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Deekay777 wrote:

Interested in the shock design, do they work "well" i mean for the age and tech back then. The reservoir tube is is wild.
 

I restored a 959 and I found the shocks pretty acceptable for a touring car, although the volume and travel is much too small for any off road use.  That's OK, because you'd be crazy to drive one off road anyway (ignoring Tamiya's ads to the contrary).

I was just curious as to how much of an affect the "tube reservoir" has on the damping. Could the tube be shortened to add more rebound. Could be fun to get hold of a set.

I always wondered if they just binned those cars after making their overly aggressive feature videos.

Soooooo, there is a pretty serious issue with the tyres. I have message to see what the deal is..........

Deekay777 wrote:

I was just curious as to how much of an affect the "tube reservoir" has on the damping. Could the tube be shortened to add more rebound. Could be fun to get hold of a set.

 

The tube is there for volume compensation.  There is no bladder in the head end of the cylinder like other oil dampers, so when the rod compresses there is less volume available for fluid within the cylinder.  Without somewhere for it to go, you'd get a hydraulic lock.  The tube effectively swells to add volume, so it needs to be flexible enough for that to happen.  This particular damper has a semi-balanced rod (it extends to both sides of the piston but isn't exactly the same diameter) so the volume doesn't change all that much.  I don't think it has any significant impact on the damping; that should still be driven by the piston.  This piston doesn't have any holes in it, the damping is controlled by the difference in size between the OD of the piston and the ID of the cylinder.  Very unusual dampers.

Tamiya engineers were on another level back then.😳 That is a whole lot of thought going into a plastic model. The tube as “bladder” is genius! Thank you for breaking it down. 

Deekay777 wrote:

Tamiya engineers were on another level back then.😳 That is a whole lot of thought going into a plastic model. The tube as “bladder” is genius! Thank you for breaking it down. 
 

I wrote about it pretty extensively in my 959 topic (portions quoted below).  It helps that I work on hydraulic actuators for a living so I understand most of this stuff.

The shocks are tiny, unique, and tricky.  These are real aluminum, oil filled shocks but at a scale different than all other Tamiya models.  The first thing to note is that the gland cap is swaged onto the cylinder and therefore not removable.  According to the cross section in the manual, there are two o-rings in there but there is no access to them for replacement.  The piston is a solid metal ring with no holes or slots, so the rate orifice is just the clearance between the piston and the cylinder.  Bleeding these shocks takes a very long time because it is so difficult for air bubbles to escape past the piston.  Note also that the rod continues past the piston head but with a smaller area than the threaded end due to the flat on one side.  More on this feature later.  The front shocks are coilover type which mount vertically to a cross bracket as shown.

The rear shocks work essentially the same except that they have no integral spring and the mounting bracket employs a 90 degree bend.  Most shocks have different fluid areas on either side of the piston head.  On the head end the area is the entire inner diameter of the cylinder while on the gland end this area is reduced by the area of the rod itself.  This means that when the shock compresses, the internal volume of the shock reduces and the extra fluid needs somewhere to go, a phenomenon called volume compensation.  If there is no outlet, this results in a hydraulic lock and the shock cannot compress.    Most Tamiya shocks use a hemispherical bladder inside the head end cap for volume compensation but these shocks do something different.  Firstly, because there is also a rod on the back side of the piston, the difference in internal volume between the extended and compressed states is very little.  It amounts to only the volume of the flat on the rod.  This means that very little fluid needs to be forced out of the shock to compress it.  However, this flat serves another function: dual rate damping.  When the shock first starts compressing, the fluid squeezes past the piston and then out the head end port.  The extra volume serves to swell the diameter of the plastic tubing on the cap (not yet installed).  As the shock compresses further, the rod actually extends inside the outlet port on the head end of the shock, partially blocking it. This results in a reduced outlet orifice effectively snubbing the shock.  Genius!

You yourself are an engineer.! Now the oozing knowledge and understanding makes even more sense.

I work for a major sustainable energy distributor, technical field support to industrial plants.

Couple of missing pressed parts arrived today, The front shock tower brace and the on/off Switch mount

 

 

 

 
 

An update on the MCI tyres, Unfortunately the quality is poor and they split even as you are just washing them in warm soapy water to remove the print residue. I was given a full refund on them and as they were part of a bulk order I wasn't out on shipping. I have ordered some GB-01 tyres sets to try instead, As this will be a runner they don't need to be OG but would have been nice.

 

 

Hi Andy, I’m gutted for you on those tyres.
Did Nathanial say this might have been a one off ??
Thanks for the update.