Bonderd

Hell Guys,
I have a stock 99 A4 Trans Am. I have noticed the rear end seems to make noise on the highway especially 50ish-65ish. It seems to happen more on deceleration,when i put my foot on the gas it seems to be normal.Also when i am going slow(like in a parking lot,coming to a stop) and i turn the rear end seems to clunk(knock). Its a fairly light noise almost LSD related? I have done some research and some people say its normal and some put in a new rear end???Any idea's i would appreciate it. Also how do i figure out what rear end ratio i have?When cruising on the highway at 65 I'm roughly 1500rpm or so.

Bonderd

any ideas?

jasongantt

look on the diff cover for a tag, it should show the gear ratio. if there is no tag, then on the axle tube there is a serial number, if memory serves me it's on the right side and you can reference that number on the net by searching AXLE #123446677788.

but sounds like a 3.23 gear which is common in all A4 cars with the exception of the SS, firehawk

as for the noise, could be many things, bad pinion bearing, bad spur gear in the true track. you should take it to someone who is expirienced with the rear ends to help keep you from buying a whole new rear unless thats were your heading anyway.

stock rearends in the F-bodies don't hold up to any more than maybe 400 horses on a M6 and 450 to 475 on A4s, and thats from expirience.

Bonderd

Thanks for the reply, i just changed the rear end lube lately with mobil 1 75w90 but added no additive too it, because mobil 1 is suppose to be for LS...Should i change it again and add the additive and maybe some lucas oil stabilizer?

Bigbee

I recently had my rear diff lube changed and pinion seal replaced at my GMC Buick dealer. Shortly after, I developed a slight pinion whine at some speeds and an odd clunking when slowing down to parking lot speeds. Turns out that the dealer didn't put in the LS additive...you would think they would know better but the guy said they don't get many LS rear ends in to the dealer anymore and don't even carry the additive. Sad to say the the pinion seal still weeps a bit and now I have a whine cause they probably didn't set the pinion nut right... I would definitely put the GM additive in. If it's an Auburn diff it is absolutely necessary, Torsen not so much. I see no reason to change out all the lube, just suck some out and throw the additive in.

fccs

iTrader: (26)

After I saw you mention the clunk noise..ya lol. When mine started doing this exact thing, I blew up the rear 2 weeks later shifting into 4th just out on a spirited run around town.