AMGRacer

Yep exactly like mine. Wierd huh. I now have the 6 gear diff installed but only have 1 race meet on it. I initially thought the diff might be leaking but it definately was not. I really cannot explain why it "thinned out". My Kyosho diff was consistent for months without a rebuild, it is a 6 gear style.

As to why the car becomes unstable it is due to probably the diff being inconsistent in its stiffness. A stiff rear diff gives less off power steering and more on power steering basically. If the rear of your car is changing this bias lap to lap that cannot be a good thing.

AMGRacer

Actually this is the set I purchased:



It comes with all the parts required to make either a complete front or complete rear 4 gear diff.

Part number is 33406.

C0NTENDER

iTrader: (1)

So after cleaning my car and putting it back together, I threw it on the scale. 1648g w/o body and fuel. I still have to make a couple of changes, so I will probably drop another 10g before the race season starts.

LILROBBY

amg, where did you get yours? i ordered mine from r-c model.com.

Fatboy Joe

Hi Rookie,

Sorry about the details I am using front one-ways. I just notice that everytime the rear diff oil thins out, my car is more unstable. I do not know the exact explanation for it but what I think about it is that when the oil thins out, it doesn't have much "limited slip" diff feel in it anymore that it doesn't push the car's rear tires to the ground as much as with fresh diff oil. My car will be so hooked and balanced when I put in fresh diff oil (50,000) in the rear diffs.

Fatboy Joe

Thanks for the info. Yes, I think that's the theory behind it. When installing the 4-gear diff, what oil do you put? Let's say 50,000 for the 2-gear diff, what about for the 4-gear? Should it be thinner? Thanks for the info

rod_b

I think the Team Drivers used 30K with the 4 gear set at the Sedan Nationals at Revelations.

AMGRacer

OK this is freaking me out. My car minus body weighs in at 1766g. This includes motor, battery, servos etc minus fuel. How in the heck are you guys getting yours so light?

I have:

Rody 3 port X12
Graphite towers
Lightened shafts
1100mah large battery
1 x 9550 futaba servo
1 x 3003 futaba servo
Airtronics 211 2 channel RX
Everything else stock.

I am like 120g overweight compared to the rest of y'all!!!!!!!!!!

S-T-R-l-K-E-R

FBJ - from what i have seen a lighter oil was used when the 4 gear set is intalled. i saw a couple of guys put together a 4 gear diff for the mtx-3. is it possible that we could use those gears?

AMGRacer

When both diffs were brand new and not run the 50K 2 gear felt looser than the 30K 4 gear diff that I built. They were somewhat similar however, so they are somewhat equivilent.

JLock

iTrader: (4)

For you guys that have your cars under 1700g, remember that ROAR minimum weight is 1725g with personal transponder. The car do not give you much area to add needed weight where you want to put it. Be careful about making it too light or you won't be able to run a ROAR race due to not meeting the minimum weight requirement (food for thought).

Solara

iTrader: (17)

Fatboy Joe..........if you are running front 1-way (assumed you are running some mid-large size track)....your rear diff must be toward STIFF to SOLID condition..........if you look at most 235mm Serpent IMPACT or MUGEN chassis that run front 1-way stock, they only come with a SOLID REAR stock........so what you are saying about your rear diff oil getting light and car is getting hard to control does match the theory of the front 1-way rear solid equation....the idea is...your front wheels are spinning almost in all condition (since no DIFF to slow them down), and IF your rear diff spin freely with a little or less diff to slow them down itself, it is like your driving a car with NO BRAKES....so the car will push and slide entering or exit corner, and in your case, overpowered and causing fish tail (if traction on the track is poor....)

If you can get the 4 gear diff, yes, that is your best answer, mating with 30K grease (or anything a little lighter then what you used on your 2 gear)........more gears inside the diff, the more CONTACT between both side gears...before, there are only 2, not is 2X = 4....so, if you used the same grease (50K), it will make your diff almost hard solid....so I would try the 30K first, beside, you can always ADD more, but removing your old grease are PAIN.

I don't know what grease you guys tried before, but since I raced my Serpent Impulse back 5 years ago, I only used 2 grease....1, it is from MUGEN...good stuff, but big bottle and pricy, like $20 plus each....and lately I changed to this one.....Yokomo, hard or medium grease.........basicly the same thing as Mugen, but much cheaper and much easier to put them on to the diff (Mugen is a bottle, take forever to see those 50K grease drop to the diff)...and Yokomos can be purchase at TOWER and much cheaper....the cars I used these grease are Impulse and HPi SNRS4.....and I hardly experience any grease leaking or getting THINNER after a long run.....

http://www2.towerhobbies.com/cgi-bin...?&I=LXCNK5&P=7

Solara

iTrader: (17)

For those who is interested in the R40 light weight diet........have you guys think about the weight of the throttle servo?
I am not saying it is going to work....but I remembered back to the old times.....they did use some chopper servo (which is smaller in size = lighter weight) for the throttle servo...

Again, the idea is...get a lighter/smaller/micro servo that has equal or a little LESS speed/torque and use it for throttle.....now a day, what servo cannot pull a 12 engine throttle linkage...but that might be easily shaved 15-20 oz from the car.

Then...use 5 AAA cells and without the ON/OFF switch....that is good 10-15oz total (I think...)

The stock carbon upper plate.........quite a lot of area that we can cut or drill....

Last....drill some holes onto the stock purple chassis.......but not too many (since the chassis is weak enough already)....but I would not recomment to do that unless you are sure you are a very good driver on the track (my stock SNRS4 chassis is like a Z shape now...)

Just some idea.....

rod_b

I was thinking about trying the Yokomo Med diff grease (mostly because it doesn't leak out) and the 2 gear set. The diff grease is supposed to be somewhere around 75K. Do you think it's too stiff for the rear?

As for making the car lighter, I was thinking about removing some material from the bulkheads. They're so bulky and there is so much support all over that a bit of material off of them shouldn't weaken the car. Also thinking about drilling some holes in the spur gears. Not that this would save you a whole bunch in weight but I've seen it done on the old Impulse spurs to try to lighten them up to get a little better acceleration response. Holes in the chassis sounds a little extreme to me...especially if you have no way to balance it. Anyone else with any ideas?

C0NTENDER

iTrader: (1)

Just a question, isn't the 1725g weight requirement with the body and fuel included?