I want to change my rearend gears to 2.76 stock,to either 2.76 posi or 3.08,on a 7.5 inch rear.

Heres my setup
1986 Camaro z-28
5.7 Liter Tuned Port(not stock,used to be LG4(might be L98)
T-5 Transmission
and 2.76 Stock(not posi)

Will the balance in this setup be acceptable,or will it tend to tear the crap out of the rear,or transmission with the change?

The car is rated supposedly at 300hp,I imagine its around that.I was also told that a stock clutch would hold this setup fine,I just need a second opinion on the matter. Also would the gear selection be okay at either 2.76 posi or 3.08 posi? What would your opinion be on this change? Give me your suggestions,I dont want to pull smoke at a stop sign,I just want some more power at the pedal,or make the drivetrain be balanced output-wise with the motor.

Thanks
Philip Parker

 

Any increase in rear gear ratio, in your case currently 2.76 going to say, 3.08 will increase your throttle response for two reasons.

First at any given road speed your engine will be spinning a bit faster now, putting the RPM further up into the 'meat' of the torque curve.

Secondly, any additional torque applied by the engine (triggered by your right foot of course) is now multiplied by 3.08 instead of 2.76, so you will feel more of a seat-of-the-pants acceleration increase.

You would gain even more throttle response going to a 3.42 or 3.73 rear gear ratio, but of course you will pay a penalty in fuel economy with any increase in the rear end ratio.

If the TPI engine you have has indeed been modified and does in fact generate 300 HP, the peak torque is likely generated at a higher RPM than stock so a gear change will help by running the engine at a slightly higher speed.

Gear ratio changes will not threaten to 'tear apart' or destroy the rear axle or transmission, so long as you are not shocking the drivetrain by dumping the clutch for drag-style starts. There is torque multiplication taking place both in the gearbox and the rear diff, generally the greater the torque multiplication the more strain on the parts, and of course shock loads like dropping the clutch at 5000 rpm will just about guarantee destruction somewhere in the drivetrain eventually.

If you enjoy the car as it is then you would very likely appreciate a moderate increase in the rear axle ratio like you suggest. Keep in mind there is even more fun with 3.73s in there!

 

Hay PParker .....
I got 3.08's I ran a 15.1@ 93 .....and my car has like 230'000 km
I can run up to 95 mph in 3rd !!!!!!!!! 4 th I am around 120 mph and 5th .......... Dam governer kicks is out

I like the 3.08's but I want more acceleration , even though I chirp in 2nd ( and have done it in 3rd once and a while )...I am installing 3.42's this winter . if you want the 3.08's PM me and we'll talk


But I agree with the above statement ...... go bigger still
unless you like fuel economy ( which you get pretty dam good with 3.08's)

 

Im waiting to see if I can get my hands on a set thats decent,and reasonable.Im hoping ThirdGen may have some 3.08 or 2.76 Posi's laying around....Ideally 3.08 is what I want.As for spinning tire thats not my game.Florida Police don't like that too much and i don't need to get into trouble.I just wanted to see how much gain I would get over 2.76,and you have answered that question quite nicely.I would definately want a few more responses as this is what I will be using till I rip the car down in another year or two. As for the balance of power thats the big question for someone who knows the car quite well,and its potentials on gears,motors,transmissions. Thats what i want to find out from a good mechanic,or race car builder.

Thanks for the input,if you have anything more I could use let me know..

Phil Parker

 

Thats the one! Rusty Dawg! Question which is best for this match? 3.08 or 3.73? maybe 3.23? II want to have acceleration mostly because people on I-95 in florida drive like ****! They have accidents everyday.I need more meat on the pedal,not burning rubber at a stop light.What happens if you have to high of a gear it tends to fishtail as the weight is in the front.I want the wheels on the pavement not sliding around like that.See the problem in South Florida is the rain and the dew in the morning.It can make any car like this slide easily.I want to make the car "balanced" in speed and power,not smokeshows.

Thanks
Phil Parker

 

Phil, I can't really pick an axle ratio for you because I think it's a matter of taste! I have 3.42s 'cause my ride was originally a V6 and I find them a good all-round ratio.

If you want acceleration, then get some 3.73 gears, or even 4.11s for that matter. You will be revving much higher on the higway with 4.11s installed. If fuel economy isn't an issue then go for it.

The choice of rear gearing boils down to a compromise of acceleration performance and fuel economy. You have very economical gearing right now, but it reduces your potential acceleration.

The problem of sliding around and fishtailing on wet roads will likely be worsened with higher (numerically) gears and especially with a posi carrier installed!

If you are not interested in drag-racing the car at all then skip the posi carrier. They're murder in slippery conditions.

 

Hi Rusty Dawg, point taken...question if your can all gm rears accept any gears? I was wondering,I looked at my service manual and it says the following:

based on F body Camaro
if your code is:

7-5/8"

Codes: 2HP
2HL
2HM

List ratio as:
2.73
3.42
3.73

Codes: 2HD
2HG
2HH
2HC

Ratio as:
2.73
3.23
3.42
3.73

Im wondering if this is indicating that only these axles ratios will fit in my rear? Are there any problems using 3.08 if its not listed on the 1986 spec sheet for that year? This is a good question,that has me puzzled.

As for the low ratio,im reading more and it seems that its 2.73 not 2.76...sorry for the mistake.

Thanks
Phil Parker

 

I kinda figured you had 2.73s. Yes your housing will accept the other ratios; 3.23, 3.42, 3.73.

Less common in the F-bodies is the 9-bolt Borg-Warner rear end with a slightly bigger ring gear and different ratios like 2.77, 3.27, 3.45 etc.

Yours is the 7 5/8" diff and these same diffs were used in the S Series trucks, the later Montes and such. It shouldn't be too hard to find them.

Likely the easiest way to go if you are seriously considering a different rear axle ratio is to swap another complete rear end in. A complete 3.42 rear from a V6 F-body would most likely not be a posi setup, and would sell at a wreckers cheaper than buying gears and the labour to install them. They don't just drop in there, it is a pretty involved installation.

 

Just thinking about that,I have a rebuilder that is going to do my transmission clutch change,slave and master cylinder(shot) and resurface and replace all parts having to do with the clutch,and balance my driveshaft along with ripping my gears for $1200.00

so they will be in there anyway.I have pulled a rear before,I just dont have the facility here where I live. South Florida is very particular about people working on cars(esp.antifreeze,motor oil..etc) I know that you take off the cover,you will see a 8mm bolt you undo that,pull the pin and take out two clips in the axle and they drop out.I did this trying to find a set of spidergears when i first got the car,they were scorched from abuse.I replaced them over 6 months ago and havent driven the car at all,I blew the slave and well the rest you know. I do know it takes a bit,Im using someone that knows GM quite well and builds nascar cars.


Thanks
Phil Parker