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Old 12-07-2004, 05:47 PM   #1
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Default diff tuning in 1/8th scale

I know the most common set ups. What I don't know is why are they the most common set ups. Can someone please explain what a light weight oil, or heavy oil will do to change the characteristics of the buggy?

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Old 12-08-2004, 12:19 PM   #2
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The thicker the oil the more the diff will act like a limited slip.

In my buggy I use 5000wt in the front, 8000wt in the centre and 3000wt in the rear.

If you lighten the front wt, then your car will have more on/off power steering (easier diff action) but less on power acceleration through the corners. If you increase the front wt then it will have awsome acceleration out of the corners but your car will have a push.

The rear diff you always want lower wt than the front. If the track is really loose or sandy then use low wt (like 1000wt or even 500wt) if the track has good traction then you can up the wt (2000wt or 3000wt). So lower wt will give you more steering but less corner acceleration, and vice versa for heavier wt.

The centre diff is to tune the way the car handles bumps and jumps. You always want a higher wt in the centre then both the front and the rear. If you have a high wt in the centre (like diff lock 100000wt) the car will accelerate better on the straights and jump better BUT you will kill clutch shoes and clutch bearings and will flame out easier. The centre diff acts like a buffer when the car makes hard landings or the drive train gets impacted in any way. If the diff is locked something has to give and the clutch shoes, clutch bearing and clutch bell and engine take the impact. Using 8000wt will give you a good comprimize between good acceleration/jumping and breaking your car.

In a nut shell, use 7000 or 8000wt in the centre for any track and change the front and rear for steering or acceleration.
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Old 12-08-2004, 12:25 PM   #3
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Another way to explain center diff fluid weight is that thinner oils will "unload" the rear causing extra front tire spin in the front. Going too heavy in the center will give too much positive rear drive which can be hard to handle during acceleration.
The previous recomendations on fluid weight are generally accepted as spot on.
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Old 12-08-2004, 02:04 PM   #4
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Davidka, that's exactly right, if the centre diff is locked the car will want to lift the front end off the ground and you will have zero control down the straight. With some centre diff action the car will stay flat under acceleration and maintain control.

Another setting that I've found that makes a HUGE difference is droop settings. Less droop on the front on smooth tracks, the cars front end can only lift so high on acceleration keeping the car flat and allowing more power to the ground. If the track is bumpy then add some droop and it will take the bumps better. On the rear less droop will allow the car to pivot (drift) in the corners under braking (won't unload to the front as much), with more droop the car will brake harder (loads up the front wheels more, better for loose/sandy tracks).

Also, always set your brakes with more rear bias (i.e.: more rear brakes than front). This will act like a one way, the front wheels will keep turning under braking allowing control, and the rears will lock up allowing the car to pivot around corners quickly (drifting).

I've found that the fastest way to get around the track is to ALWAYS keep the car in motion, master the art of drifting the car around the corners and you will see your lap times go down significantly.
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Old 12-08-2004, 02:51 PM   #5
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Thanks guys. Exactly what I was looking for.
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Old 12-08-2004, 02:59 PM   #6
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Quote:
Originally posted by ddesros2
Another setting that I've found that makes a HUGE difference is droop settings. Less droop on the front on smooth tracks, the cars front end can only lift so high on acceleration keeping the car flat and allowing more power to the ground. If the track is bumpy then add some droop and it will take the bumps better. On the rear less droop will allow the car to pivot (drift) in the corners under braking (won't unload to the front as much), with more droop the car will brake harder (loads up the front wheels more, better for loose/sandy tracks).
Hey ddesros2, what is meant by droop? I'm fairly new to all this chassis setup stuff.
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Old 12-08-2004, 07:48 PM   #7
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Droop is how far the suspension arms will travel when the car is lifted off the ground. In the attached picture the tire on the right has more droop (sits lower) than the tire on the left. On a really bumpy track the more suspension travel, the better (more droop) on a smooth flowing track less droop is better.
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File Type: jpg droop_8th.jpg (30.5 KB, 202 views)
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Old 12-08-2004, 07:50 PM   #8
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You can set the droop by adjusting the small set screw in the suspension arm. See pic.
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File Type: jpg set_droop.jpg (27.7 KB, 158 views)
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Old 12-08-2004, 07:56 PM   #9
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Back to the diff settings, after 2 or 3 good race weekends I will rebuild my diffs, pulling them apart, checking for any broken parts then using new diff seals and putting fresh fluid back in (fill up to the cross of the spider gears). Here is a pic of fresh diff seals and fluids ready to go in my MBX-5 for my next re-build.
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Old 12-09-2004, 04:51 PM   #10
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I was wondering what that set screw was for.

Also, do you have a pic of how far to fill up the diff cup with oil?

Thanks!
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