z28SSilvest

Car never sees the track; only roll racing and occasionally a first gear punch, where even with the 3.42s I spin like crazy. Do you guys think I will be alright with a set of 3.90s in the rear? Car is putting down some decent power and I am also getting an LS7 clutch installed before the gears (not sure if that will make a difference). Last thing I want is my rear to explode while on my way home from a far distance or something. Car is my daily driver by the way

VincesSS

iTrader: (1)

I wouldn't waste money on gears if I was you that money is better spent saved for a real rear end. Track gains and especially from a roll gains are almost non existant.

With that being said it will probably be fine as long as you're not launching it at the track or street, however you can not predict mechanical failures and you are overpowering the rear end.

Good luck.

BlackLS1Bird

iTrader: (2)

I agree with VincesSS. The problem I had with my 10 bolt wasn't the gears or axles, it was the spider gears in the differential. I broke those twice on hard street launches with a manual and 315's out back. If you are just doing some roll racing and soft launches, I think you will be ok as is or with the 3.90's. I run 3.55's in mine since I like to stretch out the gears a little instead of shifting every half second and maxing out at 130.

z28SSilvest

Thanks for the quick responses. I'll probably just wait and get a Ford 9 inch or something.

FirstYrLS1Z

iTrader: (4)

If you're concerned about the strength of 3.90s',the OEM 3.42s' are among the strongest for our little 10 bolt. 7 5/8" 3.42 vs 7 1/2" 3.90.
When our cars were new/purchased,the GM warranty covered the rear,do you know of any aftermarket gears that come with a warranty ?

guppymech

iTrader: (7)

OP if you can't hook with 3.42s then 3.90s will be way worse. Spinning aint winning, but it's fun for a lil' while. Now if you have gears and DRs......THAT will put a grin on your face!

With the M6 you're probably better off saving for a aftermarket rear.

HCI2000SS

iTrader: (2)

The stock 10 bolt is a mystery to me lol. I have the stock rear with with a trutrack upgrade on a M-6 with 4.10 gears, and Nitto dr's, and make around 550 rwhp/rwtq with no issues. I think the 10 bolt can handle quite a bit of power if you don't launch hard or get wheelhop

redbird555

iTrader: (14)

The 10 bolt is weak. But I love the feel of my 3.90's. I felt 4.10's were a tad short in 1st gear for daily traffic the 3.90s are a nice compromise and really wake up over 3.42's

BlackLS1Bird

iTrader: (2)

Thats why I didn't get 4.10's. All you do is spin unless you have good DR's and warmer weather. When you hit some of those late season days when it is only 50 degrees out, there is no such thing as traction. I am running a manual with a 3.55 rear and 315 Nitto ZR extreme street radials. Even when my car had just a few bolt ons, I couldn't keep traction in first and half of second when the temps would drop. This was while actually trying to keep the tires planted and get a half decent launch just out messing around. Hard launches wouldn't exist.

z28SSilvest

Sorry, I kinda abandoned thread. Thank you all for the replies. I forgot to mention, I want to upgrade the gears so I can put 6th gear more to use and not have to wait until ~50mph to switch to it without bogging the engine. Like I said though the car does make decent power now, I just want to be thrown back in my seat a little more. Thought about spraying, but I would like to stay all motor for the time being.

42273

iTrader: (3)

from my experience the 3.90 was a good gain and the gears are strong but you will most likely break the posi unit if original , and for the money gears , install kit and or new posi unit you could go with s60 for not much more. once again just my experience. i am stubborn tho lol... good luck with your decision

VincesSS

iTrader: (1)

Yea I thought the same thing.. but after the gears went in the car didn't pick up **** at the track (cut 1.7s before and after gears on nt05r's), got worse gas mileage, forced to shift quickly to keep up with traffic and I was missing $500~.

z28SSilvest

Hm, well that's definitely food for thought. Thanks for the reply

SladeX

I've had 3.90's in the car for a number of years and influenced my decision to stay with 3.89 when I went to a 9 inch.

It's much easier to get around with higher ratio as launches off the line are quicker and less bogged. You simply are a gear higher in traffic and mileage is not as terrible as it sounds as it still remains to your right foot control. I still did around 28-29 mpg on highway mildly modded (cam/heads).

Also bear in mind that 3.90 is the largest ratio you can use on a 10 bolt without significantly affecting pinion gear tooth size. 4.10's shrink down the pinion teeth size and make them more of a liability.