CV Bolts Backed Out

[North Coast Cab]

Spent the day at the track today. I had just replaced a wheel bearing and installed the axles. I had what looks like the cv bolts on the tranny side back out and drop the axle down. I was at Nelson Ledges right before the king going about 115MPH. The revs jumped up a little so I immediately lifted. I though I lost the tranny or something. When I installed the bolts I cleaned the holes out with q-tips and made sure there was no grease on the threads. The axle didn't knock around and hit anything and the cv's look ok. I guess I'm lucky.
So, do I need to wire tie them or am I missing something? Thankfully it was at the end of the day and I was able to roll my car on to a trailer and head home. I guess it's early to bed for the winter now.

John

[911pcars]

At the minimum, I would check their tightness before such a high speed event, or even periodically in any case.

Safety wiring them might provide you with an extra sense of security. The usual black socket-head bolts are usually hardened, so it takes a sharp drill (maybe Ti coated) and coolant to do it. Grind a small flat on the head and center punch so the drill starts easier/doesn't skate, then chamfer the opening. There are head-drilling jigs for regular hex-head fasteners; not sure about socket-head metric fasteners.

Sherwood

[Randy Webb]

What has been done to them? Maybe the last person did not torque right or reused the Schnoor washers?

I would pull the bolts out, inspect the threads & socket area, clean and reinstall with new washers -- new, i.e. brand NEW. Torque.

Drive around for 200 miles or so, re torque.

See how that does for you.

The Qtip thing is good but I found it never got all the grease out of the female threads. Brake cleaner helps but you can't get it in the joint.
Myabe others hav eideas on this. I suppose you could alsways uprate the torque -- if the bolt can stand it.

Wiring the bolts in will not keep them torqued -- it will keep them from falling out. There has been a lot of controversy on drilling the holes into the bolt heads. I don't like the idea. You can get them pre-drilled. My guess is they drill them and then heat treat them, preserving the integrity of the head. If you drill then try to smooth out the hole to prevent stress risers. You do not want the head to crack off.

[Doug E]

Having had my axles on/off several times now this is always a fear of mine ... glad to hear that it turned out OK for you.

For peace of mind before each DE I check the CV bolts just to make sure none have come loose and so far so good.

[Grady Clay]

John,

Count your blessings. The axle could have beaten your headers to death or worse, lock up a single rear tire.

Do you have an open differential, LSD, or a spool? The latter two can exacerbate the problem.

Always, always, always replace the Schnorr lock washers every time. In your application, I would use new bolts every time. The ID raised part of the lock washer goes against the head of the bolt. Every time you put the axles back on, re-torque the bolts after it has been driven once. Periodic checks are worthwhile.

Cleaning the threads in the transmission axle flange with a Q-tip isn’t sufficient. Use “brake clean” and a round small “test tube” brush. Also make sure the bolt bore in the CV doesn’t have grease in it. These fasteners should be installed “dry.”

Make sure the mating surfaces of the CV and flange are clean, burr free, and not greased.

I am not a fan of safety wire in this application because you can’t torque the bolts without removing the safety wire. This means you tend to rely on the wire, even when the bolts aren’t fully clamping. If there is any movement at all, the threaded end of the bolt can shier off.


Best,
Grady

[Quicksilver]

An internally wrenched bolt doesn't have a stress riser problem with drilled heads. The hole is way above the loaded part of the head. It would be a stress riser that could effect a cheap bolt from the stresses from the wrench when torqueing.
It is way easier to buy a bolt pre-drilled though. Correctly chamfering the hole where it opens in the center is a pain, plus they are tougher then wang.

Unless you are doing a 6 hour race I think safety wire is overkill. The answer is one word - Locktite. Not sure why it wasn't mentioned. If you want to be really anal then the rule is "No threaded fastener should ever be assembled dry." Every torque spec is based on the lube used and they never specify 'dry'.

I would just clean the threads well with Brakeleen and a little bottle brush and then use blue Locktite.

Wayne

[Quicksilver]

Hey Grady, I thought I had the patent on Brakleen and brushes!


Wayne

[Randy Webb]

A good point about the degree of stress and its location on the bolt. But, any crevice can still expand to a crack as there is never zero stress.

re torque specs & dry vs. lubed threads:
As I recall both Jim Sims & Grady have said to install dry. Both are experts in Porsches and/or related disciplines. Nonetheless, why are you guys saying dry? Is this in a factory manual somewhere?

[Todd Simpson]

I check mine before every track day, ever since I found a few loose.

I may do the full Grady list above this winter with all new fasteners, but I'll still check them before every event.

[North Coast Cab]

Any more comments on locktite?
Installing the greased cv's and axle is a crappy job no matter who you are. I will try my best to clean the holes and install "dry" next time. Amazingly I think the axle dropped down and stayed there. I didn't hear a sound, I just had no power. Next weekend I'll do a full inspection. The inner boot is torn so I've got that ahead.

John

[curiousone940]

In the past, I've never done anything more than clean up the bolts, and tranny side of the joint before re-installing a CV joint/axle, but when I changed all 4 boots about 2 weeks ago, I used just a drop of blue Locktite on each bolt. As a matter of routine practice, I'll re-check the torque later this month, but I really don't anticipate any "backing out" problems with this method.

[Randy Webb]

Any more comments on locktite?
- Yes. They now have a blue that will fully activate even if the metal has some oil on it.

Crappy job -- YES! I've done it six times in the last 2 years. Never fun.

[911pcars]

Just to clarify; I never proposed safety wiring as a substitute for proper tightening. Safety wiring prevents the fastener from excessive loosening or backing out completely while in operation. The next time you check tightness, remove the safety wire, re-torque, then install new safety wire. Yeah, I know it sounds tedious, but that's the nature of safety wiring.

Wouldn't the use of Loctite preclude re-torquing to compensate for any initial stretch?

Does anyone have a source for drilled CV joint-size bolts? I suspect these might be unobtanium.

These Ti drilled head bolts are nice, but they're about $12 ea.

www.mettec.com/metric.htm

..or you could have them specially made for you (www.vegasfastener.com/), probably a lot cheaper than ti.

or maybe ARP or SPS has some off-the-shelf fastener that would work.

BTW, I found this interesting article, "The Importance of the Wrench-Fastener Interface. Interesting reading. (www.wrighttool.com/news/article06A.htm)
faq.htm)

Sherwood

[Oldporsche]

When axle shafts get loose, nasty things happen very quickly. I really don't know what the answer is here.

Grady offers good advice. The problem is that its a nasty, greasy environment. Any extra grease is being slung out of the joint. It's hard to get the "dry" environment when laying on you back in the grass somewhere near a track.

Carrol Smith's book on nuts and bolts advocates safety wire. If I were racing, I probably would go this way. I wouldn't use it in place of proper torque however.

I'm pluging Wright tools. They are very well made. Often the illinformed pawn shop owner has these price below Craftsman tools.

Good luck with this one!
David Duffield

[PeteBrown]

John:
Glad to hear there wasn't any damage - I know we were pushing close to 120mph before the "kink" for most of the day.

I will be checking my CV bolts before she goes out next time.

[Grady Clay]

Some time in the early ’80, The CVs started coming with a stamped steel cap between the greased CV and the flange. Who can shed some light on this? This goes a long way to containing the moly grease.

David is correct, it is nearly impossible to assemble the axle CVs to the flange “dry” in this greasy environment.

I agree with Sherwood. Although tedious, removing the safety wire, re-torque the bolts, and reinstalling the safety wire is the best. This way the safety wire is truly a back-up system. My point is that since it is so much effort we tend to pass on the effort and not torque the bolts regularly.
For racers that have everything apart regularly for re-gearing and such, the safety wire is a real impediment in many situations. When you are trying to change gears between sessions, everyone wishes for 1/4 –turn fasteners.

What is the situation with Loctite Blue when you re-torque a fastener and it moves slightly? Does the Loctite still maintain its function?

Another trick for long-term installation might be to assemble the CVs to the flanges with used hardware torqued in place and then replace the bolts and lock washers one-at-a-time with new parts. This way you could clean the through hole and threads and assemble with proper lubricant on the hardware.

You can tell if you have assembled a fastener like this “too dry” because it will tend to “snap & squeak” as you reach specified torque – not good. Many fasteners are specified to be torqued with a drop or two of SAE 30 or some other lubricant on the threads. This is an entire subject in itself and has been discussed on this Forum.


Our local metric hardware industrial supplier (AAA Metrics, 303-892-9000x12) has Schnorr washers in stock; 6 mm for $3.60/C, 8 mm for $4.80/C, and 10 mm for $7.80/C.

Wurth Fasteners lists Schnorr washers from M4 to M14.

Our host has them available also.

I think the application for these washers is steel-on-steel. I don’t think they are appropriate for a steel fastener to aluminum or magnesium alloy unless there is a steel flat washer also.


Best,
Grady

[KTL]

Originally posted by Grady Clay
Some time in the early ’80, The CVs started coming with a stamped steel cap between the greased CV and the flange. Who can shed some light on this? This goes a long way to containing the moly grease.

To answer Grady's question, I checked the Porsche Parts and Technical Reference Catalog, Models 1974-1989 (Dec. 1995).

Tech. Bulletin #5 on p.118 says:

Rear Axle Shafts: The CV joint dia. on 911 Carrera models has been changed from 100m to 108mm (same as 911 Turbo and Carrera with Turbo Look). THIS CHANGE STARTED IN THE 1985 USA MODEL YEAR. THERE WILL BE SOME EARLY MODEL 1985 CARS WITH EARLIER VERSION CV JOINTS. The formerly applied flat seal has been omitted and an end cap has been installed for CV joint sealing. The recess req'd for the flat seal in the CV joint (transmission end) and driveshaft (wheel end) have also been omitted.

The CV joint shaft for the 911 Carrera has a bolted CV joint on the transmission end, and a friction welded joint on the wheel end. The CV joint shaft for 911 Turbo and 911 Carrera with Turbo Look cars has bolted joints on both ends with the new seal.

The rear wheel is mounted with a self-locking nut on the friction welded shaft, of with castle nut and cotter pin on the shaft with a bolted-on CV joint.

There's some pictures of axle shafts and a chart comparing the old vs. new assemblies. The important note accompanying the pictures is one that says:

NOTE: Since the new CV joints have a sheet metal housing, washers, Porsche part # 911 332 191 00 must be used when installing.

These washers are the crescent-shaped plate washers # 14a in the diagram below



So the later axles do not require the M10 Schnorr lock washers (according to Porsche) that the earlier models used.

Thanks to Sherwood for the Wright Tools link. Good info.!

For those needing Schnorr washers, you can also get them at McMaster-Carr (www.mcmaster.com) and at Metric Multistandard Components Corp. (www.metricmcc.com)

[Randy Webb]

1a. It seems like the Loctite still maintains some of its function -- it acts as a bedding agent to absorb vibration. I doubt that it retains the full function.

1b. I doubt that the friction-tension relations are maintained if you put Loctite in there... so what torque would you use? It's hard to get to the back of the joint, if you can do that you can add green loctit after torque is reached. I don't do this on the CVs.

2. I note we haven't seen Jim Sims post on this thread yet...

3. Smith's book is a good one to read. He specifically states that wire will not maintain torque.

4. Can we agree on the best "how to" for these joints? I expect that some who are viewing this thread would just like to know "what do I do"? Best doesn't mean perfect....

[Wayne 962]

New bolts, Loctite, new washers, and the proper torque (double-check your figure and your torque-wrench).

-Wayne

[Grady Clay]

Kevin,

Thanks, good post. I think #19 is the stamped sheet metal end-cap. From the description in the tech bulletin, when the end-cap is introduced the “flat seal” CV gasket (#13) is eliminated and the transmission flange is changed to eliminate the recess for the gasket. Can someone post pictures of these parts?
I will speculate that you cannot install the CVs with the end-cap without changing to the later (no seal) transmission flange. Aside from the lack of seal relief, the dished portion of the flange may be reconfigured to clear the end-cap.

Can you post the pictures from the Tech Bulletin?

I am puzzled why Porsche doesn’t show a Schnorr locking washer for this application. It could be an error of omission in PET. Also, the later flange could have “self-locking threads” installed. Who can shed some light on this?


As an aside; the CV boot (#10) is a tight fit over the sheet metal flange (#9). Many forget to additionally glue the boot to the flange and add the clamp (#12). This prevents the centrifugal force from letting the grease out of the CV. I also would seal the surfaces between the CV and the flange and end-cap.

Best,
Grady