Left rear clunk when braking or turning left

[SuperSonic05]

2005 Mustang GT 151k

Earlier in the week, I noticed my rear driver side brake squeaking when braking or turning left. I first check the tightness of the lug nuts, they were torqued to 100 ft-lbs. I then took the wheel off and took off the brake caliper to check the pins to see if they were seized, they moved freely. I then played with the axle shaft, there is a decent amount of movement and does make a clunk but I read some amount of movement is normal. I put the Wheel back on and now just here a clunk when braking or turning left. Think back, I heard a light clunking for a while now when turning left but figured it was my lower control arm ball joint, but this noise is definitely coming from the rear.

How much movement is normal for the axle shaft and how do I measure that?
Is there anything else I should check?

 

[bl817]

when was the last time you checked your rear diff fluid? there should be minimal axle play (movement) in/out, like almost none. if you can move the axle in or out a measurable amount then the pinion shaft has excess wear, which shouldn't happen. the pinion shaft keeps the C clips on the axles by not letting them move in and out. check your diff fluid level. while your at it, make sure your axle vent isn't plugged up or blocked. telltale signs are pinion seal leak. good luck

 

[2011/5.0]

The rear diff fluid could be bad,my 2011 sounded like it had a bad break or something going on after it was warm.
Turned out the fluid was bad and the rear wasn't locking and unlocking the disc properly

Sent from my Pixel 2 XL using Tapatalk

 

[SuperSonic05]

when was the last time you checked your rear diff fluid? there should be minimal axle play (movement) in/out, like almost none. if you can move the axle in or out a measurable amount then the pinion shaft has excess wear, which shouldn't happen. the pinion shaft keeps the C clips on the axles by not letting them move in and out. check your diff fluid level. while your at it, make sure your axle vent isn't plugged up or blocked. telltale signs are pinion seal leak. good luck

I change the Fluid out about 4 years / 30k ago. How do you check the fluid level? Like remove the fill plug and stick your figure in there? where the axle vent?

I took a video, right behind the tire to see the movement. I can't really see it when I don't it but you can see it in the video

The rear diff fluid could be bad,my 2011 sounded like it had a bad break or something going on after it was warm.
Turned out the fluid was bad and the rear wasn't locking and unlocking the disc properly

I think it working properly

 

[bl817]

check the other side to see if it has same amount of movement. that seems excessive to me, that said, I have never tried that with my diff. that much movement would make a clunk/thud when turning and move the rotor into the brake pad. also, applying the brakes would move the diff in or out depending on the orientation of the caliper. I would pull the cover and inspect further. good luck