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912 Axle
The cars came with Nadella or Löbro half shafts. Löbro have CV joints
covered with rubber boots. The Nadella have an exposed universal
joints. This discussion refers to the Löbro half shafts (Spare Part
No. 901.223.026.10).
Mine have been converted to Löbro with CV joints. Nadella are no
longer in the parts chain. It has been suggested that the CV joints
should be re-packed every 60K miles. There are 6 bolts at each end of
the half-shafts that are removed with 6 mm hex wrench. The factory
manual suggests these be replaced after removal. They are torqued to
high enough values to stretch the bolt by design. The factory supplied
bolts are expensive - perhaps close to $2 each. After market or bolts
used on later cars such as the 914 are available, but they have 12
point socket heads, similar to those holding on the door hinges. It
takes a special wrench. The bolts on my car are 45 mm in length
measured from the end to the bearing surface on the head. Swepco makes
CV joint grease. It takes a couple of tubes - 2 1/2 oz per joint.
The job is pretty messy. The boots are held on with inner and outer
metal clamps. The boots on later model cars were crimped to a metal
flange of some sort. The inner clamps are readily available, but the
large diameter outer ones take a bit of searching. Some people
(racing community) use heavy duty tie-wraps for these. I've tried
this technique with success. The rubber boots are available. The
joints should be cleaned and inspected. If there is any scoring on the
sliding surfaces, the parts should be replaced.
New complete half shafts with both CV joints are about $290
each. 'Rebuilt' ones are cleaned inspected and re-packed. If the
inspection shows any problem, they are often replaced with used parts.
They do not have a good reliability history.
I've seen 'new' half shafts in boxes at swap meets for $100. This is
worth a careful inspection. Buyer beware.
There is a company that re-manufactures CV joints and knows about
early Porsche ones. See CV Source, Inc. in
Norcross, Georgia.
The picture is one end of a Nadela shaft, but shows the Allen
bolts.
Removal
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1. Set the hand brake to help 'breaking' the bolts
loose. Raise the car and remove rear wheels. Place some newspaper
under the car to catch the accumulated dirt and grease that will fall
down.
2. Using a 6 mm Allen wrench, remove Allen bolts from half shaft
flange, knock the half shaft from its seat and remove.
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3. Orientation was important in re-assembling if
the parts are warn and is hard to discover. There were blue paint
marks on the outer surfaces of the flange and inner race. Clean both
enough to see these marks before they are taken apart.
4. Remove the original clamps around the boots and slide the large end
off each of the flanges.
5. Remove the C-ring at each end with snap ring pliers.
6. With a hammer or mallet and a piece of wood, tap the spline away
from the housing.
7. Slide the old boot off.
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Inspection
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1. Clean up the parts. The grease is messy, so
work on newspapers and use paper towels to clean as much of the grease
as possible. See the notes with this picture on hints to reassemble.
2. Check CV joints in half shaft for play or scoring on the sliding
surfaces. If they are worn, replace.
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3. Here is the large flange showing wear marks in
the groves where the balls ride.
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4. Similarly the inner race shows wear in the
grooves as can be seen in this picture.
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Reassemble
Re-assembly is tricky. The best technique is to use the painted blue
marks across from each other as on one of my CV joints. Another way it
so use a center punch and mark a point on both the inner and outer
piece and to put them back together with the marks lined up.
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Failing that here is a clue using the CV joints
from Craig Norton's 1969 912. See the text with the picture.
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Installation
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1. The picture shows the
parts purchased so far. To facilitate installation of the new boot,
wrap the spline and flange with aluminum foil. Slide the new boot on
then remove the foil.
2. Re-pack the boots with new MoS_2 (molybdenum disulfide) grease. The
manual says 2 1/2 oz. total for the boot and universal joint.
3. Install the new clamps, making sure that the worm gear screws
don't obstruct the bolt holes.
4. Replace the housing over the spline and tap on far enough to
receive the C-ring.
Note:
There is a washer on the inside of the universal housing. Be sure it is there and oriented properly.
Replace the C-ring.
5. Put some more grease on the joint faces just prior to assembly.
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6. Clean the old grease out of the receiving
flanges on the car. Grease will be forced out of the boot through the
cage and into this cavity from the repacked CV joint.
7. Release the hand brake, then install the half-shaft assembly.
8. Tighten Allen bolts in half shaft flange to prescribed torque: 4.3
mkp (33 lbs/ft); the Schnorr washer for the Allen bolt must face the
base plate with the hollow side.
Note:
The Löbro half shafts may be fastened only with Allen bolts M 6 x
45 DIN 912 - 12 K. Spare part Nr. 900.067.073.01 (minimum tensile
strength of 120 kp/mm2). These bolts bear markings 130 - 140 or 12 K,
respectively, on the head or the side. There are 6 of these at each
end.
Also the manual says the flange surface of the half shaft must be free
of grease at time of installation - probably impossible to accomplish.
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Last modified: Sat, 10 Feb 2001
Links
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