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PB Dart Front Suspension Bell Crank Assembly Modifications

The front suspension bell cranks (sometimes referred to as rockers) on the PB Racing Dart need to operate unhindered and smoothly for the suspension to work.

Another modification was suggested by David Hyde and this is our variation.

Front Bell Crank Ball Bearing Modification

Bell Crank Layout

David’s modification was to use a thrust race bearing (which is shown here) between the rocker pivots. We thought that using a plain ball bearing might prove as effective due to the relatively low loading on this part of the assembly.

Ball Bearing Modification

Ball Bearing

This solution (shown left) is an inexpensive one that we proposed using a standard ball bearing (shown right). The ends of the pivots are machined so that one half contacts the outer race of the bearing and the other side contacts the inner race.

Pivot Pin

PB Dart collet retained pivot pin

When we stripped one of our cars down the 4mm diameter stainless steel replacement pivot pin we had previously fitted was found to bent.

We had thought of using piano wire for this task before, but rather than cut e-clip grooves in the ends we decided to make a longer pin and use collets instead.

Although the e-clip solution is neater (and lighter) in appearance, the collet solution is far easier to fit in the confines of the Dart front end, especially during mid-meeting repairs. Flats were ground on the ends for the grub screws to locate onto and then the piano wire was polished.

Versions

When we came to do the front rocker modification, we decided that there were possibly better ways of carrying out the conversion.

Version One

PB Racing Dart Front Suspension Rocker

The image on the left shows the first version of our Dart front rocker modification, which used the standard aluminium bush. The bush was pressed out and then turned down after subtracting the width of the bearing.

As the end of the bushes are manufactured with a chamfer on the end, it was decided to just machine just one side, as the chamfer provided the necessary clearance on the bearing.

For a bigger version of the image to the left click on the image.

Version Two

PB Racing Dart Front Suspension Rocker

As we have two Darts currently in our possession, we decided to take a different approach in replacing the aluminium bushes with brass ones. As the bushes act as bearings on the pin the brass should prove to be a better material than the original.

We made both of these bushes equal length to put the bearing in the middle of the assembly. This would probably make very little difference in terms of balance, etc. to the position of the bearing in the first version.

For a bigger version of the image to the left click on the image.

Machining

PB Racing Dart Front Suspension Rocker Bush

PB Racing Dart Front Suspension Rocker Bush

The ends of the bushes were machined slightly differently to that proposed before we undertook this modification. The image on the right is unchanged and contacts the outer race of the bearing. There is no reason that this contact area could not be achieved by the use of a countersink bit. The image on the left is a nice and simple chamfer that contacts the inner race of the bearing.

Summary

The front suspension feels better on both cars and this modification is one we would recommend, especially as it is relatively inexpensive as far as the cost of the materials. The Dart should also benefit from the pivot pin made from 5/32″ piano wire.

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© 2001, 2009 by Darren Burnhill