Greetings!

So for past year i've experienced a slight whining from my rear diff. Now it has gotten worse, so I decided that I would do a full rear axle rebuild - Subframe replacement (300 EUR new from Poland), and a full diff rebuild. Not to take my friends lift for a whole week, I found a used rear diff for 100 EUR, to peacefully replace the bearings in my spare time and later just to swap the whole unit. The thing is - this secondhand diff seems to be in tip-top shape. When turning it by hand, I do not hear or feel even the slightest grinding, it spins super freely. So now I cant decide - either I should rebuild this unit anyways or just swap it as is? Are there any other ways to test if bearings are good? What would you do?

Best regards!

When Austen from Bell Engineering checked my diff while servicing the Haldex there was noticeable grinding and roughness yet during his test drive he was not certain that it was faulty (which was why he checked the diff manually).

Just swap it over as it is. If it’s okay, all well and good. If it’s not, overhaul your original unit. Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.