SC/930 conversion axles?

[911tracker85]

Mark... I did search first.

I am at the point of looking towards putting stuff together rather than tearing down.

I have a 78 SC that was converted to a 930 ... partially. the initial conversion put in a modified 3.3 turbo motor but kept the 915.

I finally got a short BH 930 4 sp. but with the SC banana arms the output shaft of the 930 4 sp is different than the stub axle from the SC.

forgot to measure them and will do.

so for those who have done 930 conversion with 930 4sp but non-930 rear suspension, what did you do for axles?

[quattrorunner]

You could use the sc stub axles if they're compatible( Both fine spline). I'd use the newer thicker shaft versions of the half shafts though if you plan to use more than 400hp. The benefit to this is that you already have them and you wouldn't need the other end 930 parts attached to the 930 trailing arm.

[spuggy]

Originally Posted by 911tracker85

I finally got a short BH 930 4 sp. but with the SC banana arms the output shaft of the 930 4 sp is different than the stub axle from the SC.

I haven't done this, so take it with a grain of salt - I seem to recall that 930 output stubs have the same larger diameter (108mm?) and larger bolt fittings (M10) that late-style G50 stubs/axles use (as well as early - coarse spline - 915s, except that these used 4 bolts/2 pins)).

If that's right (and the respective axle lengths are in the ballpark), you might be able to use G50 axles for a 911.

These don't bolt up on the wheel side; the separate drive shaft 901-332-232-00 that engages the 911/930 wheel hub on earlier cars is part of the axle; nominally non-detachable. Remove the drive shaft in the banana arm, and the CV only gets bolted up on the gearbox stub.

If you went with M491/930 G50 axles without the attached spline, you'd need to swap the wheel drive hub to match the axles.

It's also possible the CVs will interchange on the axles. That could mean you might be able to fit a 930/G50 CV on a 915 axle, or a 915 CV (e.g. the wheel end) on a 930 or G50 axle.

At least you'd always know what was going to break if you did that...

[spuggy]

Originally Posted by quattrorunner

You could use the sc stub axles if they're compatible( Both fine spline).

They might fit (930 and 915 LSDs are identical I think, so splines match), although I seem to recall there's some fitment caveats in some directions (read: "machining"). Looked into it some when I wanted to run G50 axles on a 915. I forget why, but I think 930 stubs don't work in a 915. Or need to be machined. Might have a bookmark...

(To anyone else considering that route - good luck finding the large 915 flanges the factory used for about 10 minutes - oh, OK, a few months - before switching over to G50; aftermarket or adapting seemed the only realistic option 10 years ago, and they're just rarer now).

Originally Posted by quattrorunner

I'd use the newer thicker shaft versions of the half shafts

Did they beef up late 915 axle diameter and keep the same CVs? Heh. My concern was always for the 915 CVs...

[quattrorunner]

Originally Posted by spuggy

Did they beef up late 915 axle diameter and keep the same CVs? Heh. My concern was always for the 915 CVs...

Not sure about the cv actually but later 915 half shafts use the smaller diam stub bolt circle with thicker shafts. These seem to be the replacement half shafts for earlier cars with 100mm stubs?

[lite75]

Here's a good one on axles and CVs, make sure you read the whole thread as some corrections have been made.


CV and Axle Cross Reference

[quattrorunner]

Thanks for that. Ignore my earlier info. I’m now more confused than ever about how I’ve come up with what I have. I do know that my 915 was a 915/61 from a 77 and my 930 fits the same fine splines. And also that the axles I use are up to 85.5 with8mm bolts. They’re thicker shafts and work great. I assume the 930 axles with larger 10mm bolts will give greater strength. My 450hp isn’t damaging my 8mm bolts as of yet.

[911tracker85]

finally pulled the SC axle out and took an old 3.2 cararra axle to the shop.

it appears I will be able to use the carerra axle with the 930 gearbox output shaft.

or am I delusional?

the 3.2 axle fits the SC hub, about 1/4" longer in the threads.

and the 3.2 axle accepts the 930 output flange once you remove the grease cover.

[356911930]

Nice work Bob! Very interesting research. I secretly purchased a 1972 911 that I plan on modifying. Naturally the 930 has been sitting in the garage for about 4 years waiting for me to rebuild the engine and transmission. I had just finished the paint and interior started to drive on the 18 year "rested" engine and discovered it had a broke head stud, so there it sits. I hope to get back to the 930 this winter.

Rahl

[911tracker85]

LOL
I also 'secretly' purchased an 87 924S that I planned to pull the engine to use the block to rebuild the motor in my 951 track car. but came across a good 951 engine I am going to buy and get the 951 running, have not been to a track event yet.

at some point I'll put this turd up on the lift to see how much suspension, brake, etc work it would take to get it on the road. PO drove it to the shop across the street and parked it a couple years ago. I bought it and we put in some gas and used a jump box and after some cranking it fired up, did not really expect that and it drove across the street under its own power. with lots of clanking and rattling from the bad flex plate.

auto with a bad flex plate and PO already got that when I explained what it would take to replace he lost interest. if not too much expensive work will replace the flex plate, gut the car but keep street legal, and let my partner's sons beat it on the track / autocross.

good luck on your projects.

[Alan L]

Nothing a water blaster won't fix. Will look a $M.
Alan

[911tracker85]

yea ... it'll buff out fine....

[Matt Monson]

100mm SC stub axles willbolt directly to a 930 gearbox. No changes are required to the axle. However, that obviously doesn’t get you to stronger axle.

As discovered, 108mm Carrera stubs also bolt tight in and you can use late 3.2 axles with a 930 gearbox as well.

[flightlead404]

Originally Posted by 911tracker85

yea ... it'll buff out fine....

My dad is a tv repair man, he's got this ultimate set of tools, i can fix it

[911tracker85]

100mm SC stub axles willbolt directly to a 930 gearbox

the pic I did not post is the SC axle up against the 930 output flange. I did not measure but suspect the 930 output flange is 108mm. it was rebuilt and shortened, think it is an '80 930 gearbox. did the 76-77 930 output flange 100mm?

no matter I've got a solution.

[Matt Monson]

All 930 stubs have always been 108mm, even the early ones.

[wkrtsm]

Looked into this issue of late, since I am currently planning on 300-480 foot-pounds of torque (>500 HP) and have been informed such torque would absolutely snap/shear/disintegrate anything related to the 915 including CV joints, half-shafts, and stub axles. Even with a 930 transaxle, it's easy to employ a custom-length 930 half-shaft between inner and outer 930/G50 CV joints, but there is currently no "strong" 108 mm stub axle available which provides 6-bolt 10M threaded holes for fitment in a steel LWB trailing arm. Thus, I just approached the Driveshaft Shop to get a quote on manufacturing such a stub axle. I am trying to avoid to the extent possible swapping out the center of the torsion tube or welding in new pivot points for fitment of other arms.

Frankenstein or no frankenstein, the more challenging effort is to secure a stub axle that is as easily replaceable/upgradeable and as strong as e.g. 930/G50 CV joints and half-shafts. Obviously, there are risks for other components such as torsion tube twisting, crossmember weld breaks, and trailing arm strength, which have been addressed elsewhere. But I am at least considering 935 spring plates and reinforcing the mounts, shock tower gussets, crossmember reinforcement, and buttressing the torsion tube with a welded-in engineered truss from square tubing above the rear seats. From an engineering standpoint, I consider an extreme HP upgrade to an early chassis like putting a 300 HP outboard engine on a row boat.

[quattrorunner]

Really? I haven’t heard about this as such a weak link. Obviously I’ve seen gussets but haven’t see much more done than maybe going coil over and adding gussets. I’ve always thought these chassis were pretty well built.

[wkrtsm]

Originally Posted by quattrorunner

Really? I haven’t heard about this as such a weak link. Obviously I’ve seen gussets but haven’t see much more done than maybe going coil over and adding gussets. I’ve always thought these chassis were pretty well built.

The modifications seem to never end, like seam-welding the entire car to gain "rigidity." I have heard the "torsion tube and chassis are more stronger and reliable than you think" comment, but personally, I don't trust the chassis without numerous reinforcements, especially with 315/35R17's in the rear.

[spuggy]

Originally Posted by wkrtsm

there is currently no "strong" 108 mm stub axle available which provides 6-bolt 10M threaded holes for fitment in a steel LWB trailing arm.

With a 911 trailing arm, why not remove the wheel-side stub axle and use "attached stub" G50 axles from 86-89 911, which fit directly into the wheel hub? (930 trailing arm/wheel configuration is different).

With big sticky tires, lots of torque and having eliminated obvious weak points, your concerns probably become "everything". As in, probably not entirely obvious what will break first/next.

I run SC flares and find 255/40/17 hi-perf tires to be right in the sweet-spot for price/performance/availability/fitment. Which is both a limitation and a fuse. However, I'm not really too concerned with putting 400+ ft/lbs to the road launching from a standing start, because that's not what I do with the car.