LS-ONE_DAY

I feel like I'd be wasting money when I could save that for when I upgrade the rear end (If I ever have to fingers crossed) and I love my 2.73 gears since I do a lot of highway driving, but they do make the car feel a little sluggish sometimes even with my 3500 stall. I know you can buy "thick" 3.73 gears for a 2 series carrier so that is an option but I don't think I NEED 3.73's to be happy and that would probably hurt mpg's more than I'd like. I don't drive the car everyday but I do like to take it on highway trips to work and cruising, it hasn't seen the track yet and may not very often. Another option could be finding a 4 channel 10 3.42 rear from an M6 but most of the ones I see for sale are 3 channel. I want to keep ABS and TCS. I guess the 4 channel ones are a little more rare?

Between those 3 options, keeping the 2.73's, swapping the 2.73's for thick 3.73's, or finding a 4 channel 3.42 rear, what would you guys do in my shoes?

guppymech

iTrader: (7)

You sound like the perfect candidate to keep the 10 bolt with the way you use your car. If you want more performance go with the 3.73s. I wouldn't put alot of money into your 10 bolt though if the posi is bad, that can start adding up to alot of cash fast.

LS-ONE_DAY

I don't believe the fluid has ever been changed. I bought the car July 2011 with 21,500 miles. It now has 27,500 on it. There is/was a faint whine occasionally but didn't happen all the time. I can't hear it over the exhaust anymore while cruising.

FirstYrLS1Z

iTrader: (4)

2.73s' to 3.42s' = 25% increase in torque to rear wheels
2.73s' to 3.73s' = 37% increase

ragtopz28

iTrader: (57)

I went from 2.73 to 3.42 with very noticable 'seat of the pant' response.
Don't expect much at the track though, maybe 0.1 sec.

mjs1012

iTrader: (36)

youll be fine with the 10 bolt. go 3.73s with your converter, itll be a nice combo and youll feel a big difference.

01ssreda4

iTrader: (96)

Go 3.73s. All M6 10 bolts I have taken apart have damaged carrier bearing races on the driver's side, regardless of miles. Autos typically do not. A fresh rebuild kit, and a competent rear-end rebuilder and your 10 bolt with live a long and healthy life.

justin hover

You'll love the 3.73s over the gas friendly sluggish 2.73s. Especially with your stall, which will help tighten up city driving. You will probably lose 1-2 miles/gallon, which imao is completely worth it. I hated my 2.73s, takes away all sotp just for a couple miles/gallon. After all, I didn't an ls1 to get Prius gas mileage.

LS-ONE_DAY

Would 3.73's on stickier tires on the 10 bolt be ok? Nothing nuts, something like a 555R or Proxes TQ if I was to run DR's on the street.

What other mods would I want to consider for the rear, a girdle/cover?

My converter is already really tight, thanks to it being a custom order from FTI 3500 stall with 2.35 STR and I barely have to give it any gas to get moving usually.
Gas mileage is already pretty bad with the 2.73's lol...before the converter I could see 22.5mpg now not so much. But I only drive the car once in a while so it isn't a big deal besides the rare road trip.

guppymech

iTrader: (7)

I think with the A4 you'll be fine with sticky tires at your power level, I've read of people with A4s taking the 10 bolt into the 11s.
If you're going to do the rear gears get a solid pinion spacer from Ratech and a girdle cover. The solid spacer removes one possible source of trouble and makes changing the pinion seal down the road a no-brainer. I used a TA girdle cover with the optional ARP carrier cap studs, all nice pieces made in the good old USA. A girdle cover in addition to providing support to the carrier caps also helps keep the differential housing from deforming under load when the pinion really starts pushing on the ring gear. My TA cover is .750 thick where it bolts to the diff, that plus it's heat treated to T6 hardness making it very stiff, like adding a steel hoop bolted to the back of the diff housing to keep it from deforming. As a example, sometimes in my job I have to work with aluminum sheet at T6 hardness, we have to use cobalt drill bits on it, the hard aluminum dulls regular bits too fast. So heat treating that girdle cover is no sales hype by TA Performance.
I used a Master bearing kit from Richmond, all Timken and Torrington bearings, again made in USA.
I did all this to a 10 bolt I bought on craigslist and when it was done I had around $700 into it, not such a hot idea on a M6 but with your A4 you'll be fine.

LS-ONE_DAY

Thanks for the info. I plan on going H/C/I, hopefully making 420-440rwhp eventually, I'm trying to plan the rear around that...I'm still on a stock trans too besides the converter lol which is fine for now but with that power probably not. I do know of people with autos running on 10 bolts into the low 11's, high 10's. Conservatively I want to run 11.5 but with converter, tires, gears, and h/c I assume I'd be faster than that lol

01ssreda4

iTrader: (96)

You can lift the front wheels on a ten bolt and an auto spraying out of the hole. I've seen plenty of 10 bolts that just wont die.