Monday 8 Feb 2016. DR800 Cush Drive maintenance

On the rear wheel of most large motorcycles is a cush drive. This is simple a series of interlocking metal lugs and rubber cushions and its absorbs the impact of acceleration  and engine braking. Without this absorption, severe jolts are transmitted through the chain or shaft drive to the gear box and this results in premature failure of the chain, shaft drive, sprockets, gears or gearbox. Its fairly important to be running properly.

Unfortunately I haven't given this much thought since owning the bike, some six years now and so now is the time. Servicing quite often involves inspecting and if necessary, replacing the rubbers. The cost involved in replacing the rubbers would be getting close to $100.00 and if they are very worn or have hardened this cannot be avoided.

However, if the rubbers are a little bit worn and have not yet hardened, there is an alternative. Simply shim the rubbers with rubber from a tyre tube. You can use a bicycle tube, a motorcycle tube or a car tyre tube. If fact, if you do this regularly and properly, you can easily prolong the life of the original rubbers dramatically. Here's how this job went:

Whilst the rear wheel is still on the bike test to seen if there is any movement between the sprocket and the rim. In this case, there was a tiny bit.
Remove the rear wheel and separate the sprocket carrier from the hub. If the cushions are still very good this may not be too easy.
Inspect the rubber cushions for hardness and wear. In this case they were still quite soft and a small amount of wear and so therefore good for shimming, no need for replacing. Essentially I followed the idea as per this YouTube clip:

However I would like to point out some differences with what I did. The first is that I used a car tube, which is slightly harder and thicker rubber. This allowed me to cut a single piece that wrapped around the outside left, bottom and right edges with just the one piece per cushion. Just a bit neater and I suspect a bit easier to fit in.

The next difference is that I did use some grease. I have read arguments for and against using grease and had to think this through a bit. I ended up using a slight film on Bendix Brake Grease on all mating surfaces and fairly happy with that decision. Here is my thinking:
  • I wanted it all to go back together easily and I recall the first time I tried to separate the sprocket carrier from the hub. It was not easy. With the grease, it slid back together firmly but smoothly.
  • Everything I read suggested that the rubber hardens due to heat. Heat is caused by friction and so anything that safely reduces friction will also reduce heat and prolong the life of the cushions.
  • Bendix Brake Grease is a high temperature grease and thus will not easily melt and weep out over the wheel and tyre, one of the main arguments for not using grease. It is also very thick and perhaps contribute to the cushion effect; perhaps not though as I used just enough to lubricate the area and it will get squeezed out over time anyhow.
  • Bendix Brake Grease is used for both metal-to-metal and metal-to-rubber and so is perfect for this application. Increasing the opportunity for parts to move without friction and wear also increases the cushioning effect. One of the arguments against using grease is that many greases contribute to premature failure of rubber parts that have not be designed to come into contact with oil and grease. Bendix Brake Grease is a ceramic based product that does not attack rubber. That is possibly why it is a bit more expensive than many other products.
  • The grease is very sticky and acted as a mild adhesive, keeping the rubber strips in place whilst I placed the rubbers cushions back in place.
  • Finally, I have a thick tube of it in my workshop from when I rebuilt the rear brake caliper and so I did not have to go buy something else. That appeals to me greatly.

When it was all back together that small amount of movement was definitely gone and I am fairly certain that I should be able to feel the change whilst riding. We will find out soon enough I guess. For the amount of time  about 30 minutes, the minimal cost and potential savings it may offer I think that this is a job that I will do every time I change a rear tyre, which is about twice a year.