kyosho geardiff limitations

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alcyon
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kyosho geardiff limitations

Post by alcyon »

I got a question regarding the gear diffs for 80s kyosho cars like the optima.
Nowadays with the availability of modern diff oils, i tried using some hard oils like x ray 300000 for my rear diff and ride 45 shore putty for the fronts. What i noticed was the diff action wasnt entirely consistent like modern gear diffs. It felt like there was a little extra resistance on some areas and less on some .
I deduce it must be because of the diff design that uses 2 inner bevel gears instead of 4, so the oils is squuezed where the gears are and not squeezed where there are no gears. I noticed this when powering out of corners so i hand tested the diff action and it does feel that way. Am i making any sense ? Has anyone else had a similar experience with these gear diffs ?

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Re: kyosho geardiff limitations

Post by terry.sc »

Adding extra planetary gears wouldn't make any difference. Modern gear diffs are designed to use oils, so they have tighter tolerances and better quality machined or moulded gears. The old Kyosho diffs use cast pot metal gears, which aren't smooth like a modern diff even when new as the gears aren't accurate enough due to the production process, it's why the diffs when new have plenty of play in them. The reason the diff action changes as it is turned is because the gear mesh gets tighter and looser as the gears rotate, this means it's easier for the gears to squeeze the oil out of the looser mesh and harder to squeeze the oil out of the closer mesh.
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Re: kyosho geardiff limitations

Post by isobarik »

Old optima used an sticky Grease in the diffs tried that ???

Mvh isobarik

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alcyon
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Re: kyosho geardiff limitations

Post by alcyon »

isobarik wrote:Old optima used an sticky Grease in the diffs tried that ???

Mvh isobarik
I tried many kinds of greases..but most melts very quickly. Worse still even the ride putty also melts..then redistribute itself in the areas where there is least pressure..the empty space in between gears. All my efforts become null and void. The xray 300000 oil lasts though..because it becomes kind of semi liquid and sticks everuehere. Unfortunately the diff action is not consistent as i described.

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Re: kyosho geardiff limitations

Post by rccars4sal »

I think the only really smooth kyosho gear diffs from those cars, optima lazer,, are those that have been broken in by long running and lack of grease. Seriously, the heavier and tighter they are packed, the worse they will get. Its especially bad using new internal gears. One trick to try might be to break in a set of new gears using a power drill to spin the shafts, and toothpaste inside the diff housing to polish the gear surfaces. Then clean out and try re packing with grease or diff fluid. Never going to be real perfect though because of only 2 spider gears, and leakage

I like to build my gear diffs using heavy grease and then just let them break in from running. A high powered buggy should be able to overcome the inherent notchiness when running.

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Re: kyosho geardiff limitations

Post by alcyon »

rccars4sal wrote:I think the only really smooth kyosho gear diffs from those cars, optima lazer,, are those that have been broken in by long running and lack of grease. Seriously, the heavier and tighter they are packed, the worse they will get. Its especially bad using new internal gears. One trick to try might be to break in a set of new gears using a power drill to spin the shafts, and toothpaste inside the diff housing to polish the gear surfaces. Then clean out and try re packing with grease or diff fluid. Never going to be real perfect though because of only 2 spider gears, and leakage

I like to build my gear diffs using heavy grease and then just let them break in from running. A high powered buggy should be able to overcome the inherent notchiness when running.
Well, what you said is true if you want smooth loose diffs front and rear. The thing is, the optima mid has only 3 degrees of caster in the front arms if used with 0 degree c hubs. If you have the front and rear diffs with same looseness, the car tends to be unstable going into and out of corners. In contrast, modern cars like the XX4 onwards have bigger amounts of caster so the F/R diff settings can more or less be the same. For the Optima Mid and Lazer, I feel the fronts have to be substantially harder than the rear in order for the car to drivable at high speeds.

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Re: kyosho geardiff limitations

Post by fredswain »

How are you keeping the oil in? They don't seal like the new ones do.
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alcyon
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Re: kyosho geardiff limitations

Post by alcyon »

fredswain wrote:How are you keeping the oil in? They don't seal like the new ones do.
The trick is to use very thick oil like 300000, and not fill too much, like half only. That way the pressures never build up so much that it forces its way out of the easiest path for it to flow, through the outdrives.
For the front I use Putty, which is kind of play dough like.

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Re: kyosho geardiff limitations

Post by rccars4sal »

Over the years I have experimented with shimming the internal gears, heavier grease, lighter grease, new gears with old, nothing has made much of a difference. Perhaps another option would be to machine a bit more caster into the ends of the suspension arms? Or, possibly another set of internal gears might fit the optima diff case? Also, Im pretty sure the kyosho c hubs have some caster in them. Its the yokomo zc413 that have no caster, and are a direct fit for kyosho.

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Re: kyosho geardiff limitations

Post by Coelacanth »

Guys, I'm not sure how much you want to experiment with modding an Optima/Optima Mid front end to increase kickup/caster, but I selected these Tamiya TA-05 parts for my OptiMutt build, they increase the caster noticeably. It might be an alternative to adding kickup to the chassis plate. What I haven't tested, however, are the CVD/dogbone lengths, as the OptiMutt car is a RWD-modded Mid. But the price of the upgrade items isn't expensive so it might be worth a try.

http://www.rc10talk.com/viewtopic.php?f=30&t=30216&start=62

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Re: kyosho geardiff limitations

Post by terry.sc »

The standard OT-55 C hubs have more caster built in than the OT-47 hubs. If you want more caster there are a couple of quick fixes. Trimming the front edge of the top deck will allow you to tip the front gearbox back and to add washers under the front of the gearbox. There is also replacing the front pivot pin mounting plate with a new one that raises the front holes for the pivot pins, adding more front kick up.
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Re: kyosho geardiff limitations

Post by alcyon »

Coelacanth wrote:Guys, I'm not sure how much you want to experiment with modding an Optima/Optima Mid front end to increase kickup/caster, but I selected these Tamiya TA-05 parts for my OptiMutt build, they increase the caster noticeably. It might be an alternative to adding kickup to the chassis plate. What I haven't tested, however, are the CVD/dogbone lengths, as the OptiMutt car is a RWD-modded Mid. But the price of the upgrade items isn't expensive so it might be worth a try.

http://www.rc10talk.com/viewtopic.php?f=30&t=30216&start=62

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Those look like MPP lazer ZX arms.
If I am not mistaken the TA05 C hubs are a alittle wider than the 12mm space the Lazer arms provide. But still the TA05 c hubs as you mentioned may be a cheaper option. Ahh, I remembered now,, I experimented with these hubs before, they were cheap china kockoffs but had the same dimensions, I recall they were a failure for off road..Why ?
You see, most moden c hubs are designed for the user to be able to pull out the CVD without removing the knuckles, so they have a section that is widened to allow the CVD to be pulled from the rear. The problem is this wider area will interfere with Suspension arm movement, when at high ride height which is required for true offroad use. That's why I ditched these modern c hubs and went to all the trouble to make my own.
To use the TA05 c hubs, the arm shape needs to be like this on the inner c hub mounting area.
Image
I will now get a pair of arms made for the TA05 c hubs. Perhaps I will get the 6 degree version if available.
Coelacanth, for your case, if you set the ride height low and droop low, you wont face any problems.
I guess making a castered C hub shouldn't be a problem. When I made my strong PEEK c hubs I was just trying to stop breakage and allow the use of easier to get modern ZX5 knuckles, did not think about caster. Well looks like a redesign is in the pipeline.
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Like what terry.sc said about shimming the front gearbox, will work if you run indoors, but outdoors with loose sand, it will allow sand to get into the front gearbox then get sucked in to the rear. So for where I am running this car, its not feasible.

The OT-55 do have more caster but I will have to use OT-16s which are expensive or grind down ZX-5 Knuckles which will reduce the thread area and durability of those knuckles. I am going back to ball diffs and will re test to see if they feel better than the gear diffs on low traction.
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Now back to gear diffs
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this is how I stuff the fronts with putty.
Unfortunately after about 12 packs, the putty seem to melt and redistribute itself to the easiest low pressure area, in between the small 2 bevel gears !

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Re: kyosho geardiff limitations

Post by ron »

well all i can say is thats the way she rolls, its limited by design, you can not do much there, yes the process could have been better but that is how it was, what you don't see can't hurt you. if parts or complete modern diff can be substituted, it would be great but it has a pulley molded in. not to worry, these mids, ultimas will purr like a cat when kyosho re-releases them again.

oil is good if the operation is smooth and it stays in, but here it will run out from the bearings/axle. You could use molybdenum high pressure grease, it has graphite in it, grayish black color, for real car application. Since it can withstand high temp and pressure, it will not be squeezed out from between the gears.

Since there are just 2 spiders in there, they take twice as much load as opposed to a system with 4 spider gears, thus more pressure between the gears and the lubricant gets squeezed out making them run dry.

Loving the blue c-hubs and knuckles, Coelacanth :mrgreen:

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Re: kyosho geardiff limitations

Post by Coelacanth »

alcyon wrote:Those look like MPP lazer ZX arms.
If I am not mistaken the TA05 C hubs are a alittle wider than the 12mm space the Lazer arms provide. But still the TA05 c hubs as you mentioned may be a cheaper option. Ahh, I remembered now,, I experimented with these hubs before, they were cheap china kockoffs but had the same dimensions, I recall they were a failure for off road..Why ?
You see, most moden c hubs are designed for the user to be able to pull out the CVD without removing the knuckles, so they have a section that is widened to allow the CVD to be pulled from the rear. The problem is this wider area will interfere with Suspension arm movement, when at high ride height which is required for true offroad use. That's why I ditched these modern c hubs and went to all the trouble to make my own.
To use the TA05 c hubs, the arm shape needs to be like this on the inner c hub mounting area.
Alcyon, as I stated in my post and in the build thread I linked, those are Kyosho Maxxum arms, not Lazer arms. The TA-05 hubs & carriers fit perfectly, requiring no modification to the arms. It was the Lazer carriers I used for my Barney car that required minor filing with the Maxxum arms; I only had to file a small notch in the upper surface of the Maxxum arms to allow the Lazer carriers to move enough to get the suspension travel I wanted. The notch only needed to be filed in the front half of the arm, as the trailing edge of the carrier didn't obstruct with the rear half.

I really like the Maxxum arms for the Optima front end; they're really beefy and give you options to widen your front track, or keep everything else stock. They can be swapped right in for stock Optima/Turbo Optima front arms.

Sorry if this seems off-topic but I shared these mods as kickup and caster angles came into the discussion. 8)

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Re: kyosho geardiff limitations

Post by alcyon »

not to worry, these mids, ultimas will purr like a cat when kyosho re-releases them again
Oh I sure hope so ron, and if they fix the problems with their old gear diffs, even better ! Kyosho did improve the scorpions gear diff right? any one got pics of the scorpions re re internal gears?

Coelacanth, I have ordered a set of Yeah racing 4 degree hubs , they were cheap and when I get them, I will experiment on allowing maximum arm travel . Yes its kind of off-topic, but since the geardiff problem cannot be resolved, increasing the caster angle should help keep the car more stable, hence a much harder front diff will not be needed. I notice my friends caster racing S10B buggy having almost the same diff looseness F/R, but he has a large castor angle, like almost 10 degrees, that probably explains his cars stability. In fact I noticed all the modern buggies have much more castor than the standard Mid or Lazer ZX.

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