Four speed gear box, any differences from 64 to 72?

[Certified Lotus]

I am looking to buy a 4 speed transmission from a 1972 Elan Plus 2 for my 1964 Elan S1. Are they the same configuration for an even swap or are there differences? Would like to know before I pull the trigger on this. Any help would be greatly appreciated.

[msd1107]

Be aware that the transmission ratios are different between the two years.

The '64 transmission used the close ratio box with a 2.51 first gear. The '72 (unless special ordered) used the so-called mid-close ratio box (actually the sedan ratios).

If you have the standard 3.9 differential ratio, you may not like the low ratios in the '72 box.

Cheers,

David
1968 36/7988

[prezoom]

Actually, the middle close ratio has a 2.972 ratio 1st gear, 2nd is 2.009 and the 3rd 1.396. The close ratio has a 1st gear ratio of 2.510, 2nd 1.636, and 3rd is 1.230. I believe the sedan ratios start at about 3.6, more suitable for a heavier car.

Rob Walker
26-4889

[msd1107]

Rob is correct in that the early small sedans used a wide ratio box with a very low first gear. The prototype Elan's were built with this box, and were widely panned for trying to use such unsuitable ratios for such a light sports car. But, Chapman had no choice. The Elite had suffered a cost penalty from using a bespoke ZF box, and cost was very important in developing the Elan.

The rally program for the Cortina's were what got the 2.51 ratio box, and the Elan benefited from this.

The Cortina's used the middle close box with the 2.97 first. Later Elan's used this box since many people were not comfortable with the 2.51 first and the 3.55 differential ratio of the SE cars, although this combination could be ordered and many people consider this the optimum combination.

Of course, a five speed box, like the Alfas used, would have been better. But Chapman had no access to any suitable five speed, and eventually had to settle for the largely unsuitable Maxi five speed cluster.

David
1968 36/7988

[Panda]

Also
The input shaft spigot bearing diameter changed from 17 to 15mm in 1967.
The front input oil seal also had 3 different sizes depending on year.
Three different types of mainshaft were used, up to 1966, 66 to late 70 and 71 on.
Two different types of synchro baulk ring were used.
cheers
Alan P

[Certified Lotus]

Thanks for all the insights. I am learning to be careful on replacement parts for an early Elan as it is clear that some parts changed quickly from model to model year.