CV’s – replace or repack?

[surflvr911sc]

While the 3.0 is out, and getting things ready for the 3.6, I was planning on replacing all the CV joints. I’m starting to think that would be an unnecessary expense that I don’t need to do.

The CVs don’t make any noise and seem solid, but I would hate to have the extra power prove to me that I should have replaced them when I had the chance.

The alternative is to take them apart, clean them, repack them, and install new boots saving about $250. What do you guys think?

[jmohn]

Take them apart, clean and evaluate. If there's any scuffing replace them, if not, re-grease and re-install. If they're truly undamaged, there's no advantage in replacing them.

Jerry M
'78 SC

[surflvr911sc]

good point, I won't really know until they're apart.

EDIT: if I find one that is bad, should I replace them in pairs?

[island911]

Just replace any severely worn CVs.

[Gunter]

Here is what I did: Dismantle, making sure not to mix up any parts, clean, inspect. Light wear marks are acceptable. I moved the outer joint (Wheel side) to the tranny side without flipping the joint. That way your shaft has the same torque direction as before, but the joints have a new position/working surface. The joints came off the splines easy in my case, you'll need large Circlip pliers. If you don't have any washers under the 8mm Allen bolts, use new "Schnorr" types. I didn't use any gaskets but made sure about the torque: 30/32 ft-lb for 8mm. See my thread. Good luck.

[caliber60]

I don't have time to repack so asked the shop to replace the whole shafts. Shops charges about the same price to either replace or repack. If you do the repack yourself, it's probably cheaper.

[Randy Webb]

I am trying to get teh tech guys at a couple of greace co.s to tell me if we should replace the CV grease at a certain # of years -- regardless of mileage. I will post when (if) I get any info.

Repacking won't hurt -- esp. since they are already out.

Repacking vs. Replacing depends upon how much a. you enjoy making mud pies, and 2. your sensitivity to $$ outflows from your wallet.

[Gunter]

Moly, like any other grease, will become more liquid over time because of the churning/whipping action in the joint. That is part of the reason why the balls in the CV joints get less good lubricant. Most shops run on time and will replace parts rather than re-use. Do what meets your needs.

[Superman]

I can tell you the correct answer to the "Should old grease be replaced" question. CV joints grind grease into mush over time. That is why the grease in them is special, and is also why they should be cleaned and repacked regularly. Annually is sufficient. Some folks can probably get away with leaving them for a couple years or so. But, remove the boot on a CV joint that has not been maintained for a hundred thousand miles, and the grease will pour out like thick motor oil.

I'm a big fan of disassembling and inspecting these things prior to making a decision about replacement (assuming you can do this yourself). I can also tell you that the only way to reverse the joint's wear surfaces is to put them on the other side of the car. If the joint is moved from the outside to the inside but on the same side of the car, the joint will still be using the same wear surfaces. Unless you have installed it backwards. So, I say flip them to the other side of the car.

Use Schorr washers and proper torque. Especially proper torque.

[Joe Bob]

A really filthy job....sub out the repack after you clean and inspect.

[island911]

Originally posted by Superman
. . . I can also tell you that the only way to reverse the joint's wear surfaces is to put them on the other side of the car. . .. .

If you're saying you "reverse the joint's wear surfaces by swapping axles side to side" . . that would be incorrect.
With swapped axles, the balls will still be in, pretty much, the same sloppy groove, pounding back & forth, with every load & unload.

As Gunter correctly points-out; the joints have a new working surface when the CV's center-race is moved (axially) to a new position.(WRT the outter race) You can get there by smartly flipping, or moving these parts around. You can, for example, flip (and clock 120°) just an inner race. . . .if just the inner race has a bad pit.

[surflvr911sc]

Now I’m really confused. Are you saying that I can swap joints around, left outer to right inner for example, or are you saying that I would need to swap parts from one joint w/ parts from another?

Of course this is assuming that they are worn. Good chance of that since I have no idea how long they have been on the car other than the last 25k miles. Wouldn’t it just be a better idea to replace any joints that have wear?

[Superman]

Well, I'm going to lose if I try to go head-to-head with Glenn on engineering matters, but parts of this question are simple "spacial relations" problems. I am not familiar with installing inner races backwards in a CV joint. Indeed, I am not comfortable installing the entire joint backwards either. The outer edge of my joints' outer races have a groove at one edge, so I have assumed that they are not meant to be installed "either way." Assuming that they are to be installed just one way, and assuming that inner races will not be installed backward in the joint......

The two joints on a given shaft get stressed in the same direction as each other. In other words, if you remove an axle, complete with CV joints, and turn it 180 degrees and reinstall it, (with the inner joint now on the outside and vice versa), then you will not change the surfaces against which the balls will press during acceleration. If however, you move the left side joints to the right side and vice versa, regardless of which goes inner and which goes outer, the surfaces against which the balls will press during acceleration will be virtually new. When done, the surfaces against which the balls will press during acceleration are the surfaces that used to be loaded during deceleration.

That's what I was saying before Glenn pressed me into the longer version. Without some inside information about CV joint design and function, I would not be comfortable spinning inner races or installing whole joints backwards. Make sense? Then again, Glenn may have information I lack. Doubtful but possible (smily waving face goes here).

[RoninLB]

I know what the recommended grease is.. but what I use is Mobilgrease XHP-222.. my joints and grease are always beautiful. the grease looks brand new.

Mobilgrease XHP 222 is recommended for industrial and automotive antifriction bearings, chassis components, universal joints and disc brake wheel bearings. It finds particular application in passenger cars, light trucks, taxi fleets and farm equipment. It is also recommended for marine, paper mill, sugar mill and mining applications
Mobilgrease XHP 222 Special and is used in chassis components, clutch bearings, ball joints of suspension and steering systems in all kinds of passenger cars, trucks, farm tractors, contractor, construction, earth-moving and mobile equipment. It also finds application in king pins, U-joints, fifth wheels and bucket pins


http://www.mobil.com/USA-English/Lubes/PDS/GLXXENGRSMOMobilgreaseXHPSeries.asp

[pbs911]

What's another couple hundred in the grand scheme of a 3.6 conversion? Ok, about 40 beers at the local pub.

Seriously, clean and repack with CV grease. Replace if necessary. New gaskets, "Schnorr" type washers and you'll be fine. With the fine machine shop maybe you can drill the bolts to have them safety wired.

[RoninLB]

Originally posted by pbs911

With the fine machine shop maybe you can drill the bolts to have them safety wired.

I bought a decent gizmo from Aircraft Spruce. I've also seen kits at good parts joints.. wasn't even interested in Snap-On.. probably $50-$75 and you can wire plenty of things. I use 2 sizes of wire routinely.........Ron

[dad911]

I would take them apart & clean them. If they are fine, grease & re-use, but if any are not perfect, buy 2 new axle sets, and in my leisure use the best of the old cv joints to make a spare. Last time I priced them, a complete axle assembly was cheaper than the 2 joints.

[Randy Webb]

I'm not sure what these comments really mean: "grind grease into mush over time" and "will become more liquid over time because of the churning/whipping action in the joint"

Apparently you are both referring to destrction of the saponified component in grease forming the spongy matrix that keeps the lubricating oil in contact wtih the working parts of the joint. Thereis nothing wrong with your concept but ti gives no quantitative guidance as to when the CV grease ought to be chenged. Also. it is not clear what the interelation of time and mileage are. That's why I contacted the technical people at the grease companies.

[RoninLB]

the historical routine was/is 30k miles for CV service.......Ron

[Gunter]

Hi Everyone: I'll invite you all to do some serious thinking about the CV joint issue. The axle shafts are receiving torque/stress in one direction when accelerating. The balls in the CV joints run against the same surfaces inside the races. You want to keep the torque on the shafts the same, DO NOT switch the shafts from one side to the other and DO NOT switch parts from one joint to another. You want a new surface (running area) for the balls in the races. Therefore, move them straight from the outside to the inside and vice versa on the SAME shaft. NO FLIPPING. Ignore the position of the groove on the outside of the joint, it has no function. If you think about the whole issue, while closely looking at the CV joint in your hand, it will become clear. That did it for me and I proceeded accordingly ('80 SC). This will only work if there are just slight wear marks in the races, any galling means the joint is kaputt. Earlier 911's had joints that could not be switched. When dismantling, make sure to keep the parts exactly matched as they come apart. Use MOLY grease for repacking. Of course, you can avoid all of that by just getting new joints, or new axle shafts.