Knocking--driveshaft or axle?

[dlhoovler]

My '87 325 (eta) has had an intermittent knocking sound from the rear since before I bought the car. The previous owner attempted to swap an axle but couldn't get the replacement in (probably bad splines on a rebuild), so he put the original back on. That was 3 years and 40k miles ago. Here are the symptoms:

• Rhythmic hollow knocking sound connected to road speed, somewhat like dropping marbles into a can.
• Sounds like it's coming from the rear; my wife rode in the back seat and narrowed the sound down to the right rear.
• Pushing in the clutch silences the sound.
• Usually happens when coasting in a lower gear (1st-3rd), but in the most recent iteration it is occcasionally knocking on acceleration.
• The noise tends to get slightly worse when turning right.
• The noise will stop for several hundred or thousand miles before returning. Changes in outside temperature and driving patterns (highway/city) have sometimes caused the noise to stop or return. It's usually worse in cold weather.

Based on the above, I think it's the passenger axle. I'm concerned that it could be the driveshaft/CSB, but the change in sound when turning gives me hope that it's not the problem. Any thoughts?

-Dave

[jlevie]

It sounds to me like you have a bad half shaft. Replace both of them.

[CarsSuck]

Do you know the condition of the parking brake? I only bring this up because you're in the rust belt. The holes for the pivot pins (in the rear backing plate) can rust and let the pin pull through, which is then free inside the hat of the rotor and will make all kinds of racket.

[dlhoovler]

Thanks, Jim and Will. The parking brake works fine, and the backing plates are ok. I redid the rear brakes (including parking brake shoes and hardware) a year or so ago.

-Dave

[barry]

Just rebuild your old ones..

[dlhoovler]

It was in fact an axle. The inboard CV joint had belched out a bunch of grease all over the outside of the diff flange, even though there was no visible split in the boot.

Replaced it yesterday--one of those rare car projects (for me, anyway) in which everything went smoothly with no hangups. Got all of the diff flange bolts out without stripping a one, and the axle came out of the hub with just a few taps from a hammer and drift. With a new axle on there, it's quiet and smooth once again. Thanks for the input!

-Dave