Urethane Suspension Bushes – A DIY Project.

Urethane Suspension Bushes – A DIY Project.

The standard suspension bushes as fitted to the lotus elan are called Metalastic, they consist of an inner and an outer metal sleeve bonded with a layer of flexible rubber during manufacture. These particular  types of isolating bushes are commonly used in industry, they come in many different shapes, sizes and configuration’s.

But there is only one problem with rubber bonded bushes. When they are new, the bushes work quite well, they provide good cushioning and compliance,  good handling, as well as providing reasonable NVH (Noise Vibration Harshness) properties. But as they age, and they become contaminated with oil and suffer from general atmospheric deterioration, the end result can be poor handling, along with annoying rattles & clunks from within the suspension system, the rear A frames in particular have been known to move or walk about, creating problems with wheel alignment and handling problems.

If the renewal of the front or rear suspension bushes is contemplated, the Metalastic bushes can be difficult to remove if corrosion has set in, the job is made easier if a garage press and special mandrels are machined and used for the job. Heating of the outer part of the wishbone ferule can also help to break the rust bond, followed by treatment with CRC or similar.

The outer rear susp bush is similar to the front suspension bush, but there is not all that much rubber between the inner and outer (See photo above) sleeves to provide a large amount of cushioning.

The rear inner bush is quite different, notice the large amount of rubber which provides excellent cushion and road (NVH) isolation. The biggest bug bear with the inner bushes is that they eventually become impregnated with oil leaking from the differential, and over time, the rubber simply rots away, many an elan driver has probably wondered why the rear suspension walks around making the car behave oddly, nine times out of ten, it will be the inner bushes that have succumbed to rubber rot.

Imagine then, if you could produce a set of special urethane suspension bushes for your elan that had none of the downsides of the old type of bushes?

Well take it from me, it is indeed possible to make a complete set of excellent quality urethane suspension bushes for your elan. But you will need some lathe machining skills, and be prepared to learn and understand how to get the utmost from urethane bushes. And if the prospect of making the bushes daunts you, they can be purchased from several suppliers, but buyer beware, make sure you understand what you are buying.

There are also some special tools to construct so that each bush can be fine tuned to provide the ultimate in performance. But the first thing is to source the urethane material in rod form which can be easily machined in a lathe, the cutting tool piece is sharpened to be more like a knife rather than a metal turning tool.

Urethane can also be purchased in pouring kits, but if you go that way, a full set of multi-part casting dies will also need to be machined, this will be time consuming and quite expensive if it is not possible to be done as a complete DIY project. Urethane rod can be easily and quickly machined on a lathe in the home workshop…. providing you know what you are doing.

Urethane rod material, standard length is 300mm or 12″.
Urethane rod can be purchased in many different diameters, the diameters required for elan suspension is:
Front Bushes- Upper & lower: 1.25″ Dia (32mm)
Rear Outer: 1″ (25mm)
Rear Inner: 1.5″ (38mm).
You might be interested to also learn that almost every bush in the elan can be changed over to urethane bushes, such as:

The diff upper chassis mounting bushes – Recommended only for racing due to noise transmitted.
The diff torque rod bushes – Excellent
The front anti roll bar bushes – Excellent
And anywhere else that requires a tough, but flexible bushing material.

The items that go to make up the suspension bush kit assembly for each wishbone arm, there are two urethane top hat shape bushes, one inner stainless steel crush tube, two machined steel side thrust washers, and two narrow 1/2″ UNF lock nuts.

The bushes as discussed are machined from the urethane rod, they are designed to be a hand push fit into the wishbone ferrule, and when the stainless crush tube is pressed through the bushes, the final outward pressure will be applied to the bushing. The side thrust washers are machined from bright solid round steel, they are about 2.5mm thick, do not use ordinary washers. The narrow lock nuts are machined from normal hex nuts sourced from the local bolt shop. Do not use nyloc nuts, twin plain lock nuts must be used.

This is really all the urethane bush kit assembly consists of, it is simple and basic, but note that it is the way in which they are set up that makes the system work correctly.  One of the most important steps during installation is to adjust the “length” of the inner distance crush tube to the correct length.

When the complete assembly is on the car, it is the inner crush sleeve which controls how much compression force is applied to the sides, or to each end of the urethane bushes, and that is achieved by having the tube just a few thousands of an inch longer than the bushing material. The side thrust washers are essential, as they are designed to control the fore and aft thrust, and to hold the bush and wishbone in place.

Looking at the image above it is difficult to observe if there is actually a difference of length between the steel crush tube and the bushing material, the stainless steel crush tube is slightly longer than the urethane bush, and that is what makes the difference between the bush either working correctly or not.

You may well wonder what the easiest method is to achieve the ideal set up?  If the bushes are clamped too tight, the suspension will appear stiff, lifeless, and it will bind between the components, causing the suspension to jam in one particular spot and not return to a normal working position, and you don’t want that while driving through a series of tight, twisting corners. The wishbone arms must be free to move through full droop and full bump working angles with out binding.

On the other hand, if the bushes are set to loose, the suspension will have far to much free play which may induce undesirable handling…. but if the time is taken to fine tune the suspension, adjustments will not be required for quite some time, and the suspension will perform as required.

The bench jig testing tool shown above is the secret to a well set up urethane suspension bush conversion, each tool is detailed in the image (Click to view in larger size). The main jig holding bar is bolted to the workbench and each bush in turn is fine tuned using this tool. It is designed to replicate exactly how the bushes will be set and tensioned on the chassis. When the bushes are preset and numbered to match which ferule or wishbone arm each bushing set belongs to, a highly accurate and well tuned suspension can be produced. of course, it is important to carry out a final check and adjustment when the final assembly and fit up is done on the chassis.

Yes, it is quite a lot of work, but once completed, the suspension should not require any further adjustment apart from an occasional check. Don’t be afraid to tackle a job that you may not think you can handle. The important thing to note is that you will need access to a lathe, as there is quite a bit of time spent making all of the small bits and pieces.

And The Advantages Are:
Urethane suspension bushes will markedly improve the chassis & steering response of the elan, (Or any car for that matter) the lifespan of urethane bushes could be as much as fifteen or twenty years.

Final Notes:
To obtain optimum performance with urethane bushes, they must be set up correctly. There are bush kits available that are supplied with a flange at one end only, please stay clear of these, as they will only cause you grief after fitment. Urethane bushes must be of top hat design, and the stainless steel crush tube is adjusted during installation by machining one end of the tube which enables the correct fit or crush of the installed bush, it takes time and effort to achieve best outcomes, but 90% of people wont bother, and then complain that the bushes don’t deliver the desired outcome.