777Shock777

iTrader: (5)

Hi all,

First off I don't know too much about the rear differential. :/
I have a 99 WS6 A4 with about 110k miles on it now.
I haven't noticed any hard shifting or anything, but I have been reading this is about the mileage amount where you change out rear diff...

I got under my car last night to find this:
http://www.youtube.com/watch?v=MD4tn...el_video_title

How bad does it look?
The rear diff is missing a bolt & the transmission seems to be leaking and spitting fluid onto the exhaust.
(sorry for shaky video)

Thanks!

Macs98Z

iTrader: (16)

Couldn't see much of the exhaust, but it looks like the fluid is all coming from the differential--both the missing bolt and the pinion seal seem to be leaking. It depends on how long this has been going on as to what the damage, if any, is. If the fluid has been low/leaked out for a while, then you could have damaged gears, differential, and pretty much everything in the housing. It just depends. The only way to really tell is pull the cover and inspect everything and post pics up if you're not sure what to look for. My pinion seal was leaking and it had run the diff fluid low--really low, but I pulled the cover and everything looked fine, almost brand new, in fact. This was with ~115,000 miles on the car. I have no idea if it is the original rear and gears or not, but they all looked good with very little metal on the magnet.

Long story short, pull the cover and check things out. If you think the trans is leaking too, post a video showing the trans--the pan and the tailshaft would be two main areas of concern.

777Shock777

iTrader: (5)

Ok! I'm going to have a friend help me take apart the diff, I'll aslo get new fluid for it as well so I can just get that done right then and there.

I was reading that regular fluid is better then synthetic since its still the stock one?
Any advice or tips for that?

Thanks again!

JRENIGAR

iTrader: (37)

If its not howling or whining then change the fluid with a good gear oil syn or regular, and run it. Might also replace the pinion seal while your under there. You dont need to tear the rearend apart to do this either. My factory rearend has 189k on it still running stock everything holding 450rwhp...

777Shock777

iTrader: (5)

Hmm... I think it may be howling/whining.. I hear this "air" like noise coming from the back left of my car, only when going above 40mph with very light throttle.

Does that sound like the diff? >_<

JRENIGAR

iTrader: (37)

If it sounds like air swooshing through the mags on the wheels thats the carrier bearings going bad. They hold the carrier in the center chunk, easy to fix.

777Shock777

iTrader: (5)

Oh yeah? Is it an easy sign if I were to take off that tire?

Yeah I didn't think it was the diff, mainly because I think the diff would be making noise whenever the car was moving at all.

Thanks man for replying XD

JRENIGAR

iTrader: (37)

Normally gears start howling more noticeably when going 50 or faster. They usually howl when lightly accelerating or decelerating. The only way I know of to check the carrier bearings is pull the cover and diff and visually check the bearing races and rollers for pitting or marks and maybe discoloring of the metal. I use a air grinder with a cutoff wheel to diagonally cut through 90% of the bearing material and then use a big chisel and hammer to hit and break the race where the groove was made by grinding, make sense???

Macs98Z

iTrader: (16)

If you have a 99, you can prob get away with using synthetic. I have a 98 and the auburn clutch type posi, so I have to use regular gear oil. The 99-up cars got a Torsen gear type posi which shouldn't need regular gear oil, but don't quote me on that. Best way is to check your manual.

777Shock777

iTrader: (5)

JUST checked the manual and it does say Use Synthetic.

Yeah I saw a guy with a 96 saying to use regular, while a guy with a 2000 said to use synthetic... in the end I was just confused X(

777Shock777

iTrader: (5)

I guess I'll have to take it apart and snap some pics and look for metal in there too... I'll probably be doing this in a few days. I'm going to get a gasket & fluid so I can get that going now.
And of course a few bolts haha.

JRENIGAR

iTrader: (37)

There will be metal in there on the magnet due to gear break in from the factory. I would pull axles, remove diff, change carrier bearings, re install gears, check backlash per GM guidelines. I installed used gears and set backlash to002" and they worked great. Torque the carrier bolts to 55ft/lbs. If gears are still good (I personally think they are due to your description of the noises your hearing) they wont make any noise now... GL...

777Shock777

iTrader: (5)

Alright! I'm back!

So I just got my fluid swapped over to Royal Purple synthetic gear oil with that GM additive, and a brand new cover/gasket/bolts on there.

(I had my mechanic do it, the old bolts were rusted on to the point I could not get them off)

Now when I'm going from a complete stop to moving there isn't any vibrations or "chatter" from the rear anymore and it feels much more solid.

I still hear the howling at around 50mph with low acceleration, but it definitely feels much stronger then before.

Any advice on that? thanks all