An Article by Tom Hall

June 1999

Page 1

Figure 1. The Urethane Bushings with their Inner Sleeve tubes. Note that the tubes shown have been modified with a radial groove at the center for uniform grease distribution.

At long last, the wait for a good quality urethane suspension bushing for Tiger enthusiasts is over. Rick at Sunbeam Specialties is expecting his first production run in mid July 1999. Many owners have waited patiently as this vital component was developed. The manufacturing quality of the old rubber based “Metalastic” bushings and their sporadically available alternatives have been going downhill in quality for several years. This urethane bushing development project has been a long program but we all hope that the final results will make our Tigers handle and perform even better than ever.

The new urethane bushings will be available in two hardness levels. The black urethane compound is intended as a standard replacement for the OEM rubber bushings and are specified as having a durometer rating of about 70. The red urethane compound is intended for high performance applications and will have a durometer of about 95. Other than the compounds, the bushings will be otherwise physically identical. Rick's (SS) part numbers will be found near the end of this Tech Tip.

There are two differences in the design of these urethane bushings that are important to understand. The first is that urethane bushings are designed to "rotate" on a surface as opposed to the OEM rubber bushings which operate by twisting the rubber between the bonded shells without actually rotating. This means that the rotational surface must remain smooth and rust free in order to prevent that annoying squeak that frequently develops in solid bushing installations. The second difference is that the cross-section of the urethane is about half that of the OEM rubber bushings. This will tend to make the bushings "feel" stiffer and more responsive because there is less room for them to deflect. In order to avoid the potential for the development of squeaks, Rick requested that the bushing manufacturer use a stainless steel material for the inner sleeves that the bushings actually pivot on. Like many manufacturers, they think they know better and rejected the idea. They stated that they had never had a problem with squeaks as long as you used their grease at the time of assembly. Taking all that with a few grains of salt and many years of experience with solid bushings, this installation tip recommends two possible alternatives that will make silent operation a more assured outcome.

Figure 2. Here’s the completed A-Arm subassemblies ready for Ball Joint fitting and installation. These ball joints and bushings are Rick’s latest suspension components.

The first alternative is to replace the sleeves supplied with stainless replacements. They are simple tubes to fabricate and Rick may end up offering them as an accessory in the future. A sketch of these tubes will be found at the end of this tip for those that would rather do it themselves. The second alternative is to install grease fittings that will allow lubrication to reach that twisting surface. The photos and descriptions in this tip show this second method of assembly.

Fortunately for us, the manufacturer provided Rick with a prototype set of the urethane bushings in advance of production and that allowed the double checking of production dimensions and the following pictures and descriptions to be developed. It also allowed me to develop a set of drill fixtures which properly guide the modifications that locate the grease fittings. These locations were selected to allow easy access for the grease gun and proper grease distribution to the bushings rotational surfaces. The grease fittings modifications shown would be appropriate

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Our thanks to Tom Hall and STOA for sharing this article.

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