915/68 q&a

[chongito-blanco]

can any harm be done to a 915 if i place each of the shafts in gear (2 gears at the same time) in the interest of torque the pinion shaft to measure back lash. the factory tool is very expensive. im trying to complete the assembly for under $1100

[Trackrash]

You can use an old clutch disk clamped to not turn to hold the input shaft for torquing.

[Grady Clay]

Neither of these is adequate to hold the pinion in position for measuring backlash.
The rotational ‘play’ of the gears, sliding sleeves, hubs, etc. far exceeds the backlash measurement.
The normal sliding clearance of the clutch splines only adds to the problem.

Not only do you need to hold the pinion rigidly in the rotational direction, you should also devise a consistent method of forcing the pinion away from the center-line of the differential.
This puts pressure on the pinion ball bearing that locates pinion position axially.
During operation, the bearing is forced this direction both under power and ‘trailing throttle’.

The confirmation of your method is to have repeatable measurements for various positions around the ring gear and all within the specified ‘error’.
You should be able to get repeatable measurements ±0.01 mm at a 0.001 mm reading dial indicator

Also critical is to ‘lock-up’ the differential.
The ‘backlash’ and axial play of the differential spider gears far exceed the pinion-to-ring backlash you are attempting to measure.
The tool P-357 piece is nothing but a special washer to install between the transmission axle flange and the spider gear.
When you tighten the flange bolt, it pulls the spider gear and flange against the differential housing, eliminating any ‘play’.

You also need to replicate the radius of the P-357 dial indicator holder in order for the measurements to be relevant to the specification.

It is useful to have a consistent method of forcing zero-clearance the same in both directions of the ring gear when measuring the backlash.
I use a weight on a lever-arm.

There has been a lot of discussion about this.


Either of these above techniques is adequate to retain the parts to torque the nuts.

Best,
Grady