There are three basic parts to the ring & pinion setting procedure:
- Setting the pinion position.
- Setting the differential bearing preload.
- Setting the pinion-to-ring gear backlash clearance.
In fact, if you are starting with a transmission or few, you should measure:
- The existing position of the pinion.
- The existing bearing preload.
- The existing backlash around 360°.
- The existing pinion tooth to ring gear teeth pattern.
When you think you are all finished, the final proof is the pinion-to-ring tooth
contact pattern.
Porsche devised the instructions for R&P setting
assuming you are
replacing the gear pair with new parts. In our case we are stirring around
used parts, attempting to make them act like new – well, at least work the
best possible.
OK, on to more on
measuring ring-to-pinion backlash on a 915. This has
application for 901, 904, 906, 911, 914, 915 and 930. Probably more.
Here is an illustration from the Porsche Factory Workshop Manual.
Overview:
Note P-259a clamping the pinion nut to the input shaft nut, P-259 in place on the axle flange.
© 1971 Dr. Ing. h.c. F. Porsche KG, Stuttgart, West Germany
Here is the P-259 bolted on the axle flange. Note P-259b touching a side cover
rib. Not seen is the P-357 washer installed between the axle flange and the
differential. P-259a or equivalent is holding the pinion stationary. The axle
flange seals and the side cover O-ring are removed. When tightening the side
cover, keep checking for backlash. NEVER, EVER let there be no backlash.
Serious damage will result.
© 1971 Dr. Ing. h.c. F. Porsche KG, Stuttgart, West Germany
Here is pinion bolt clamp P-259 for a 901.
© 1965 Dr. Ing. h.c. F. Porsche KG, Stuttgart, West Germany
Here is pinion bolt clamp P-357 for 905 Sportomatic
© 1967 Dr. Ing. h.c. F. Porsche KG, Stuttgart, West Germany
If you are making your own pinion-clamp tool, it is preferable to build one similar
to P-259 or P-357 above but with a 36 mm socket. There are many circumstances
where you will want to lock the pinion and the input shaft is not installed. The
915 P-259a works great but requires the input shaft to be in place with nut
installed.
Here are all the tools necessary for
measuring backlash.
Note the shank of most dial indicators is 8 mm. The bore for the dial indicator
in the P-359 holder is 10 mm. The P-365 is a split adaptor between 8 mm and
10 mm. There are commercial adaptors for this.
I like to use a dial indicator with 0.001 mm minor divisions. While
somewhat ‘jittery’, it allows for good measurement. Like any
precision measurement, it is wise to repeat it several times.
The P-259b Sensor is easily made out of a piece of metal.
Porsche specs a M10 x 110 mm bolt. As you see, I use an old head stud and
some spacer washers. This bolt needs to be tight but
not torqued to
the spec 18.8 – 21.7 ft-lbs of the axle flange stretch bolt.
The washer from P-357 measures 45 x 35 x 2 mm. The Factory tool is a hardened
and ground part (complete with ‘P357’ etched on the 2 mm side
). Any nice
flat washer will work. Err on the side of <45 mm, >35 mm and ~2 mm.
You will need the bearing puller for the differential bearings, the centering tool
P-263 for the puller, P-264b and a large selection of differential shims. These
P-tools can be simple 'pipe-tools' and the puller is a commercial tool. The dificulty
is getting a large selection of shims and then what to do with the leftovers.
These are Porsche parts
!
Here are all the pieces in place on a 915.
© 1971 Dr. Ing. h.c. F. Porsche KG, Stuttgart, West Germany
Do not use the P-259 dial indicator holder to move the differential back and forth
as shown. Use both hands to rotate the axle flange. Using P-259 as shown can
cause error in readings.
Here is the location of the P-357 washer when installed.
© 1971 Dr. Ing. h.c. F. Porsche KG, Stuttgart, West Germany
Note that the P-357 washer takes up normal running clearance that you can feel
as axle flange (axial) end play.
Backlash specification range for a 915 is 0.12 to 0.18 mm.
The actual backlash for any given ring & pinion is etched on the side of the ring
gear. This is measured with the marked pinion tooth between the two marked
teeth on the ring gear.
The variation in backlash around 360° rotation of the ring gear indicates the
degree that the differential is concentric to its centerline. It should not vary
outside the specification range. If it does, you should replace the differential.
When
adjusting the backlash, remember to add size to one side spacer and
subtract the exact same amount from the other spacer. This takes lots of spare
spacers and a micrometer that reads to 0.001 mm. We should illustrate and
describe this part of the procedure. More on this.
When you are satisfied with the backlash, remove the pinion and re-check the
differential bearing pre-load. Reinstall the pinion and do a final check of the
backlash.
Keep in mind that the backlash procedure is
almost the final step in the
R&P setting sequence. As a final check you should inspect the pinion tooth to
ring gear tooth contact pattern with a paint substance. This is the subject for
another thread.
Best,
Grady