Gear diff or Ball diff..?

[Aire valley]

What are the advantages, one over the other..? What type of track favours one diff over the other..?
General "rule of thumb" guidance would be appreciated..

[Danny Harrison]

Originally Posted by Aire valley

What are the advantages, one over the other..? What type of track favours one diff over the other..?
General "rule of thumb" guidance would be appreciated..

General rule of thumb is that a ball diff is the better option in low traction, with similar performance in high traction.

Gear seems to require less maintenance is is much less prone to failing. Transmits more drive. Takes more time to make set up changes but is easier to reproduce.

Ball diff is probably easier to drive and quicker to fine tune. A little safer and less aggressive. Needs rebuilding fairly often and is harder to achieve the same feel every time.

[Oscar]

Originally Posted by Danny Harrison

Ball diff Needs rebuilding fairly often and is harder to achieve the same feel every time.

Really??
I don't disagree that once a ball diff reaches the "knackered" stage, it makes a difference to the car, but to say a freshly rebuilt unit feels different each time...
Maybe you are correct, but since starting racing in 1986 it's not an opinion I have formed

[Danny Harrison]

Originally Posted by Oscar

Really??
I don't disagree that once a ball diff reaches the "knackered" stage, it makes a difference to the car, but to say a freshly rebuilt unit feels different each time...
Maybe you are correct, but since starting racing in 1986 it's not an opinion I have formed

What i meen is, you are relying on 'feel' with a ball diff to set it, so setting it exactly the same each outing takes some fiddling.

With the gear diff, I know that putting 10k in will produce the exact feel it did last time, no messing.

[NeilRalph77]

Does the viscosity of oil not reduce if it's driven for a long time? so if you'd run 10k for a while without changing it and then put fresh in it would feel different anyway? Thus negating your argument.

But yeh generally ball low grip, geared high grip

And a well built well set ball diff doesn't require rebuilding that often!!!!

[Danny Harrison]

Originally Posted by NeilRalph77

Does the viscosity of oil not reduce if it's driven for a long time? so if you'd run 10k for a while without changing it and then put fresh in it would feel different anyway? Thus negating your argument.

But yeh generally ball low grip, geared high grip

And a well built well set ball diff doesn't require rebuilding that often!!!!

It doesn't if your putting fairy power through it

Just going on my limited experience, I'm sold on gear diff. The viscosity will change over time, but each rebuild will produce the exact same feel. Mine have been going 2 months since last rebuild and are still dead smooth.

[RogerM]

My rule of thumb is ball diff everywhere LOL

Seriously though so long as you can get all the forward drive you need from a ball diff it will always be safer in feel than a gear diff.
Only place I would consider running a gear diff is ultra high grip (say Silverstone indoor) where you do have to nip up the ball diff to be sure of getting all the drive available which does dull the diff feel a little and increase wear rates.

The trick to ball diffs is;

1) use the right greases, especially on the main balls. I have found none better than the Xgear XGS153 (now listed as K.96506) available from all good Kyosho stockest.

2) good quality balls, I'll now only use either genuine Kyosho or RudeBits carbide balls. There are other really good ones out there but those are my preferred ones.

3) the initial tightness on build - best way I've found is to lock the two outdrives together and set the tightness so that when gripped between finger and thumb you can just (with real effort) force it to slip slightly - don't force it too much!

4) Break in - I run 2mins per side with the other wheel off the ground (hold arms to make driveshafts straight to reduce vibration feedback during break in) then swap to the other side and repeat. Normally find that using max throttle trim on my Sanwa radio is about right, something like 20-25% throttle is enough.

5) The slip test - after break in is complete I check the diff by putting a drive into the screw head and turning the opposite wheel between finger and thumb with a relatively light grip until you feel the rotation go dead - the same feel as you get when you spin a nut down a clean bolt and it just bottoms out. Don't over do it. I then add about 10 degrees extra.

6) Recheck after each of the first 5 runs if it was with all new components, 2 or 3 runs if reusing components.

7) When stripping the diff down always sand the main plates, even if they look ok, until an even dull shade in the ball contact areas. I tend to use 2000 grit and motor cleaner to wet the paper and moving the plates over the paper in figure of eights turning the plate through 60 degrees after about 10 figure 8s.
If you find that after two complete rotations of the plates using the above method that you still don't have nice dull surfaces and/or ball tracks still showing it's time for new plates.

Tune to suit driving style from there.

Perfect ball diffs every time

[Aire valley]

Thanks for the advice..and Roger for the detailed building advice...
The reason I asked is because I was given the same advice previously, yet, after I obtained a gear diff and tried it in my B4.1 1/2..... indoors, bare floor and some carpet (fairly slippy) it felt fine and easier to drive, but ,outdoors, grass and astro it felt weird..!