A Quick PCD Check.

The following, is a little story that might be of interest if you’re thinking about converting to one of our awesome CVDS conversions.

When it comes to the lotus elan, you should be aware that not all things are equal when it comes to the PCD of the differential (Diff) output shafts, and the outer wheel axle shafts.

The early S1 Lotus elan, for some strange reason, was fitted with diff out puts and wheel axle shafts/spiders, where the drilled bolt holes were of a slightly larger PCD (Pitch Circle Diameter) than the later PCD featured on the S2, S3, S4.

This anomaly, has caught some elan owners out, because unless you really know all of the previous history of your elan, you don’t really know what its got, and what it hasn’t.

Its a case of; You don’t know, what you don’t know.

You wont be able to tell what the PCD is by taking a quick glance under your elan, and if the PCD’s of the outputs, and inputs are in fact the same.

Over the past few months, we have had two CVDS customers who have suffered some frustration when they discovered that their elan was fitted with a combination of the early PCD and later model PCD diff out puts and wheel axles, both owners by coincidence, had a series three lotus elan.

The difference was only discovered when they were working through the installation process of the elantrikbits CVDS conversion, in both cases, the inner diff out put shafts had been replaced or updated with the later PCD, but the outer wheel stub axles were of the early series one type, the PCD of which is larger than what the S2, S3 and S4 was fitted with.

So our two customers could fit the CVDS to the diff output shaft, but not the outer shafts… and that’s when the frustration began, and we received a help request to help sort things out, which we duly did.

So before you go ahead and place your order, to save you from any head aches, take the time to crawl under your elan and make some quick measurements of the diff out-put shafts, and the wheel stub axle of your elan… keep reading to find out more.

Below is a sketch of a simple round plate with three holes, the quick check we are speaking about is carried out by measuring across the 7/16″ UNF bolts that hold the do-nuts to the spiders, using a vernier caliper, carefully check the measurement across two of the bolts, outside edge to outside edge.

If the measurement is 97 mm or 3.81″, you have an early S1 diff output, or wheel stub axle. This measurement is NOT the bolt PCD, this is just a simple, quick check method to verify what is installed in your elan.

In the sketches above, notice the difference between the across the bolts distance (Outer edge to Outer edge) The early S1 measurement is 97mm, the later S2/3/4 measurements should be 93.84mm.

In the photo above, the adapter plate is a freshly CNC machined plate for an S1 elan wheel axle shaft, the Lotus wheel axle shaft sitting on the studs is the later, S2, S3, S4 wheel axle shaft.

It is easy to see that the different spec parts simply wont fit, and you should never ever try to force them to fit. DO NOT ream or file the holes out. Make sure to order the correct parts.

We have the CNC software programs to machine mill and drill adapter plates to the early PCD, and the later PCD bolt holes, the latter of which are the most common today… BUT, you can still get caught out as we have outlined in this article.

Looking at the checking plate above, with the bolts located in the S1 PCD holes, your eye will have a tough time noting any difference between the early and later PCD.

Hence the reason why we have put this simple PCD measuring guide together, purely to help you to avoid the headaches that other elan owners have been through.

And while we are still on the CVDS subject, we have also developed a 26R style of CVDS which has a four bolt adapter plate which connects to the diff output, and the outer adapter plate which is the normal three bolt arrangement, common to our classic CVDS conversion.
This design is more common to the lotus elan developed for the race circuit… Read and Learn More Here