TOPIC:

Hey guys,

I was just rebuilding some original Frog shocks that I got from Louisbaby a while back...
They are the official racing hop up for a Grasshopper so they would be a nice match for my current build.

Having a look in the manuals, I noticed they are quite different from the reissued kit.
Two things about the ones I have are questions marks to me...
Maybe someone can shed some light.

First of all - why on earth are they using the extra valve seat m10?
You can have a cup of tea by the time the shock's back to the original position with that on it...



Secondly - what's inside the bottom end of the damper cylinder?
The bits on the reissued version are detachable and have o-rings in them. But that doesn't seem to be the case here...
What's preventing the oil from leaking out?

Cheers in advance.

Edou wrote:

...
First of all - why on earth are they using the extra valve seat m10?
You can have a cup of tea by the time the shock's back to the original position with that on it...

It's a thin, clear plastic washer, acting as a valve on the holes in the damper piston, allowing for different compression and rebound damping rates - compression causes oil to flow through the holes, pushing the plastic out of the way & oil to continue flowing through the holes, which means there's very little damping on compression strokes.

Rebound damping on the other hand, the oil pushes against the plastic, closing the piston holes & meaning a lot of damping on the rebound (extension) strokes.

I guess it was meant to cure the bounciness of the back end of the Frog, but IMO Tamiya misdiagnosed the problem - it's not lack of rebound damping that caused the problem, it was the hardness of the springs. Leaving the collars off doesn't help that much - the springs are just as hard, but it does lower the ride hide & allow for some droop, masking the problem a little.

I don't know what the fix was, back in the day, but I'd leave the valve washer off & try & find some softer springs.

Edou wrote:

...
Secondly - what's inside the bottom end of the damper cylinder?
The bits on the reissued version are detachable and have o-rings in them. But that doesn't seem to be the case here...
What's preventing the oil from leaking out?
...

Factory fitted o-rings & spacers ... the bottom one is metal, not sure about the middle one. I can't say I've ever tried to take one apart - they seem to be held in by the bottom of the shocks being belled over instead of a circlip.




As a footnote, IMO the shocks didn't really get any better on the re-release Frog - although the springs are different, they're still far too hard & the car still bounces about chronically at the back end ... ... it's just clicked _why_ the shocks were recommended for the Grasshopper - that bounces around uncontrollably too

They do work a bit better on the Brat re-re though - I guess the extra weight of a large ABS body is a better match to the spring strength.

Took the valve seat off and filled the shocks with some #500 oil.
Springs are indeed very hard. Maybe I'll try to find some softer ones. Curious diameter though, Hornet springs are too wide.
I've taken care to fine sand the inside of the cylinders and the edges of the valve/piston. So the shocks are hard but smooth...
Also replacing the floating piston and spring for some modern oil seals. Easier to rebuild that way too.
Even though the dampening is hard with the Frog shocks, it may turn out to be a good combo with the double (rear) shock mod.
That should take care of some of the minor bumps...

Also note the unequal coiling of the spring - technically it's a two step spring rather than a truly progressive spring, the theory is that as the spring is compressed, the coils on the tightly wound end touch, and as a spring with less coils is harder to compress, the 2nd step is harder than the first ... in practice the Frog springs do have two steps - but as the first step is "hard", and the 2nd "immovable", Tamiya might as well not have bothered.

Off the top of my head, I can't think of any other early Tamiya cars that used a progressive or step spring ATM ...

I'm still wondering why the Frog shocks were suggested for the Grasshopper ... but thinking about it, were they the 1st coil over oil shocks/dampers, and therefore the only option, at least until the Hornet came along?

I did notice the stepped spring but it might work to my advantage in this case.
With limited motor rotation angle in mind because of the extra shocks...
For that same reason I'll use the Hornet mounts for the top so the movement will be slightly more vertical.

The topic about the Grasshopper MkI chassis makes me think the manual was printed before the plan for the Hornet finalised.
So the Frog shocks would have been the only decent option.
Reissued manual lists no official shock upgrade (although the rere Hornet came out a bit earlier)...



Gotta say they came out quite nicely after the detailing I did today.