Funky_ned

Hello folks,

I have a 77 Vette with an LS2 and a T56 from an 06 GTO. Just bought the thing and I love it. It has the stock rear end and I've been thinking of going with 3.70 or 4.11. Mostly road and highway use, and very little interstate driving. Is going 4.11 overkill?

Also, how big of a job is it to change out? Is it normal to just change the ring and pinion or the whole differential?

Thanks

bmans vette

First of all, you need to determie the first gear ration of the transmission.
Ideal final ratio is 10-1.
The final ratio is the first gear ratio X the rear end gear ratio.
So with a 4.11 rear end you need to be close to 2.5 for the first gear. A little higher will mean you will shift out of first gear sooner.
But a 3.27 or even a 2.94 first gear ratio with a 4.11 in the rear will be over 12-1 and you will be out of first gear before you even hit the power curve of the engine.

As to changing the existing rear. You need to figure what the present ratio is. Without removing the rear cover which is a chore with the rear leaf spring, you can jack up the rear and manually turning the rear end. Make a mark on the drive shaft near the rear end and a similar mark on the rear housing. Have someone make a mark on the top of the rear tire and put a piece of tape on the rear fender that lines up with that mark. Now have them turn the wheel slowly while counting how many times the mark on the tire passes the tape on the fender. You watch the marks underneath. When the drive shaft makes just one revolution and the marks line up, ask you friend how many revolutions the tire made. That is your rear end gear ratio. 3 3/4 turns = 3.75 rear, 4+ a little bit turns = 4.11 (4.10), etc.
As to interchanging simply the ring and pinion - maybe, maybe not.
4.11 gears need a larger series posi unit. And if the rear is really low number 2.3, 2.6 etc even going to a 3.7 will require a different series posi unit.
There are several member who do outstanding work on rear ends Gary - GTR1999 and a couple others will give you great advice and help if you need it. I would not take the rear to anyone who has not worked on vette rear ends before.

Good luck. Hope this info helps.

For me I already have a beefed up 4.11 to put in my project. Finding the right trans is my next task. I am converting from auto to stick and going with either a 5 or a 6 speed. Engine is a 500+hp 383 stroker.

Bman


BTW - in order to turn the rear and drive shaft you will need the trans to be in neutral. Make sure to block the front wheels and support the frame before climbing underneath Putting it on a lift would be easiest.

Learning_Curve

I'm doing a lt1/t56 swap, and I found six gear useless at normal highway speeds in the Camaro it came in. So my reasoning was to step up from the 3.42 gears that came in the Camaro and use 3.70 in the Vette. After reading this post, it turns out that I lucked out as the Camaro had a 2.66 first gear and that gives me a total first gear ratio of 9.8. A quck check online shows the GTO had a 2.97 first gear, meaning a 3.55 ratio may be the best fit for you.

Funky_ned

Thanks for all the good info guys. Yeah, I just did some checking and found the GTO gear numbers.

Thanks again

Gordonm

I am running a T56 from a GTO also. I have a 3.70 rear and it is about the best way to go. Good multiplication in the 1st 4 gears and the 2 overdriven work well with the 3.70. 5th usable and 6th is great for the highway. I think 4.11 is to much gear unless drag racing is your goal.

3JsVette

I would go with the 3:70s also. I think the 4:11s are too steep also, unless as Gordonm just said you're a drag racer.

lionelhutz

My C5 with 3.42 rear gears works fine to me. I have yet to find a hill on a highway that the car won't go up in 6th at 60mph with the cruise set and not lose speed. There are a few hills I've tried where every other vehicle I've driven them has lost speed and kicked down to get up. Still, you might find some more secondary roads an issue to go up in 6th if you live in a mountainous area and I don't know where you live.

I'd think you likely have a little taller tire than a C5 so you might want a little more gear meaning a 3.55 or 3.70 gears would be about right. I'd check your current rear gears. Just going by the rpm's on the highway I'd have to guess that Dad's 78 has a 3.55 gear in it so your car could too and you'd likely find that works well as is.

Bman has the description to determine the gear ratio a little backwards. You turn both tires 1 revolution (they should turn together with the posi) and could the number of driveshaft revolutions.

bmans vette

Lionel
Both methods give the same ratio.
Bman

71454Chevelle

Depending on the engine combo, transmission gearing and tire size, a lower rear gear (numerically higher) will work just fine.

I'm running a T-56 Magnum with a 2.66 1st gear coupled with 4.56 rear gears and 30 inch tires, it works very well with my engine combo. It launches hard and I have plenty of power in the upper rpms (7k rpm) to utilize the lower gears. The 5th and 6th gear ratios are .80 and .63, which translates to a 70 mph cruise rpm at a little over 2200 rpm. The best of both worlds.

bmans vette

Sweet ride!

Always liked the 454 in the bigger cars, more torque to get it moving faster.
Nice combo.

Bman

lionelhutz

They can but you do it differently. If you turn the driveshaft 1 turn you have to figure out how much of a single rotation the wheels made and then divide that into 1. Say the wheels turn 0.28 of a revolution that would be 1/0.28 = 3.55 gears.

You posted that you turn the driveshaft 1 revolution and count the number of times the wheels rotate and that would be the gear ratio but the wheels don't turn multiple revolutions for 1 driveshaft revolution.

Easiest is to turn the wheels 1 revolution and count the driveshaft revolutions = gear ratio.

bmans vette

I see your point.