Reconstructing Constant Velocity (CV) Joints

[Wil Ferch]

Concavity of Schnorr washers is with dome ( smaller diameter) under head........

[Grady Clay]

The following is a post for thread:
“Two CV Joint Questions”
Two CV Joint Questions
I’m putting it here to help add to this important thread.

GUYS, Slow down.

Keep in mind, the driving torque through the axle is not transmitted through the CV joint bolts. The tight bolts provide a clamping force across the junction between the CV joint and the flange. The sum of the forces provided by the four or six M8 or M10 bolts is this clamping force. This clamping force provides the shear stiction in rotation across the interface between the CV joint and the flange. So long as there is enough force to prevent the CV joint from ever moving relative to the flange – there isn’t a problem.

The issue comes when once, under some circumstance, the CV joint slips relative to the flange. When that happens, it tends to loosen the bolt’s clamping force. (There are other things going on but this is the ‘big deal’.) Additionally the bolts can rotate, becoming looser. As this progresses, things can “go to hell in a hand basket” quickly.



The correct method is to torque the bolts to spec dry. This is best done with new bolts and new Schnorr washers. If your bolts are in good condition, including wrenching feature, they can be reused.

The bolts ABSOLUTEL need to be re-torqued after a hundred miles or so. Re-torquing is a wise part of annual inspection.

Some like safety wire. This is OK after you have re-torqued at 100 mi. This is a pia for regular checking.

If you want to use an ‘inspection mark’, a dab of nail polish over the junction of the bolt head, Schnorr washer and ‘moon plate’ works well. If a bolt has loosened enough for a Sharpie mark to show, failure is immanent.

Loctite is counter-productive as your re-torque must break the Loctite bond to regain the clamping force.

If your CV joint uses a gasket, it is absolutely necessary to insure the gasket is not installed with any bit between the mating surfaces of the CV joint and flange. Having a pinched gasket will lead to a CV joint coming loose. Most Factory gaskets have one side ‘sticky’ to attach to the flange or CV joint. If you have gaskets without a sticky side, use contact cement and glue one side to the flange or CV joint that has the gasket recess. Do not glue both sides.


The mating surfaces of the face of the CV joint and the face of the flange must be clean, dry, without oil or grease and without any raised damage. Slight dents below the surface will not significantly impair the connection.



The issue of installing bolts dry is difficult with grease everywhere. I have sets of old (slightly longer) bolts that I have cut off the bolt heads. Where the head was is tapered slightly and has a screwdriver slot. I hand thread these into the flange and use them as guides to get the CV joint onto the flange without getting grease where I don’t want it.

Once the CV joint is in place, I remove one of the guide pins and install an old CV joint bolt and used Schnorr washer. I repeat on the opposite side of the CV joint. I then draw-up these two bolts so the CV joint is flush with the flange. If I haven’t gotten grease on unintended surfaces I proceed. If I need, this is an easy step to repeat.

Once I have all four or six bolts snug, I then torque them to spec. Then, one-at-a-time, I replace each bolt in turn with a new bolt and new Schnorr washer. I torque to spec each one as it is installed. When complete, I re-torque the entire CV joint.

If you feel at the end that you have grease on bolt threads, it is reasonable to use ‘Brake Clean’, a suitable size ‘test-tube’ brush and compressed air to clean them. This is best done when you install the new bolts and new Schnorr safety lock washers.


ABSOLUTELY re-torque after a hundred miles or so. The life you save may be your Porsche’s.

Best,
Grady

[Fishcop]

Timely!

Thanks Grady.

[robhamster]

Thanks Grady,

I will be rebuilding my CV joints next week and your help is very timely indeed!

Are you joining us for the run to Colorado Springs this weekend?

[uwanna]

Grady,
Have read all 15 pages of this thread, and have received quite an education on CVs and axles! My problem is, I have a set of '86 Carrera swing arms (complete w/108mm CV axles), that I want to put into my '80SC (has 3.6 transplant).
I have an '84 915/70/LSD transaxle w/the 100mm output flanges. My dilemma is locating the 108mm output flanges (fig 2) to fit the "end cap" type CVs. Just can't seem to find them, and our host shows them at $550 each, ouch! Would it be possible to bolt the "endcap" CVs to the 108mm "gasket type" flanges (fig 1)(if I can find them!), or would there be clearance/interference problems? HELP!!
Thanks,
Grant

[HarryD]

I saw this thread over at Rennlist.

Group Buy (ACTIVE): Stage 8 locking CV bolts, Round 2 - Rennlist Discussion Forums

Anyone have any thoughts?

[Grady Clay]

I'll go look.

Recovering from shoveling snow, 75F yesterday. Aah Colorado.

EDIT
Interisting.
I'll order a set and see for myself.


Best,
Grady

[Carrerax]

Earerly awaiting Grady review and response!!!!

[sc_rufctr]

Originally Posted by Carrerax

Earerly awaiting Grady review and response!!!!

x2

[HarryD]

Originally Posted by HarryD

I saw this thread over at Rennlist.

Group Buy (ACTIVE): Stage 8 locking CV bolts, Round 2 - Rennlist Discussion Forums

Anyone have any thoughts?

Related thread:

Stage8 Locking CV Bolts for ALL 911/912

[proffighter]

Just my 2 cents:

On a 930 there are neither moons nor Schnorr washers...

[Maxx1]

Thanks Grady!!

My 930 CV came loose last year and I never re-torqued it. I'll be doing that before I drive it any more!!

[jcsjcs]

So I am electing to use Schnoor Washers (aka Disc Springs / Serrated Safety Washers) even though my car is an '84 and did not have them OR moon plates. I got the washers in 1 day (much to my surprise) from McMaster-Carr.

And now some possibly dumb questions:

1) They are concave - so which way do they go on? CV ) Bolt or CV ( Bolt ?

2) And are the standard bolts long enough to accommodate these washers? I would expect so since they are only a mm thick or so.

Thanks -Jonathan

[midnight911]

1. different boot/ flanges have different thickness
when i rebuilt four CVs on my 84, two years ago, I bought less expensive boot/flange kit from the host.
Recently one of the boot gave up after only two years, 8,000 miles, and this time i bought more expensive boot/flange kit.
I noticed that when I installed the new boot/flange, the end of the bolt sticks out more, say 3-4mm at the transmission flange, while the use of less expensive boot/flange makes the bolt end near flash to the flange thread hole.
So, if you bought these more expensive boot/flange kit, you are likely to have more bolt slack to accommodate the schnorr washer.

2. schnorr washer and moon plate for 84
my car, 84, did not come with any washer nor moon plates. when i did the boot/flange replacement, few days later, i saw the bolts come loose! I torqued them quite securely but still, they came out. I was at a track day few days before and it shook me when i thought about all the bolts come loose at the track.
So, I went to order the M8 schnorr washers at mcmaster-carr.
I had a hard time finding porsche p/n for a moon plate for M8 100mm CV, but I saw my friend's Audi 4000 up on the lift and found out the car had M8 100mm CV with nice moon plates. Audi part quoted for $7.50 a piece. Doing a little more search in the part wholesale database, found out vw rabbit uses M8 100mm and they had several suppliers listed with different price points. I naturally went for the one from empi (p/n 875081) which was $1.50 a piece, which fit perfectly on my CV.

M8 Schnorr Safety Washers P/N~?? (CV thing)

I just did another track day with this setup and the bolts are in place. The washers and the plates are doing their job.

Now, I could do insert the washers and the moon plates because I had more slack at the bolts from the expensive boot/flange I bought. For the other boot/flange, I do not have any slack at the bolt, so I'd need to get longer bolts.
Three other CVs have bolts securely in place and I'm not touching it until when I had to detach them from the flanges. When I did, I'd definitely go get additional moon plates and install with schnorr...

3. schnorr orientation
i don't have the vocabularies to explain it but I know the orientation. someone please chime in... you might be able to see it in the pic i posted in the linked thread above.

[jcsjcs]

Thanks for the details - glad I got the Schnoor washers.

I actually asked this on the bottom of the thread you referenced....

What do the moon plates do? And why only 1 per CV Joint?

[midnight911]

3 moon plates per CV, 1 for 2 bolts.
the pic i posted was taken right after I did the first two bolts. at the end, i had all 6 bolts using moon plates.
the purpose of having moon plates is to spread the load over greater surface area (you are talking to a non-technical, worse, non-native english speaking person) so that the bolt head does not crush the tin of the flange resulting in getting the bolts loose over time.

[jcsjcs]

Understood - thanks. I was referring to the picture - but now I understand that was an "in progress" shot.

Any chance you have the link to the VW moon plates you purchased? Can't find them via google..... or anywhere for that matter. The only link on the web to 875081 is your post and what I think might be your japanese website?

[midnight911]

yes, indeed, i dumped tons of information down on to my website but they are all in the most useful language (at least for me...ha ha...). ;-)
no, my website does not give you good info for the vw part I bought, either.
i bought them at the local Discount Import Parts. I walked in with the part number on my note. I obtained the part number from an online part catalog my friend's german car repair shop uses. we searched for the part for vw rabbit. should give you several options and for me it just happens that they listed one from EMPI.
I'll be at the shop tomorrow and will get you more info on part numbers from other manufacturers than EMPI.

[jcsjcs]

Thanks! I'll keep and out for an update.

So what happened to the 930 and the M3? You have had / have a nice collection.

[midnight911]

we sort of forgot how we ended up with that part number so we called vw dealership.

asked for lock plates for 100mm cv, and they said 84 rabbit, 91 golf gti used 100mm.
and the part number given was 1J0 407 357 A.

we also know that 84 audi 4000 quattro front axle uses 100mm cv and the part number for that is 803 407 357.

we can also find in empi's website the part, and probably this is what i bought.

EMPIUS.COM : 2010 Catalog, Page 367 - All New Complete Drive Axles
the part that says 100mm. #87-5081-0

hope this helps. (typing this from the shop computer. will be here for the next few minutes...may be able to address questions if i capture before i take off. ;-) )