Throttle Return Spring

Anyone who runs a nitro truck is aware of the danger of a runaway. If you run out of range, have near dead batteries in the receiver pack, or in the event you lose power to the receiver completely, the servo will continue to do the last thing you told it. More often than not, it's full speed ahead. This can cause many problems, such as a full speed crash or a blown motor. A throttle return spring will pull the throttle servo back into a safe position when these conditions occur.

Installing a throttle return spring is easy, and well worth the effort required. I chose to use a A-9409 Losi spring, which only costs a few bucks and gives you a spare spring.

All that's required is for you to install two spring brackets and then attach the spring between them. The first bracket installs between the throttle's servo horn and nut that holds the brake lever in place. Make sure you do not tighten the nut back down too tightly. This bracket should swivel easily as the servo horn rotates when moved by the servo.

The other bracket mounts between the shock cap and the front shock tower. You'll want to tighten the screw down tightly in this case to prevent the bracket from moving. The spring attaches between these two brackets.

Despite the benefits of a throttle return spring, it will not protect you from radio interference. So to offer the best protection against a runaway truck, you should also install a failsafe which would cover that circumstance. For more information regarding a failsafe, see my section on Installing a Failsafe.

I've also heard many people mention that installing the throttle return spring on the servo horn in this manner will not protect in the event that the linkage would break or come loose. However in that scenario the throttle return spring that is installed inside the 2.5's carburetor slide boot would come into play. The only situation it would not, would be if only the side of the arm where the throttle return spring was attached to broke, and the rest of the horn was still attached to the servo. That would be a very rare occurrence, in my opinion, but could easily be prevented by installing an aluminum servo horn such as I have done.