In effort to provide the best handling and fastest cars on the track, Specialized RC presents this documentation on HOW TO BLUEPRINT YOUR RDX. The RDX out of the box is able to perform at the highest levels of competition. If you are looking for that last extra bit of performance then read on. The following are some tips and tricks our team use to increase the performance you have come to expect from the RDX.


The RDX drivetrain is super smooth and free out of the box. If you are looking for that last extra bit then read the tips below that we do to make our cars perform at their best on the track. Always wear safety glasses when using power tools. Be sure to click on images for close up views.

  • Insert the bearing holders in the down position and check for tightness on them. They should slide in and out with ease to prevent the bearings from being pinched once inserted into the bulkheads.

  • If the holders are tight you will want to dremel the bulkheads a bit. Due to molding tolerances on the bearing holders this is sometimes necessary.


  • You will want to start with a coarse bit if the holders are tight to help in the process. Then go back with a smooth bit to finish it off. Alternate holding the bulkheads side to side to keep the dremeling even.

  • Be sure not to remove too much material, this can cause the holders to rock too much in the bulkheads. Do not dremel the notches.


  • Once completed you will have a matched set of bulkheads to holders. Do not mix them up otherwise they may not fit as smooth.

  • Once complete you will want to spray everything down with Motorspray to remove dust and debris. Check holders one final time with bearings installed.

REBUILDING TIPS If rebuilding a car, be sure to check all bulkheads on a piece of glass for flatness. Glass will be the only true flat surface unless something is ground down to tolerance. Check the bearing holders for dirt and tire dust buildup behind the bearings. Clean out the corners with an X-acto knife to insure they sit down in.


The Diffs in the RDX are smooth as glass when built up properly and follow a few simple things. The following steps will ensure you get the silky diffs you are looking for and perform perfectly. The diffs put the power to the ground so we do not recommend skipping any of the steps and make sure the parts are always in top notch condition. Be sure to click on images for close up views.

  • The biggest upgrade we recommend is swapping the stock diff balls for either Carbide (COR1011) or Ceramic (COR1010) balls. It will vastly improve the longevity of your diffs between rebuilds.

  • When assembling the diffs there are 4 beveled washers that are put onto the diff bolt. We recommend a different pattern for placing them onto the bolt. We recommend one face down, then two facing each other, then the fourth washer facing upward. We feel this prevents any possible slanting of the washers on the bolt.


  • Remove the snap ring from the short diff hub. Do not pinch the snap ring closed otherwise it will cause premature fatigue and give you other problems. Pinch it enough to pull it out and no more. After 2 or 3 times of removing the snap ring you will want to go ahead and replace it as it will fatigue.

  • Take out the thrust bearings and clean everything down with motor spray. Check the groove on the diff hub where the snap ring sits for any wear marks or debris.

  • The thrust washers are two different diameters, so be sure to put the smaller one in first. Coat the washer with black grease, insert the thrust bearing, coat the bearing with more black grease. Install the final thrust washer and use the back of an X-acto knife to seat the thrust assembly.

  • Before installing the fresh snap ring, be sure to examine the ring as there is a flat edge side and a more rounded edge. You will want the flat edge side facing outward so it locks into the groove better.

  • Reinstall the snap ring into the diff, making sure not to pinch the ring too tight. You can make sure the snap ring is seated into the groove by pushing into the hub with the back of an X-acto knife. You can then check to make sure the snap ring spins freely inside the groove with the blade of the X-acto. Finally remove any excess black grease from the diff hub by pushing a wrench through the middle.


  • You will now want to apply a bit of diff grease to the diff hubs to help hold the rings on. Coat the diff rings with diff grease before placing the pulley onto it. Fill each of the diff ball holes with diff grease and then insert the diff balls.

  • Next place the other diff hub onto the pulley. Apply a dab of loctite to the diff bolt before inserting into the diff hub. Tighten the diff bolt until the slop is removed and the diff is held together, do not tighten any further yet.

  • Check the smoothness of the diff before tightening any further. The diff will be super loose and smooth feeling with no hang ups. If everything checks out, then tighten the diff 1/4 turn and no more. Again, check the diff for smooth feeling and no hang ups.

  • If everything checks out then check the tightness with a wrench inserted into each diff outdrive. If the pulley turns easily then tighten the diff another 1/4 turn. Repeat until pulley is pretty much locked. It usually does not take more than 2 or 3 of the 1/4 turns to lock the diff down.

TIPS TO REMEMBER If your diff develops a high spot then you need to replace the snap ring. When replacing the snap ring we recommend the new HD Snap Ring (SRC79165) offered by Specialized RC. If your diff will not tighten down and acts up no matter how many rebuilds, then you need to check your Snap Ring and/or the sequence of the thrust washers. Be sure to have the smaller OD washer in first. Do not over tighten the diff bolt. You will crush the coned washers and create other problems with your diffs.


Shocks need to be super smooth to perform at their best. The tips below will ensure your shocks are super smooth with no air gaps or leaks. Follow these steps and you will have smooth action shocks for a long time. Be sure to click on images for close up views.

  • When assembling shocks, the first thing we do is disassemble the kit shocks completely, this includes removing the G-clip on them and pulling out the o-rings and washers in the shock body. Be sure not let the G-clip spring out otherwise you may lose it.

  • The first thing we do is replace one of the o-rings in the shock body with a thick washer. We find the thickest washer included in a Losi parts bag, LOSA5050, works perfectly. The reason is to improve the reactiveness of the shock for transitions on the track.


  • If you are racing on carpet and are utilizing the lowered shock tower (COR79238) you will want to cut down the shock eyelets and shock shafts for the front shocks. You should cut the shock shafts down about half way, along with the eyelet. You will be able to use the stock spring perches once this is done. Once the shock shafts are cleaned up with motor spray, install the pistons you plan to use.

  • Before putting the shock shaft back through the shock body, be sure to put a drop of shock oil onto the o-ring in the shock body to prevent any damage to it.

  • Once you fill the shock body and get the air bubbles out you will want to put the bladder in seperately from the cap. Place the bladder into the body and it will sink down a bit. Use the back of an X-acto knife to push it down and seal it up. You should have a good tight seal now.


  • When putting the cap onto the shock body, do not grip the plastic part of the cap. Only let your fingers twist on the aluminum portion of the cap. Otherwise this is how the seal of the bladders is broken and causes leaks once assembled. The plastic cap may or may not turn but it does not matter.

  • When putting the shock eyelets back onto the shock shafts, be sure not to crank down on them too much otherwise they will crush and bind up the pivot ball in the shock eyelet.

  • Once the eyelets are installed and the shock rebounds the way you want you will want to measure the shocks to ensure they are the same length side to side. Obviously the front and rears will be different due to the lowered shock tower. If you are using the standard front tower then all four shocks should measure the same.
  • Once the shock is done and you are putting the springs on, if you are using any of the silver springs you will want to crush them down once. Using a pair of pliers as shown in the picture helps with the stiffer springs in the package. It will help the springs break in and sit more even side to side.







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