915 Repair - What tools needed to change carrier bearings?

[RarlyL8]

I had someone with more differential experience than myself come over and look at my ailing 915 R&P.

He showed me that one of my carrier bearing races is badly burned. Both bearings need to be replaced. He is new to Porsches and does not have the proper tools to remove the races or the bearings in this application. We both assume there are specific tools for this.

What are they, where do I get them, and how do I use them?
Please help - I'm having severe boost withdrawl.

[Grady Clay]

Those two bearings do a LOT more than just support the differential carrier. They locate the position and clearance of the ring gear (crown wheel) to the pinion gear. There are very high tolerance adjusting shims behind the bearings.

The basic procedure is:

Measure the position of the pinion to confirm it is in the specified location.

Measure the existing pre-load on the carrier bearings.

Using layout blue, some paints, or even dry markers, inspect the contact pattern between the R&P all the way around the ring gear.

Measure the existing back lash in at least four places around the ring gear.

Replace the bearings using the existing shims (keep track of the size).

Measure the bearing pre-load.

Adjust to increase (usually) the preload by increasing the shim on the starter side bearing (this tends to increase the clearance between the pinion and ring gears). The reason for this is you don’t want the clearance to ever close up – that can damage the parts.

By reducing the starter side shim and increasing the cover side shim an equal amount, reduce the clearance to the specified amount.

Once you have the desired clearance, check that the carrier bearings still have the specified pre-load.

Inspect the contact pattern all the way around the ring. It should roughly match the original patterns. It is possible to improve the contact by finessing the position of the ring gear and the pinion gear outside the specified placement but the specifications are from the manufacturer and also consider quiet operation.

When doing these measurements, always reinstall the intermediate casting so the pinion is properly supported.

After the transmission is almost completely assembled, check the backlash again to just make sure.

There is still more to this.

If I were going to the effort, I would replace the side cover with the aftermarket reinforced version that uses the larger Turbo bearing on the cover side.

You should also look to see why the bearings are failing (run low on oil or way to hot at some point?) What else is in distress?

Best,
Grady

PS: This is an almost identical procedure with a 901,911, 904, 906, 914 and 930 transmissions.

EDIT to correct typos

[RarlyL8]

Thanks for the info Grady.
The problem I am having is a whine that began abruptly after three runs at the drag strip. The car was driven home and the differential removed. What we see is excessive wear on the BACK side of the ring gear and a burned carrier bearing race on the passengers side. Obviously something has happened to create this mis-alignment. Don't know what that was.
The plan (right now) is to replace the carrier bearings and races. I have no idea how to do that given the tight tolerances in this 915 configuration.
Are there special tools to remove the races? Where do you buy the shims? Are you telling me that you leave the existing races in place and replace the bearings (that doesn't seem right)?

[Grady Clay]

The carrier bearings come as a complete bearing, including races.
The shims are a Porsche part. You will need to find a complete
selection to do this correctly. They don’t have to be new, just
in undamaged condition.

When you pull the bearing off you need a puller that fits in the
indentations in the differential carrier and doesn’t damage the
bearing cage during the process. The shim is pulled off with
the bearing.

The outer race will almost fall out of the side cover if you heat
it to 100-125C. Be ready with a press piece (preferably) or a
modified brass punch. Remove the seal and O-ring first.

Here is how Porsche does it:
IMAGE: DifferentialToolP263_02.jpg"
"
© Dr. Ing. h.c. F. Porsche A.G.

Here are three views of the tool P263.
I think this is available from our host or you can easily
make one on a lathe.
IMAGE: ToolP263_01.jpg


IMAGE: ToolP263_02.jpg


IMAGE: ToolP263_03.jpg



Here is my puller. Note the modification (blue arrow) where the
puller contacts the shim. P263 (red arrow) is in place. The shim
(green arrow) is not in the place where it would be when pulled.
Ignore the nut (brown arrow), that was to support P263 on the
scanner.
IMAGE: ToolP263_04a.jpg


If you want to do this correctly and reset the ring and pinion, I’ll
lead you through the entire process in gruesome detail and
images of every tool, part and procedure. I’ll even get a 915
to do at this end.


I don’t understand your description of the contact pattern. Post
some images of everything.

For your use a type 930 transmission is MUCH stronger.
You might give that some consideration rather than beating
the 915 to death.

Best,
Grady

EDIT to correct a typo

[RarlyL8]

Thanks again, that is great information.

The noise I am hearing is consistant with the damage we see. The whine is more pronounced when you let OFF the throttle. The "new" wear on the ring gear is on the back side of the teeth, the side that normally would not be in contact with the pinion gear when you are moving forward. The carrier bearing race located on the passengers side is also burned. All these things would manafest themselved during off-throttle events.
I do not know what changed in the transmission to cause this specific mis-alignment. That is my concern. Replacing the carrier bearings and races will only fix the damage but may not fix the cause.

Using a 930 or any other tranny is out. The swaps are too expensive. My plan is to stay away from sticky surface drag strips, this tranny was just fine for the 3 years leading up to that event.

I will do this correctly, anything less is a waste of time. While I hate to ask you to go to all the trouble that you have offered I would like to see a picture of the shims that are so all-important. Another person told me to just leave the shims where they are and simply replace the bearing and race. Your description sounds like the shims come out with the bearing. Can you simply leave them alone and replace the bearings?

[john walker's workshop]

did you disassemble the entire transmission and check to be sure you haver no shaft end play because of worn out bearing retainers and/or 4 point ball bearings? unless the side bearings are really worn, not just discolored, i have a hard time believing that they are causing much noise.

[RarlyL8]

No John, I have not taken the entire transaxle apart, it is still in the car. Only the carrier/ring gear has been removed and observed. This noise occured all at once after abusing the tranny. I don't think anything is worn out, I beleive something is damaged. The one burned race and the wear on the back side of the teeth reveal where the noise came from. The pinion gear is good and tight. I want to replace the part that is damaged, so far it looks to be the Carrier bearings.

I don't want to waste any more time on this. Do you beleive, given the information I have provided, that replacing the carrier bearings and races may cure the symptom (noise)?
Is it a worth while experiment (sense that part of the tranny is already apart and I have the replacement bearings and gaskets)?

I won't go inside the tranny. I have no experience in there and any damage will cost more than the 915 is worth. If replacing the carrier bearings and races does not fix the noise I will buy a used 915 to swap in.

Here is a picture showing the back side of the ring gear teeth. You can see new wear from the top to 3/4 down the depth of each tooth.

Thank you for your help.

[john walker's workshop]

pinion shaft end play can do the same thing. i guess for now you can do the side bearings and see if that fixes the noise. not a lot of time required to do that.

[RarlyL8]

Thanks John.
Do you think that my circumstances require the proceedures above as described by Grady or can I get away with a simple R&R with the shims left in place as-is? I want to do it right but also not overkill as in an initial set-up might require.
How would you remove the bearings and races given my situation?

[john walker's workshop]

bearings, regardless of manufacturer, are universally the same dimensions for the same bearing. nothing will change, other than putting the supported unit back in the place it was designed to be in. grady's description is quite detailed, if you feel you need to go through it that way.

[Grady Clay]

The Porsche Workshop Manual says:
“Adjustment of the ring gear and pinion is important for
quiet operation of the rear axle assembly. For this reason the
pinion shaft and ring gear is already matched as a pair during
production. They are checked on testing machines for correct
contact pattern and low noise level in both directions of rotation.
When ring gear and pinion is tested, it is set according to the
design dimension “R”. Dimension “R” is the distance from the
face of the pinion to the ring gear centerline. The pinion is then
moved in and out of mesh until the quietest operation is determined.
The deviation from the design dimension (the in and out
movement of the pinion) is called “r” and is etched on the face
of the pinion. While making this test, the ring gear backlash is
kept within a tolerance of 0.12-0.18 mm. The ring gear and
pinion shaft is designed in such a way that the deviation “r” is
added to the design dimension “R”.

Earlier pinion assemblies had either a plus (+) or minus (-) etched
in front of the deviation “r” whereas on the newer [915] pinion
assemblies, the letter “N” precedes the deviation “r” on the
pinion shaft.

Ring gear and pinion shaft sets are also stamped with a matching
set of numbers and always should be replaced as a complete set.”

IMAGE: DifferentialBacklash-DeviationDiag01.jpg "
"
© Dr. Ing. h.c. F. Porsche A.G.
R – Design Dimension (66.30 mm)
r – Deviation from design dimension, shown in 1/100 mm
1 – Deviation r
2 – Matching set numbers
3 – Backlash




Now referring to the IMAGE below (DifferentialPinionShims01a.jpg):

There are at least three thickness of pinion shims #65 (red arrow):
0.10 mm – 915.302.268.03
0.15 mm – 915.302.268.04
0.20 mm – 915.302.268.05

Several are used in combination to obtain the correct pinion
position. It is normal for there to be two, three or four shims
stacked together. This illustration only shows one #65 (red arrow).

The shims position the 4-point ball bearing clamped in place
(green arrow). The more shims the greater the “r” value in
the positive (+) direction.

The shims also go under the 4-point ball bearing on the input
shaft but are not an adjustment value. It just keeps the gear
pairs in the same relative axial alignment.

It is very common to damage (wrinkle) these shims. Have plenty
of spares on hand. Never use damaged shims; the clamping
force won’t straighten them out.

When doing this operation you do not have to install the input
shaft. You should assemble the pinion stack of gears and as
you get close to your final numbers install the intermediate
tunnel casting and 5-R parts and torque the pinion stack.

As you can see, there is a lot of repetitive assembly and
disassembly. Don’t be in a hurry. Think through everything
before you do it.
IMAGE: DifferentialPinionShims01a.jpg “
"
© Dr. Ing. h.c. F. Porsche A.G.





Referring to the image below (DifferentialCrossSection01a.jpg)

The differential shims 1 (red) and 2 (green) serve two functions.
First the total of S1 and S2 (S1 + S2) establishes the preload
on the carrier bearings. This is first set by measuring the side-
cover clearance to the case when not bolted in place. Once
bolted in place it is further refined by measuring the torque
required to turn the differential. More on those specifics later.

The other function is to position the ring gear axially in order to
achieve the correct backlash. By reducing the shim S1 (red) and
increasing the shim S2 (green) by the same amount, the preload
is maintained and the ring is moved away from the pinion. This
increases the backlash.

This diagram only shows a shim. Your 915 should have both a
shim and a “compensating washer” in these locations (red & green).
The shim goes between the washer and the bearing. The washer's
function was to not have the puller contact (and potentially
damage) the shim.

The washer is 901.332.263.11

There are 14 different thicknesses of shims.
You only use one shim in each location (S1 and S2).
2.4 mm – 901.332.265.21
2.5 mm – 901.332.265.22
2.6 mm – 901.332.265.23
2.7 mm – 901.332.265.24
2.8 mm – 901.332.265.25
2.9 mm – 901.332.265.26
3.0 mm – 901.332.265.27
3.1 mm – 901.332.265.28
3.2 mm – 901.332.265.29
3.3 mm – 901.332.265.30
3.4 mm – 901.332.265.31
3.5 mm – 901.332.265.32
3.6 mm – 901.332.265.33
3.7 mm – 901.332.265.34

For ’74 and later:
The 0.25 mm washer is 915.332.263.00

The shims are:
2.4 mm - 915.332.265.00
2.5 mm - 915.332.265.01
2.6 mm - 915.332.265.02
2.7 mm - 915.332.265.03
2.8 mm - 915.332.265.04
2.9 mm - 915.332.265.05
3.0 mm - 915.332.265.06
3.1 mm - 915.332.265.07
3.2 mm - 915.332.265.08
3.3 mm - 915.332.265.09
3.4 mm - 915.332.265.10
3.5 mm - 915.332.265.11
3.6 mm - 915.332.265.12
3.7 mm - 915.332.265.13

With a large collection of new and used shims you can work with
the 1/100 mm decimal place. A digital micrometer that reads to
0.001 mm is very handy (most read to 0.01 mm). Keep a running
log of every measurement and adjustment.

IMAGE: DifferentialCrossSection01a.jpg "
"
© Dr. Ing. h.c. F. Porsche A.G.

In this diagram “E” is the measured value using the tool P258 or
VW385. E = R + r. In practice you don’t use “E” because P258
or VW385 can be set to zero at “R” and then indicate the
Deviation “r”. More on that later.





What year is your 915? What type number 915/??
I think some of the problem is that under the drag racing loads
the side cover has become deformed, allowing too much
backlash. This causes the contact to change from the design
value, consequently the noise. This also relieves the carrier
bearing preload.

If this were mine, I would first measure the pinion position now
that you have the differential out. Second, I would remove the
pinion and input shafts, remove the differential seals and O-ring
and measure the carrier bearing preload (if any). That would
give me a good starting point for deciding what to do next.

If you have the magnesium side cover you should replace it with
the later reinforced aluminum version or, even better, the
aftermarket cover that uses the larger 930 bearing.

“Can you simply leave them alone and replace the bearings?”
Yes you CAN. No, I wouldn’t if you want to fix the problems.


Best,
Grady

EDIT to correct a typo it's VW385 not VW365, eye-brain failure.

[john walker's workshop]

it's not like you are setting up a new R+P. the one in the trans was adjusted by the factory, and hopefully nobody has messed with the original setting. that setting is optimum and the R+P has matched itself to that setting with a wear pattern, however slight. moving things can cause extra noise and future wear. all i'm saying is replacing bearings won't change the original setup dimensions, but only return the R+P to the original setup position, if it's been compromised by bearing wear. if gear face wear has manifested itself during the time the gears were out of spec, then it's possible that they will remain somewhat noisy.

[RarlyL8]

WOW!
Thanks guys!
Let me digest all of this and see what tools I have that will check those specs.
One question - if the factory shims are damaged can you simply replace the damaged shims with new ones of the same part number? Seems logical to me that everything should go back very close to the way it was if the exact parts are replaced. All I have to do then is re-measure everything when its done.

[john walker's workshop]

the side shims will probably be ok, unless you gouge them when the bearing is pulled. the shims that get pounded are the pinion depth shims, but you're not going in there....yet.

[Grady Clay]

The shims virtually never get damaged and yes you can replace with the same size.

I suspect the carrier bearings aren’t the cause of the problem. Perhaps a symptom or a result of something else. That’s not to say they shouldn’t be replaced.

What year and type 915/??

With care and patients YOU can easily rebuild a 915. When you get to measuring the R&P settings, yes you are going to want to find someone close with the Factory tools. You can do 90% of the work and with this Forum you can do it better than an inexperienced clod on flat rate.

My recommendation still is to find out where the R&P is now setting, compare that to the etched numbers and specifications THEN make a decision.

You CAN do it.

Best,
Grady

[RarlyL8]

The numbers on the bottom of the tranny are as follows:

915/61 718 7314 Car is a '78 SC

This car was bone stock when I bought it. I'm pretty sure the tranny is original.

I expect that you may be right about the bearing/race/whine issue being only a symptom. Replacing these items will let me know the answer to that one. If the damage is internal then I will tear the tranny down and evaluate the cost to fix it. If the cost is over $1000 then I will buy a used one and replace it. Rebuilding this one for fun would be interesting to do - if I had the time. That ship sailed when kid #2 came along.

Thanks again to both of you. I'm still pounding my head against the wall for being goated onto a drag strip. I knew better.

[Tom F2]

My recommendation still is to find out where the R&P is now setting, compare that to the etched numbers and specifications THEN make a decision.

You CAN do it.

Best,
Grady [/B][/QUOTE]

Grady, are you saying that it's possible to check the pinion depth without the VW 365 tool?

Thanks.

[Grady Clay]

Tom,

The easy way is to have everything clean and dry (not dripping
gear lube) and take it so someone with the P-tools. If someone
brought me one with the pinion firmly in place, the intermediate
tunnel tight, the pinion stack torqued, the differential bearings
and spacers clean, the seals and O-ring removed – it wouldn’t
take 15 minutes to get the tool out, set, several measurements
made, and put everything away. With the P-tools it is that easy.

If you find a VW shop with the VW365 set for all VWs, it might
take buying a pair of VW385/4 rings to fit a 901, 915, 930 or
whatever. Buy them and trade for the work.

Any competent machinist can make the tool. For a few uses it is
generally worth “renting” the tool and operator. I can’t imagine
there is a reasonable size city in North America without one or
more of these tools.

NOTE: I corrected my typo in my post above. It is VW385 not
VW365.

Here is the set of pieces necessary for a 915:
IMAGE: DifferentialToolsVW385a.jpg “
"
© Dr. Ing. h.c. F. Porsche A.G.

1 – VW385/1 Setting gage shaft
2 – VW385/4 Gage block (fits the bearing races)
3 – VW385/14 Gage contact plunger
4 – VW386/53 Gage contact extension, 14 mm
5 – VW385/52 Master plate (for setting R = 66.30 mm for a 915)
6 - -------------- Dial indicator, 3 mm travel
7 – VW385/17 Setting pad 5.000 mm x 50 mm Ø

See what is available locally for you.

Best,
Grady

[RarlyL8]

Update -
I changed out the carrier bearings and put everything back together a couple of weeks ago.
The noise is much reduced and very specific now.
It occurs when the throttle is lifted above 60mph.
It is also present but much more quiet between 55-65mph.
It COMPLETELY goes away when you depress the clutch.
It ROARS if I get on it really really hard and let off at high RPMS.

From all you folks have described it look like the pinion bearing has been damaged allowing the pinoin to move out of allignment with the ring gear during decelleration.

Options? I am looking for a 915 with a LSD and 8:41 gears. If I can't find one I can afford I will try to replace the pinion bearing with the WEVO unit.
Thank you all!

[dentist90]

Sorry to drag up this old thread, but I haven't been able to find anywhere the value for preload on the differential bearings. I am in the position where I am going to have to swap my gear shafts and differential into a newer (used) final drive case. I discovered a crack in my existing case between the bores recently.
I expect I will have to ship my reassembled tranny out to reset the pinion and ring gear relationship as I don't have the VW385 tool, but I thought I might try to gather as much info about my existing setup prior to swapping over. My final drive was quiet and looks to be in good shape, but as it has over 100,000 miles I don't know that setting it back to factory specs will be an improvement.
What is the factory setting for preload, and do I measure it simply by putting a beam-type torque wrench on the flange nut and turning it at a constant rate?
I have also given thought to checking the current mesh pattern with indicating paste and photographing it to have something to compare to after reassembly in the new case.
Unlike RarlyL8 I don't have a whine yet, but I don't want to end up with one afterwards!
Here's the cause of my present predicament:

Any advise appreciated. I'm pretty sure that individual casings are different enough that a straight swap over won't work, even if keep the original side cover and bearings.
Its a 915/68 and the diff housing hasn't been opened yet.