Lotus Elan and Lotus Elan Plus 2 Forums

Hi all,

is there any chance of identifying the ratio of an Elan Diff from the outside? I mean of course, without opening the diff and counting teeth.... A number or a code on the casing?

I don't think so - and even if there was a number that identified the original ratio, someone could have swapped in a different CWP. You can count how many revolutions of the input are needed to make one revolution of the output - easy if it's not in the car, more difficult but still possible if it's in.

I did this the other day, and found it to be much easier than I expected:

- Jack up one rear wheel. Just off the ground is enough.
- Stick a bit of tape to the tread to use as a marker as you rotate the wheel. Or use the air valve.
- Lie down next the wheel and put a lamp under the diff, lighting the prop shaft/diff coupling
- Make a mark on one of the coupling flange nuts (I just put a small scratch with a screwdriver).
- Slowly rotate the rear wheel counting how many coupling bolts swing past. Every four bolts is, of course, one propshaft rotation.
- Count for 20 turns of the rear wheel.

Since you only have one wheel off the ground, the count is equivalent to 10 turns of both rear wheels. For a 3.77 diff you will have counted just over 151 pinion flange nuts going by. Divide by 4 for propshaft rotations = 37.7. Divide by 10 for the rear wheel rotations. Bingo.

Nick

Just a thought, but if you know that your speedo is accurate then you can remove the gearbox angle drive and pull out the plastic drive gear -
Blue - 3.9
Green - 3.7
Black - - 3.5

Might get a bit oily though and you will have to top the box up afterward.

Thank Guys
One diff is in the car (and whining and making noises). The other one is on the shelf and waiting to be examined....

Mazzini, no idea if the speedo is accurate. But I will check the colours anyway!

If you jack the car up on the right hand side it will minimise the oil loss, but it's smelly EP oil, it will leak up your arm...it's a law of physics