Sorry I just had to post. The XX4 is by far, my favorite car, ever. Here is a pic for a fix for the rear brace. Now the hinge pins are captive and the brace bolts to the chassis. Also the fix for the brittle shock towers (carbon braces). If you look closely, on the right hub, you can see my little braces. I made those braces for the hubs 6 years ago and haven't broken a hub since. Also my custom sway bar setup that I can make so stiff (if I want) that if you move one wheel full up the other moves up about 3-5mm, of coarse I never run it this stiff, I usually have it just stiff enough so it won't move the other wheel. I run CVD's at all corners and have yet to have a problem with them. The front dog bones had two inherent flaws; 1) Very thin bearings (1/4 by 3/8 as apposed to the standard 3/16 by 3/8), and 2) Very small thin plastic yokes. These two things add up to a recipe for disaster. I switched to CVD's on my first XX4, 8 years ago, and haven't ran dog bones since. Now as far as the belt change is concerned, you have to cut the rear/side belt cover. Now this makes the chassis flex more but I also built a brace that goes from the aft motor clamp screw, to the screw right by the servo and the screw at the corner by the motor (see pic 2, not my car but an altered pic to show what I mean). The brace transfered flex to the screw by the servo so, I drilled it out and added another threaded insert set up exactly the same way as the 2 for the motor clamp. I even took a 3/16 nut and put it on a screw, heated it up with a lighter, and melted a hex shaped recess in the chassis cover so the threaded insert sits flush. This seems to have fixed the problem of the chassis flexing. Now as far as efficiency/durability of the drive train, its all about breaking the belts in. First make sure the rear belt adjustment blocks (rear diff outdrive bearing holders) are B with the arrow pointing back, then pop off the camber links and pull the CVD's/dog bones out of the outdrives, then hook a dremel up to the slipper shaft, set it up so its on a stand and nice and stable (dremel too, duct tape works wonders), use the dremel to run the drivetrain for about an hour, at a moderately low speed. Then (if your a prefectionist like me) dis-assemble the car and clean all the belts and pulleys, and the chassis/chassis cover. This is all with brand new belts and pulleys. This is of coarse if you want the best/freest (pronounced free ist) drivetrain possible. On my XX4 if the motor is out and you turn 1 front wheel the drivetrain is free enough to roll, instead of the clicker clicking (and I set my clicker very loose). As far as belt durability, I don't run a slipper, that right Street Weapon direct drive (also cuts down on rotating mass ALOT), with a Mamba Max 6900, and I don't go through belts any faster than anyone else at my track. In fact other than a side belt about 2 months ago, I can't remember the last belt that I broke. This, I think, has more to do with driving style, as I am very smooth on the trigger. I have about 15 other things I have done to my XX4 also, so if anyone has any other problems they need solved with this car let me know (I know just about every one of the solutions), I have been developing and working on XX4's for about 8 years off and on (mostly on), and as of about a 9 months ago, I completed, what I (and everyone at my track) considers to be the perfect XX4. My car is just as durable as by B4, by this I mean, as long as I don't run it into the wall at full tilt, it doesn't break. I can drive the car as hard as I want and not have to worry about something breaking (although I still can't run it into the wall at full speed
). The only thing I have left to do is to put the car on a diet, so the last two upgrades to my ultimate XX4 will be a titanium screw kit and I want to try Aluminum CVD's (if they don't work out I'll switch back to shiny). The XX4 is a good car, and with a little work it can be made really good, and with a lot of work it can be perfected. Now I do understand that some people want a car that they don't have to do this much work to get it to work really well (BJ4WE, D4, B44, MR-4BX, 501x), but for me, half the fun of this hobby is perfecting my cars to the point that it makes peoples jaws drop and eyes widen when they see my cars. Just because they are the same car they are running, but at the same time sooo different.