Reconstructing Constant Velocity (CV) Joints

[}{arlequin]

Originally posted by rcecale

sorry for resurrecting this quality thread (or you're welcome )
but i have a snag.

after my rebuild i've noticed that the cv's are flinging grease all over the trailing arm. i don't remember any more whether i replaced or reused the gaskets, but obviously i'm going to replace them for sure this time. pelican's kit comes w/ 4 gaskets. i'm not sure what spot exactly they belong in and am hoping that out of the pics above someone can point to where they belong. thanks.

[76carrera3.2]

So my 1976 911s Has no washers- just the bolts. Is that safe? I am a little paranoid now after reading this post.

[Jim Sims]

Not wise to run with only the screws; the 1976 911 comes with Schnorr lock washers as original equipment on the CV joint screws. The washers should not be reused; in bags of 100 the 8mm Schnorr lock washers are about 11 cents each. 24 total are required for the '76 CV joints.

[rcecale]

Originally posted by }{arlequin
...pelican's kit comes w/ 4 gaskets. i'm not sure what spot exactly they belong in and am hoping that out of the pics above someone can point to where they belong. thanks.

Dave,

Take a look at the top axle in the pic below. I believe Item # 13 is what you're looking for.



Hope this helps!

Randy

[Tut]

I purchased a box of 1000 M10 Schnorr washers. $2.00 for 24 if anyone wants some.

[76carrera3.2]

Thanks JIm, for the info. Randy the schematic you have is for an '86. Do you have one or the 76 911's.
Scotty

[Wil Ferch]

I really can't add anything meaningful to this excellent thread...but the goodness of Schnorr washers cannot be over-stated.

Odd thing, though...Schnorr washers are likened to be "serrated edge Belleville" style washers..but there *IS* a difference. The real Schnorr washers have serrations where the "peaks" are at an angle ( not straight up like a pyramid) ...and the serrated ridge is not totally radial, but also at some angle I believe. So get the "real deal"...

However..here's another twist I recently found out from Schnorr, Schnorr-USA, and the web site. The washers come in "regular" grade ( thickness / compressibility)...for low grade or non grade fasteners ( < USA grade 5 or < Metric property class 8.8 equivalent)...these are called "S" style....OR..they come in a higher strength grade for property class 8.8...called "VS" style.

Maybe Grady or others can chime in...but since we want property class 12.9 Cv fasteners....how do we handle this? There is no apparent 12.9 washer..only 8.8...unless the VS style is for 8.8 *and stronger*..but I don't get that impression...

Hmmm..

- Wil

EDit- to compound the problem...Schnorr-USA will only sell in quantities of 1000+..and they say that McMaster-Carr is a big client for whom they "bag" small quantities. However, in all cases, these are the "regular" S style..and not the desirable/necessary VS that I think we ( at least) need for this application. I can't find any sources of VS in small quantities.

[rick-l]

I just read through this and the only thing I would add is if you don't want to mess with the crowbar when tightening the CV joint bolts just stick a screwdriver into the vent slots cast in the brake rotor and let it turn up against the caliper.

[}{arlequin]

Originally posted by rcecale
Dave,

Take a look at the top axle in the pic below. I believe Item # 13 is what you're looking for.



Hope this helps!

Randy

it sure did! thanks randy.

[Jim Sims]

Source of 100 pc. bags of S series or VS series Schnorr washers is listed below. I believe there is a $25 minimum order but I and my friends usually manage to find other metric fastener items to fill out the order: such as the engine tin screws and washers in yellow zinc for pennies apiece.

I recall looking into the S series versus VS series issue and the early Porsche 911 paper parts catalogs call out S series Schnorr washers for the CV joint screws and the spring plate screws. Measuring the thickness of what I believed to be OEM stock Schnorr washers installed on an early car appeared to confirm this. I therefore ordered and use the S series.



http://www.metricmcc.com/catalog/Ch2/2-242.pdf

[AvonGil]

I got them from mcmaster.com. About 11 bucks for 100 of them, with no minimum.

[Wil Ferch]

AvonGil...right...but "S" spec only....

Jim Sims...you're a proper nuts-'n-bolts guy...I'm surprised at your answer. The Schnorr web site that details the use of the various washers indicates that VS would be more appropriate...as it would more closely match the tensile load developed by the class 8.8 fasteners. What's the point of 12.9 class cap screws, then ??? IMHO...something like VS + is what is needed.....

Comments..other than "Porsche used these". ( i.e....the "S" style).....as can be seen by this thread, Porsche makes mistakes on stuff like this !!

- Wil

[Jim Sims]

Based on the limited amount of data I have available (I have a summation of the Schnorr loosening tests) this is my "take on it": The VS series are only significantly helpful if they improve and maintain the mechanical locking effect of the "bite of the serrations" into the contact surfaces. That is the main purpose of the "spring action of the Belleville shape"; the spring force generated is a small fraction of the tensile load of a tightened screw and doesn't significantly add to the clamping force generated on the CV joint flanges (which in combination with the friction generates a traction to carry the torque). The VS series is useful when used against hardened surfaces or limited area surfaces (slots or oversized holes) or with hardened bolts. On softer contact surfaces there is no point as the serrations of the S series are already embedded far enough (check out the some used "moon plate" washers). On the surface it would appear that the higher strength bolts should use the VS washers. The highest bolt strength class mentioned in my Schnorr test literature is also 10.9 ( and is associated with VS washers) which I believe achieves a significant portion of it's strength due to higher carbon content and hardening. I recall that the 12.9 strength class had an alloy content that may allow it to achieve it's strength without being as hard. Hence a VS thickness washer may not be helpful. I'll have to look up the head hardness of 12.9 versus 10.9 socket head cap screws. I do note that with the 8.8 strength class screws Schnorr appears to conclude the Schnorr serrated washers can be reused which is not the case with the 12.9 screws. Cheers, Jim

Additional information. Metric socket cap screw Rockwell thread hardness: 8.8 is C23-C34; 10.9 is C33-C39 and 12.9 is C38-C44 compared to C39-C45 for Schnorr serrated lock washers. So the Schnorr lock washers are of comparable or higher hardness than the 10.9 or 12.9 screws. However further consideration of the situation in a 911 CV joint still points to little or no gain in using a VS washer as it will merely embed itself more deeply in the softer steel of the moon plate or cv joint flange instead of applying more force to "dig deeper" into the hardened head of the screw on the other side. Think of the the Schnorr washer bearing against a "bed of putty" (the soft steel of the moon plate); it can only push back against the hard head of the bolt with the load the "putty" can support.

Enuf.

[Wil Ferch]

Jim:

Thanks for your thoughtful response.... but perhaps consider this view...

Belleville style washers also come with no serrations. I don't know how much of the "goodness" of Schnorr is derived from the biting action of the serrations...and how much is apportioned to the stronger "spring-constant" of the basically thicker/stronger washer. I agree that to "squish" either style flat...that this force is not materially different ( as contributing to *clamping* force or tensile-load)...BUT...it *may* be significantly different as it tries to prevent the loosening-tendencies of the bolt... relative to the increased torque a "rated" ( 8.8...12.9) bolt uses. Couldn't this be a factor?

Let me review the Schnorr test data again....you may be on to something as I recall that the "relaxation" ( or "remaining") clamping force was more ( as a % of original clamping force)...for soft surface items being connected vs. hard surface items. If so, then there is a great percentage apportioned to the serration-effect...good point.

Wil

[Wil Ferch]

Jim :

Here is some more from the Schnorr site...

The 12 page test they show ( http://www.iecltd.co.uk/bearing/products/schwash/images/wirksame_sicherung_deen_072.pdf)...indeed does show that the asymptotic line is about 85% remaining pretension over time ( "S" type on soft surface) ...to something just under 80% for "S" type a hard surface test. However, a later chart shows that a "VS" combined with hard surface ALSO ends up slightly above 80%..so the VS/hard ends up higher than S/hard.....hmmm

However, note the description by Schnorr on the S and VS styles...( quoting)...

---------------------------------------------------------------

Original SCHNORR Safety Washers "S"
The Original SCHNORR® Safety Washer "S" is suitable for normal requirements and available for screws from M 1,6 to M 36. Other sizes as well as customized dimensions can be inquired for.

Original SCHNORR® Safety Washers "VS"
with greater thickness
The Original SCHNORR® Safety Washer "VS" can be used with high-strength bolts of the grade 8,8 without any restrictions. This strengthened safety washer has a greater thickness and for this reason achieves higher pre-tensioning loads. The outside and the inside diameter as well as the toothing correspond to the type "S". It can be delivered for screws M 5 to M 3.
Special sizes are also available upon request.
--------------------------------------------------------------------------

So the serrations ( size/type/configuration) are the same for both but that VS has higher pre-tension...... double hmmm.....

- Wil

[Jim Sims]

When pushed flat a Belleville washer of comparable dimensions and material to a Schnorr S8 generates a load of around 30 lbsf while one comparable to a VS8 generates a load of around 300 lbsf. This is a significant increase but it must be compared to the proof load capability of a 12.9 strength class 8mm socket head cap screw which is almost 8000 lbsf. There may be some other mechanism that comes into play using the VS version but with a joint that has a soft side I don't quite see it. Cheers, Jim

[rcecale]

Originally posted by 76carrera3.2
Thanks JIm, for the info. Randy the schematic you have is for an '86. Do you have one or the 76 911's.
Scotty

Scotty,

Will this schematic for a 77 help? Looks like the same setup...item 19 vs. item 13. Pulled this image right from the PET.



Randy

[Wil Ferch]

Jim:

Is this summary correct?.... we upgrade the Porsche standard cap screw from property class 8.8 to 12.9 ( BTW..is this in itself true that OEM is 8.8?).... but since the mating surface under the head of the screw is "soft" ( relatively)...there is no value to going with VS spec Schnorr washers compared to "S" spec...even though there is a substantial increase in the pe-load with the VS.....

Is this a fair summary of your thoughts?.....

Why wouldn't you want the benefit of greater preload of the VS unless the additonal amount of load-to-compress deforms the host material too much. Is *that* it ??

- Wil

[Jim Sims]

12.9 is the OEM strength class of the CV joint screws. Other than that you made a reasonable summary of my conclusions. There is probably no downside in using the VS series other than they "consume" more of the tightening torque in friction so higher torque wrench values should be used to achieve proper bolt tension and they'll "chew up" the mating surfaces more which may prompt replacement if the joints come apart many times.
My opinion could change if there is more data. On my '76 I use the S8 Schnorrs with six 12.9 8mm screws and my son on his '73 uses the S10's with four 12.9 10mm screws and "moon plates" plus there are two "Spirol" roll or spring pins in each joint to transmit shear (the OEM configuration). Cheers, Jim

[Grady Clay]

I just looked over a bunch of OE used CV joint socket head
cap screws (both M8 and M10) and can’t find any other
than property class 12.9 or 12K. I understand 12.9 is the ISO
class and 12K is the earlier DIN class.

Under the head of the bolts there are no signs of the Schnorr
washer teeth having gripped into the bolt material. On two
examples there is a “shadow” of the teeth but it isn’t
detectable feeling with a scribe and I would estimate <0.0001 mm.
Clearly the Schnorr washer teeth grip the support plates and
leave a pronounced seriated pattern, easily felt with my
fingernail on some estimated at >0.2 mm.



Above are both M8 and M10 support plates showing the
Schnorr teeth marks.


I interpret this as the bolt head being much harder than the
support plates. I will speculate the bolt head hardness is
coming close to the hardness of the Schnorr washer. It
appears that when the fastener is loosened, the Schnorr
washer stays fixed to the support plate and the head of
the bolt slips on the washer. This could “erase” any tooth
marks under the fastener head.

This raises the question: Is the 12.9 too hard for the Schnorr
washer to grip it? Is the 12.9 tinsile strength sufficiently
greater than, say 10.9 to permit higher clamping force with
greater assembly torque? Would the 10.9 be more suitable
with the Schnorr washer? Where is the trade-off for best
performance?

Jim, what is the failure mode of this system?

I perceive it to be there is insufficient clamping force to
prevent the CV joint from slipping relative to the flange
(for whatever reason).

I see three normal situations where this can first occur:
1) Under high acceleration in a low gear a tire drops into
a “pothole”, looses traction and regains traction on the
far side.
2) Sudden releasing the clutch in a lower gear when
down-shifting.
3) A “jackrabbit” start from standstill.
I’m not talking about abusive driving, just what a 911
is normally capable of and was intended to do.

Note 1) and 3) are in the acceleration direction and 2) is
in deceleration direction. If the joint-to-flange slips a few
times (even over months) what happens to the clamping
force from the screws? Can this repeated slippage unscrew
the fasteners?



According to the Schnorr technical info, clearly “settling” is
an issue with all fasteners. This graph shows 20%, the
text on the prior page says 10-15%.

Jim & Wil, am I interpreting this diagram correctly? The
fastening starts with the bolt loose at (0,0) and torque
is applied (horizontal axis), the clamping force (vertical
axis) increases. The little “wiggles” in the graph at
upper-right are when the fastener “squeaks” from
stiction at about 70-75 Nm. The horizontal line across
the top is releasing torque with the fastener maintaining
clamping force at 100%.

After the assembly and prior to disassembly, the clamping
force “settles” to 80%. I wonder how much time/use this
takes to stabilize?

It takes a torque about 15% greater than the initial
application to “break loose” the fastener at about
87 Nm. (Normally I would draw this part of the graph
in the negative torque side of the graph but this works.
Note my + and – signs.) The torque necessary to
unscrew the fastener decreases with the decrease
in clamping force until it is loose at (0,0) again.

I wonder what happens when you apply +75 Nm after
the assembly has “settled?”

Jim, did I miss hardness data for the washers or is it
part of SAE 1060?

“
"
© 2003 Adolf Schnorr GmbH + Co. KG Art.Nr. 900914

In all my measuring, I’m pretty sure OE Porsche was/is
Type “S” and not type “VS”.

I’m sure glad this is being discussed again. We don’t
need any more CV joints coming loose in service. I think
it is only a matter of time before someone is injured or a
911 destroyed from this happening at speed and “just the
wrong time.” Part of preventing that is getting the word out.

Best,
Grady

Sorry for being off-forum so much. I had a flu bug from
Christmas, got back in it too soon and then hung in for
most of the 24-hour. Added, the docs are testing me to
death.
I’m getting too patriotic: I’m a red blooded blue-blood
American but the white cells get high and not enough
red then I turn blue. HeHe. Oh yea, there are silly-meds
also.
G