RWHEELS

I have a 2011 mustang gt, 41K miles, my rearend makes a small but noticeable clunking sound at low speeds when going over bumps or changing directions, I'm pretty sure its the rear axle which when jacked up you can pull the wheels in and out a little, my question is how much endplay is normal, if any? And should I keep driving it and monitor it, or is it urgent? I'm doing an open track day in a few weeks and don't want any issues

thanks
Rob

SpartaPerformance

Just for preventative maintenance you can do a differential service and replace axle bearings and seal. It's not a big project and decently budget friendly. All you need is a few hours on jack stands.

P51C

Money it's your sway bar end links starting to shyt the bed. Very common problem on s197s. Mine went out at about 15,000 miles on my '12...warranty.

RWHEELS

I had it looked at by the dealership today, and without opening the rear diff, they couldn't find anything wrong, he said the passenger side axle had a little movement, maybe a bent c clip, but they said it would take 4-500 just to check, how hard is it to open it up and check myself? it looks easy, but what do I look for when I open it up?

tbear853

Wear will not add to axle end play in the 8.8 Ford. The splined end prevents the axle rotating within the confines of the differential side gear to which it's splined and which captures the C-clip in use. When you push in what stops the axle is the cross pin that goes through the two spider gears. When you pull on it, what stops it is the C-clip in the machined groove in the end of the axle shaft, the C-clip is larger OD and sits in a recess in the side gear. The C-clip can't just "fall" out either, because it is captured. To remove a C-clip, you have to remove the rear cover, the cross pin from the spiders, then push in on the axle and then you can pull the C-clip and pull the axle out afterwards .... assuming you've removed the brake caliper.

How axles come out without pulling C-clips is usually where the axle end breaks or axle twist in two between ends.

Every rear I ever had that had C-clips, and that includes several 8.8 Ford rears I have now as well as many Chevrolets back in past years .... and also, just about every one of 14 police cars I was assigned over a 31 year career (Plymouths in the late '70s and '80s, a '81 Ford, Chevys in the later '80s to late '90s, and CVPIs after '98 to 2010 .... and they got worked) .... they all had or have some axle end play .... they have to have some. Not a lot .... but some that you can feel if you jack the wheel up, release the brake, and jerk the wheel. You can hear it. 1/16" or 1/8" easy , maybe a hair more..... though it seems more if you aren't expecting it I guess.

RWHEELS

Update: the dealership looked at service history and when they changed the fluid last yr, they didn't put any friction additive in it which is usually recommended, although he said the movement is normal, he thinks adding the additive will quiet it down, I'll let you guys know after its in

P51C

That's bull****. The friction modifier additive is there for the diff plates and if they didn't put any in a year ago, that diff would have been moaning up a storm in turns after a few days, not a year.