Reconstructing Constant Velocity (CV) Joints

[Wil Ferch]

Another tidbit.... I just found out ( by experiment) that the 10mm Schnorr washers available under the Porsche part number ( listed within this thread, M10 999.523.103.01)..is the 1 mm thick version ( "S" type)...that is typically used under non-rated strength hardware.

Same goes for "small" purchases made thru McMaster-Carr....these are all "S" spec, even if they aren't labelled.

Strange..... as the CV stuff should be metric proprty class 12.9.

However, Jim Sims addresses this as being proper in that one-side of the fastened pair ( either the moon washers or the face of the CV joint).. is comparatively "soft" and doesn't lend itself to beneficial use of high-grade washers.

Nonetheless...for those that want to go this way, there is another version of the Schnorr washer available. It is 1.5 mm thick for 10mm size...and more closely matches the pre-tensioning required of "rated" hardware like metric property class 8.8 and higher. These are Schnorr "VS" style..and are typically available only through Schnorr-USA ( AFAIK) , or through supply houses, but only in large purchase quantities ( 100-250 minimum, or somesuch).

I think the VS style may be way to go, if you need Schnorr washers for CV applications.

Final note... I looked at some of these same washers ("identical", actually, to the 10mm CV Schnorr washers) that are used under the socket head cap screws of the top/front suspension members ( shock tower area). Removing these, it was apparent that they were squished flat....so the spring component was lost. I would think that these become "one use" items and should be renewed . The teeth were flattened and deformed, too.

- Wil

( EDITED for add'l text).

[emcdan]

Another note worth mentioning again, I just replaced all four cv boots including new Schnorr washers and bolts.

The newer boot flanges are typically thicker. Sometimes 3mm to 5mms thicker than the OEMs. My older boots with 50mm were recessed in the trans flange about 2 or 3mms. I was happy with the new boots, new washers, new 55mm (12.9) bolts protruding a perfect 2 to 3mms. Now I measure up to Gradys' standard.

A side note that may be helpful. It is a very sloppy job to keep your new cv grease from getting on all your mating surfaces. I pre-assembled everything together without the grease. With the boot slid a few inches down the axle, I filled only the boot with grease. I then pulled the boot flange to the cv, inserted the bolts and mated to the tranny. Once everything is torqued, you can squeeze the boot to allow the grease to lubricate the cv components.

I can say that the bolts were completely free of grease when torqued.

[Wil Ferch]

I wonder, however, if you got grease *into* all the nooks and crannies of the CV joint itself.... ????

like bearings...isn't this done with a "packer" or with lots of grease on your palms "working" it in ???

- Wil

[island911]

Originally posted by emcdan
.. . I filled only the boot with grease. . . mated to the tranny. .. . squeeze the boot. ..

IIRC (from my VW days) those are the instuctions that came with boot-kits and new CV's.

Wil, it mixes in quickly . ...don't go worring about dry nooks & crannies.

[Wil Ferch]

Okey dokey then...a further part of the puzzle solved.....the dry-contact surface torque numbers ( vs "wet" or "lubed")... make this goal an important consideration, especially for us 8mm bolt guys.....

- Wil

[Tut]

Grady,

Following your advice, I removed one of the 50mm bolts and put in a 55mm bolt, new Schnorr washer, torquing to 60 ft.lbs. Pushed the flange toward the transmission. Have a minimum of .030+ in. clearance between the end of the bolt and the transmission at several points of rotation, with 1 to 1.5 threads exposed. Is the 0.30 in. clearance sufficient?

I'll recheck this situation when reinstalling the axles after servicing the CV boots.

Regards,

Tut

[Tut]

Grady,

I looked at at the PET. It calls for M10 50mm bolts on my car, not the 55mm bolts that you thought may have been on the car originally. So it came from the factory without the 1-2mm of thread exposed. And no Schnorr washers.

There was no evidence that Schnorr washers had been used with the moon plates that were on the car.

When I measured the clearance using a properly torqued 55mm bolt with a Schnorr washer, pushing the flange toward the side of the transmission, I had .030+ in. of clearance. I'm concerned that when the flange and axle are subject to the forces of use, as opposed to me pushing on the flange, that .030 will not be enough. Don't want to end up with the end of the bolt scoring the side of the tranny. This is only and issue on the driver's side, where the .030 is measured between the bolt and the webbing in the side of the tranny behind the flange. Clearance on the passenger's side is not an issue.

Regards,

[Grady Clay]

Tut,

How many turns of threads from just flush to final torque with the 55 mm screws?

It is uncharacteristic of Porsche to be so sloppy with hardware, not to mention this critical application. On the other hand they seem to have dropped the ball along in these years.

What tin boot flange was installed? Is it the same now? Any sign it had been replaced? For 100 mm CV joints there were two different boot flanges – a thin tin one and a thick (5 mm?) one. Changing the boot flange either way changes the CV joint socket head cap screw length requirement. Is/was there a thick boot flange for the 108 mm CV joints or only the thin tin?

Do your 108 mm CV joints (with M10 bolts) have a tin end cap? If not, a useful solution might be to install one on each inboard end. That will use about ½ turn of thread and give you an added ~0.75 mm (~0.030”) of clearance without modifying the bolts. It also solves the issue of grease on the juncture of the joint to flange.

The end caps come with the boot kits from PAG. The first thing to check is the fit of the protruding (bulge) end of the cap into the transmission flange. There shouldn’t be any interference of the bulge with the flange that would prevent the cap from seating on the perimeter of the flange. There are some early flanges where the end cap won’t fit without modification and some not at all.

I am somewhat concerned about Porsche’s instructions for sealing the end cap to the CV joint. They show a bead of sealant on the cap surface just inboard of the bolt holes. It appears the sealant is squeezed between the end cap and the CV joint when everything is tightened (assuming the sealant hasn’t hardened.) This procedure adds a sealant layer in the “sandwich” that is critical to transmit the driving torque. I see two potential problems.

First, I have no idea what the shear strength of the sealant is compared to the shear strength of the desired steel-on-steel provided by the clamping force of the CV bolts. Is this just not quite as bad as having molly grease on the clamped surfaces?

Secondly, does the sealant “creep” under pressure or temperature after installation? If so then the clamping force is relieved somewhat and we all know where that leads.

My questions are: Is there a better method of sealing? O-ring, brass shim “gasket” (say 0.005”), other? Is there a better sealant? Crankcase Loctite, other? Is there a better method of application? Aerosol with masking, other?

Clearly the sealing of the tin boot flange and the tin end cap to the CV joint should be accomplished in one speedy operation if cure/drying sealants are used. I can see using long SAE Grade 8 bolts and discarded CV joints as backing to clamp the tin and sealant onto the CV joint until cured. Remember the bolt holes in the CV joint and tin pieces have to be properly indexed so the M10 (or M8) bolts fit without interference.


Tut, back to your bolt length issue. Shortening the bolts isn’t simply cutting off the end. Carefully inspect the first thread. Note how the thread increases in diameter from the “root” diameter of about 8 mm to 9 mm at ½ turn to the full 10 mm on the 2nd thread. These two threads allow the screw to start properly without “cross-threading.” Jim can also help here.

If you shorten the screw, you need to accommodate the starting feature. If you DIY, you need a thread file and a Drimel. Always thread on two nuts and tighten them against each other and wrap tape around the bolt shank and other exposed threads. You don’t want any damage to the critical tension parts of the fastener.

This is one of the reasons for having the screw protrude through the flange. There is reduced engagement of the first thread or two.

If PAG installed the CV joint socket head cap screws with them 2mm shy of flush that is really shoddy manufacturing. I guess it is up to us to recognize the issues and find the best solutions.


BTW,
Don’t ever use two Schnorr washers in tandem. The teeth between two are cross-wise and will totally defeat the locking ability. If you want to shim the assembly (I thing a bad idea) use shim stock between the plate washer and the CV joint.

I am still not clear about the Schnorr “S” and “VS” issue. My measurements tell me the original washers were “S” and not “VS.” I haven’t measured any recent parts (OE or replacement).

Best,
Grady

[Wil Ferch]

Grady sez ..."I am still not clear about the Schnorr “S” and “VS” issue. My measurements tell me the original washers were “S” and not “VS.” I haven’t measured any recent parts (OE or replacement)..."

Sorry if I wasn't clear. Yes...the Schnorr parts from Porsche , with the parts numbers mentioned in my reply for the 10mm size.... are "S" style. I don't think this has changed. Still "S".

Although Jim Sims gives compelling reasons why a low clamp force "S" washer ( for non-"graded" hardware) is OK for our CV applications...and was even spec'd by Porsche...it still seems odd to me that the "VS" style ( i.e....the style for property class 8.8 and greater)... wasn't used for the class 12.9 CV bolts.

- Wil

[Grady Clay]

Wil,

I guess we need to discuss weather to recommend changing from the “S” to the “VS” in none/any/some/all of these applications. As in any engineering consideration we need to consider the pros, cons and failure modes. For our concerns, cost isn’t an issue. I don’t think this is necessarily a slam-dunk solution. There are issues on both sides. Engineering is about finding the optimal compromise.

In this situation I will discount the fact that Porsche used Schnorr “S”. I don’t think Schnorr “VS” was available when Porsche first started using Schnorr washers with the change from Nadella to Lobro in late ’66. I’ll speculate that they continued using the Schnorr “S” because they worked properly and there wasn’t a perceived problem. I’ll also grant them the engineering responsibility to not up-rate things for no reason.

As I have said above, I think the problem arose because of the decision to use the 923 100 mm CV joints and the decision to omit the Schnorr washers and/or plate washers. We normally ascribe this to the “bean counters” but the engineering staff didn’t raise sufficient stink to prevent these changes. None of us are privilege to the warranty cost or the possible liability Porsche had. Our goal here is to find the best reasonable solution. If you want an unreasonable one, you can TIG weld the CV joints to the flanges. HeHe.


Does anyone have original “VS” Schnorr washers?

The obvious difference is the Schnorr M8S measures 0.8 mm thick (compressed) and the Schnorr M8VS measures 1.2 mm. The Schnorr M10S measures 1.0 mm and the Schnorr M10VS measures 1.5 mm.

Best,
Grady

[Jim Sims]

Screws are easily shortened using the double nut method outlined by Grady to hold onto the threads. I set the outer most nut suface to make a cutting plane guide for the hacksaw or cut off wheel. After the cut, I back up the nuts to grind or file the tip chamfer to re-establish the thread start at the tip. Finally, I wrench off the nuts which provides a chasing action to the thread tip.

A further data point on the Schnorr washers in service: This weekend I've been inspecting and bleeding the brakes on my '76 911 and used the opportunity to check the CV joints (Six 8mm screw 100mm size with Schnorr washers and no "moon" plates). 20,000 miles ago the joints were cleaned, re-greased and re-installed with new Schnorr S-8 lock washers and one new screw out of the 24 (it's wrenching feature was bad). Inspection found all the screws in place and tight; car use has been daily commuting (~55mph speeds) to work six months out of the year, long distance trip cruising (800 to 3000 mile round trips), with an occasional high speed run thrown in.

Cheers, Jim

[Wil Ferch]

A while back on this thread we also considered a side trip to discuss areas where lock washers are ( and are not) used.. or preferred to be used. Interesting that areas like wheel bolts / studs....engine oil plugs...and even oil filters themselves...all in the vicinity of a high vibration area....*don't* use... nor recommend using... any kind of lock washers.....

- Wil

[Tut]

Originally posted by Grady Clay
Tut,



How many turns of threads from just flush to final torque with the 55 mm screws?
-------------------------------
Grady,

Sorry, I don't know the answer to that question. I installed a 55 mm cap screw when the axles were still in the car. The axles are out now.

-------------------------------
It is uncharacteristic of Porsche to be so sloppy with hardware, not to mention this critical application. On the other hand they seem to have dropped the ball along in these years.

What tin boot flange was installed? Is it the same now? Any sign it had been replaced? For 100 mm CV joints there were two different boot flanges – a thin tin one and a thick (5 mm?) one. Changing the boot flange either way changes the CV joint socket head cap screw length requirement. Is/was there a thick boot flange for the 108 mm CV joints or only the thin tin?

-------------------------------
I believe it would be the thin one, but I'll check tonight.

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

Do your 108 mm CV joints (with M10 bolts) have a tin end cap? If not, a useful solution might be to install one on each inboard end. That will use about ½ turn of thread and give you an added ~0.75 mm (~0.030”) of clearance without modifying the bolts. It also solves the issue of grease on the juncture of the joint to flange.

--------------------------------
Yes, I have the tin end caps.

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

The end caps come with the boot kits from PAG. The first thing to check is the fit of the protruding (bulge) end of the cap into the transmission flange. There shouldn’t be any interference of the bulge with the flange that would prevent the cap from seating on the perimeter of the flange. There are some early flanges where the end cap won’t fit without modification and some not at all.

I am somewhat concerned about Porsche’s instructions for sealing the end cap to the CV joint. They show a bead of sealant on the cap surface just inboard of the bolt holes. It appears the sealant is squeezed between the end cap and the CV joint when everything is tightened (assuming the sealant hasn’t hardened.) This procedure adds a sealant layer in the “sandwich” that is critical to transmit the driving torque. I see two potential problems.

First, I have no idea what the shear strength of the sealant is compared to the shear strength of the desired steel-on-steel provided by the clamping force of the CV bolts. Is this just not quite as bad as having molly grease on the clamped surfaces?

Secondly, does the sealant “creep” under pressure or temperature after installation? If so then the clamping force is relieved somewhat and we all know where that leads.

My questions are: Is there a better method of sealing? O-ring, brass shim “gasket” (say 0.005”), other? Is there a better sealant? Crankcase Loctite, other? Is there a better method of application? Aerosol with masking, other?

Clearly the sealing of the tin boot flange and the tin end cap to the CV joint should be accomplished in one speedy operation if cure/drying sealants are used. I can see using long SAE Grade 8 bolts and discarded CV joints as backing to clamp the tin and sealant onto the CV joint until cured. Remember the bolt holes in the CV joint and tin pieces have to be properly indexed so the M10 (or M8) bolts fit without interference.


Tut, back to your bolt length issue. Shortening the bolts isn’t simply cutting off the end. Carefully inspect the first thread. Note how the thread increases in diameter from the “root” diameter of about 8 mm to 9 mm at ½ turn to the full 10 mm on the 2nd thread. These two threads allow the screw to start properly without “cross-threading.” Jim can also help here.

If you shorten the screw, you need to accommodate the starting feature. If you DIY, you need a thread file and a Drimel. Always thread on two nuts and tighten them against each other and wrap tape around the bolt shank and other exposed threads. You don’t want any damage to the critical tension parts of the fastener.

---------------------------------------
If I had them shortened to 53 mm at a machine shop, as you had previously suggested, would the machine shop address the 8 mm to 9 mm to 10 mm issue?

---------------------------------------
This is one of the reasons for having the screw protrude through the flange. There is reduced engagement of the first thread or two.

If PAG installed the CV joint socket head cap screws with them 2mm shy of flush that is really shoddy manufacturing. I guess it is up to us to recognize the issues and find the best solutions.


BTW,
Don’t ever use two Schnorr washers in tandem. The teeth between two are cross-wise and will totally defeat the locking ability. If you want to shim the assembly (I thing a bad idea) use shim stock between the plate washer and the CV joint.

I am still not clear about the Schnorr “S” and “VS” issue. My measurements tell me the original washers were “S” and not “VS.” I haven’t measured any recent parts (OE or replacement).

Best,
Grady

[Tut]

bump

Grady?

[Tut]

Grady,

Please take a look at the post immediately before the bump. I placed some questions in the body of your previous post.

Regards,

[Grady Clay]

If I had them shortened to 53 mm at a machine shop, as you had previously suggested, would the machine shop address the 8 mm to 9 mm to 10 mm issue?

Take a look at them and compare to some of the old bolts.

What did the machine shop charge? I was quoted locally 25¢ each in 100+ quantity.

Best,
Grady

[Tut]

Grady,

My question was if I had a machine shop shorten the 55 mm bolts to to 53 mm would the machine shop do the 8 mm to 9 mm to 10 mm step-up? I haven't contacted a machine shop yet.

Regards,

[safe]

What about using loctite on the bolts? There's no mention of that in this otherwise very comprehensive thread.

[regency]

OK, great info. I'm going to clean-up & re-do my cv's on my ' 73 coupe ( I reused my old schnorr washers ). Just received a new set of Schnorr washers.

Q: What is the correct orientation of the "dish" concavity on these washers?

thanks

Steve

[RWebb]

Originally Posted by safe

What about using loctite on the bolts? There's no mention of that in this otherwise very comprehensive thread.

not needed at all

clean threads, proper torque & Schnorr washers will work fine