Axles shaft conversion questions.........

[boyt911sc]

I've been helping a Pelicanite get his car back on the road and I came across some problem in which I need some advise from those who have encountered similar situation. This is the background of the story:
1). A 3.0 liter SC engine was removed from a '74 Targa including its original trans.
2). A '78 SC roller was purchased by the owner as the receiver of the above engine.
This is the problem:

The 915 transmission from the '74 Targa has 4-bolt (10 mm), 110 mm in diameter and has course spline. See picture below.



The bolt pattern and size for the SC CV joints are completely different. It has 6 bolts (8 mm) and 100 mm in diameter.



This is the picture of the axle flange from a '78SC transmission with 6 bolts (8 mm) and 100 mm diameter.



Side by side comparison: The one on the left of the pictures is the 6-bolt (8mm) 100 mm dia. from a '78 trans and on the right is the course splined, 4 bolts (10 mm), 110 mm dia. plus two (2) dowel pin holes. The flange diameter, bolt size diameter, spline size, and end of rod contour are all different from each other.




What do I need or do to be able to install the SC half shafts (axle shafts) to the transmission side? For the wheel sides, the stub axles are 6 bolts (8 mm) and fit well. Any suggestion, tip or recommendation is highly appreciated. Thanks.

Tony

[Grady Clay]

The best and easiest solution is to use the axle & CV joint assembly and the outboard stub axle from the 1974 911. These will be the big 108 mm CV joints and use the larger M10 bolts and 10 mm roll pins.

Use new M10 Schnorr washers. Carefully inspect the M10 bolts, particularly the wrenching hex. Replace any that are not perfect.

The spline between the stub axles and hubs are the same across these years.

This is a very desirable axle conversion.
I’m about to do the same with my ’79 911SC.


One difficulty you may not (yet) addressed is the speedometer. The ’74 transmission does not have the provision for the ’78 electronic speedometer. You will need to either install a mechanical speedometer cable and speedometer instrument or replace the ’74 main transmission casting with a ’76 and later version with the provision for the electronic speedometer sensor.


Best,
Grady

[boyt911sc]

Grady,

Before I proceed asking more questions, I would like to thank you for sharing your experience and knowledge with us specially with this particular post.

Originally Posted by Grady Clay

The best and easiest solution is to use the axle & CV joint assembly and the outboard stub axle from the 1974 911. These will be the big 108 mm CV joints and use the larger M10 bolts and 10 mm roll pins.
Best,
Grady

So the '74 CV's are 108 mm in diameter to match the existing axle flange on the transmission? I thought the 108 mm CV's were available from '84 & earlier Turbo/ Turbo look cars and in '85-'89 Carrera's? If I understood you correctly, a complete '74 CV assembly including a stub axle ('74) are all I need? Is the '74 stub axle different from the SC's? I have already a pair of SC stub axles on the car.

Originally Posted by Grady Clay

The spline between the stub axles and hubs are the same across these years.

This is a very desirable axle conversion.
I’m about to do the same with my ’79 911SC.
Best,
Grady

Could you elaborate more on this topic? What's the advantage over current stock set-ups?

Originally Posted by Grady Clay

One difficulty you may not (yet) addressed is the speedometer. The ’74 transmission does not have the provision for the ’78 electronic speedometer. You will need to either install a mechanical speedometer cable and speedometer instrument or replace the ’74 main transmission casting with a ’76 and later version with the provision for the electronic speedometer sensor.
Best,
Grady

I believe there is an electronic speedometer sensor on the transmission. This 915 trans look identical with my '78 transmission except for the axle flanges. Where is the trans. code number located?

I would really appreciate if you could be more patient in educating me (senior citizen with failing memory) and have this problem sorted out. Many thanks.

Tony

[Grady Clay]

Tony,

Originally Posted by boyt911sc

So the '74 CV's are 108 mm in diameter to match the existing axle flange on the transmission?

Yes.

Originally Posted by boyt911sc

I thought the 108 mm CV's were available from '84 & earlier Turbo/ Turbo look cars and in '85-'89 Carrera's?

Yes, that was when the Porsche engineers won out over the ‘bean counters’.

Originally Posted by boyt911sc

If I understood you correctly, a complete '74 CV assembly including a stub axle ('74) are all I need?

Yes.

Originally Posted by boyt911sc

Is the '74 stub axle different from the SC's?

The stub axles only differ in the diameter and bolt/pin configuration where the CV joint attaches. The spline to the wheel hubs are the same.

Originally Posted by boyt911sc

Could you elaborate more on this topic? What's the advantage over current stock set-ups?

Porsche changed to the 100 mm, six M8 bolt CV joints in 1976, These are the same as the ’76 2.0 912E and have the same Type 923 part number. Bean counters uber alles.

As it turned out, these were not sufficient for 3.0 and 3.2 torque. I think there were many undisclosed recalls and pay-offs after accidents. Porsche went back to the 108 mm version (now six M10 bolts, no roll pins). This axle assembly has a 928S part number.

The advantage of the ’74 axle assembly is it has the 108 mm CV joints and M10 bolts – and you have them.

The six M10 bolt, 108 mm CV joint, 928S axle would be the best choice of all. The problem is you start replacing many parts including the differential housing, the spider gears, transmission axle flanges, stub axles, re-setting the R&P and much more.

Originally Posted by boyt911sc

I believe there is an electronic speedometer sensor on the transmission. This 915 trans look identical with my '78 transmission except for the axle flanges. Where is the trans. code number located?

The codes are under the transmission, on the rib that supports the clutch cable and parts. Engineer von Stülpnagel decided on this location. It is the lowest on the transmission and is typically scraped off or illegible.

The ’78 911SC Transmission Number should be of the form: Probably 718xxxx, where the ‘xxxx’ is the sequential serial number. It also should have a Type Number of the form: 915/61. If there is a number “12” between the Transmission Number and the Type Number, you have a real ‘find’ with a ZF LSD.

The 1974 numbers are: 734xxxx and 915/06.

If the ‘1974’ transmission has original provision for the electronic speedometer, it is not a ‘74 model. There is a casting date on the side of the transmission main casting. It is in the form of a circle with xx/zz inside. The ‘xx’ is the week of the year (01 to 52). The ‘zz’ are the last two digits of the year cast. The casting date will always pre-date the date of manufacture on the driver’s door-jamb decal.

Best,
Grady

PS: Carl-Heinrich von Stülpnagel was the German general involved in the plot to kill Hitler in 1944. He tried to commit suicide by shooting himself in the temple. He only succeeded in blinding himself. The Nazis later strangled him with piano wire.

His name is associated with gross incompetence – not even able to kill himself.

G. (another senior citizen with failing memory)

[boyt911sc]

Grady's has given me a good direction in dealing with this problem. Anyone out there have some novel idea to share? Right now, there are two (2) options I could follow:

Option A:
Replace the 110 mm (10 mm x 4 with 2 dowel pins) axle flanges to 100 mm (8 mm x 6) axle flanges. A pair of 100 mm (8 mm x 6) half shafts with stub axle are available for installation.


Option B:
Keep the 110 mm flanges and procure a complete '72-'74 110 mm half shafts (axles) with stub axle.

Option C:
I'm not sure this is feasible but an idea that was suggested to me. Is to convert the transmission side of the CV/half shafts from 100 mm to 110 mm (CV joint). Anyone could shade light to this idea? Has anyone done this conversion?

Comparing the two (2) options, I think doing option A is a more prudent course of action than option B. Could someone share their thoughts/experience or what would you have done if you're in this situation. Thanks.

Tony

[Flat6pac]

The 100mm coarse flanges for the 74 trans, if you look mid 75,to77 uses the 6 bolt coarse flange. Simple change and this will meet with the 78 halfshaft.
Bruce

[Grady Clay]

Tony,


I had interpreted this:

1). A 3.0 liter SC engine was removed from a '74 Targa including its original trans.
2). A '78 SC roller was purchased by the owner as the receiver of the above engine.

as you still had the 108 mm axle assemblies available from the ’74.

Yes, buy the 100 mm, coarse spline transmission axle flanges.
They should be inexpensive as it is a common part with no market.
Absolutely replace ALL the M8 CV joint bolts and Schnorr washers.
Re-torque the M8 bolts (33 ft-lbs) after a hundred miles or so and at every service.

I still want to know how a ’74 transmission has the provision for an electronic speedometer. Images and numbers please.

Best,
Grady

[boyt911sc]

Originally Posted by Grady Clay

Tony,

I had interpreted this:

as you still had the 108 mm axle assemblies available from the ’74.

Yes, buy the 100 mm, coarse spline transmission axle flanges.
They should be inexpensive as it is a common part with no market.
Absolutely replace ALL the M8 CV joint bolts and Schnorr washers.
Re-torque the M8 bolts (33 ft-lbs) after a hundred miles or so and at every service.

I still want to know how a ’74 transmission has the provision for an electronic speedometer. Images and numbers please.

Best,
Grady

Grady,

I have not inspected the transmission number. The 3.0 liter & 915 trans were removed from a '74 Targa and installed in a '78SC roller by me for a Pelican member who needed some assistance. I believe the PO changed the 100 mm trans flange to 110 mm flange to accommodate the bigger '74 halfshaft in the 915 trans.

I don't have any '74 half shafts but a pair of SC half shafts with stub axle. So replacing the 110 mm trans axle flange to 100 mm is what I plan to do. Since I got already the SC axles and stub axles in the car, installing a replacement 100 mm (course spline) axle flanges could simply solve this problem. Any comment or suggestion?

So the next strategy is locating a pair of 100-mm course splined transmission axles to finish the project. Anyone know where to find such replacement parts? I'll post a WTB tonight. Thanks.

Tony

[RR711]

In case you have'nt solved your problem yet, I have a pair of '74 axle assemblies with 110 mm cv joints and outboard stub axles for your project. The cv joints have less than 100 miles on them. If you're interested I can email pics. I put a later 915 into a '74 chassis and did the reverse of what you're doing.

[Captain Ahab Jr]

Calling Grady Clay, I need your help please.

I am trying to come up with a conversion for the wheel end. I am using 930 CV joints a(110mm flange, 94mm PCD, 6 x 10mm Bolts) and needsome help in choosing the right stub axle and wheel hub.

What would you suggest for the outboard end if we were to ignore the dimensions of the swing arm bearing machine features etc? I will have some aluminium uprights machined so am pretty flexible on what I use.

Am I correct in thinking that maybe an early 928S stub axle and wheel hub would be the best choice?

[Flat6pac]

You need to find the hubs for a 76/77, 911. It will have 6 8mm bolts and coarse spline to mate the early trans into the SC. I would call G. Fairbanks in Norwalk, Ct and in the next days mail you ll have your needs. No relation with Gary but always happy with his knowledge.
Bruce

[boyt911sc]

Update: Option A was my solution. A week after I posted the inquiry, I was able to locate a pair of 100 mm diameter trans flanges with 6 bolts (8 mm) from a Pelican member. The owner of the car, another Pelican, took the car home to NJ in early spring. I spent about 350 man-hour during the winter restoring the car for $6 an hour rate. It was just a hobby to keep me busy in the winter. I miss the blue SC roller sitting on my lift.....it's like losing a foster child.

Tony

[Grady Clay]

Tony,

Good. Finished projects are good.
Would you like to spend this winter in Denver?
I have a couple of projects that need finishing.
The weather is nicer than Philly.

Originally Posted by Captain Ahab Jr

I am trying to come up with a conversion for the wheel end. I am using 930 CV joints a(110mm flange, 94mm PCD, 6 x 10mm Bolts) and needsome help in choosing the right stub axle and wheel hub.

What would you suggest for the outboard end if we were to ignore the dimensions of the swing arm bearing machine features etc? I will have some aluminium uprights machined so am pretty flexible on what I use.

Am I correct in thinking that maybe an early 928S stub axle and wheel hub would be the best choice?

I suppose it depends on what you are building.

The 930 parts are substantially different from the 911/928S parts. The 930 has a very long stub axle that does not interchange with the 911. The 930 uses two tapered roller bearings (like front wheel bearings only much larger). This is far stronger than the largest 4-point bearings used for the 911. Since you are building uprights, this is stronger.

I think (not sure) the 928S uses a 4-point bearing.

Both use 108 mm, six M10 bolt CV joints. The 930 axle assembly is shorter to accommodate the longer stub axle.

We need pictures of this project.

Best,
Grady

[boyt911sc]

Originally Posted by Grady Clay

Tony,

Good. Finished projects are good.
Would you like to spend this winter in Denver?
I have a couple of projects that need finishing.
The weather is nicer than Philly.

Best,
Grady

Grady,

Since my retirement began, I've spent most of my time between babysitting my grandchildren, play golf 4 or 5 days a week, travel, and work on 911 cars (not mine but belongs to Pelican members). I have a 3.0 engine rebuild project that needs some attention.

As long as I'm working in my garage and close to home, doing a car restoration or fixing somebody's car is workable. After the roller's restoration work in spring, I've dropped and installed 2 motors for free this summer. One member (Pelican) whom I've never met before showed up in my place for a new clutch and pressure plate including throw out installation, oil pressure switch replacement, and many more 'while you're there'. It took 2 full working days to completely finish the work and he left with a big smile on his face.

Unfortunately, no phone or email after that day. He offered to buy me dinner after the work was completed and I graciously accepted it. It has been 2 months now and still waiting. I hope nothing serious happened to him because I'm still waiting for the steak dinner he promised me.

Visiting Colorado is great. But last time I visited California this summer for 4 weeks, my five-year old granddaugther tagged along with me. I like to meet the famous Mr. Grady in person..........someday.

Tony

[Captain Ahab Jr]

Originally Posted by Grady Clay

Tony,
I suppose it depends on what you are building.

We need pictures of this project.

Best,
Grady

Grady, you've cleared up another area of my project I was struggling with, thanks

I will be building a 917/908 inspired pre-73 narrow bodied car. Stock looking narrow bodied pre-73 on the outside pure race car on the inside. I have no rules to follow other than my wallet so I'm making up everything as I go along.

Can you clarify what you mean by a 4 point bearing, do you mean the outer and inner races are built into one housing as on all the later cars such as 993, 996 etc.?

If so the Turbo twin taper bearing will give a much stifffer installation as you mention. All I need to do now is find some

Sorry no pictures at this stage, I'm collecting parts, trying to come up with solutions, asking lots of questions and doing a little CAD work.

Thank you again for your help.

[Carrerax]

On this same subject, Im putting a 1983 915 in a 1970t. Im looking for a set of 110 (108?) fine spline 915 output flanges for the trans. I need the 4x 10mm bolt ones. I have a set of newly plated 100mm 6 bolt fine spline output flanges for sale or trade....Please let me know if anyone has a pair available. I would really appreciate it

[Fishcop]

I thought I'd also add that you cannot put the two different CV joints on the one shaft due to shaft spline differences... I definitely tried!

[jmitro]

Bump for some help.
My situation is opposite of boyt911sc.
My 915/63 gearbox (from an 83SC) has the original 6 bolt 100mm stub axles. The inboard and outboard CV joints on my axles have been replaced with the 4 bolt/2 dowel pin CV joints. So the CV joint flanges don't match the stub axles.

I presume it would be easier to replace the axles/CV joints than to replace the stub axles? Does this mean the outboard stub axle has to be replaced also? Will it even fit the trailing arms?

edit - here's a photo of my axle shaft

[Lucifer912]

Hello Boyt911sc, Are you willing sell the Phlanges that are course splined, 4 bolts (10 mm), 110 mm dia.? I have a problem my flanges do not fit my Axels either so I need the larger Phlanges. with coarse splines.

[mepstein]

11 year old thread.