Team Driver Tips: Xray Diff Mods for XB2 & T4

Oil change or adjusting the diff's oil viscosity can be a pain sometimes. Our team driver Aleksi Reiman has come up with couple modifications to make it a bit easier. These mods will make it easier to fill the diff same way time after time.  Reiman has modified his Xray T4 diff with one  and Xray XB2 2WD buggie's diffs with these both two modifications. Both mods are such which is recommended to do for new parts and doing them is completely on the owner's responsibility.

Modification 1: XB2 and T4 Diff cup's thread saver

Many has come across the case where the thread on the diff cup gets worn out from time to time.  Usually there are two different ways which will cause the thread stripping.  First is over tightening.  For example with electric screwdriver that happens quite quickly (bet that many has done this). Second is the case where the diff oil ends up in the screw's hole and flows on the bottom of it. When you are tightening the diff  the oil on the bottom will make a so called hydrolock and the screw bottoms up before than it should and causes the over tightening.

To prevent this hydrolock of happen you can drill out the screw holes with 2mm drill.  This will prevent the situation of oil filling the screw hole. When hole drilled the oil can flow through and the screw can be normally tightened all the way.  
Note that this should be done to new diff cup, so you do not damage the existing threads during drilling.

In the picture below you can see the holes which are drilled out in XB2 diff cup.

Modification 2: XB2 diff's cap "Bleeder" screw

Filling up the diff can be a little tricky job to do with exactly same amount of oil each time. It is important that it is done so to make the diffs  feel the same time after time. If the amount of oil varies between oil change the alternation of viscosity is not exact since the oil mixes up with air differently each time. Xray advises to fill up the diff by weight of the oil which makes the oil volyme to be same each time. To do so you will need to use a precision scale to measure the oil's weight each time.   Reiman modified his diff so that it has a bleeder screw which allows all extra oil to get out and the diff will be filled to the maximum level of oil each time.

Bleeder screw is drilled with a 2.5mm drill and the screw itself is a M3x2.5 set screw with a flat head. You start with drilling a hole under the cross pin's end like shown in the picture below. After drilling the hole it is a good time to pre-thread the hole by screwing the set screw into it and making the screwing it on it's place later much easier. Remove the screw after this and put a side to wait the last step.

Next you can assemble the diff normally to the point where you fill up the oil.  You can now fill up the oil to the top of the diff cup.  After placing the diff cap on top of the cup you can see that all extra oil will bleed out from the bleeder hole.  Tighten the cap screws normally.  Turn the outdrives few times (bleeder hole up) to let all the extra oil out  and finally screw down the set screw so that it is flush with the cap surface.

Oil bleeding and the set screw on it's place.

When using this bleeding screw modification you will ensure that your diff is always made with the maximum amount of oil and minimal amount of air is inside to mess up the oil's viscosity.