Bogus CV Joints

[Bobby Smith]

Heys guys, I thought I'd throw this out there and see if anyone else has had this problem. I've got a 74 911 with 3.0 approx 210HP. About 6 months ago I broke an outer CV joint (the cage shattered). I didn't think much of it. Just bought a new one and repacked the rest. Well last week the outer CV on the other side broke. (In 20+ years, I've never had a problem with 911 CV joints), so I thought something must be wrong. Well sure enough the joints that broke appear to be non- Porsche. They had no markings. Normally you will find Lobro and a number or the factory Porsche triangle. I looked at the receipts from the previous owner and he had purchased axle assemblys from an outfit in FL. The inner joints were genuine Porsche. It makes sense that the bogus joints would be placed on the outside, since they are less likely to fail in that location. It might be worth the time to check your own. Put it on jack stands and rotate the CV joints and make sure that they have the Lobro or GKN markings or the factory Porsche triangle on the outer surface.
If they don't, I would replace them. Mine left me dead in the water, 10:00 at night a 100 miles from home. I got lucky and had a friend going my direction and I picked the car up the next day on my trailer.
Comments welcome
Bobby Smith member #299
www.porsche911dude@aol.com

[dvkk]

You are right about "rebuilt" CV joints being junk. The way they rebuild them is to grind the grooves larger in dia until the former pitting is gone. Then they re-assemble with larger balls. Sounds ok, but that larger ball makes the cage thinner. That's why yours broke. Another problem that happens is that sometimes they grind the new grooves so big that they grind right through the hardened steel into the soft steel. They don't last long when that happens.

.... It makes sense that the bogus joints would be placed on the outside, since they are less likely to fail in that location. ........

That is a myth.
The forces applied to the inner CV joint are exactly the same as those applied to the outer CV joint, so there is no one location that will break first.

[911scfanatic]

I'm sorry...where precisely are you saying I should be looking for the logo/pn?

[Bobby Smith]

The markings/numbers should be on the outside surface of the CV joint. It's the only surface that is visible when it's installed. It's not on the cap where the boot attaches. I'm not saying that all CV joints with out markings are bad, but I'm simply sharing my experience with 2 that failed on my 911.
Good Luck
Bobby Smith

[john rice]

I am not sure how much of this is accurate BUT:

I recently had a noise start up and determined that it was one of my right side CVs. [79 930]

Called my picky fussy tempermental but dedicated Porsche [I feel bad calling him a mere mechanic] brother.

I wanted a reference for a good price on a new CV joint.

He told me: You can count on it. If you just replace the bad one the others will fail in short order. He swears it is a waste of time to just replace the one and wouldn't even provide a reference.

Furthermore, he says the rebuilt CVs are another waste of time and money. What you save up front you give up in longevity and reliability.

..and a remberence from me. In the early 90s I was looking for and found a good price on "rebuilt" half shafts from Automotion. The price was so much cheaper than new and even a lot less than buying the CV and parts. I called them and got a bit of a runaround until I finally found someone who admitted that their concept of rebuilding was to take a pile of used ones, clean them up, then take the best ones and put these together with fresh lube/covers/seals. Yes, really.

I still cringe when I recall how I interrupted an SCCA race at Sear s Point in the 80s when a drivetrain failure THREW me into the uphill side in the esses [and the car rolling sideways uphill!]. Nasty. Even worse - was after it stopped and then started rolling over and over back down to the track..... depositing what was left of me and my car facing traffic and right on the racing line. I try to imagine what would happen if something vital like this should break when I am on boost in my puffer beast. This is really frightening.

So, I follow [and pass on] my brother's advice. REPLACE both of the halfshafts with new. ALL of it. Do it once. Install new gaskets when applicable and new bolts and then you can forget about them.

I realize these things are expensive and there was a day I simply could not afford to do this. It still bites but if I am going to run a car like this I am not going to short change myself on safety. If it were my barn find 912 I probably wouldn't bother but if you are pushing any kind of power through yours I highly recommend replacement.

[RandyWebb]

"The forces applied to the inner CV joint are exactly the same as those applied to the outer CV joint..."

- Why is this? The movement is much greater on the outside. Wouldn't that cause the magnitude of the angles and hence forces to be different?

[dvkk]

Since the outer axle stub is almost exactly parallel to the output shaft of the diff at all times, that means the angle of the inner race relative to the outer race of the CV joint is almost exactly the same on the inner and outer CV joints. The only difference in the angle is due to the slight de-cambering as the suspension compresses. This change in angle is so small compared to the swing of the axle that it is trivial.

If your diff is twisting your trans' output flange with 100 ftlbs, the inner CV joint is twisting the axle with 100 ftlbs. Then the outer CV joint gets twisted with that same 100 ftlbs.

Since inner and outer CV joints are identical, no one location will see failure before the other.

No significant difference in angular travel
No difference in load.
No difference in design.

This myth could have originated from the FWD world. Those cars typically have completely different design CV joints on the inner and outer. Plus the outer CVs articulate through massive angle changes compared to the inners.

[roblav]

Agree with dvkk...