TOPIC:

I've referred to the "third shock" mod on the Lunchbox/Midnight Pumpkin a couple of times - I thought it might be helpful if I posted some pictures on what is actually _is_.

In theory, the slotted gearbox pivots give the car slightly independant rear suspension, but in pratice, as soon as the motor starts spinning, the gearbox rotates to the tops of the slots (usually with an audible clack), effectively locking the gearbox pivot up, so that a bump on one side lifts the whole rear in the air.

The "third shock" controls this by exerting some force on the centre of the gearbox pivot line, so that the gearbox doesn't rotate, and each rear wheel is free to move semi-independantly.

Obviously you need a spare shock absorber for this - although it doesn't have to be damped - but it does have to be fairly short (65 to 75mm is ideal, though you will have to decide the upper mounting point & method based on the length), and firmly sprung. I used a motor protector widget from a TL01, but anything that allows you to fix in two directions at 90 degrees to each other will do - an angle bracket, servo fixing block etc.


Remove the gearbox & mark up the gearbox for cutting...


cut a notch out ...


Retain shock by refiiting pivot bar...


Top mount detail:


Top mount fitted on car:


Both ends fitted ...





At the front end, the cheapest/easiest mod is to slip 5mm or so of tube on the top of the "shock" bolt above the chassis - this puts some extra preload on the spring, and sets the camber at a better neutral angle:

Jonny
Great info on the third shock! You came with this just in time as I am busy fitting oil shocks to my runner Pumpkin and was wondering about the bespoke third shock.
Cheers,
Marius

Great info. Could also be a good mod for a Grasshopper or Hornet.

Edou wrote:

Great info. Could also be a good mod for a Grasshopper or Hornet.

There's no point on a Grasshopper, unless you upgrade to slotted gearbox pivots, and there's not really enough room on a Hornet ... I tried an alternative on a Super Hornet, it's marginally bettter than not having it, but doesn't work anything like as well as a shock:

good idea
will do it when i need to

Jonny wrote:

There's no point on a Grasshopper, unless you upgrade to slotted gearbox pivots

That would indeed be a first requirement - done that on my Hopper.

This TC member did the mod on his car : GHopper 3rd shock

That Super Hornet really has some special parts...

Edou wrote:

Jonny wrote:

There's no point on a Grasshopper, unless you upgrade to slotted gearbox pivots

That would indeed be a first requirement - done that on my Hopper.

This TC member did the mod on his car : GHopper 3rd shock

That Super Hornet really has some special parts...

Nice work - might have to try that on my Super Hornet

I have a pile of GHopper and Hornet parts waiting for a next project.
Very tempted to give this 3rd shock mod a go also...

What is a good shock to use for this upgrade and could you use two one on each side of the gear box?

I think he (edit - the guy on TC) used the damper from an F103, the one connected to the friction plate.
Did a little mod where I used Grasshopper front suspension parts and some custom brackets to do a double sided version :







This just fits. Don't think there will be enough room for an F103 damper and a 540 motor...
Some action from a prior stage (different, less functional Grasshopper brackets) :



tamiyabase.com/...t=10#22143