I suspect the driver's side axle on my 280SE is worn out. When accelerating from a stop, or when accelerating onto the highway, it makes a rhythmic knocking.

I got underneath and pulled on the axle shaft. There was no play up and down or front to back. When I tried moving it side-to-side the driver's side axle moved about 1 inch and the passenger axle moved about 1/2 that.

Does that indicate a worn axle?

not necessarily,

Use two small bottle jacks under the trailing arms near the lower shock mount. Get the wheels off the ground. Then rotate the wheels, and drive shaft by hand.
Check for smoothness of rotation. Shake the wheels up down and sideways, check for looseness.
If you are adventurous, block up underneath the trailing arms and put the car in gear. Be careful run it thru the gears.

"I got underneath and pulled on the axle shaft. There was no play up and down or front to back. When I tried moving it side-to-side the driver's side axle moved about 1 inch and the passenger axle moved about 1/2 that."

If you are lucky, it could be upper mount (cheap and easy replacement, inside trunk under the cover) and centering mount rubber parts deteriorated. And just need a complete re-rubbering on the rear.

Sorry, I meant that the axle shaft would move 1 inch side-to-side between the cans. The differential didn't move and the wheel carrier did not move. If the axle was pushed all the way towards the differential, I could push it about 1 inch towards the wheel.

Good idea about jacking it up and rotating by hand. I will try that.

Which side? The drivers side goes into the differential and the passenger side fits into the sliding joint.

Check this page and the next:

http://www.m-100.cc/forum/topic.asp?TOPIC_ID=3443&whichpage=7

One of the locking rings may be loose or the bolts may be loose.

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Thanks for the link. That looks like one of the diffs with a compensator. Mine doesn't have that - in fact it is exactly like the one that was on my W126.

I put the rear in the air and started spinning the wheels while observing the CV joints. It didn't take long to find the problem. The inner joint on the passenger side had a torn boot and was full of road grit. The outer joint on the driver's side had the boots intact but the joint felt very gravelly. I dropped the diff and removed both axles. I'm not sure which one was protesting but they are both getting replaced.

Thanks for the help everyone.

OK, so it's a W116 or a W126. Please update your profile to reflect which one. The 280SE I thought was a W108, which is a big difference.

There is a link in 'Resources' at the top on replacing the rear axle bearings in the W123 and W126.

http://www.peachparts.com/Wikka/W123RearWheelBearings

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Makes sense now you have a w116 280SE?
Please ID your car type for better answers.
Ripped boot and bad CV joint is a normal problem