Tweaking Tamiya twin clutch gearbox

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a65l
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Tweaking Tamiya twin clutch gearbox

Post by a65l »

Ok. Haven't seen a post directed to this topic specifically.

I don't have any pictures, as I tend to get busy and forget about the camera.

I've wound up with 3 Tamiya KT's. One is a kit , in a box, and it's twin motor. It's on standby. The other 2 are old twin clutch monsters. The first one had an issue with a bad gear, I actually bought the second thinking I'd just pull the gear out of it, but it's in better shape than the seller indicated... so I stuck an ESC in it and a receiver and put it on the ground. It moves! but it dosen't turn. Well, not reliably. And only in one direction, usually. I see, and can feel, that the clutches seem to be de-clutching, and the tracks can turn independent of the motor. I tried adjusting the linkage position, and played with endpoints in the radio. No joy.

So I pulled the gearbox out of the tank to have a look.

Now, the tank was turning reliably to the right, but not to the left. So I pulled the left clutch assembly out of the gearbox to have a look. I found that there are apparently two designs of the clutch. The earlier one seems to have one set of cork friction material. The one in this tank has 2 pieces of friction material, and an intermediate pressure plate. The construction of the shaft is also different, there are flats for the set screws already there, and the hex, that engages the plastic clutch housing, is held with a set screw, where on the "older" design, it's apparently just swedged to the shaft. In any case, I found that the hex was loose on the shaft. Very loose. Horray! I've found the problem! I put a little locktite on the set screw and tightned it down. NOw, I note that the flat is fairly long, and one could position this piece in about a 1/4 inch range, or so. I saw an existing mark from the set screw, and tried to hit that when setting it back up. Once i had it back in the tranmission, I pulled the other clutch out to check and see if that setscrew was tight. It was, and I re-assembled that side. Now, problem number one surfaces. If you look at the driven gear on the end of the clutch shaft, one side has more shaft sticking out that the other. I assume this is because I put the hex in the wrong spot on the first clutch. But, both clutches disengaged, and it -seemed- that they were in the same position, relative to the transmission housing.
Next bit of fun is re-installing the actuating lever assembly... when i removed it, I noted that the screws were almost exactly in the middle of the slots provided. This was my starting point when reassembling, but that resulted in a lot of play, so much that I couldn't reliably get the clutches to disengage. So after quite a bit of fiddling around, I got it secured with minimal play, but observable play, and both clutches seemed to de-clutch the same.

Ok, so back into the tank, and re-install tracks and down for a test run.

This time, neither clutch will disengage. Tank will only go straight. What really puzzles me, it seems like there is plenty of movement in the clutch housing to disengage, and I can, with fingers, disengage the clutch and move it independent of the motor.

So that's where I am, there's no real guidance I can find in any manual, and not much on the internet. So I'd love to hear any thoughts or experiences... and I will, actually, try and take pictures in the future while I'm fiddling around.
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a65l
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Re: Tweaking Tamiya twin clutch gearbox

Post by a65l »

So a little advance on the project. I have the gearbox out and was trying some other clutch assemblies to see if that made a difference. I note that with the gearbox removed from the hull, it seems to function perfectly. There's a little drag on the de=clutched side, but the weight of a finger will stop the sprocket from turning, so I would imagine that the weight of the tracks would work as well. Unless the hull is bent/tweaked and causing issues.... I don't know.
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a65l
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Re: Tweaking Tamiya twin clutch gearbox

Post by a65l »

Long delayed update.

I learned from another project that there are also brakes on the shafts. I disassembled and found the brake disks were soaked in oil. So, I made new. Out of gasket material. Reinstalled, tweaked servo and horn, and.... nothing. Still bad.

So I then installed the aftermarket track adjuster I had sourced from Schumo. Now it works! No idea why, but having proper tension on the tracks was the fix. So, on to painting and detailing. I need to find a cheaper substitute for Tamiya Dark Yellow... it took 3.5 cans to spray the Jagdpanther.... figure at least that many to do the KT.
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tankme
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Re: Tweaking Tamiya twin clutch gearbox

Post by tankme »

A good airbrush is your friend. Even a cheap one can lay down a base coat of paint cheaper than Tamiya cans. I actually have two airbrushes. One of them is a cheapo Harbor Frieght one that I paid like $12 for that I use for priming and basecoats as it doesn't need cleaning between paint colors because it uses interchangeable bottles. My nice Paasche Talon is for detail work.
Derek
Too many project builds to list...
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