Dodged a bullet - bad luck or bad work?

[98GTW]

The background:
I had my rear wheel bearings replaced about 4 weeks ago, by a shop I've heard good thing about, but hadn't used before. I have to say I liked the mechaninc a lot and felt very comfortable having him do the work. While he had it apart he replaced all 4 CV boots (with my approval) because one was torn.

The event:
I was feeling a little celebratory yesterday and got up above the legal limit a bit on the way to work (a quiet stretch of 6-lane at 5AM). There was a little vibration I put down to worn or out-of-balance tires, nothing I paid much attention to.
I stopped at a light on the way home from work. When I let out the clutch there was a whirring sound but no forward motion. I checked that I was in gear, tried another gear and shut down. After pushing off the main street to a side street, I looked underneath and saw the transmission end of an axle and CV joint. Can't tell you much about what I saw, but I think I saw the ends of 4 bolts protruding from the disk I took to be part of the joint.

The question:
Did the shop fail to tighten everything properly or did the CV joint just coincidentally fail so soon after being out of the car? Is there any way I can tell for certain?

Thanks for your help.

[Jim Smolka]

Hard to say... However, if the special washers are used with new bolts, they typically do not back out. Ask the shop to install the special groved washers and the problem should be solved.

[ChrisBennet]

I've seen several 911SC joints with loose bolts. I think the the 8mm CV bolts require special attention that the 10mm ones don't seem to need.
Put in some new bolts with new Schnoor washers and you should be good.
-Chris

[98GTW]

I'm trying to figure out who's going to pay for this.

I'm hopeful the mechanic will step up if he messed up, and I want to have a better understanding of what went wrong so I know what stance to take with him.

[Nine9six]

What Chris Bennett said...

I removed my axles to replace CV boots, and noticed there were no Schnoor washers, so I reinstalled without them. I did however, clean the 10mm mounting bolts, along with the internal threads of the trans flanges. I also blue locktited the bolts during installation, and torqued to spec. (60 ft lbs. for 10mm bolts) No issues after re-checking the torque, after 1000 mi. of driving. Again, as Chris stated, the 10mm bolts may have less of a tendency to back out, as opposed to the 8mm bolts.

No telling what your mechanic did or did not do, but I believe that since he removed and installed that portion of your car, he is responsible for the incident, and should repair it.

You may want to check the outside CV boot flanges, as they may have been oblonged (distorted) if the half shafts flailed about when they fell from the trans mount flanges. I say this because you CANNOT purchase these flanges separately.
Here is what an oblonged CV boot flange looks like...
Pictured is the CV joint, half and stub shaft, from a turbo model. This is the 108mm CV joint, with the M10 bolts, as Grady so eloquently describes below.

[Grady Clay]

This is a BIG issue.

Certainly the shop should stand behind their work and make this right for you. They should know all these facts. I also feel that every shop (and DIY) should re-torque the CVs a second time after installation and at regular services (at least annually). There is a bigger picture.

Part of the big picture is design, part is procedure and part is components.

Porsche decided that the SC didn’t need the big 108 mm CVs that had been successfully used since ’69 with only one minor change. Instead they felt that the 100 mm 923 CV from the 2.0 L 912E was up to the task. Simultaneously they changed from four M10 bolts plus two steel 10 mm roll pins to six M8 bolts. To make matters worse, they further decided the Schnorr Safety Locking Washers and plate washers weren’t necessary. This was all at a time when there was a dramatic increase in vehicle weight and the development of much better grip tires. The result - CVs came loose even on new vehicles.

In about ’86 Porsche announced that all the vehicles were now going to use the large 108 mm, six M10 bolt 928 CVs to “have all the vehicles use the same parts and ease the parts proliferation situation.” Ha, I think there is much more to that.

As far as the procedure is concerned, everyone seems to agree that CV bolts need to be assembled dry and certainly not lubed with Molly grease. Anyone who has done this procedure knows that is virtually impossible. Lobro’s (the axle manufacturer) provided a common solution – a tin end cap to contain the grease. Everyone (end cap or not) still just holds the CV in place and runs up the bolts. A quick torque and you’re done. I prefer to re-install the CV with the old bolts and over tighten to get the CV firmly in place. I finally remove the old bolts, one-at-a-time, clean the flange threads of any lubricant and replace the bolts with new 12.9 bolts with new Schnorr washers. I still re-torque the bolts after some use and at each service.

Even though many (myself included) have reused CV bolts and Schnorr washers, the only good and proper solution is to replace them with new every time. The plate washers (moon plates) can be reused if in good condition. If a 911 doesn’t have plate washers and Schnorr washers, they should be installed. Care must be taken because Porsche specified the bolt length without the washers. The norm is for the bolt to protrude through the flange threads 1 ½ turns.

The best, abet expensive, solution for the 912E 100 mm CVs is to up-rate to the larger 108 mm CVs that have always been used on the Turbo with no problem.

I also don’t think the tin end cap solution is ideal. The grease is constrained in the CV not by a gasket, but by sealant between the end cap and the CV housing. That isn’t bad but if you go by the Factory Manual repair procedure the sealant is between the end of the cap and the face of the CV. That makes it necessary for the CV bolts to try and crush the sealant. The consequence of this is you no longer have steel-on-steel interface between this sandwich of components – flange, end cap, sealant, CV, tin cover, plate washer, Schnorr washer and bolt head.

Yes, some of the small CVs seem to last just fine and not fall off. I wouldn’t bet my life on it.

Best,
Grady

[Steve Marshall]

The mechanic didn't tighten them. They should pay.

[Nine9six]

Originally posted by Steve Marshall
The mechanic didn't tighten them. They should pay.

Mr. Marshall,
The mechanic may have indeed tightened them, but may not have followed proper procedure as described by Mr. Grady Clay.

[indigowhale]

If you have a long extension for the socket on your torque wrench, say 18-24 inches, you can have someone sit in the car while you sit at the wheel well and tighten each bolt as it passes through the top, your wrench will end up on top of the disk brake. The person inside applies the brake while you torque. Much easier that doing them under the car. This is for the tranny side, and wheel must be off.

[mskar]

Yep, happened to me a couple of years ago. I have an 84 RoW Carerra and in addition to stranding me, the loose axle beat the transmission oil cooler within an inch of its life. Eurosport in Virginia Beach had done the work and they stood behind it. They covered the repair and the cost of replacing the oil cooler parts that were destroyed. They are not cheap, but they do good work and stand behind it. The (probably several hundred) they spent on parts for the job is made up for in good will.

[Steve Marshall]

I'm still betting the bolts weren't tightened enough and fell out.

[Clay Perrine]

This is a common problem on 914s. We know about it and most of us have devised methods to prevent it from happening.

The proper way is to use a torque wrench EVERY TIME the bolts are removed.

Another way is to buy bolts with holes drilled in them and saftey wire them in.

A third way is to put in longer bolts, and put nylock nuts on the back side of the drive flange to act as a lock nut.

If the mechanic is a good one, he will fix this for free. He took it apart, so he should warranty it.

Good luck!!!

[98GTW]

Originally posted by Steve Marshall
I'm still betting the bolts weren't tightened enough and fell out.

The shop owner took responsibility for exactly this occurence, and apologiezed several times. He replaced the bolts on the CV that loosened up, rechecked the other 3 joints, and reimbursed me for the towing charge.

I'm concerned about giving him future work if this sort of thing can happen. On the other hand, he tracks the cars he works on and there are lots of other local track drivers who rely on his work.

I'm inclined to give him another chance and to be very clear that I expect everything to be double-checked.

[911SCfanatic]

anyone recommend a "medium" bond locktite?

[steve911]

Dave--
I would have a face to face conversation with the shop owner about your concerns (which are valid). He seems like a stand up guy. I'm guessing that he will make SURE that your car is handled correctly when/if you decide to bring it back to his shop. My guess is that he has had a word word with the mechanic who did the work about the incident.
Just my .02
Steve

[Gunter]

Dave: I expected that the shop would take responsibility; they were just glade that not more damage was done!
A loose axle at high speed will act like a sledge hammer.
Not to mention the danger to your life.
It sounds like a mistake was made in torqueing; it'll be a wake-up call for the mechanic. I think you can go back there again but, I would have a closer look at the CV's in the near future and find a way to re-check the torque. Do you know if new Schnorr washers were used?

[Steve Marshall]

If the dude fessed up he's probably worth dealing with. The mechanic probably got a call mid-way through tightening up the CV's and forgot to finish. Could have happened to anyone, although if you're a professional there's really no excuse.

[ChrisBennet]

I would not be so quick to assume they weren't torqued correctly. The loose ones I've seen weren't installed carelessly. I believe you can torque those 8mm CV bolts "by the book" and they can still come loose.
I haven't done enough of these to tell for *sure* if this works but I clean off the grease from the flange holes and CV joint holes with a Q-tip and a little brake kleen, use new bolts and new Schnoor washers, leave out the gaskets, torque in a star pattern - and cross my fingers.
-Chris
-Chris

[CBRacerX]

I have done the 8mm version "by the book" and had them get loose under track conditions. My solution on that car was to drill the heads of the bolts for safety wire (not fun on 12.9 bolts, but doable with quality bits, drilling oil and a drill press) and use safety wire properly applied to keep the bolts tight. Problem solved.

[PatrickB]

Did '85 have the M8 or the M10 bolts?