Rear Axle Problems
 

I've been getting a clicking noise from my car at high speeds when it's engaged in gear.

It would start up after maybe forty minutes of driving on the highway around fifty five or sixty miles per hour. Sometimes it'll get louder, then it'll back off, then start again. If I left the car in gear and let it coast down a hill, the sound would also stop. This leaves me to believe that it is not a transmission problem, also the sound seems to be coming from farther back on the car. I've inspected the flex discs, both seem to be in great shape. Also, the transmission shifts very smoothly and there doesn't seem to be a problem with it at any other time.

This leads me to believe that there is something wrong with the rear axle. Does this sound like a correct hypothesis? Any ideas as to what part of the rear axle are prone to failure?

I'm surprised you can hear the clicking @ hi-speed, these beasties are so loud on the highway. The clicking must be really loud.

Have you checked the boots on the axle? unless they are cheap re-mans, they usually only fail after the boot fails and lets the magic lube out.

My car isn't too loud once the engine warms up, and the noise coming from the rear isn't usually super loud.

I checked the boots and they seem to be in okay condition. I'm not sure when the rear dif. fluid was changed last.

One of my CVJ-rebuilt axles did that for a thousand miles when it was new but suddenly stopped and has not returned. CVJ said not to worry about it and I'm not.

If your boots aren't torn and leaking, it may be that one of the balls in the linkage has slipped out of position and is getting knocked around by the fingers of the joint. I know from my experience that you can hear the clicking just fine at highway speeds, even over the engine noise of a 617.

Unlikely to be the differential making that kind of a noise. You could drain the oil and see if it has metal in it, just to be on the safe side. Refill with any good 85-90 weight gear lube or Mobil-1 synthetic if you want to get fancy. Remember to remove the fill plug first!

Jeremy

Sounds like a classical cv joint problem. I would add some oil to one outer joint . Drive it and see if the noise is gone. Some people have used a turkey baster to add the oil. A small very small tube would be my personal prefferance once the clamp is removed from the small end of the boot.
If the noise is not gone add some oil to the other outer joint and drive it. If either proccedure stops the problem you are good for awhile. Plus you have identified the exact joint that was noisey.
Better than a seventy five percent chance it is a joint in my opinion. After it warms up the noise starts is a very good clue. You just may have lost some lube in there over time.
The reason that you may save it is the noise or clicking is not there all the time yet. Once it becomes constantly noisy it is far too late.

Thanks a bunch for the tips, I'll take care of it tomorrow. I'm glad to know that I can diagnose the problems fairly well.

Why would it be the outer joint as opposed to the inner joint? I'm trying to figure out how they work so a little explanation would be great.

Good question. I am not sure why but usually the outer joints go bad in my experience far more often than the inner joints.
That does not mean it is not an inner joint though. Just not nearly as high a probability in my opinion. Yet still in theory it should probably not be selective. First check on all four joints is the boots though for any signs of oil leakage.
The nice thing about adding a little oil and a new clamp is that it is cheap to do. I would use about 3-4 ounces of a fairly heavy weight oil for the test on each side. Most cv joints are lubricated with grease. Mercedes uses oil and I suspect that is why they last so long. . Grease sometimes changes in comparison as it gets old.

Do they just use a gear oil like for the rear dif?

Oh, and I imagine the outer joints get more wear since they're closer to the wheel and the ground than the inner joints.

How much am I looking at to get the CV rebooted?