As I recall, my '87 has moon plates but no Schnor washers. I have new original-length bolts, as well as Schnorr washers. Is the thichness of the Schnorr washers going to cause a problem by "shortening" the bolt, thereby leaving fewer through-threads exposed?

Tut:

The answer to your question was posted by Grady somwehere within this post.....I touched upon it briefly in my note about thread engagement and protrusion beyond "flush"....

Wil

Tut,

With your ’87 you should have the 108 mm CV joints and six M10 bolts. If so, you have the support plate 911.332.191.00. If you somehow have the 100 mm CVs with M8 screws and support plates, we need to find the part number – it isn’t in PET. An easy way to tell is by the Allen wrench for the CV screws. An 8 mm wrench is for the M10 screw, a 6 mm wrench is for the M8 screw.

To answer your question, you probably need to try it in situ and measure the penetration.




Assemble the CV joint to the transmission flange with clean steel-to-steel = 4760 ft-lbs. Get grease on the interface (the usual situation) = 950 ft-lbs. Normal full throttle in first gear with a 3.2 is 1191 ft-lbs (dynamic loads may be 2-3X that).

I find it hard to believe that Porsche didn’t consider this when changing from the big 108 mm to the 100 mm 923 part.

From Jim’s calculations it appears that the 100 mm CV joint is normally very close to the limit regardless of Schnorr washers and such. If there is grease on the joint surface, the connection will almost certainly slip in normal operation. It is next to impossible to attach the CV joint to the transmission axle flange and not get moly grease on the mating surfaces. This makes the case for installing an end cap on every CV joint that doesn’t have one.

It now makes sense why Porsche includes an end cap with the CV boot kits.
The 100 mm kit is 923 that I can’t find a P/N with the end cap.

What does everyone think of THIS “cap” that replaces the gasket on a 108 mm joint? Please be polite.

Installing the end cap isn’t a perfect solution because 911s with end caps still have CVs come loose.

Something we need to look at with the end cap is the effect of having “another piece of meat in the sandwich.” With the end cap, there is now a plated thin steel spacer between the CV joint and the flange. The instructions for installing an end cap include applying sealant between the CV joint and the end cap. It seems to me this is similar to greasing the interface. It might also make “settling” a greater issue. There has to be a better way to seal the grease inside the end cap and boot flange while insuring metal-to-metal contact. Suggestions?



Of course the real solution is to replace the 100 mm CVs with the 108 mm, six M10 screws, Schnorr washers & support plates and an end cap without sealant in the “sandwich.”

The 108 mm Turbo set-up
2 each Stub axles 930.332.232.04
2 each Lock nuts 900.910.093.02
2 each Axle assemblies, 108 mm CV 930.332.037.04
2 each Transmission axle flanges 915.332.209.12
24 each M10 socket head cap screws M10x50 900.067.123.01
12 each Support plates 911.332.191.00
24 each Schnorr washers M10 999.523.103.01

The 108 mm Carrera set-up
Stub axles not needed
2 each Lock nuts 900.910.093.02
2 each Axle assemblies, 108 mm CV with friction welded stub axles 911.332.024.14
2 each Transmission axle flanges 915.332.209.12
12 each M10 socket head cap screws M10x50 900.067.123.01
6 each Support plates 911.332.191.00
12 each Schnorr washers M10 999.523.103.01

Please don’t take these P/Ns as gospel; there are supersessions and these might not be the right parts for the conversion. Some research help would be appreciated.



Porsche should supply these parts kits to owners at a bargain price – one that would cover their unburdened manufacturing, shipping and distribution costs. They probably could even get GKN Lobro GmbH to pitch in.

They may be practicing the “let sleeping dogs lie” philosophy from prior incidents but one of these days someone is going to have a CV joint come loose – with disastrous results for everyone. A phineg of prevention is worth a €B of judgments. Classic 21st century CYA.

Best,
Grady

How do you spell the unit that is 1/100 Deutsche mark?

Thanks, Grady. Will do.

You had indicated that you'd like some Schnorr washers when I received them. How many?

However, your question was how much extra thickness is a sandwich of Schnorr washers and moon plates...Grady says 1mm + 2.5mm, respectively, or = 3.5 mm.

If you didn't have these pieces installed OEM...and you intend to add the washers and moon plates...then you'll likely need bolts 3.5 mm longer. Since bolts come in ( usually) 5 mm length increments, this may be a problem, but maybe it's not if you first check the backside penetration is still 1.5-2 threads.....

Your option then is to find these as Porsche parts that may be used elsewhere and come in 1 mm length increments...or having them pro-machined to length w/o damaging the shank or remaining threads.

Grady or Island....the only alternative is to keep the mating surfaces really clean. This has benefits regardless of the design safety factor applied.

Any advice here how to do that?... or is it simply a matter of being REAL careful and trying to be surgically clean?. Is this a case like the plumber's trick to stuff white bread into a copper pipe ( to hold back some water) so you can get applied torch heat to work on the solder- joint?. The bread later is "consumed" in the flowing water to no ill-effect. Do we need to find something like that ( in principle) applied here?

Wil

re: clean thread surfaces
I tried to be careful.. then used Q-tips, and brake cleaner on more Q-tips to clean the femal threads. next, run the clean bolt in, pull it out and inspect. Repeat cleaning until done...

Randy:

Taking nothing away from what you said in terms of thread cleanliness...

I think...(in the context of torque load capability)....that we're talking about clean mating surfaces of the CV joint with the matching surface on the drive axle flanges.

Look at the substantially different torque transmitting values of the CV.... clean vs greased.

- Wil

yeh - but just wipe that - cloth w/brake cleaner on it

seems like the roll pins should carry nearly all the torque (?) what am i missing w/that?

If clean mating surfaces are so vital why not a cross hatch or something similar on the surfaces so they would adhear to each other better when clamped together. Do smoothly machined surfaces offer better clamping and therefore higher torque or is there a better alternative.

smoothly machined surfaces

- maybe - machinists blocks can be 'wrung'together and cohere so well that they will support heavy objects in tension

Jim can probably be more accurate here but my take is:

The screws when torqued provide “clamping force” between the CV joint and a flange (stub axle or transmission).

It is the steel-to-steel interface that, with clamping force, provides the shear strength that allows the transmission of torque without the joint slipping.

The screws should only provide clamping force by their tension. They should not be part of the shear between the CV joint and flange.

If the interface slips, then the screws are in shear (and bending) and bad things happen. The screws are put in bending and shear while still in tension. If this is cyclic (repeated slip back & forth) the screw is likely to unscrew. When that happens the clamping force is reduced and the failure becomes progressive.

It is the interface that needs to be free from grease (difference of 4760 ft-lbs vs. 950 ft-lbs) for the joint to not slip. The more the mating surfaces are oil-free, flat, parallel and smooth, the better the clamping force-to-shear strength ratio. Sure, gauge block level of surface finish is ideal but impractical.

I think Porsche had it right with the 4-bolt & spiral pin arrangement with 108 mm CVs in ’69. Too bad the bean counters prevailed. I’ll bet had the engineers stood their ground, PAG would have made more money and customers would be happier.

Best,
Grady

"4-bolt & spiral pin arrangement with 108 mm CVs in ’69."

One problem with these was getting them separated; probably more than one wheel hub or transmission output bearing met an early death from the "pounding" that was usually applied to get them apart. They badly needed a couple of tapped holes on the back side to use to jack them apart with screws - likely the bean counters again.

So.... for us 100mm guys with 8mm bolts....lets keep the mating surfaces clean...eh?.

Once done, then what ?.....Schnorr/moonplates added too? ( my 85 ...as noted....has demountable CV's on both ends of the halfshafts..with 100mm CV/ 8mm cap screws...no Schnorr/moons).

Not to derail....but why isn't a lock washer needed for "wheel" bolts and/or studs...it sees the same type of cyclical forces? Size? Contact area?

- Wil

yep, dry . . that's been my soapbox for a while now.

since you bring up hole patterns and forces...

I saw that Grady posted three reasons for the moonsplates . . .thought I do doubt that those reasons hit any nail on the head - so to speak.

Anyone who has done much machine design knows about tolerance build-up that exists when matching multiple holes of matching parts . . .that is; the more holes you have to match-up, the harder (costly) it is to execute.

. . . if you had both the CV's and the flange match-drilled, you could have very precise bolts in very precise holes . . . such that, even if the fasteners are lightly torqued, the CV and flange can have little relative motion.

Of course that particular CV isn't too likely to fit on the opposite side tho -- thus the need for either tight ($) control over dimensions, or loosening of the tolerance.

The moonplates only have to hold 2 tight tolerances each (hole size, and the linear distance between.

that's my thought for the day. :cool:

Wonderful thread, but seems to be missing the piece of information that I need...

Yesterday, turning right out of a parking lot I heard a load bang followed by a rumbling in synch with the wheel speed. Drove real slow and pulled into the nearest parking lot.

Looked under the car and saw the loose outboard CV bolts. Removed the drive axle and found two bolts sheared. One spun easily out of the hole. The other is stuck. I made a drilling fixture but even so my bit walked and drilled the outer edge of the bolt and possibly some of the threads...

Minimum it seems I need to pull the thing that the six M8 bolts of the outboard CV screw into. From my reading it seems that I need to remove the large 32mm nut. Is this correct?

If so I will pick up the requisite 5'ft of galvanized pipe...

Thanks for the help.

Matt,

You'll find all the info you need in this thread.

Randy

Thanks Randy,
Took off the axle nut, easy job with a five foot cheater bar. That provided great access to the sheared bolt.

I drilled a piece of bar stock and used two bolts to mount the flange to it. Clamped the bar stock in the drill press vice and used a center drill to start a hole in the bolt.

Switched to 5/32 drill and went all the way through the sheared bolt. Used an EZ out to remove the bolt. Chased the threads with a re-threader and am ready to reassemble tomorrow.

Will of course review this thread again to be certain to orientate washers correctly etc... I am also thinking about searching for that picture of the wired CV bolts.

Thanks again for the help.

Grady or Wil,

A while ago there was discussion about the bolts extending 1-2mm beyond the flange as being the ideal situationto to assure proper purchase, holding, call it what you will. Yesterday I crawled under my car. I have M10 50mm bolts. At the trans. end from the surface of the moon plate (no Schnorr washers present) to the end cap on the CV is 36-37mm. The flange is 15mm thick, including a "bump-out" to increase the thread depth. So the bolt is recessed 1-2mm into the bump-out. For the purposes of this discussion I'm assuming they are the original bolts, but we all know what happens when one assumes.

If I add the 1mm Schnorr washer that would mean that the new M10 50mm bolts that I have would be recessed 2-3mm, but would still have 12-13mm of thread depth in the flange. If I purcahse 55mm bolts I would have 2-3mm extending beyond the flange. The flange is awfully close to the sides of the case, and I'm concerned about the extended bolts coming in contact with the case. If my assumption regarding the originality of the bolts is correct, thereby indicating that Porsche didn't feel the need to have the bolts extend beyond the flange, and acknowledging that Porsche is not infallible, am I running a real risk (real risk vs. ideal situation) if the bolts do not extend beyond the flange given that there would still be 12-13mm of thread depth in the flange with 50mm bolts?

Thanks.

Tut,

I would get the longer bolts and new Schnorr washers.

Before you disassemble anything, remove one bolt and check the clearance between the end of the new bolt and the case (without the Schnorr washer. Remember the axle flange has about 1-2 mm of axial free-play so you need to force it toward the transmission.

If there is contact you can add washers under the head of the bolt until you get the desired 1 ½ threads through the flange. This will let you calculate how much needs to be removed from the threaded end of the new bolts.

My local largest metric fastener supplier tells me I should figure on 25¢ per bolt to have them shortened in 100 quantities. In these lengths they are standard in 5 mm increments.
.
I think everyone agrees that the bolt should always extend through the flange.

These bolts have a thread pitch of 1.50 mm/turn. If your 50 mm bolts are recessed 1-2 mm and you add a 1 mm Schnorr washer, that should leave a 55 mm bolt protruding a correct 2-3 mm (1 ½ - 2 turns).

You said “…if the bolts do not extend beyond the flange given that there would still be 12-13mm of thread depth in the flange with 50mm bolts?
No, I just measured a flange and it is only 12 mm thick less some countersink on the CV joint side. I recall on of my earlier posts counting slightly less than six turns of engagement from the first thread to flush on the back side.


I’ll speculate you originally had 55 mm bolts and a PO replaced them with 50 mm. Upon installation they left off the Schnorr washers to get any thread engagement. When you have things apart; look for the tell-tail Schnorr markings in the plate washers under the heads of the bolts and on the back side of the plate washers (in case some were turned over).


Pay close attention to having the mating surfaces of the CV joint to flange clean and free of grease. Jim’s calculations above were an eye-opener for me.

Best,
Grady

Grady,

Thanks for the info. I'll order 55mm bolts from McMaster today.

By the way, I purchased a box of 1000 Schnorr washers directly fro Schnorr some time ago. You had indicated that you wanted some. How many sets do you want?

Regards,

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).

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.

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

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.

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

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

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,

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

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

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

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

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

bump

Grady?

Grady,

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

Regards,

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

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,

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

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

not needed at all

clean threads, proper torque & Schnorr washers will work fine