XRAY - Model racing cars

I'm not sure what you're referring to concerning the "plastic nut".

Make sure the cone washers are all positioned correctly according to the manual. They can easily reverse themselves if you take the screw out. Make sure you used two bearings as well. I've made the mistake of using only one bearing before.

he means the bit installed at the factory in the out drive/diff cup

More than likely the problem will be the clip that holds the thrust race in. Try changing the clip, its probably worn/bent so it will be moving out of the groove in the outdrive.

Having driven Xrays for the last 2 seasons i've seen this problem numerous times. The most common reason for the diff untightening itself is the clip moving out of the grooves, due to it being overtightened when built or using a damaged clip.
Lets see what the original author has to say once he's put a new clip in and gradually tightened the diff while running it in.
Hope this helps tomasfb.

I had the same problem when i first started to use Xray's. The best thing to do is to change the clip.
But the most important part of getting the diff to work properly is the running in process.
1 Build the diff exactly how the manual tells you, a little grease behind the diff rings is ok just to hold them in place while building the diff.
2 Do not tighten the diff up before you put it in the car! Tighten the diff just enough so there is some differential action (turn one outdrive so the other turns the other way) Do not tighten the diff fully yet.
3 Run the car around a track or in circles, every lap or two slightly tighten the diff. This may take some time but it is worth it in the long run.
4 Set the rear diff so that it slips very slightly and the front diff (if your using one) tighter than the rear.
Hope this helps, BTW i'd like to know if this works for you.

there is a corect way to fit the circlip too, look cloley and one side will be sharpe and one smooth where its stamped out
put the sharpe bit into th diff the side its pulling on

if its the clip it will have moved down the diff housing out of its grove

ok i have finally had two race days with the diff. the problem is fixed. it seems that the plastic nut was worn out. i put some zap-a-dap-a-goo on the screw and screwed it into the nut, then put some tamiya thread lock in the nut. i tightened it to feel with the tyres on and let the glue set.

it has kept it's setting well. you you will probably have to do this each diff rebuild.

i also noticed the nut moved out a fair bit, so i tapped it back down into the outdrive.