I bought a complete set of Hyper ST diffs before. They work just as good as the other 1/8 diffs. I have an assortment of Ofna diffs; Yper 7/8/8.5/9, Hyper ST, violator/mutilator etc.

Should i have any oil between the bevelpinion and diff?

Not oil, but a little bit of grease is a great idea; I like the tamiya ( white lithium ) grease, but anything fairly 'sticky' will work fine- like that 'gorillasnawt' you see on ebay etc, or automotive grease even. Just to lube the gears and keep them smooth really, doesnt have to be anything too special or too much.

can i use any kind of motor pinion that fits 5mm shafts?

will my diffs be broken if i dont have the grease?

Depends what you mean by 'any kind'. if you use a MOD1.0 spur gear, you need a MOD1.0 pinion gear ( same deal with 32pitch spurs and pinions ). If you mean materials though, then hardend steel pinions are the best, or hard-anodised aluminium ones. Mike sells arguably the best hardend steel pinions around, then there are also the RRP ( robinson racing ) pinions, Novak's pinions & a few other brands- hardend steel is the best to prevent a steel spur from eating the pinion within a few runs; standard aluminium ones like you find on ebay wont last very long at all.

Your diffs wont break if you dont use grease, but they will probably wear down a bit quicker and be noisy- any kind of grease can be used, so long as its a bit sticky and preferably symphetic. That tamiya grease is easy to find on ebay, as are automotive greases used in 1:1 car gargages- check out your local hardware store or shop that sells stuff for 1:1 cars.

Is it stupid to use a plastic spur? Mike have 44t kyosch spur, but it is plastic.

Plastic spurs are fine- some people would say plastic is better because its quieter, and you wont get worn-out gears so quickly. I prefer the idea of a metal pinion and plastic spur, for the reasons I just said- my emaxx and txt-1 do it that way and I've never stripped a spur unless the motor came loose.

So with a plastic spur a can use any steel pinion?
And if i use the ofna steel spur, how do i know what kind of steel pinion i can use?

With a plastic spur you can use pretty much any pinion material, though the harder the material the longer it will last ( I've seen aluminium pinions worn down by nylon spur gears quite baddly ).

If you use the ofna steel spurs, then a hardend steel pinion is the best choice- one of Mike's or a RobinsonRacing being the most popular ones Im familar with.

Thanks

I dont think the kyosho spur will fit my ofna spider diff.
The spider spur have 6 screws and standard have 4. Look:http://www.amainhobbies.com/product_...-46T-Spur-Gear

it should work if i mod. my FLM chassi and use a bygger pinion

i think i will start like this..


Differential Ratio: 4.3
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 46
Pinion Tooth Count: 10
Total Voltage: 18.5
Motor KV: 2200
Tire Diameter (inches): 5.84
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.006
Spur/Pinion Ratio: 4.6 : 1
Total Ratio: 19.78 : 1
Tire Circumference (inches): 18.35 inches (466.01 mm)
Rollout: 0.93:1
Total Motor Speed: 40700 RPM
Vehicle Speed: 35.75 mph (57.43 km/h)
Effective KV Value: 2200
KT constant: 0.61 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

To be honest, that seems a bit slow for that kind of motor and 4S?
Do you want to gear it for that speed?
My main concern would be the motor, it could be under to little load and might get hot.

5s...
Please help me. I can use a bygger motorpinion. i would like the truck to be fast, strong and not hot... if k kan run 75, please help me with suggestion.

Right, 5S, got that wrong.
But there is not much to help: Use a bigger pinion/smaller spur gear if you want to go faster.
I geared my g-maxx for 75-80 kph and it runs fine.
But easiest way is to just gear it for your wanted speed (75 what? kph? mph? huge difference!) and monitor the temperature of motor, esc and batteries. I think everyone who bilds a truck like your's or mine should have a infrared thermometer.
Building a truck for severel hundred dollars, motor/esc combo for another 200-300$ but but saveing on a thermometer that you can get for 10-30$ allways seems a bit strange to me.
Because it's one of the easiest ways to check if everything runs cool and healthy.