Shocks Sticking?
 

I recently had a problem with one of my front shocks when on landing off a jump with my SX3. It didn't seem to compress on landing causing the front wishbone on that side to break. It was as if it had just locked up? Has anyone else noticed or suffered the same problem? If so, how did you remedy it?:confused:

It could be either a bent shaft or the shock body.

Does the wishbone move freely when you take the shock off?

Check the following things:

- Tightness of the nut on the inner hingepin. This sometimes tightens itself, causing binding of the wishbone.
- Shock shafts: these are, on the front, sensitive to heavy or frontal crashes.
- Cartridge: maybe your o-rings snapped and cause a lot of bind in the shock movement.

The car is brand new, wishbones all move freely, I was told to remove the nut as it can, as you said tighten itself, causing some binding. Just came across this from the Belgian GP this year involving Derek McCloskey from Ireland "A manufacturing error known as cold-shock was evident when a front wishbone on Derek’s CAT broke without warning. Phil Booth from Schumacher explained that this effect was extremely rare but was known of." Seems there is a problem with this.

Take the shock off, and the spring off, does the piston move smoothly in both directions?

Piston moves freely in both directions, really smooth. I'm baffled as to why this happened. I know it's an easy fix, just replacing a wishbone, but I don't want the same thing happenening again. Everything looks and feels as it should be. Read on RC tech forum that some guy suggests inverting the pistons to avoid this problem of "Cold Shock".

Hey David, you using any shaped pistons or a low number of piston holes?
This might increase the PACK resistance of a shock and lead to a significant "tightening" under heavy impact?

On the front I have 3 hole pistons with 32.5wt oil and 3.5F springs

I dont know much, but that sounds like fewer holes than the team would run.
However, I cant see 3 holes and that weight of oil causing enough pack that the shock wouldnt compress properly - no matter how hard the impact.

Sorry mate, thats the "wealth" of my knowledge all spent! :)

Perhaps if Chris Ashton pops on later he can shed some more light on this problem.

if the shock moves free,have you looked to see if you have to much droop and the drive shaft pin is coming out the diff cup,then poping back in when you put the power on,this will look like the shock has locked up

How tight are you doing the nut/screws up on the shocks, they need to be a little loose to allow free movement.

The droop seems fine, when the shocks are fully extended with the wheels just off the floor, the driveshaft pins are still about 1 quarter of the way into the cup. When tightening the nut at the top of the shock, I always nip them up then back it off about half a turn so it is not too tight. You can move them back and forth ever so slightly with your fingers. I guess this is the way it should be?

Could it have just been that the wishbone had a fault somewhere? This was a standard kit wishbone. We race on an astro track in a big warehouse, there is no heating and it wasn't a paticularly warm night. I'm just wondering if this would have an effect on the plastic? I have medium flex wishbones which I intend to fit in the hope that it will go some way to eliminting the problem

the standard wichbone's are a lot harder plastic than the medium flex one so yes they break a lot easyer .
and I now danny and grant williams run 3 hole pistons all aroud just as I am and I havent broken a wichbone in a long time sinds i am using the medium flex one's . the team dous drills the 3 hole pistons .

I have designed for plastics and do not know the term 'cold shock' unless it is an RC term or an Americanism I am assuming they mean a brittle failure due to cold temperatures (i.e. cold morning), the technical terms if so is referred to as being at the brittle end of the ductile-brittle transition temperature. This is likely to be even more sensitive for materials with a high carbon content, such as wishbones.... some high carbon plastics are brittle at 60 - 70 degrees C, but also are very stiff....

Unlikely to be a manufacturing error, however if material was not packed suitably in the cavity of the tool or there was a weakness (plastic not fused) on a weld line within the moulding then this could cause a failure and would be a manufacturing error.

figure 6-21 illustrates it well..... as an example

http://itu2011cim.blogspot.com/2011/...-9th-week.html

really want to find why it locked up tho...

make sure you havent overtightend the nut at the top of the shock, this pinches and restrics the movement,

yep, just tried this on mine (didn't want to go too far otherwise it may damage the shock), and it binds the shock really badly, you do not really want to tighten this nut, just run it upto nip the plastic and let the nyloc do the work....

Thanks for all the advice...:thumbsup::thumbsup::thumbsup: