Lotus Elan- S1-S2 Bolt On Hubs.

The aim of this blog post is to share some of the writers repair/rebuild experience over the past thirty eight years of S2 elan ownership, “Lets call it, at the coal face experience”, hopefully there will be a couple of takeaways here for you.

The rear bolt on hubs and axle shafts of the S1-S2 Lotus elan require very careful assembly to make sure they are completely secure and are unable to work loose.

The taper of the axle shaft and the hub flange must be an exact match, other wise problems will slowly manifest themselves as time and kilometres increase.

We have put together a video below to outline some special tools that can be used when dismantling, and or reassembling the hubs to the axles, and also to point out some areas that require very close attention.

While this article and video do not cover all aspects of removal and assembly, this is an overview and raises points of interest and outlines potential problems that could arise if sufficient attention is not given to certain items.

Looking at the cover photo above of the rear hub assembly (S1 and S2 bolt on hubs) these are not standard elan items, the only standard parts are the disc brake rotors, all other components are high quality competition bespoke components, which also match the purpose built competition CVDS conversion that is fitted to this S2 elan, a legacy of the S2 elan previous life spent on Australian race tracks during the 1970’s.

The original S1-S2 rear bolt on Lotus elan hubs were manufactured from cast iron, they were suitable for low stress general road work, but not suitable for competition work, and maybe they might even show their known weakness (Cracking of hub boss) if they were used long term for some pretty hard road work.

The observant reader will note that the hubs shown in this article have been machined from billet steel. The writer actually took on the task of machining both steel bolt on hubs way back in the early 1980s during the lengthy four year long rebuild.

The steel hubs were turned on a manual lathe, no DRO, no CNC, just old school machine shop work, they took countless hours to produce.

If the hubs were being machined today, the choice of course would be CNC machining, and they’d probably be done in less time than it would take to do the weekly shopping.

Of course, the machining work does not stop once the hubs and new axles have been produced.

The internal hub tapers have to be perfectly matched and bedded to each axle taper otherwise rear hub problems will be encountered, and the worst that can happen is that the hub will work its way loose on the axle shaft, and if that occurs, rapid wear could take place, making both components non serviceable items, and very expensive to replace.

The taper of the hub must match the entire length, it is poor engineering practice to have the taper matching only on the outer, or the inner most section, a miss-match of this kind will only lead to hub flutter, and worse case, (axle breakage caused by metal fatigue) and no amount of tightening and extra torque applied to the axle nut will fix the problem of a loose hub, and don’t think that a goodly amount of loctite will cure the problem either.

A smear of loctite is a worthwhile addition onto a perfectly matched hub/axle pair during the final assembly, then torqued up to 110Lb Ft, and they should not give any further trouble.

Matching of tapers requires that engineers bearing blue is lightly applied and the parts mated up, and rotated 120Deg, and then pulled apart and carefully inspect and note where the blue is located, if the match is perfect, a smear of blue will be seen for the entire length of the taper section, if it is noticeable at the outer or inner taper section only, then I am afraid you have some work to do.

It could be that the tapers have not been machined correctly, and the only way to correct that is with further accurate machining work, which in most cases will entail a visit to the local machine shop, unless you have the required machinery to do this work your self, but most owners don’t. Sometimes, further machining is not possible because the OD of the axle, or the ID of the hub wont allow it. Any machining carried out will move the hub inwards along the axle, it may be possible to machine a small amount from the inner shoulder of the hub to provide clearance.

It is a well known fact that a properly matched taper pair of axle and hub, assembled correctly with a smear of loctite retainer, and correct amount of torque applied, will provide the positive drive required. But the writer is a stickler for making sure that things will remain reliable, so a short round key is employed between the hub and axle for added security.

The photo above illustrates the axle and hub assembly mounted between the centres of the lathe so that a final and a light machining cut can be removed from the outer face of the hub flange, this procedure which is carried out after the hub is perfectly match taper mounted, will guarantee the face will be one hundred percent dead true, which in turn should make the road wheel run dead true, and not create any sideways out of balance problems when mounted to the car. (Providing the wheel rim has not been previously damaged)

Below is a photo of a special bolt on rear hub puller the writer fabricated many years ago. This is a very strong heavy duty puller, and is highly effective in the removal of the rear hubs.

Features – it is mounted on the hub with existing studs and wheel nuts. The bolts are high tensile, and can exert a lot of pulling pressure. There is also a very special machined tube shape anvil which locates over the threaded spigot and abuts up against the shoulder of the axle shaft, that is where the pressure is applied and NOT on the end of the threaded spigot. If the end of spigot is hit with a hammer, the thread will be belled and the nut will never screw back on again.

The simplest way to remove the hub is to undo the nyloc nut as explained in the video above, assemble and mount the puller as illustrated, (Or similar) and pull up as much pulling pressure as can be applied. Then evenly heat the inner hub boss with an oxy torch, then hit (With sudden impact) the head of the central high tensile bolt, say two or three times, the hub will be heard to make a very loud pop on release from the taper, a couple of attempts may be required.
If after the first attempt, the hub refuses to release, screw the central bolt up a bit more, repeat with heat, and then impact again on the central bolt, the hub should let go second time around.

If the hub and axle are badly corroded together then it may need soaking in a penetrating fluid for a couple of days. But well maintained components should be quite easy to separate.

The image above shows the rear strut assembly mounted in the bench vice. The writer has found that the hubs are far easier to remove from the axle with the puller while the rear strut unit is still on the car, the impact strokes of the large hammer seem to work better, and the tyres being flexible absorb some of the shock.

Once the DIY enthusiast has been through the process once or twice, the method and process will become clearer and the physics behind it will begin to make sense.