion end.  However if you have a UJ shaft then keep it, as they generally tend to be smoother and easier to maintain (although purists will be howling now).  

If your car is a special then, to be honest, anything goes (and probably anything went when it was built).

As I said some pictures would allow some better analysis.

Cheers

Howard

[goodwoodweirdo]

Hi Howard,
thanks for your comments, I can certainly understand someone would want to use the best parts available... especially as I personally think the car was made in the 50's / 60's (now trying to find some sort of history but thats another story).

Here are a few pictures, if not clear enough I'll take new ones...


   

   



cheers Matt

["Slack Alice" Simon]

The front spring is the sort of thing I have on my special.

The car is very light compared with the original, so I kept taking leaves out until it felt ok, I think I assessed this by jumping on it!

Though I do not have a dropped axle I have not had problems with the spring bottoming on the axle when doing the odd trial.

[Chris KC]

Matt, I agree with Howard, keep the U/J propshaft, unless you are going to great lengths to achieve an 'original' feel.

Your rear axle unless I'm much mistaken is a 1930/31 type, which is consistent with the rest of the car and probably the pick of the bunch anyway. You will have to count turns in vs turns out to establish what ratio it is - typically it would have started life as 4.9:1 but may have changed. You can buy new crown wheels and pinions from our cherished suppliers, not cheap but probably worth the investment. Think carefully though about gearing before choosing a CWP ratio, depending on your intended use of the car, wheel and tyre size, all-up weight, state of engine tune, etc etc. Generally A7's are over-geared and will go faster if you drop to a lower axle ratio. You may however lose a bit of the 'period charm' by doing so.

The front spring looks about right (though possibly it would benefit from a new one); but is that a 'straight' axle beam? The sports ones were lower (curved) and - again, depending on your aspirations - a touring beam can be bent to simulate this. Either might look odd if the body does not complement it. If the car is to be used for trials the extra ground clearance is a boon.

[Howard Wright]

Hi Matt

You've got a nice chassis for a special which doesn't look to have any rust or twist (might be worth checking these!)

The rear axle is, I think, one that you can easily change ratios (but at a price! as Chris has said)

As others have said the front spring is quite flat but is coupled to a straight axle.  As Simon has said you may have problems with the spring bottoming especially if you are a bit energetic with your driving! and you may need to have your axle "bent".  It is quite possible that when you investigate the king pins the eyes on the axle will need to be shrunk.  In which case Ruairidh does a great job at both shrinking the eyes and bending axles.

I notice you have Bowdonex brake cables on the front.  This was a common modification in the 50's and I believe does improve the braking.

Are you a member of a club?  If so ask some members round for a pint and you'll get lots more detailed info for the cost of a few beers!

Cheers

Howard

[Ian Williams]

Chris advice is pretty good, 5.25 CWP are probably the best option for general use on a road going special, they fit into those axles and were not difficult to find, although things may have changed in the UK since i was last there. There was some excellent advice on gear ratios, wheel sizes etc on the old Speedex site if you are considering anything more than basic road use.

[goodwoodweirdo]

Thank you chaps,

I'll proceed with the build and for sure will have lots more questions :-) still the plan is build as is with the intention of trailing / hill climbs, oily rag, pub car and I'm very happy to be far from original spec as long as its all pre 40's Austin.

Back to chassis cleaning, removing the rear springs, haa haa that will never happen (WD40 hammers, heat) and removing the axle, also not going to happen till I find a hub puller ....

I live near Ghent Belgium so if anyone is passing and would like a beer, talk Austins or touring and needs garage space for running repairs - please drop me a mail !

cheers
Matt

[Reckless Rat]

The fact that you're in Belgium does complicate things a bit, but despite the geography you are never far away from sound advice on this forum PLUS you have the support of our specialised A7 supplier network for all your parts needs. Click on "Website Home" at the top of the page and then "Cherished Suppliers".

[goodwoodweirdo]

thank you reckless rat !

Indeed forum is fantastic and the parts are all slowly making there way via my parents in Sussex !!

thanks again to all for the pleasant and helpful comments...