Installing a 915/72 (aka 86 Euro 915) in my 73

[Dodge Man]

My 915/61 717 needs a winch to get it into 2nd gear so I went bit over the top and got an 86 low miles 915/72 complete with factory oil cooler. I run a 1983 930/10 motor (euro 3.0) with SSI & no TE or CAT so I should have more than enough power/torque for 5th. The 915/72 has the 6-bolt “Joint Flanges” (aka hubs) and I want to solve the mating issue without having to open up the transmission or change rear suspension. It is a street car that is not auto-X or tracked; just a few sprints here and there. Is there a special CV joint, custom axle, or simple bolt on solution? I already have the electronic speedometer conversion but my axles are the 1973 OEM 69-77 4-bolt & 2-pin hubs/flanges.

[Eagledriver]

I think you might be lucky. The bolt spacing on your flanges should match the bolt spacing on your CV joints. You could just drill out 2 opposing holes to fit the pins on your CV joint. Of course the flanges you have are worth their weight in gold so it would be a shame to drill them. Alternatively you might be able to replace the pins in your joints with bolts.

-Andy

[jpnovak]

Most likely this transmission has the 100mm 6-bolt flanges. The easiest solution is to get the matching SC half-shafts and rear hub flanges to match.

The 108mm 4 bolt (or 6 bolt) CV shafts are a different diameter. so swapping joints is out of the question.

You can not easily swap drive flanges as the spline pattern is different internally.

[trak ratt]

Originally Posted by jpnovak

Most likely this transmission has the 100mm 6-bolt flanges. The easiest solution is to get the matching SC half-shafts and rear hub flanges to match.

The 108mm 4 bolt (or 6 bolt) CV shafts are a different diameter. so swapping joints is out of the question.

You can not easily swap drive flanges as the spline pattern is different internally.

Or go all in and replace the rear control arms with the later aluminum ones (near bolt-in). then upgrade the axles to the later ones too.

Might make even more sense if your old axles are worn anyway.

[Dodge Man]

Trak Ratt, Which year rear arms? Are the 78-70 the best fit or will the 80-83 arms fit too? Is it a bolt on installation or is there cutting & welding involved?

[E Sully]

When I installed a 1986 915/73 in my 1973 I just drilled out the 2 holes opposite the 2 pins and it bolted up perfectly.
Sorry Eagledriver, I did not know they were valuble. I figured if ever needed, I could have them welded and then drilled and tapped back to stock. Why are they worth their weight in gold?

[Dodge Man]

Sully did you take any photos of the joint flange modification? Did you remove the flanges use a machine shop to locate & size the holes or just drill & ream?
I think that Eagledriver is referring to the joint flanges on the 915/72 having the coveted fine splines which means it has the stronger fine spline carrier & stronger spyders. It may also be able to carry a nicer LSD unit too. Fine splines and fine threads are usually associated with higher load carrying pieces.

[J0hnny]

There are 2 threads in which compatibility and combos you can make with cv's are explained...
You should be able to get away with that swap without too much hassle

Give this a read:

CV Joint and Axle/Half Shaft Compatibility

Reconstructing Constant Velocity (CV) Joints

[E Sully]

I simply got out the hand drill and matched the size of the pin with a drill bit and reamed it in place. It was quick and simple. Except for using 2 pins the holes in the '86 transmission flange are identical to the 1973.

[arrivederci]

Originally Posted by E Sully

I simply got out the hand drill and matched the size of the pin with a drill bit and reamed it in place. It was quick and simple. Except for using 2 pins the holes in the '86 transmission flange are identical to the 1973.

Right, you can do that. But you give up the additional clamping strength of 6 10mm bolts that the 108mm 6-bolt 10mm fine spline flanges offer.

I have an '84 euro trans going into my '72, but I sourced the 108mm flanges. For stub axles, I'm still debating what I'll do. I have alum trailing arms already.

[Eagledriver]

86 flanges are bigger (108mm), unlike the SC and early Carrera flanges. They are the same size as the early (1973 etc.) flanges but with fine splines. A nice upgrade for your car would be banana arms and drive axles from an 86 Carrera.

-Andy

[Dodge Man]

Thanks to everyone for the posts. The posts have been most helpful to planning my transmission installation. Thanks to JOhnny for the link to the CV Joint and Axle/Half Shaft Compatibility thread from Tom ’74 911. Tom's post has the most caliper measurements of CV joints & splines to see what will fit on the late 915 fine spline trans flanges & early axles. Hats off to Tom ’74 911 for posting his detailed results.
The 108mm 6-bolt/hole relationship between the early CV joints (69-75) and the 85.5 up 915 CV joints indicated a probable engineering reuse of CV dimensions that were reused because they had worked well on earlier models. Hey, “If it ain’t broke, don’t fix it”. Engineers love to make things interchange; just look at how many parts on the 911 interchange between year models. Also, the two locating pins were probably used for locating or holding flanges during manufacturing and should give additional shear value like the additional two 10mm bolts.
According to the Tom ’74 911 measurements & results, replacing the inboard CV joints with the 85.5-89 CV joints should give me a true bolt on installation from my early axles to my 915/72 trans flanges. Now I am trying to get some additional confirming spline & flange fit installation results.

[Dodge Man]

Originally Posted by arrivederci

Right, you can do that. But you give up the additional clamping strength of 6 10mm bolts that the 108mm 6-bolt 10mm fine spline flanges offer.

I have an '84 euro trans going into my '72, but I sourced the 108mm flanges. For stub axles, I'm still debating what I'll do. I have alum trailing arms already.

You may just look for a way to make some consistent themes in specific areas like install the new trans with $200 in CV joints & bolts, drive it to get a feel, and then come back later for the rear suspension changes. I just wanted a solid new transaxle with the minimum of changes to make it work because the 915/72 was not cheap.

You probably won't but if you need custom length axles, I ran across a few suppliers in my searches for CV info. The off-road community has quite a few non-standard lengths in the catalogues. Sway-A-Way has a page just for Porsche 930 axles.

[Dodge Man]

Eric at PMB was kind enough to test fit the 85.5 up CV joint on a long hood axle he had removed. It fit on the 28 spline axle to confirm everything so I am on my way with the 2 new inner CV joints and no drilling.

[Roger 911]

I'm doing a 3.2 swap from an '84 into my '72. I'm thinking about taking the 915 w/LSD from the '84 as well. The flange/axle/cv joint issue has me a bit concerned. I do not want to have to replace my axles and rear suspension. I've been reading a lot of these threads regarding compatability, but I'm still a bit confused about what works with what.

My question; Can a '84 915 be used with '72 axles?

I read in this thread about drilling out the two holes on the 915 flange to accept the roll pins from the early CV joint. However, I'm not sure if this was only for a '85.5+ 915, or if this method would also work on a '84. I appreciate any assistance.

Thanks.
Roger

[arrivederci]

Originally Posted by Roger 911

I'm doing a 3.2 swap from an '84 into my '72. I'm thinking about taking the 915 w/LSD from the '84 as well. The flange/axle/cv joint issue has me a bit concerned. I do not want to have to replace my axles and rear suspension. I've been reading a lot of these threads regarding compatability, but I'm still a bit confused about what works with what.

My question; Can a '84 915 be used with '72 axles?

I read in this thread about drilling out the two holes on the 915 flange to accept the roll pins from the early CV joint. However, I'm not sure if this was only for a '85.5+ 915, or if this method would also work on a '84. I appreciate any assistance.

Thanks.
Roger

Your '72 has 108mm flanges with holes for 10mm bolts + 2 pins. Your '84 has 100mm flanges with 8mm bolts. So you are correct that drilling will only work on the '85.5+ which has the 108mm flanges.

[Roger 911]

Originally Posted by arrivederci

Your '72 has 108mm flanges with holes for 10mm bolts + 2 pins. Your '84 has 100mm flanges with 8mm bolts. So you are correct that drilling will only work on the '85.5+ which has the 108mm flanges.

OK, so could I use the 108mm flanges from the '72 915 on the '84 915, i.e., unbolt and swap them?

[vinyl_tien]

Hi
I am doing the same thing to my 73 911E, sorry to ask question here.
Can I use 87 930 axles for 915/72?

[Roger 911]

Originally Posted by Roger 911

OK, so could I use the 108mm flanges from the '72 915 on the '84 915, i.e., unbolt and swap them?

I think I may have answered my own question...

I can NOT simply swap the 108 mm flanges from a '72 915 with the 100 mm flanges from a '84 915 because the '72 uses course splines and the '84 uses fine splines.

If this is correct, it would appear my only option would be finding a pair of late 85.5+ 108 mm flanges (which I read to be rare/expensive), or change out my entire axle hub assemblies to the 100 mm cv joint type.

Neither of these is appealing to me. If this is true, I think I may pass on the '84 915 and just stick with my '72 915.

Any other suggestions?

[arrivederci]

Or I think you could change over your hubs and axles to '85 and earlier 100mm hubs. Those will match up to your '84 trans and might be more readily available. I remember reading that all hubs are not interchangeable - your '72 has steel trailing arms and may not work with 100mm hubs. I switched my '72 to alum trailing arms, but the 108mm hubs from my '72 fit them without any issues.