Diff comm No.s

[kneescratcher]

I am the new owner of this car and it runs very high revs for road speed. Did the check of one wheel off the ground and got just over 4 revs of prop shaft to 2 revs of the wheel. I suspect it's had a replacement diff out of a Herald at 1:4.11.
commission no stamped on the hypiod case is GE 54132. can any one verify which model this is off?
if this is the case what's my options to change to 3.89 or better 3.63.
what other model crown and pinions fit? or am I better to source a diff from something else?
It's very nippy about town but a pain at highway speed

[heraldcoupe]

The GE prefix identifies the diff as a 13/60 unit with 4.11:1 final drive. The favoured diff for a 6 cylinder is the late Spitfire unit at 3.63:1, being the furthest along the line of development it is the most robust standard unit. Only 4 spring mounting studs in the top of the casing, may or may not be a problem with the standard fixed spring. At a push, you can swap the rear diff casings quite easily if you are concerned about this, or fit a swing spring conversion as cheap and effective handiling mod,
Cheers,
Bill.

[Tinweevil]

Handy page to play with on this subject on mintylamb - http://www.mintylamb.co.uk/gearspeed/

Tinweevil

[kneescratcher]

What about rebuilding with new crown wheel and pinion of required ratio. anyone know any pitfalls other than price, in doing this?

[heraldcoupe]

The 13/60 isn't the strongest diff (though it's not the weakest). Best starting point is a late Spitfire type as this is the strongest design, and that which is usually used as the basis for competitioon units. It also conveniently has a 3.63:1 final drive ratio, so if it's in good condition you won't need the new crownwheel and pinion....
Cheers,
Bill.