Had a reason to be under my '87 S4, and I noticed the outer boots were torn. OK, 'nother bit of maintenance to take care of...
But, while I was fiddlin' around there, I noticed the halfshafts moved WAY easy! Like, no tension to their movement at all! They move like a trombone slide.... or easier! Is this correct/OK, or a disaster waiting to happen???
Inside the torn boot, there was all sorts of the black molybdnum grease, no rust that I could see. Should I count on replacing them anyway?
'87 S4 Cassisrot auto
The shafts are supposed to move in/out of the CV joints. Some freeze on one end. You have a winner!
If you see grease that's a good sign. Give the shafts a twist to see how much play there is on each end. Should be very small, like a degree or three. This is a judgment call. Easier to get them apart and look for grooves in the races.
I wouldn't pre-order new joints. I would get boot kits for all four ends.
The trombone move is correct. If you think about it they have to telescope to
account for angular movement. Unlike splined u-joint style drive shafts the
movement is built into the angular grooves of the joint. Quite clever those VW
engineers. I think that was a VW patent WAAAAAAY back (Thilo?). Anyway if you
don't have clicking while driving and have only liberated moly disulfide you are
good to clean, repack and reboot (Microsoft joke).
Not sure about the S4 with the one piece hub assembly but on my early car you can reboot without disturbing the jeezus nut on the outer end of the axle. You just rebuild the shaft from outside in in place.
As Jay said, do all four. Disassemble them completely, All the balls and the two halves totally clean. If there is any wear you will see it in the slots where the balls slide. It will be a little scary at first but don't worry, you can't put it together wrong. Do one at a time so you have others to look at.
Actually you can put the joints together wrong. It is possible to assemble
them so they are in lock up mode.
There are several things to look for. The first is blue balls. If the ball bearings get hot then will acquire a blue tint. If this happens they should be replaced. It is also common for the ball bearing to acquire a brown or gray tint. This is from the grease and not a problem.
Both the inner race and the other race can get scored. When you disassemble and clean them you will see some shiny areas on the inner and outer races.
This is normal, but if you see some tearing on the races then the ball bearing will begin to fragment. You might see some pitting on the ball bearing too. By tearing I mean pits or abrasions in the metal on the races where the ball bearings ride.
Another thing to check is movement in the spline. This is particularly common on the fixed end of the axles. Once they are cleaned up try rotating the joint separate from the axle. There should be no movement. On the removable end the joint can sometimes be reversed to tighten things up and even to compensate for wear.
One other thing to look at is the center cone. These can break. Examine them closely for cracks.
If you find some wear on all of the joints but have enough good parts to make up some joints it is ok to swap in parts to make the best joints thus saving some money on buying all new joints. The tolerances on the joints is not such that they are select fit or machined together.
I ran into a problem with the clamps I got with the last boot kits. They did not clamp enough to keep the grease on the outer boots from spraying all over the inner wheels. I replaced them with some hose clamps and fixed the problem. Be sure to get the boot kits with the hose clamp style clamps.
Gasoline works great on cleaning up the joist. Dangerous - but a great cleaner.
Dan the Pod Guy
The helical grooves in the races work together in one rotational direction
and lock in the other. Most japanese manufacturers use straight ball grooves
which gives more wear and more chance for binding at the margins so less angle.
The helical design is tricky to manufacture but gives smoother overall
operation. But you can put it together wrong. Looking at the races the grooves
have wide and narrow spacing alternating around the periphery walking around one
face. They also normally have a groove machined near one end of the outer shell
surface. The inner and outer groove patterns have to be opposed to have it work
properly. It can be assembled wrong but it is a bitch and it is near impossible
to actually install it on the car (but possible, ask me how I know :) .
How the thing works and how the spherical/helical criss-cross inner to outer groove pattern actually works is VERY hard to visualize looking at the parts even if you know how they work.
Good pictures in the manuals. These are very traditional VW/Audi style parts.
Every other groove around the race is canted with the opposite rotational hand
so on one end of the shell or hub the grooves are near and then far spacing.
They work like little cams but the every other groove opposite configuration
provides a garbage in garbage out function so that the movements all cancel.
Kudos to the one who visualized that and figured out how to make it.