R - Final Drive
This is a weird piece of engineering! It is based on a GKN Salisbury axle where the axle tubes have been severely shortened and brake units from a Ford Capri 3 litre fitted upside down. The whole assy has a frame welded to it for mounting into the chassis. Note the on the S2 cars, this frame is reinforced with a "X" cross member above the front of the diff.
The Crown Wheel & Pinion (CWP) was not a commonly used part, even in the 70's, and it appears true that the only other known application for these parts is a fork lift truck! There are two ratios available, so if you install the Getrag gearbox, you need to know which ratio you have and check the number stamped on the speedo drive. By cross-referencing the numbers in the Lotus Parts book you can see if you have the correct drive unit to give correct speedo readings. I was lucky!
The Salisbury axle is incredibly tough and virtually unbreakable, which is why it is used on all modern Land Rovers. If you want to pull out the CWP you will need a special tool to stretch the casing, but this applies to all Salisbury axles and is not unique to Lotus.
In my car the diff unit was corroded and the oil seals leaked over the brakes, so I had the seals changed at Paul Matty's, painted it, installed it with S2 bushes and it has been quiet and trouble free. Note that the S2 bushes have six holes drilled through them to make them softer.
Prop Shafts
This subject is related to the Vibration issue below. The S1 manual car had, as far as I know only one type of prop shaft fitted, but the S2 had several. Lotus knew that had a driveline vibration problem and worked hard to solve it by trying all of these mods:
| Lead weight on the top of the gearbox (all Getrags on Lotus Elite/Eclat's have this) |
| Lead weight on the bottom the gearbox |
| Reinforced Diff frame - the additional "X" frame to stiffen the diff carrier |
| Softer diff mounting rubbers (six hole type) |
| 2.2 Engine in Elite/Eclat, uniquely, has engine mounting "wings" as part of the ladder frame casting. You can see where these have been cut off on all 912 engines! These probably alter the balance point of the engine in the car. In my conversion I have an Esprit engine (no wings) and use the standard S1 907 engine mountings. |
| Rear Getrag box mounting is adjustable for height and sideways location, which would enable the prop to be accurately aligned. [See below for my proposed alignment tool] |
| Prop with rear CV joint mounted on prop shaft |
| Prop with CV joint mounted on diff flange |
| Use of rubber (concentric) connection between CV joint casing and the propshaft |
| Use of rubber (concentric) connection at the front of the prop |
| Use of Flexplate flywheel |
Note for Getrag conversions: the S2 prop is a different length and has a different gearbox fitting.
Tip: when fitting a Getrag, use new gearbox mounting bushes as old ones collapse, leaving the gearbox sitting on the supporting cross-member.
Drive Line Vibrations & Heterodyning
Some cars suffer more than others so it is a matter of experimenting to solve a problem. My car is pretty good, but I have another unused prop to fit the next time I take the diff out. This prop has been balanced to zero tolerance and has the CV joint mounted on the diff flange rather than the propshaft. This design of using a CV joint must have been popular in the 70's because the Triumph Stag is very similar. I will also align the prop properly rather than guessing.
Heterodyning: I have heard this term used only in relation to the Elite/Eclat and mostly by the late Graham Arnold. It was Graham who told me that Lotus never solved the problem as they should have gone to the expense of fitting a prop with a centre bearing since it is quite long. He described Heterodyning as the problem of too many different sources of vibration combining. I am not sure that Heterodyning is a proper automotive term, but Graham was basically right since it is analogous to the combining of currents in an electrical circuit. In the Lotus there are vibrations from the engine, gearbox, prop and diff, all varying with load and speed in such a way that the net result is a harshness which is transferred to the occupants of the car. In this respect the Elite was simply under developed, and yet all these problems were cured in the Excel, which being of similar dimensions, did not require a split propshaft!
Propshaft Alignment Tool
My plan is to use a toy laser beam (popular kids toy brass pointer from about 7 or 8 years ago) mounted in a dummy gearbox output shaft, and inserted into the gearbox in situ. This tool will be centrally aligned on the workbench before use. Since the Getrag can be fully adjusted for height and sideways, the gearbox shaft can be aligned optimally to the offset diff flange.
V8 Modders:
For a long time I considered going down the V8 route, but having done a V8 conversion on a Land Rover I know that you have to get the overall gearing correct to match the power and torque of the V8. Capri 3 litre cars, Jags and Rovers with similar engine performance use final drive ratios around 3:1, whereas the Lotus is much lower. I have met people who say its fine, but I think a higher ratio is highly desirable.
The options:
Since the Lotus final drive assembly is a Salisbury axle, one option is to take a Capri 3 litre back axle (which is also a Salisbury unit) and remanufacture it as a copy of the Lotus design. Gives 3:1 and uses the same brakes. All you have to do really is cut down the axle tubes and refit the end plates. This mod has been done on a V8 Elite.
Or you can keep the Lotus unit and change the CWP. For years it was believed that there were no alternative CWP ratios available, but I have met a V8 Elite owner who knew that Morgan V8's had a 3:1 ratio in a Salisbury axle, so he obtained the CWP parts and fitted them, just like that! If I had known that years ago I may still have done a V8 Elite.
The final option is to do what Lotus should have done in the first place (but probably didn't for cost reasons) and use the Jag diff unit. These units have a wide choice of ratios, and some have LSD's, and they have inboard disc brakes. Perfect, except for the fact that you will have to do a lot of engineering to make it fit. It is my understanding that this has also been done on a V8 Elite.