drew

I have heard talk of exchanging the CV joint assemblies from side to side as part of the routine maintenance and lubrication procedure. I believe this would change the rotation direction of the CV joint whereby extending it's life.
Has anyone done this? Does it work?

Hans

I dont maintain them, just check regulary for play and condition of boots, basically every time the car is off the ground.
Whenever something is wrong with one of them, I replace the both that have the same position (both tranny side or both wheel side).
The price versus the life time of the CV does IMHO not justify the work. The increase of life time when rotating is depending on what goes out: a ball or the inner race.
If the ball goes, the lifetime will not be extended.
I have seen both happening and my best guess is that in only 50% of the cases the life will be extended when rotation direction is changed.
Take Care

drew

Thanks Hans, so just check the boot condition fill 'em up grease and reinstall? Are they worth taking apart cleaning and repacking since it's my labour and they're off already?

TomH

Repacking will extend life. So if you feel like it then yes, clean and repack. That's the only way you are going to be able to inspect them for wear. I couldn't see the burns in my races, until I had completely cleaned and dissambled the races. Only then did I see the burns, and the bearings that had turned black from overheating.

Repacking implies removing all old grease, not just adding new on top of old.

Wachuko

Also take a look at the post CV Bolts in this forum...
From that post (but go read it completely, there is more good information... ) :

"I will have to agree with the comments here, except for the one of using an impact wrench for this task (and believe me, I am a serious user of an impact wrench!!), an impact wrench will increase your chances of damaging the bolt. Your hands should be enough to get them out.

If you stripped a bolt, wash/clean/degrease the bolt, get a good quality tool and tap in the tool into the bolt and try again. The first time I did this the same thing happened, before I panic I cleaned the area tapped the tool in with a hammer, held the wrench as straight as possible, used both hands to apply pressure in and pressure to loose the bolt and it came out. Worst case scenario, remove the rest of the bolts and cut the offending bolt with a metal cutter or first try one of the tools mentioned here.

1. Get a good/quality tool (12 point)for this, it is worth every dime.
2. Raise the car enough to work comfortable under it. You want to be able to get the wrench as straight as possible to avoid slippage.
3. Clean the bolts with a solvent before attempting to remove them (with special attention to the inside, where the tool is going, of course). If the previous boots where broken, you might have grease all over the transmission and surrounding areas. This is a good time to clean everything well.
4. Tap in the tool to make sure it goes in as far as possible. Remove it and inspect if you still have dirt in there... clean again if needed. The key here is making sure the bolt is clean and you have a good grip in the bolt before attempting to remove it. Tap in the tool again.
5. Get the wrench and un-tighten the bolts, making sure the wrench and tool is as straight as possible. Any angle can cause a stripped bolt.
6. Do not use the Allen bolts (sometimes sold even by Porsche parts suppliers). Make sure you ask when ordering...
7. When replacing, clean the mating surfaces. The grease is for the bearings only, make sure there is no grease on the mating surfaces.
8. When replacing the bolts, put some Loctite on them as a preventive measure.
9. Replace ALL bolts when changing the CV joints.
10. Cross tighten the bolts (tighten one and then the bolt opposite to that one… you know what I mean) Torque to spec.
11. After driving a few 100 miles, check the bolts again. If you took the time to clean/degreased all the area before hand, everything should be dry, no signs of grease anywhere. If there is, please check the CV joints for loose bolts.

Danno

Well, I wouldn't do it THAT often. Mine started clicking at 125K-miles, so I greased them and swapped them from left <--> right sides. My car's now on 200K-miles and they're holding up just fine. I think there was a note somewhere that said they came from the factor with insufficient grease. Anyway, I used a hyperdermic needle attachment and injected 2-3oz of the sticky blue stuff normally packaged as "boat-trailer wheel-bearing grease". It's really tacky and sticks to parts well

On the swapping/flipping thing, the reason you have to swap left to right is because of the way the axles twist. Flipping outside <--> inside and keeping them on the same side doesn't do anything. That's because the axles are driven first from the outside cage from the tranny. Which twists this forward and twists the middle axle part forward. Then the axle twists the outside joint from the inner CV-joint. This results in the inner & outer CV-joints having opposite wear patterns from each other and flipping inside <--> outside them would have the same wear patterns. You really have to swap them left <--> right to move the wear spots to the opposite sides of the cages.

Hans

Drew: Not completely:
When the wheels are off the ground I push-pull the shaft trying to feel the "smooth" move of the bearing, and rotate the wheel listening for weird sounds.
While rotating I wach the boots for cracks.
I do not normally disconnect anything.
If boots are showing minor cracks, I replace them and clean / re-pack the CV.
If one of the ***** is coloured different (blue or black), CV is replaced.
As per Danno above, you can probably get more life out of them when rotating the load to the other side of the CV, but this will only work as long as the ***** are OK.
Whichever way you go, note that whenever you undo the bolts, you got to replace them.
They are one time use only!!!
Take Care

drew

Oh really, one time use only for the bolts? Any reason why?

Wachuko

It is not worth the risk of getting a stripped bolt when re-tightening the bolts or taking them out the second time around. Having said that, I have taken them out after inspection of a loose one and reused them with loctite, but any sign of a stripped bolt gets replace with a new one.

Type_LT

I just repacked and rotated my cv's, I could let you know all the steps/tricks I used if your still interested. Took about 7 hours on the first and 4 on the other. In my case I simply flipped the cv's themselves over, this has relatively the same effect as swapping the entire axle assemblies.

Hans

Now you need to know some more about metalurgy:

1) Crack stress is the highest stress the bolt can handle. It will snap at higher load.
Note that this is stress, not torque!!
(Diameter when stressed is reducing so load (lb/sq-inch) goes up because due to reduction of diameter)
2) Yield stress for normal bolts is about 10% (varying with the material) below the crack stress. This is the point where material characteristics change permanently and the material is no longer "linear elastic".
3) normal bolts (and all other mechanically stressed items) are normally stressed to a max of 85% of yield stress, so well within the normal area of elasticity, and the material will return to the original structure when relieved.

The torque loads on the spline head (cheese head / 12 sided /..)bolts in a VW/Audi/Porsche is beyond the yield point.

The new yield point (from used bolts) will be at an higher value and elasticity will be different (stiffer), too close to cracking for comfort.
The material characteristics just beyond the yield point are the ones required for the clamping force of the CV (with VW also cylinder head, with 944 also clutch - pressure plate).
These characteristics are only there at the required point with fresh bolts.
You will find cracked bolts or loose CV joints mostly when the bolts are re-used, this assumed they are torqued right first time.
Conclusion: Standard replace cheese head bolts on P-cars and get a good quality set of cheese head sockets and a pro class torque wrench....

I am Dutch and my knowlege of English is limited. Hope tere is someone out there that can explain more clearly, thanks

Take Care

Danno

Hans is referring to the various strength properties that steel has and how they're determined.[list=1][*]fatigue strength - is the lowest level and if stress on the material is below this level (fatigue limit), it will last forever. Some materials have NO fatigue limit, like aluminum. Which means ALL stresses, no matter how small will accumlate and eventually break the part. Yes, you can arm-wrestle the aluminum rear trailing-arm in our car and it will eventually fail. Sure it may take a couple thousand years at that stress-level, but it will fail at some defined point. Steel, however, does have a fatigue limit, and depending upon the alloy, can be quite high.
[*]yield strength - is the point where the material takes a permanent deformation (bend, stretch, etc.).
[*]ultimate strength - is the point where the material breaks apart (cracks, breaks, splits, etc.)[/list=a]So what Hans is saying is that the CV-joint bolts are tightened to the point where the stress on the material falls in between its yield and ultimate strength points. This is the part I'm not particuarly sure about without knowning the alloy composition of the material or its design parameters.

But in general, the best clamping characteristics of most fasteners fall below the yield point because that's where the metal is still elastic (can pull like a rubber band). Beyond its yield point it behaves like a plastic and doesn't provide much tension. Again, this is a generalization and the CV-joint bolts may be a special application of some sort.

However, we can look at empirical data (field experience) to see what the trends are. I personally have, and others have as well, re-used these CV-joint bolts. And as Jaime says, its condition determines whether it should be reused. I have also measured the length of the bolt before and after installation to the proper torque and have found no permanent elongation, indicating that the bolt was below its yield point.

I think a lot of the fear around these bolts have come from improper removal and installation. Stripping the bolt-head ever so slightly would not allow you to re-torque it back to the proper tension. And if you do not completely clean off all grease between the mating surfaces of the CV-joint and the tranny's flange, you will subject the bolts to shear forces, which will break them. That's because it's the friction at the interface that transmits the force across. So I think you have to worry more about damage, improper torque and installation more than the strength of the bolts themselves.

Hans

Danno, thanks for your clear explanation above.

I did re-use bolts myself (on VW and Audi for clients), did this "by the book", cleaning and all.
Stopped re-using when I had a fail in the left inner CV bolts on my '79 scirocco.
That was with the first re-use of the bolts.
Car was only slightly tuned to 100 DIN HP so nothing to get exited about.
You can imagine that the cost for repair of the damage was way more than the OEM price for some bolts...
So you can re-use the bolts, but it will be a risk.

What does Ferry says about this? Anyone with a manual?

drew

Thanks for providing them Metala\urgy lesson , saved me from pulling out all my old metalurgy books.
I can see the retighting problem here as Danno mentioned, how many people would actually clean out all the grease from the flange mounting threads as well as the bolts. With the different friction coefficent that could translate to higher tighting torque than required.
Where can the bolts be purchased, in the standard head (triple square) configuration.

Hans

Dealer, and Skip no doubt.
Searched for them in the industrial suppliers world but no luck.
Take Care