TiDbiD #5
What is 'backlash' ???
Backlash is the 'play' between any mechanical moving parts, as in series of gears.
Two main areas where you would see this is in the spur gear / pinion gear, and the rear differential between the ring gear and drive gear (on DP style diff and not on YD style diff). Some chassis configuration may also have a set of bevel gears.
Having 'too much' play can cause vibration and damage to the gears or possibly destroy the gears when turbo kicks in.
Gears set 'too tight' will cause the drivetrain to not spin/rotate freely and the pressure can cause excessive wear.
So how do you adjust 'backlash'?
Many use a sheet of paper or a plastic wrap and run it between the spur gear / pinion gear to find the right amount of backlash. On most chassis, the motor mount would have an adjustable slot to move the motor to adjust the position of the pinion gear to the spur gear.
Once you have a good feel of what the backlash should be, you should be able to feel it with your fingers by moving the pinion gear or the spur gear.
On a ring gear / drive gear in the rear diff, or the bevel gears in the drivetrain, you will need to use shims down to 0.01mm in thickness, preferably stainless steel), to adjust the position of the gears in the axial direction. Using shims at the axle bearings to adjust the left/right position against the drive gear will make the ring gear closer or farther from the drive gear.
The drive gear in this case must have minimal play in the axial direction as well.
Having the right amount of 'backlash' will not only make the drivetrain smooth, but will prolong the life of the gears and the bearings by reducing vibration and any excessive wear. In any steel gear application, make sure to check the backlash once the gears are worn in, then the gears will last even longer.
January 26, 2019
Charlotte NC