Broke the driveshaft outer axle...

[safe]

Broke this part on my -69 911 during a trackday. Luckily the rear caliper held the wheel....

This is the original 69 part, I use aluminum trailing arms from an SC and a G50 gearbox.

Is there a stronger part I can use.
Would a complete 3.2 G50 driveshaft bolt in? It should, shoudn't it?



Deep inside my spacers....

[winders]

Not that I am aware of....the Factory part is quite strong. The hubs are usually the weak point.

[stownsen914]

Looks like it failed at the threaded portion. Was there any damage to the threads? There appears to be some rust near the failure area, that could be a stress riser.

[safe]

Originally Posted by stownsen914

Looks like it failed at the threaded portion. Was there any damage to the threads? There appears to be some rust near the failure area, that could be a stress riser.

Yes, somewhere in the threads, no idea if there was any previous damage. Yes some rust, haven't had this apart since I put it together 6-8 years ago.

I was leaning pretty hard on the left rear and also hit the outside curbs on a few occasions, so I'm not surprised it broke. It could also have been over tightened or maybe the other way, too loose.

The hub has issues too, it just pulled out of the bearing with the bearing intact in the control arm. It looked rough.

I'll have to check the other side too.

[spuggy]

Originally Posted by safe

Would a complete 3.2 G50 driveshaft bolt in? It should, shoudn't it?

For '69, I believe it will. PET shows 901.332.232.00 for the axle, used 69-77. 1978 changes to 901.332.232.01 - I don't know the difference, but probably minor.

You already have output flanges to match.

[PeteKz]

Hmmm. It broke where the nut threads on. That connection should not be subjected to cyclic stress, unless something was too loose or worn. A "stronger part" should not make a difference in this application. I also noticed that the ends of the spline appear to be worn down. What does the outer spline look like? Does the axle spline wiggle around inside the outer spline?

[safe]

Originally Posted by PeteKz

Hmmm. It broke where the nut threads on. That connection should not be subjected to cyclic stress, unless something was too loose or worn. A "stronger part" should not make a difference in this application. I also noticed that the ends of the spline appear to be worn down. What does the outer spline look like? Does the axle spline wiggle around inside the outer spline?

Haven't looked at the outer spline, but I agree with you, maybe the nut had loosened. The bearing was loose on the hub and it looked very bad. So I need new hubs too.

I ordered a set of G50 drive shafts. The threaded part is M22 compared to my old 69 parts that are M20. So they are stronger.

[Locker537]

Won't you need to change the output shafts on the transaxle as well?

New hubs are rather expensive.

How's the bore on the trailing arm?

[safe]

Originally Posted by Locker537

Won't you need to change the output shafts on the transaxle as well?

New hubs are rather expensive.

How's the bore on the trailing arm?

I have a G50, at the time I was lucky that the original 69 drive shafts bolted up.

Haven't removed the bearings yet.

[mikedsilva]

Gee... I didn't know that these could break here... I just learned something new.

[safe]

Originally Posted by mikedsilva

Gee... I didn't know that these could break here... I just learned something new.

You probably have to abuse them a lot. I got 18x10" wheels with 295 tires.

I just talked to an independent Porsche mechanic friend.
He had seen this failure on a 996 GT3 RS (with typical mileage of a GT3 RS, not a lot). The drive hub got worn and loose in the bearing, then it broke the same way.

New hub 8-900 Euros.... WTF! Time to scan eBay.

[winders]

Can you post a photo of the area where the part cracked? The surface that was exposed when the part broke in two....

[safe]

Originally Posted by winders

Can you post a photo of the area where the part cracked? The surface that was exposed when the part broke in two....

Focus isn't perfect unfortunately, but its the best I have right now.
Edit: Breakage looks fresh.

[Sboxin]

Originally Posted by safe

Focus isn't perfect unfortunately, but its the best I have right now.
Edit: Breakage looks fresh.

We had the same failure in our race car - 1978 911SC with Turbo flares and 315-35-17 Hoosier A7 tires - found less expensive axle hubs - but now we have replaced the hubs because of scoring with Porsche parts $$$ (because race car)

photo of the failure - decided this is a "wear" item . . .

Regards,
Roy T

[PeteKz]

That nut does not take any of the suspension or drive forces. It only retains the CV joint flange and spline in the hub. I'm thinking it was either overtorqued (causing damage and cracking at the nut) or undertorqued, causing it to work around. Or possibly poorly made parts, so that the splines had too much clearance and worked around.

[Jim2]

Like Sboxin pictures show, I've seen a heavily tracked 911 wheel flange break at the bearing collar snout, only without the stub being broken (yet). Pull your wheel flange and remove the outer bearing race then inspect your wheel flange to make sure you don't have a similar failure going on. On the race car, the symptoms appeared as a loose or very worn wheel bearing.

[r_towle]

Replace with stock.
Add to list of checking before racing
Do not over torque it
Keep a couple of complete axles in the trailer, with stub axles

[Jeff Burger]

Back in the early days of club racing it was not uncommon for someone in our 3.2 and 3.0 race car group to break the a rear hub. After the first one broke we were always equipped with spare hubs, stub axles, new bearings and the bearing install tool. The tool did not go unused,

Sticky big tires and big spacers increase the loads they see.

[safe]

i checked the right side. Looks like the nut has tried to back off.
The left that broke might have done the same but more.

[Magyar Kiwi]

Hi
Really important to torque the stub axle nut to the correct torque using a torque wrench.
Also important to install full size split pin.
For any racing car I would recommend that the stub axle and hub are crack checked, (MPI) each season.
Cheers