To understand how to prevent servo failure you have to understand why they fail
Losi has chosen to have a radio tray instead of a radio plate like a lot of other manufacturers. This makes life easier when maintaining your kit but it causes all kinds of problems because of how flexible the plastic is. This tray flexes like crazy when you’re out on the track and if your EPA’s and linkages aren’t just right the radio tray flexes even more. When the tray flexes it literally twists the gears inside the servo causing them to bind up and then either strip or fry the motor driving them. In addition to radio tray flex causing servos to bind up inside the servos it also causes the servos to flex from side to side and can cause the servos to hit the side guards on the chassis or even worse the chassis itself. If your servo suddenly hits the chassis or side guard it can put an extreme load on already bound up gears and now you are really asking for trouble.
Servos only have to be made to a specific length and width for the mounting holes. Contrary to what you may believe the shims that you have to use with different brands of servos are not to keep the servo in line with your carb and brakes but instead to keep the servo from bottoming out on the chassis. This is why "cheap" servos seem to last longer they are generally shallower because they lack the digital circuitry. A shallow servo doesn’t bottom out and isn’t really affected by chassis flex so they seem to last longer.
To add to this problem there are two available chassis options for the 8IGHT and 8IGHT-T. The RTR chassis and then there is the "Flex Tuned Chassis" the difference between the two is that the Flex tuned chassis has cutouts to give the servos more vertical clearance and that helps keep the servos from bottoming out during chassis flex. Yes you are more likely to burn up more servos if you don’t upgrade to the better chassis.
There are so many theories/fixes at my track and everyone has problems. I believe that there are a few major variables here that cause these servos to fail. Any of the items listed below can cause a servo to fail by itself and the effect is only compounded when there more than one thing is wrong.
1.) EPA's… If your servos are pulling so hard that your radio tray flexes you are doing it wrong. Losi has a very specific guide for this on their website and I have summarized it a few posts above this one. If you are causing your radio tray to flex on the bench then it is only amplified out on the track with chassis flex. Everyone says their epa’s are correct and they still fry servos… Keep Reading…
2.) Improper Carb Alignment... This one is probably the most overlooked that I see, if the throttle linkage isn't perfectly parallel to the chassis it will cause the gears inside the servo to bind up. Add this to the chassis flex from hitting those jumps at full throttle and then boom your servo fries because it bottoms out or hits the side guard.
3.) Not enough clearance around the servos… This is the one that no one seems to know about. While it is really easy to make sure that your EPA’s and linkages are perfect you probably wouldn’t think to see if your servo is touching anything… Chances are that if you have replaced your stock servos with something more expensive your servo is already touching the side guard or the chassis. This is especially the case if you are on your second or third high end servo in less than a gallon or two of fuel. Chassis flex will cause your servo to fail extremely fast if the servo is in direct contact with the chassis or side guard. Servos are not designed to handle the extreme vibration and shock that your chassis goes through. I had several 7955tgs burn up within 15 minutes of being on the track because they were touching the side guard. Fortunately there is a pretty easy fix for this; use shims to keep the servo from touching the chassis and if the servo is touching the side guard you just cut away where it touches the servo and problem solved.
4.) All electronics can die for no reason at any time… Yea blame god for this one even with everything perfect a servo can just die for no reason... Not a lot you can do about this one…
If you don’t check all of the above every time you change a servo then you can expect to spend a lot of time mailing your servos in for service.