Metal grinding/scraping noise from rear axle

Post Sun Apr 12, 2015 2:38 pm

Hi there,

I would like to know if some of you could help me solve a problem I have been facing for several years now on my 1983 318.

Ever since I first swapped my differential back in 2009, I have been noticing a metal grinding/scraping noise coming from the rear axle. The noise can be easily noticed from the inside of the car as of 30 mph and not only at throttle since the noise is mostly permanent as long as the car is moving.

It is more like a high-pitched noise as it can be heard on the video posted below (not the low sound coming from worn wheel bearings but the metal grinding sound).

[youtube][/youtube]

Over the past few years, I have changed the differential twice again (thinking the noise came from a worn rear-axle drive) but I noticed no change at all. The noise still remains the same with no difference between one differential and another (even though they have different mileages and ratios whether that could matter). The differentials were all bought on line from reliable sellers so I doubt I ended up buying worn part from three different sellers (even if that remains a possibility as I am generally not a lucky kind-of person).

Last winter, I got the rear wheel bearing changed thinking they could eventually be responsible for such a noise. I noticed a slight change in the tone of the noise but the car is still overall as noisy as it used to be. Even though possibilities are many, I still think the noise is coming from the rear as it can be even more easily noticed from the back of the car (yet noises easily travel between different parts). I read on line that worn front wheel bearing could be mistakenly taken for a worn differential yet the noise is not that highly pitched when it comes to wheel bearings. Can you mates confirm this ?

So here are the remaining suspects:
- gearbox: not so sure about this one as the noise can be heard constantly and not only when I am driving in one specific gear.
- drive shaft: maybe during my first differential swap (a large case one) I messed something up down there... Could it be responsible for the metal grinding noise that can still be heard today even though I went back to small case differentials ? Which part of the shaft could actually be worn ? Does a worn shaft usually make that kind of high-pitched noise while driving ?
- differential: easy suspect again.

I am a bit lost and would like to fix this issue as soon as possible to enjoy driving my car again.

Many thanks for your help and please excuse my English.

Mathieu

Post Sun Apr 12, 2015 3:29 pm

Bent back plate rubbing on disc or drum, did mine last week after bending it slightly whilst changing the wheelbearing

Post Sun Apr 12, 2015 5:08 pm

Thank you for the lead. Will try that one too

Post Sun Apr 12, 2015 5:49 pm

When you did the rear wheel bearings, did you change the handbrake shoes as well?

Often you have to renew the disc back plates too, because they get very rusty causing the shoes to misalign and then make all kinds of noises rubbing inside the disc without the matter if the handbrake is applied or not...

Here's what I mean:

Post Sun Apr 12, 2015 6:49 pm

Hi there,
Thanks for your follow-up !
I actually have drums at the rear but I don't know if that matters regarding what you said.
I am starting to think this really has something to do when the brakes or the brakes area after all - even though I changed most of its components (drums, pads and cylinder) two years ago and the noise before/after was exactly the same. I didn't really pay attention to the back plate at the moment. Considering the pitch of the noise, it could however be a serious lead to find the guilty parts

Post Sun Apr 12, 2015 10:12 pm

If the back plate failed due to rust, then it could still cause the handbrake shoes to sit incorrectly and make a noise.

The easiest way to find out, just take off the drums and check the state of the shoes.

Post Mon Apr 13, 2015 7:20 am

zd3bx wrote:If the back plate failed due to rust, then it could still cause the handbrake shoes to sit incorrectly and make a noise.

The easiest way to find out, just take off the drums and check the state of the shoes.

Many thanks for your kind help.
I'll check the back plates and will keep you posted.

Post Mon Apr 13, 2015 7:39 am

Does the sound alter when the handbrake is lifted slightly?

Post Mon Apr 13, 2015 8:52 am

Have you tried jacking up the car from the suspension so that the rear end still assumes the normal drive configuration (wheels not hanging)? Then chock the front wheels and get a trusty friend to run the car throgh the gears while you stand at back and listen for the sound. You could take rear wheels off if required.

You can also do the above on a garage 4 poster with rear end lifted

Just be careful doing the inspection, no loose clothes etc etc

Post Mon Apr 13, 2015 7:46 pm

sweep wrote:Does the sound alter when the handbrake is lifted slightly?

Thanks ! I will have to test this too

Post Mon Apr 13, 2015 7:47 pm

k wrote:Have you tried jacking up the car from the suspension so that the rear end still assumes the normal drive configuration (wheels not hanging)? Then chock the front wheels and get a trusty friend to run the car throgh the gears while you stand at back and listen for the sound. You could take rear wheels off if required.

You can also do the above on a garage 4 poster with rear end lifted

Just be careful doing the inspection, no loose clothes etc etc

I'll try my best. Thank you for your great advice !