Rear differential noise on decel

[travish325]

Currently at 101k miles on my 2020 ST and have had this rear differential noise for a while, probably the last 25k miles at least. It was noticable but just sounded like some road noise before. I recently put on a AWR diff brace and now the noise is MUCH louder as I assume it's transferring the diff noise and vibration through the mount to the chassis.

The noise is only on deceleration off throttle/coasting, nothing while acceleration or under load. It's not a grinding or knocking noise, it just sounds like very excessive road noise like very worn tires (tires are new), no clunking or anything either. I am planning to change the diff fluid this week to see if that helps but I'm assuming it won't fix the issue.... any ideas?

 

[Cdubya]

I would think the diff fluid change would help immensely. Maybe it's old or the level is low.

 

[FORZDA3]

You’re describing classic worn differential gear noise, likely due to lack of fluid changes, or the original setup was off a bit.

 

[travish325]

Flushed and changed the diff fluid today and added some Barsleak Gear Repair. The noise on decel is still there, it is a tad less noticable but very obvious still. From reading it seems like it's a pinion bearing issue at this point... Anyone know how hard it is to replace that? I can't even find just the pinion bearing on a parts breakdown for the diff and I really don't want to replace the entire rear diff if not necessary

 

[butt_yodel]

Dealer diagnosed this as a bad pinion bearing for me today. Started at 3k miles, got very loud by 5k. No leaks. Just bad setup, I think.

 

[Caster]

Flushed and changed the diff fluid today and added some Barsleak Gear Repair. The noise on decel is still there, it is a tad less noticable but very obvious still. From reading it seems like it's a pinion bearing issue at this point... Anyone know how hard it is to replace that? I can't even find just the pinion bearing on a parts breakdown for the diff and I really don't want to replace the entire rear diff if not necessary

@ 101K Miles you change the ring, the pinion and the pinion bearing. Might as well change the wheel bearings and seals while its all being worked on. If you have never worked on differential ring and pinions and set the backlash before or don't have someone working with you that has, DON'T DO IT YOURSELF. Pay to have it done and done right.