newbie need help parts list for overdrive mod on mrc pro

[fyrstormer]

I know this is an old thread, but I have a question directly related to the topic: How is it possible to run a larger diff pinion with the stock diff, without making the mesh too tight? Is there really enough slop in the stock setup that there's room for a larger diff pinion? Or do people just accept the tighter mesh and wait for it to wear-down on its own?

[89redranger]

Originally Posted by fyrstormer

I know this is an old thread, but I have a question directly related to the topic: How is it possible to run a larger diff pinion with the stock diff, without making the mesh too tight? Is there really enough slop in the stock setup that there's room for a larger diff pinion? Or do people just accept the tighter mesh and wait for it to wear-down on its own?

In short, yes there is enough slop to allow a single tooth larger pinion. The gear to use is the pinion from TRA7079 Mini E-Revo diff set.

Honestly, even with the larger pinion there is room to shim the pinion in. With stock gears I use 2x Traxxas 5x8 fiber washers behind the pinion bearing to give more pinion depth, then shim the diff itself in tighter with Associated ASC21141 shims. Usually one on the ring gear side, two on the opposite. To allow this many shims you first have to trim off the little lip on the pinion shaft. Failure to do so will crush the bearings and result in an axle that won't turn.

When using the Mini E-Revo pinion I usually use 1x Traxxas 5x8 fiber washer behind the pinion bearing to provide more tooth engagement, and the same combination at the ring gear/locker.

When shimming gears ALWAYS set your pinion depth first for adequate tooth engagement, THEN shim the ring gear in tight to set the lash. No different than setting up 1:1 ring and pinions. If it helps at all, a small blob of grease on the ring gear and a single rotation of the pinion will show you both pinion depth AND lash. Shim it tight enough that you get a little light clicking. Under torque there will be deflection in the pinion bearings, as well as the ring gear bearings, that will cause the gear set to try to separate. Building them a tad tight keeps this deflection to a minimum, even after the gears break in/settle in.

[fyrstormer]

Thanks, I had no idea the stock gear mesh was so loose. That's kind of annoying, but on the other hand it's nice that it offers the flexibility to use a part never intended for the vehicle that improves its performance.