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RC18T Diff Build
This page will outline the easiest (and correct) way to build an Associated RC18 Series differential. Start with a clean, dry, lint free surface. Also have some paper towels handy for clean up.
1. Lay out the parts and check to see if you have everything: 1 left outdrive, 1 right outdrive, 2 d-diff rings, 1 diff spring, 8 large diff balls, 7 small thrust balls, 3 thrust washers, 1 diff bolt, 1 diff gear, 1 spring retainer and 2 diff shims (Pic 1).
2. Compress the diff spring completely. Be careful not to compress it so much that it deforms the spring (Pic 2).
3. Apply a small amount of diff lube to the surfaces shown in Pic 3. Align the d-diff rings and set in place. The diff lube will help keep the rings from moving during the building process.
4. Apply a ring of diff lube to the backside of the diff gear (Pic 4).
5. Install gear to the short diff outdrive (Pic 5). Notice how the lube protrudes through the diff holes.
6. Install 8 diff balls into the lubed diff gear holes (Pic 6).
7. Assemble the thrust screw as follows: Screw, 1 thrust washer, diff spring, 1 thrust washer. Apply black grease to the second thrust washer (Pic 7). Roll the assembled thrust screw over the thrust balls (there is where a clean, lint free surface comes in handy), allowing the black grease to ‘pick them up’ (Pic 8). Install the final thrust washer (Pic 9).
8. Slide the assembled thrust screw into the long diff outdrive. Make sure the thrust balls do not release from the assembly. Now slide the assembled gear/short diff outdrive onto the screw (Pic 10). Slowly tighten 2 or 3 turns, then ‘work’ the diff to make sure all the parts seat. Tighten 4 or 5 more turns, then ‘work’ the diff again. Continue this process until the diff is tight.
9. Insert an Xacto (or similar) into the short diff outdrive and continue to tighten the diff (Pic 11). You should be able to tighten it an additional 3 or 4 full turns. BE CAREFUL NOT TO OVERTIGHTEN THE DIFF!!!!! As soon as you feel resistance, stop tightening and back the screw off 1/2 turn (to start). You may need to adjust it after the first run.
10. Diff adjustment (Pic 12). A quick and easy way to check the diff setting is to slide the diff onto a pair of scissors (as shown) and, using your thumb, try to rotate the diff gear. If it does rotate, your diff is too loose. Tighten it a 1/4 turn and re-check. Optimal setting tight enough that you can’t ‘slip’ the diff gear but you still have diff action.
11. Install the spring retainer into the long diff outdrive (Pic 13).
12. Install the diff shims to the short side of the diff. Number of shims may vary from vehicle to vehicle…start with the supplied 2. Install the bearings (Pic 14).
You have successfully built an 18T differential. Be sure to check it after the first run or two to make sure it has not loosened up.