Gears & Axles - Whining rear that needs replacement.
06-12-2012, 05:34 PM
I've been researching with all my spare time for a few days but my time is simply running out. My 99 z28 A4's differential over the past couple years has developed an absolutely terrible whine, especially when letting off the accelerator at 50mph+. It's simply unbearable and I've had several mechanics tell me it needs to be replaced before it locks up and I die. My questions are how do I know which rear to purchase? I'm looking for a replacement and I don't know if I have the 3.23 or 2.73. And where can I purchase one? I figured I could acquire a new one and have a mechanic put it in so I pretty much just have to pay labor because the quote for a new rear I have gotten were. A couple mechanics recommended finding my own new rear since I may find it cheaper. I'm 95% looking for a stock replacement rear, unless there is a very strong argument to get something different. I don't currently plan on trying to make it more powerful for anything because it's a 13 year old car with 74k miles on it.
In short: my rear differential is on its last legs and needs replacing, how do I find out what rear I have and where can I purchase an entire new rear for replacement. Thanks!
Edit: I don't need the entire rear axle assembly, just the rear differential in full.
Would one of these be what I need?
06-12-2012, 05:53 PM
I know its not exactly what you asked, only trying to help; but I would start with replacing carrier bearings and races, axle bearings, and axles if worn.
Rent a slide hammer, borrow a Dremel.
At the very least, inspect it before thinking you have to buy a new rear.
06-12-2012, 06:05 PM
Thanks for the advice, but I'm in no way able to do this on my own. The mechanics I've had diagnose it have each said those items were likely all bad and that it'd be easier to replace the entire rear or at least the majority of it instead of spending tons of hours on labor replacing each part only to find out that hasn't fixed it.
06-12-2012, 06:28 PM
What do they mean replace it before it locks and you die?? - just curious
I had the same exact problem..Mine finally blew at the track on Saturday..I really don't believe it's just going to let go unless you are doing burnouts or drag racing the car like myself. Mine blew up off the line & the car just rolled to a stop, You are not going to die. Either drive it until it breaks or get a used replacement. I had AAA 200 mile towing for a reason :) I am willing to bet you have 2.73 gears and a 3 channel if I am not mistaken. If I am wrong someone correct me..3 channel ABS only, 4 channel ABS & TCS??? Look in the classifieds on here, That's what I am doing. I am at work so I cant check, but the door jam will tell u what gear u have..I am sure someone else will chime in here, maybe GU2 is 2.73, I can't remember.
06-12-2012, 06:47 PM
Even if it doesn't blow, I'm going to blow my own brains out if I have to hear its high pitched annoying whirl/whine any longer. For a while now, nobody wants to go in my car lol. I could deal with a used replacement. I was hoping I didn't have the 2.73, that's a high gear lol. I wonder if I do have a 2.73, if a 3.23 can drop right in? Thanks for more of the advice. I'm not quite sure about the channels and whatnot you mentioned.
edit: after research, I have abs and asr so I would have a 4channel.
06-12-2012, 07:51 PM
Look at the RPO codes on the driver's side door and see if you have GU2 or GU5 there. GU2 is 2.73 gears and GU5 is 3.23 gears. Another indicator is a stock steel driveshaft usually means 2.73 gears and an aluminum driveshaft is for the 3.23 gears. This is assuming that the rear end and driveshaft are original on your car.
06-12-2012, 08:03 PM
Checked the RPO codes, I have GU2, so I have a 2.73 then. It's a stock rear end and that's all I need. Are the 3.23 and 2.73 mutually interchangeable rears or do I need to get more things replaced if I can only find 3.23 rears?
You would just need to get your speedometer re calibrated. Speaking of which, I actually have 3.23 gears for sale lol..
06-12-2012, 08:30 PM
I would find a used complete rear (minus brakes) and just swap entire rear ends. I would also look for a 3.23 or even a 3.42 rear end.
06-12-2012, 08:55 PM
http://www.lkqcorp.com/search-inventory.aspx put in the info something will come up and have it shipped to the mechanic you are going to have fix it
06-12-2012, 09:48 PM
lkq only has one for my car but it doesn't tell me the ratio. If there's no other work aside from adjusting the speedo to put in a 3.23+ in then I'd do it if that's what I can find. The only problem is in the actual differential, the rest of the axle is fine.
06-12-2012, 10:16 PM
The only reason I said that i would get an entire used rear end is that I can get a used rear for the price (maybe even cheaper) than buying replacement parts and paying someone to install the parts. Rear end swap is very easy and straight forward.
just my .02 though.
06-13-2012, 12:35 AM
Ya you can buy another rearend... But u may end up with someone else problems... U never know. Buy new gears... If u have a A4 and lookn for a lil upgrade I would go 373... They may whine a lil tho. But not as bad as 4.10 I hear...
Also u need to find out what series carrier u have... Ther is 2 series and 3 series. But Motive gears sells a wide variety of kits for both carriers