Hey guys. I've purchased a month ago a Brushless Mustang and a Brushless Ken Block, one for me and one for my father.
We both went to the same track, running with the same setup and my Mustang tends to do a 180º everytime I'm in the middle of a turn. When I drive his Ken Block, I can do exactly the same and the car stay 'glued' to the track.
After many suspensions changes - nothing managed to solve that issue - we decided to take a look at both cars differential and transmission. We noticed that when we spin the rear wheel of his Ken Block, the opposite wheel spin in the opposite direction and the main transmission shaft stays still, not turning at all. When we do the same with my Mustang (manually spinning the wheel with the same amount of power), the opposite wheel doesn't turn and the main transmission shaft starts turning, spinning the front 2 wheels.
The same occours if we turn the front wheels, the opposite wheel of his car will turn and the main transmission won't and mine will turn the transmission and not the opposite wheel.
That behavior changes if we turn the Ken Block's wheel faster, then the transmission will turn and the opposite wheel won't, just like my Mustang (slow or fast).
We jumped in the conclusion that there is something different about our differentials, maybe mine is using a heavier oil, maybe leaked, and so on.. Any thoughts ?
I'm no expert at all and relatively new to RC cars and trucks.
My 1/16th Slach came with the front differential full and the rear totally empty. sense i have filled up the rear it does handle differently however my tires are also worn alot more now.
You're onto something. I don't know about what weight oil is supposed to be in each diff, but it is spelled out in the manual. My Slash has heavier weight in the front than rear. I have also found that the shock oil and spring rates can be different(but you addressed that). I have also found that a new car can have two shock/spring combos work very differently when supposedly they are set up the same. Maybe an assembly issue. Regardless, if you turn one wheel of one diff and it turns the wheels of the other diff, then it has relatively thicker fluid. A "looser" diff will generally turn the wheel directly across. Personally, I might prefer a thicker diff fluid up front and lighter in the rear, but both diffs not tight, say with 50K up front and 30K in the rear? Or both with 30K, or 30K up front and 10K in rear just depends and to me is part of the fun with experimenting on set ups? I only wish Traxxas had quick change diffs like real race cars.
Also, you can complicate/help things by adding a center diff.
I'll have a look at my diffs, 99% sure that will solve it's handling problem. I think I'll try to put 10k on the rear diff and see how things go...
The weird part is that I manage to drive the car 10 times better when using an old, less grippy tire... Never thought I would have a "too much traction" problem !
4wd cars don't handle as a normal rear wheel drive car. The front is pulling while the rear is pushing. High traction tires on the rear can cause the rear of the car to get unsettled when they try to bite/break loose/bite/ break loose, etc as the rear diff tries to drive both tires at the same rpm.
I also had a handling problem under full acceleration, wouldn't steer straight, and with LiPo's, I couldn't keep the front end on the ground. I did a complete tear down, installed a center diff, changed the diff oil weights to what I have in my Slash 4X4 with the Slayden setup. One of my diffs was dry from the factory, which could have been part of the problem. I'm running a mix of 30/10K in front 10K center, and 10K rear, basically a LOT of diff action. Now with high grip tires, My Boss and KB Fiesta go where I point them, and steer very well!
I'll try anything once, maybe twice!
So I opened the differential, personally I think it was a bit low on oil, so I did a complete clean up and filled with 30k oil (just as stock). Almost no change at all on it's handling problem... the rear wheels still tended to slide and do a 180º in the middle of any high speed curve.
Then I decided to loosen up the slipper clutch and that my friends, solved the problem! Now the car is very responsive, I can drive the same way as with the Ken Block, entering and exiting high speed corners without making a 180º every single time !!
Another way to fix that problem is to roll into the throttle. The looser slipper clutch is taking away some of the motor acceleration, reducing the chances of the wheels breaking free.