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April 6, 2011

DESC410R Centre Diff Option

Filed under: News,Tricks and Tips — Tags: , — Stuart @ 2:42 pm

The DESC410R Short Course truck comes with a locked centre drive unit which can easily be turned into a centre differential. Purchasing the optional TD210031 ‘Conversion set for centre slipper-diff’ gives you all the parts that you need to replace the ‘locker’ with the diff parts.

ttt-desc410r-centrediff-parts The standard ‘locked’ setup will put all the available power down to all wheels under acceleration (depending on slipper settings) and is the most agressive setup, best suited to smoother tracks with high traction. The centre differential works by limiting the power transmitted to the end with the most load to prevent it breaking traction. Running high powered motors – especially the 550 motors popular in the 4WD SC class, not only puts strain on the transmission but can make the truck hard to drive over rough surfaces or in low traction conditions. The centre diff will help smooth out the power delivery, absorb bumps and jumps to keep the truck headed on desired course.

Building the centre diff on the DESC410R uses the same differential parts as used in the other differentials on the truck – which have been bundled together in the slipper-diff conversion set specifically for the DESC410R.
Building the slipper-diff is similar to the other differentials on the truck. The truck already comes supplied with the X-ring seals which require some lubrication – so if you didn’t already do this when building the car you’ll need to disassemble all the parts and make sure to lube these X-rings and the shaft / drive cup that will ride in them.

ttt-desc410r-centrediff-oilxring Put some diff  oil where the Xring will sit ttt-desc410r-centrediff-eclip

It’s a good idea to test-fit the larger 14 tooth gears on the hexagonal shafts before reassembly as they can be quite tight. Tight or not – you can still fit them by tapping them into place but it will make disassembly more time consuming which is something you’ll need to think about if you’re wanting to regularly swap between running a diff or locked centre.
You can use some fine abrasive paper to take some of the black coating off the hexagons which should be just enough to allow the gears to drop into place.

ttt-desc410r-centrediff-sand You can lightly sand the Hex’s to make assembly/rebuild quicker ttt-desc410r-centrediff-tap Tapping the gears down gently with the box spanner

It’s a good idea to put some diff oil around the output shafts under the gear before pressing it onto the shaft as it can be hard for the oil to work its way back there on its own.  Likewise – if you’re going to run some very thick oil it’s a good idea to partially fill the diff casing with oil before dropping the spider gears into the housing.

ttt-desc410r-centrediff-oilbehind Put some diff oil behind the gears ttt-desc410r-centrediff-fill Some diff oil before dropping the spider gears in

Top-up the oil to just below the top of the spider gears and tighten the diff together using a cross-pattern to ensure the diff casing goes together straight.

The centre differential will help protect the drivetrain from shocks but you still need to use the slipper in combination with the differential.  Testing the slipper in the truck will be hard since the newly installed centre differential components will mask the effect of the slipper – so setting the slipper as suggested in the slipper build guide ( and testing in the hand is a good method.

Tightening up the screw that secures the slipper-side drive cup can be tricky since you need to clamp both the opposite drive cup and the diff body itself to stop them spinning.  You can use one of the included slipper wrenches in the opposing drivecup to give more leverage and clamp both parts with one hand as you tighten the screw down.

ttt-desc410r-centrediff-full Centre diff filled ttt-desc410r-centrediff-tighten Tightening down the drive cup

Centre Diff Oil Effects:
The centre differential gets a real work out and depending on track conditions, you’ll want to run different oils to get the optimum setting. Generally you’ll use a thicker oil in the centre than you’d use elsewhere and a baseline of around 20K CST is a good starting point. Too light an oil will be obvious as the truck will lean back on hard acceleration and allow the front wheels to spin with the tyres ballooning excessively, meaning the truck is slow to take-off. Running a very heavy oil such as 50K CST will have very little ‘diff’ action and allow for hard acceleration.

Thinner oils are more suited to bumpy and low-traction conditions. Off power there will be more steering whilst on-power there will be less steering. The tendancy for the rear end to wash out under power will also be reduced – so you can be a little less gentle with the throttle, making the car easier to drive.

Thicker oils will feel progressively closer to the locked centre setup. With more drive to the rear wheels there will be more chance for the rear to break traction. Over uneven terrain or slippery surfaces the truck will be more reactive and potentially harder to control – especially if very fast motors are used. On-power steering will be improved.

Because braking is applied to the spur gear, rather than having a mechanical setup as in a 1/8th buggy, oil thickness will also have an effect of braking. A thin oil will prevent the truck from nosing-down too much under braking but could reduce the effectiveness of the brakes too much on high traction surfaces where you’re trying to late-brake into corners.  Like everything, you need to find a balance that suits your driving style and the track you’re running on.


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