Are 'Moon Plates' necessary with CV joint replacement?

[juicersr]

Cant argue your expertise Grady, or the horror stories out there. Going with the plates. Hell, after all the thousands i'm spending to restore and improve my 'first love', what's a measly $120 more? When u throw in the safety factor, i guess it's a no-brainer.

[jimbauman]

Regarding moon plates - if they WEREN'T necessary, would Porsche spend the $$ (or Deutsche Marks) to include them? Figure the cost of the plates per car times X per car - that's quite a savings Porsche could have realized by eliminating them.

JB

[juicersr]

Originally Posted by jimbauman

Regarding moon plates - if they WEREN'T necessary, would Porsche spend the $$ (or Deutsche Marks) to include them? Figure the cost of the plates per car times X per car - that's quite a savings Porsche could have realized by eliminating them.

JB

Geez guy... didja not read the thread?? Per Grady, Porsche DIDN'T include them on certain model years. That's the whole point of this discussion.

[jimbauman]

Nope, didn't read the whole thread - just skimmed it on my new Blackberry.

[surflvr911sc]

I have not found a M8 solution to the moon plate issue. Were M8 moon plates even made? I can't find any evidence that they were.

If M8 moon plates are available, then my hat is off to those that are much more experienced and better researchers than myself; and Randy and Grady are in that category regardless.

But if there was never a M8 Moon plate made, then all the advice given to 75-85 owners to buy moon plates for their car is worse than just moot. Pelican doesn't even sell M8 Schnorr washers that I've been able to find. Replacing the axles and "converting to the later 108 mm 928S style with M10 bolts and moon plates with new Schnorr washers" isn't practical to the average DIYer; even if it is the best solution.

I safety wire all my M8 CV bolts w/ great success (it's good enough for airplanes), but I realize that it is also not "practical" for most owners. I would agree that there are better solutions, if it didn't mean replacing the axles, hubs, flanges, and I'm sure some other expensive parts that I can't think of.

Again, maybe I'm lost and and the answer has been repeated many times. If I'm right, I just don't understand all the advice if there was never a M8 moon plate made, and the only way to get M8 Schnorr washers is finding them outside of Pelican, and it would be bad to use them on replacement CV joints anyway because of the soft metal.

So what's the Last Word on 75-85 cars?

[T77911S]

I have had 2 come over the years. one was my 914-6 in first gear. the second was last year at about 30 mph. not much damage. put a dent in my heater box. i went to fastenal an got a bag of 50 bolts and washers for the prsice of replacing all the bolts and washers. i think mine came off because the bolts/threads were not clean and the washers were old. fastenal sells the bolts in 5mm lengths. so i was able to get bolts that protuded the flange by about 2mm. i also put loctite on the threads. oh, i did half the moon plates.

[safe]

On my 77 I have the thick flange boot (like the lower on juicersr picture), no halfmoon or lock washers, as it came from the factory. I have had them apart several times and only used these methods:

-Clean threads
-Clean mating surface
-New gaskets to keep the grease out.
-Proper torque, first half value in no special order, then full torque in a criss-cross pattern, followed by full torque in a circular pattern, just to be 100% I didn't miss any.
--I have also used high strength Locktite (243) on the the threads sometimes.

I have never (good God, I'm gonna jinx this...) had any bolts come loose, maybe I'm just lucky.

The thick flange isn't a smooth surface, its only level under the screw head. I agree that schnorr washers or equivalent are good, but I fail to see the use of the halfmoons...

[T77911S]

Originally Posted by safe

On my 77 I have the thick flange boot (like the lower on juicersr picture), no halfmoon or lock washers, as it came from the factory. I have had them apart several times and only used these methods:

-Clean threads
-Clean mating surface
-New gaskets to keep the grease out.
-Proper torque, first half value in no special order, then full torque in a criss-cross pattern, followed by full torque in a circular pattern, just to be 100% I didn't miss any.
--I have also used high strength Locktite (243) on the the threads sometimes.

I have never (good God, I'm gonna jinx this...) had any bolts come loose, maybe I'm just lucky.

The thick flange isn't a smooth surface, its only level under the screw head. I agree that schnorr washers or equivalent are good, but I fail to see the use of the halfmoons...

+1
clean is the trick, and it is tricky. replacing the washers is also a good idea.

i think there were thick flange and a thin flange on the CV joint, the part that the rubber boot attaches to.
grady has some very good advice on this.

[RWebb]

Last Word - I thought Grady posted it above -- convert to the "good" axles/CVs.
I guess a cheapo Last Word would be to make moon plates of appropriate material (or get Elph. or somebody to do that and buy them).

And didn't Grady explain why they were needed above also? It isn't smoothness as post 27 says, it is the material they are made of, which allows the Schnorr washer to "bite." Maybe thickness is an issue also...

[Cooper911SC]

Any sources for the M8 Schnor washers? I have tried a couple of good local hardware suppliers with no luck.

McMaster? or another place?

Coop

[KTL]

McMaster will give you all the M8 Schnoors you need. Go to page 3168 in the online catalog

Not trying to be contrarian here, but i've never had Schnoor serrated washers on my '87 M10 x 6 count CV screws and i've never found the screws loose. The increased torque spec from 30 ft-lb (M8) to 60 ft-lb (M10) certainly is a factor in this case.

I started to get complacent and stopped checking them every time before a track event. Then I kicked myself and thought how Murphy would rear his ugly head if I kept ignoring them. Point being is when the moon plates were introduced on the later 85.5 axles, the serrated washers were no longer spec'd for the installation. But they are cheap insurance so there's no real harm in using them. They're very thin, so they don't force you to use longer screws if you do decide to use them.

I've also noticed that the screw length Grady recommends is beyond what you'll find on a factory installation. Not saying Grady's wrong. I'm pointing out that the standard length that Porsche used is deficient- the screw threads do not protrude out of the inside of the transmission drive flange. So if you want to replace your CV screws and want to meet Grady's recommendation, you'll have to buy screws a bit longer than what you'll get if you go by Porsche's part number/their specified length.

[Cooper911SC]

Thanks Kevin. My SC didn't have Moons or Schnors...I check mine whenever the car is on the lift and have never noticed them being loose...but you never know...

[Grady Clay]

I thought our host stocked them. Search again, they may be in a 'bolt & washer' kit.

They are available from McMaster Carr ans Schnorr USA.
Quantities are very inexpensive for these 'use-once' parts.

I recomend everyone read & study the receale (sp?) thread. While long, it has all the basic info and links. It is worth the effort.

Best,
Grady

EDIT
Both my good computers are down and this one (that works -sorta), I can't read the screen well.
Anyway...
The Porsche parts manuals (PET) give the CV bolt length but I have found that does not always agree with any given 911. Part of that is Porsche not being as consistant with the bolts as they are with almost everything else. It is ALWAYS best to follow the 1-2 thread rule.

The aftermarket high-grade bolts usually come in 5 mm increments. It is easy to have a few mm turned off the end of a too-long bolt. Be sure and grind a 'lead-in' first thread. NEVER use more washers under the head of the bolt.

I wish there were a clear-cut answer as why some cars have CV joint bolt problems and others don't. Clearly the 923 (912E( 100 mm CV joints weren't adequate or Porsche would have continued using them. The 'clamping effect' of the six M8 bolts torqued to 33 ft-lbs on a smaller circle can't be even close to six M10 bolts torqued to 66 ft-lbs on a larger circle.

Jim Simms is the expert. It is not the shear or bending of the bolts that transmit the driving torque. It is the clamping force provided by the tension of the bolts and circle diameter that determin the torue limit before the CV joint can slip on the flange. It is the slip that (usually) results in the bolts becoming loose. Things go to hell quickly after that.

G.

[T77911S]

grady, good comment on the bolt length. mine were short. im sure that and the threads not being clean contributed to them coming off. it is any easily over looked solution to a potential disaster. fastenal has the 8.8 bolts in i think 5mm lengths.

[egertk]

Not really certain what the spacing is on the original posters CV joints, but if it's 100mm, M8 bolts, 50mm length I take it? Early to late 90's vw's like the passat and jetta had a 100 CV axle and used M8X50mm stretch bolts (torqued to spec they should not back out, works like a head bolt) and they use moon plates that are probably the same dimensions. Could grab some off a car at the junk yard for probably less than 10 bucks. New stretch bolts are 1.95 a piece at online parts places. Hope that helps.

[Gunter]

Good stuff.

No matter what you have, #1 would be to periodically go under there and check the bolts, re-torque.
There is other stuff that need to be done anyway like grease/oil for the clutch levers etc.
I am lucky to have a pit.

I prefer metal on metal and don't use gaskets because I think the gaskets may add to the problem of CV's coming loose.

No moon plates but serated washers, no Loctite, just the right torque cross-wise has worked for me.

I don't think the 12.9 Allen socket M8 x 50 are stretch bolts?
Anyone?

[KTL]

Originally Posted by T77911S

fastenal has the 8.8 bolts in i think 5mm lengths.

Everyone should be using 12.9 grade cheese head screws. 8.8 is less than the original strength /property class used for these CV screws.

These are not stretch bolts as far as I know. They're basic 12.9 property class partial thread fasteners and are not a one-time use fastener. The only reason to replace these bolts is if their threads are messed up or if the heads are starting to strip-out.

[RWebb]

yup - That is what Jim said in an old thread.

BTW - you can translate the Gradian 1-2 thread Rule into an easy to feel or view "just a rounded nubbin plus a tad sticks out" rule... maybe examine carefully on the easy to get to ones before relying on it on the wheel side of these things.

I did a test once by putting a couple of used and "just barely sharp" Schnorr washers on a couple of bolts. Sure enuff, they were getting loose after a few thousand miles.