Just wanted to update this thread. I ended up picking up a 40k mile used differential from a local RL member, taken from a 996tt, for $300. Showed no signs of leakage and had the flanges intact. Decided to have my indy do a straight swap rather than sending it or my existing one out for refurbishment. Picked my 4s up today in the pouring rain, drove home 15 minutes, but already can hear/feel the difference ....no more whining sound when off throttle and overall significant reduction in NVH. Can't wait for better weather to take it on a longer drive with windows down and confirm success.

 

Gotta admit, not too expensive and an easy fix. Awesome.

 

Went for a longer ride this morning and the difference is night & day. Not only are all whining sounds gone, but all front end harshness I had been feeling/hearing, especially a slight rubbing sensation I've been complaining about for over a year through the steering wheel, is gone! Car feels like it day Day 1 again. Super happy.

 

That's cool to see a market for them. I will probably sell mine once I have converted to rwd.

 

I saw many for sale on ebay at various prices. Shop I consulted with mentioned they had good luck with straight swaps of low mileage ones vs spending $1,100 for refurbishment of seals and bearings. Obviously recommended finding lower mileage one and possibly one from a non turbo since turbos tend to get driven harder. Told me to avoid any with leaks or missing flanges.

 

Do these just typically fail or do they leak first?

 

From what i've learned it starts with a leak. Then noise comes from carrier bearings. I was told it was safe to drive until i picked up the replacement but I assume if the leak is large (mine was very light, hadn't even really noticed any stains on my garage floor) that the gears can fail and cause more significant issues. My indy seemed to indicate this was a known issue (maybe more on 996tt models) and many got replaced under warranty. Seen posts where people replace seals and bearings as DIY project. Not something I was comfortable trying. One shop I consulted recommended examining the diff fluid if you have a leak. If no metal particles are present then a rebuild of seals and bearings should work, whereas metal showing up in the fluid would be a sign the gears had suffered damage and most likely the part is toast.

 

Glad this worked out for OP -

Curious where these "leak" from. Where the axle enters the box? I have a slight whine, hard to tell if it decreases on throttle but it is there coasting in neutral. I don't have any leak as far as I can tell but want to take a closer look.

Thanks!

 

I believe the leak is at that spot, yes. the flange? I had the coasting sound as well. Might suggest a flush, change, and examination of differential fluid. Might be a cheap fix.

 

Oh man, just another thing to worry about now! First I'm hearing/reading of this issue. Of course I'm reading about it after a week and 2 days of picking up my C4S. Glad it worked out for you.

 

I push my car hard but dont track it. Assume that puts added stress on the differential. This isn’t a problem that will total the car by any means and luckily many used differentials are available due to all the AWD to RWD conversions. Even the parts to fix it DIY aren’t expensive. In my case labor was the majority of the cost, but worth every penny as the car feels refreshed.

 

I doubt tracking has anything to do with it. The diff only allows 2-5% power going to the front and it takes a whole lot of rear tires slipping for the fluid to heat up and send more power to the front. I'd guess that it never actually does send more power to the front. Even with rear slipping the PSM will then come on and brake the slipping wheels, preventing and power to be transferred to the front. I think that the age is why this happens the seals don't last forever.