Question for those who used to race Optima Mids

[fredswain]

I never had one so my memory is fuzzy. To the best of my memory, and please correct me if I'm wrong, the Optima Mid came with gear diffs and the SE came with ball diffs. I remember people running the ball diff in front and a gear diff in the rear. Did anyone here do that? What was the reasoning? What got me thinking about this is that many 4wd people today run much looser rear diffs than front and they seem to be getting more and more loose all the time. Are people today just figuring out what many people knew 25 year ago?

[DennisM]

Back then in the local club we were two kids running Mid´s and we did all sorts of tricks to get that smooth runnning geared front diff to cool the diff action down - Play clay? mixed with grease for one. What we aimed for was higher bite going out of the curve.
My mate had folks who worked in the city, so of course he ended up with ball diffs

[Coelacanth]

My OptiMutt build was a Turbo Optima Mid SE, so I can confirm that the car came with a ball diff, and that the regular Mids came with gear diffs. As for the mixing-and-matching fronts & rears, I can't comment...but I think many people liked the gear diffs because of the low maintenance. Those Optima gear diffs were excellent right out of the box and once you got the right grease inside, you could just forget about 'em. Maybe the ball diffs got slightly better performance, but required a lot of tweaking and adjusting.

[fredswain]

What I just thought was odd was that the local guys here who raced mids, used to swap the gear diff into the rear only. They still ran the ball diff in front.

[DennisM]

I guess it was for better grip when accelerating out of the curve - To minimize the push from the rear.

[rccars4sal]

Ive got 2 mids that we run in the street. One has a front 1 way, and gear diff in back. The other has both gear diffs. I much prefer the front 1 way, and a ball diff in back would be even better. Generally, I like my diffs a bit tighter than I can get from a gear unit, or no diff at all(1way).

[isobarik]

What I just thought was odd was that the local guys here who raced mids, used to swap the gear diff into the rear only. They still ran the ball diff in front.

yeah thats because when you put in the geardiff its supported by the 2 outer bearings, when using un balldiff in the rear the bearings just support the diff axle and outdrives the pulley/gear is not meshing alright due to the belt is pulling it on one side.

so balldiff in front ok in the rear not ok...

the front oneway is ok used it when i drove my TOMS in the swedish nationals in -97

if any want some spool action there is an kit for it , made for the spider series but they have the same internals so it fit inside an geardiff have forgott the part number dough.

mvh Isobarik

[DennisM]

What I just thought was odd was that the local guys here who raced mids, used to swap the gear diff into the rear only. They still ran the ball diff in front.

yeah thats because when you put in the geardiff its supported by the 2 outer bearings, when using un balldiff in the rear the bearings just support the diff axle and outdrives the pulley/gear is not meshing alright due to the belt is pulling it on one side.

so balldiff in front ok in the rear not ok...

the front oneway is ok used it when i drove my TOMS in the swedish nationals in -97

if any want some spool action there is an kit for it , made for the spider series but they have the same internals so it fit inside an geardiff have forgott the part number dough.

mvh Isobarik

[rccars4sal]

That makes sense about the belt pulling a ball diff spool a bit. So, the spool might run a bit out of conc from the out drives? I guess Ive never pushed my mids hard enough to tell. The yokomo yz870 diffs have 3 separate internal ball bearings that support the outdrives, and the center pully, so everything should run straight. I cant remember how the kyosho diffs are, but apparently not as good eh.

I built brand new gear diffs for 1 mid, and they actually suck. Dont know if some parts numbers are different,, but the front diff housing is not tightened 100% because if I do, it is very notchy.

[DennisM]

The gears might need breaking in.
Mount one side of the diff in Your battery drill chuck and give it some low revs to start with - after a couple of days, it´s butter smooth.
The geared Kyosho diff´s are some of the most smooth running diff´s only beaten by a well broken in Tamiya Hornet gearbox

[rccars4sal]

Oh hey, i bet nylon gears would work wonders in a notchy optima diff.

[HKS_TRD]

There must be a way to machine out the pulley and fit a bearing in it though not sure how much that would stabilise things

[EvolutionRevolution]

Oh hey, i bet nylon gears would work wonders in a notchy optima diff.

Try manually running a drill bit in the holes for the outgoing axles on the diff case halves - I've had diff cases which were a little bit off in that spot, causing the diff to feel notchy.