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PB Racing Dart 1/5th Scale - FG Shock Absorbers - Part 1

We have fitted our PB Racing Dart with FG Modellsport shock absorbers at the rear.

This article was published part finished due to some racers wanting to further info quickly as the race season is always with us somewhere in the world.

Update: As well as fitting an anti-roll bar we have now fitted the shocks.

FG Shock Absorbers - The Story So Far

I wanted to mount the FG Modellsport shock absorbers as far out on the bottom rear wishbones as possible. This presented a small problem due to the lack of ball ends on the standard shock absorbers as the bottom of the shock absorbers need to move because of the toe-in adjusters.

I considered using the metal ball ends off the new Lauterbacher cars, but they cost real money and they need an adapter making that to reduce the thread size by only a small amount, which would create its own problems.

I used the 7mm ball ends off the PB and Heli-Coiled them in a cost-effective manner.

Heli-Coiling into Plastic

Slotted screw

Stubbed nut

The 7mm PB ball ends needed to have a 4mm thread in them to be able to fit them to the FG shock shafts. An inexpensive solution was to Heli-Coil® them using a home made tool.

The tool was made by cutting the head off an M4 bolt and then cutting a slot in the end as shown in the image to the left. This allows the tang on the end of the Heli-Coil to locate and be driven in.

Plastic heli-coiling tool

The nut shown to the right is optional, but allows the Heli-Coil to be driven further into the plastic moulding. Two plain nuts locked together at the appropriate distance stop the Heli-Coil unwinding itself.

The completed tool is shown to the left. The Heli-Coil is fitted by putting the tool into a cordless drill and driving it into the plastic. Possibly a crude solution, but an effective one!

Pictures

The images below show the current development state of the fitting of the FG shocks.

Click on the thumbnails for a bigger view.

The G-clamps should be fine with some Loctite on them ;-)

TopRearCornerSide

The above is a preliminary geometry set-up using a shock tower off an obsolete PB car.

To get the clearance for the shock absorbers I have switched the brake callipers to the front of the axle blocks, which has actually cured a small problem with the length of the brake cables.

Some Notes

The height of the shock mounts was set by using an effective ground clearance of 30mm on the car. The tower height/position will be used to set the initial ride height position.

The greater the angle of the shocks, the softer they get due to the leverage. This angle, coupled with the progressive springs gives a certain amount of anti-roll bar effect.

Shock Oil - the FG shockers were built using the standard pistons and I think around 3500wt oil should be a reasonable starting point for damping (they were initially filled with 1000wt which was far too light).

Springs - the FG red progressive items were the ones that all I asked recommended, but as the Dart is lighter at the rear than the FG, HARM and Lauterbacher cars, yellow or orange may have been a better choice.

Anti-Roll Bar - this will have to be modified or replaced. The standard turned bar (part number 76/240) could be replaced with a longer version so that it could connect with the suspension link holes in the wishbones.

I have, however, been measuring up the ball and cup arrangement type anti-roll bar off my SVM and it will mount nicely in between the now redundant rocker pivot pins. Initial concerns are that the pivot pins will bend unless supported correctly.

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© 2001, 2009 by Darren Burnhill