EDIT
I reached in a drawer and pulled out the wrong bracket.
The correct bracket / holder P-259 has dimension of 76.5 mm.
This is used with the washer part of P-357 (45x35x2 mm).
I posted a better explanation on page 2 of this thread.
Best, Grady /EDIT
The dimension you want measures 70.60 mm on the actual P357 tool in my hand.
I measured the center-line distance by measuring the inside distance between
the two shafts. I then measured the diameter of each shaft. I added the
distance between shafts to half of the diameter of each shaft. Measurement
accuracy should be about ±0.04 mm.
Critical to measuring the backlash accurately is the thin P357 washer (shown in
your 1st image above). This goes between the axle flange and the differential
housing. When you tighten the bolt through the center of the axle flange and
P357, this removes any axial clearance between the flange and differential
housing. This clamps the P357 tool and flange directly to the differential
housing. Without this, you will have the additional clearances of the
differential ‘spider’ gears added to the R&P backlash. I posted the washer
dimensions in some previous thread.
The Factory backlash measurement is etched on the side of the ring gear. This
measurement was performed with the pinion tooth with the single mark
positioned between the two teeth on the ring gear also etch marked.
I like to make many measurements completely around the ring gear several
times. I simply loosen the pinion nut clamp P259 or P259a and rotate the pinion
one flat on the nut.
This measurement (and even pinion position) is slightly subject to the torque load
while running. I like to simulate this with a pry bar and weight prying the pinion
5-R gear (or 1-R on a 901/911) away from the differential. Most will move only
about 0.005 mm but can have a noticeable affect on the backlash measurement.
When replacing a casting, bearings or the differential, it is best to measure all the
positions, pre-loads and backlash first so you have numbers to set to. This is
particularly important if you are transferring a R&P from one transmission to
another.
NEVER, EVER risk tightening the side cover without ring-to-pinion backlash
clearance. Serious damage can result. If in doubt, set the ring gear farther
away from the pinion and move it in with small steps.
Best,
Grady