Rob Gray :: ontheroad :: wothahellizat :: wot1 :: diaries :: issue-011


19 May 1999

So how does one attach a body to this heaving platform we call a chassis. I guess there's a thousand ways and I also guess I chose one of the more complex and expensive ones but here goes.

We've already determined that the body should be mounted at three points, but those points still have to flex a little, you can't just weld the body onto the chassis. There's also the question of vibration from the road, it would be nice to reduce this as well.

My first thought was air bags, why not mount the entire body on three air bags? Well the answer to this question is "cost and complexity". I spent quite a lot of time designing an air bag system before I decided that it was getting too complicated. As the air bags have no lateral stability a lot of torsion bars and levellers are needed. It all got too much and probably beyond my engineering ability.

Next I started looking for rubber mounts. I found a few options and settled on some rubber "donuts" made in England (available from Shock & Vibration Technologies in NSW). These mounts are designed for off road equipment and large trucks. Sounds just right.

The mounts come as two rubber pieces that clamp either side of a steel donut, see below.
The three pieces as supplied.
And clamped together.

The steel part is supplied by SVT because the shape and dimensions of the hole are important. This lot is designed to be used something like the following.

My version looks like the drawing below. We'll cover the front body mounts first then look at the rear mounts in a later diary entry.

Note the extra snubbing washer, I decided that it would spread the load more evenly than if the rubber was in direct contact with the RHS beams. The above drawing is a side elevation and the large rectangles are 6x3" RHS beams. The drawing below is a front elevation (appologies to those with small screens).

This rather large drawing shows the two mounting points of the front mount. These points are as close to the outer edge of the body as possible. Note that, at this end, the body is quite tightly bound to the chassis, it's at the back that the flexing has to be allowed for.

The supplied steel donut is round and quite unsuitable for mounting directly to anything so it must be fixed into a more suitable plate. As this is 32mm thick I decided to get a local engineering firm to do this for me. This is the drawing I supplied.

The photo below shows the resultant plate bolted in place. Note that the donut has been welded into the large hole in the plate with the result being a large plate with a small(ish) hole.

I decided to bolt the plate rather than weld it so future removal of the body would be easier.

Here we see the support cross members placed in position on the chassis.

These in turn are welded to some fish plates which are bolted to the chassis rails as per one of the drawings above.

Here's the finished product with support plates and rubber mounts inserted. The body will sit on top of the rubber mounts. Note that this photo was taken several days later, The mount did not just drop on, it took hours to make it fit, the story is in entry #13.