ianmcgee67179

I am in the beginning stages of saving and researching a trans swop for my 79, L82 bored out 383 automatic to a 5 or 6 speed. After some quick research Ive seen the T56 Magnum as a decent choice for a 6 speed...but supper $$$$ so first wondering if anyone has any opinions on that, as well I am trying to figure out what ratio I have in my back end and I cant. I know the different codes but this is what my sticker looks like....





I was wondering if anyone knew a different way of finding it out the rear end for a 79, L82?

Thanks for the help I appreciate it.

Alan 71

Hi i,
The rear differential ratio and assembly information is stamped in the bottom edge of the rear flange of the case.
So it's read from underneath the car.
That code will tell what the original ratio was.
Regards,
Alan

This is a 71 model year case… LR indicates an original ratio of 3.36:1 Positraction
It was assembled on the 12th day of 1971

bmans vette

You really cannot tell what rear end ratio you have by numbers as it may have been changed internally since the car left the factory.
Best way is to lift rear end off the ground high enough for the wheels to turn freely. Count the driveshaft revolutions for one turn of the tire.
That is your gear ratio.
Transmission needs to be in neutral and block the front wheels so not to roll off jack/jack stands.
Good luck with your project.

Bman

theandies

And if you do the "turn the tires" test make sure your trailing arms are not sagging to make the half-shaft u-joints bind up while turning. Try to brace your trailing arms up so the half shafts are close to parallel.
Be safe too.

BKarol

In 79 the std rear for a L82 Auto was 3.55:1. If after your turning it appears to be about 3 1/2 that's it. Your rear stamp will begin with the letters OH if all is original.

corvetero

Alan, do you have a list with the diferent nomenclatures?

If I'm not wrong mine has an AA stamped.

corvetero

I found this

http://corvettec3.ca/axle.htm

ianmcgee67179

wow thanks guys, I appreciate the help and most of those are obvious and I should have thought of those already..duuh! haha didn't mean to waist yalls time.

But does anyone have any opinions on the 5 or 6 speed?!

Grahamred70

I was going to go SST 5 speed but with the changes in exchange rates, shipping and duty it all got too expensive so I rebuilt my Muncie instead, tweaked the ratios and went for a 3.55 rear from a 4.66, still haven't driven it more than a few yards but does feel a lot more sensible now.
Graham

jb78L-82

Karol is correct that the auto L-82 came with a 3.55 and the 4 speed L-82 cars came with 3.70 gears. I would love to have a 5/6/ speed with my L-82 355 (would definitely go for the .64 OD with the power the motor has now and pulls easily from 1,000 rpm in any gear) BUT the conversion prices from all the vendors are way out of line (crazy expensive) and I can't justify that amount of money for a car that sits 99% of the time.....The only way to justify a conversion at the price point these 5/6 speeds are now would be if I drove the car as a daily driver which will probably never happen with a 40 year old car. When and if I ever need a rear diff rebuild, I may opt for a 3.36 rear gear instead of the 3.70 with the 4 speed....especially since the upgraded/rebuilt 355 L-82 has about 450 Gross HP now which can easily overcome just about any rear gearing with ease....

Revi

Not sure how much you plan on driving your car or what the cost of switching to a 5spd will be, but here's a quick and simple comparison of 4 vs. 5 speed. (I know you have an automatic, but this gets my point across. Auto or manual, final drive is still 1:1.)

4spd - 15mpg x 1k miles =66.6 gallons of gas x $2.00 per gallon = $133 to drive 1000 miles at highway speeds.

5spd - 20mpg x 1k miles = 50 gallons of gas x $2.00 per gallon = $100 to drive 1000 miles at highway speeds.
(An increase from 15mpg to 20mpg would be a 33% increase in fuel economy. Your results will most likely be less.)

A $33 difference for every 1000 miles at highway speeds(4th gear vs. 5th gear). When you drive around town and aren't in 5th gear there's virtually no savings.

If you're driving 20k miles per year, great. If you drive 1k miles per year....well?

Grahamred70

Yes even at $6 a gallon the savings would still take many miles to pay for a 5 speed :-(
Graham
P.S. I'm in the UK!

ianmcgee67179

wow thanks a lot I didn't think about! What is an L48 Auto rear end?

EarlyC34me

I actually have this same question. I have a m20 transmission and i'm trying to figure out if i have 3.70's or 4.11's. This is a highway shot in 4th gear. I jacked up the car but could not make out the factory stamping on the rear end.

Metalhead140

I went for the 5 speed, and mostly as I was concerned about breaking the 4 speed behind my upgraded engine. Fuel economy will never repay the difference, but it makes it a much more pleasant drive on long trips, and less wear on the engine, as well as the stronger box. I have a tko600, very happy with it. I only have 3.36 gears, and only went for the shorter 0.82 overdrive - works out to be a perfect highway gear with my rear end and cammy engine, and I have more than enough grunt to easily spin sticky 17" tyres through 1st and 2nd gears, so can't really imagine a need for more rear end gear. A sixth gear in my car would be almost unusable. Abovethelogic recently installed a six speed in his car (not sure what rear gear off the top of my head), and has also said 6th is basically useless in his car with his current rear gears. He has a thread here following his conversion.

OldCarBum

Another way to easily determine what your rear end ratio is, use a gear ratio calculator. If your tach and speedo's are on the mark, just check your rpms at any given speed cruising down the highway. You will need to enter your tire size and transmission type as well. At 70 mph my tach reads between 3000 and 3100 rpm, which calculates that my rear end ratio is 3.36 with my TH400 and 245-60-15 tires.
Here is the link to the gear ratio calculator I've used for years.
http://tri-5.chevyrides.com/rpm.php

OldCarBum

I've been doing research on this topic for quite a while. The cost for an auto overdrive or a TKO 600 conversion is outrageous. I know I will get more use out of my 73 BB if I can cruise down the highway at 2000 rpm at 70 mph rather than 3000 rpm and 70 mph. I can't justify buying a corvette and dropping thousands of dollars into it just to cruise down the highway in the slow lane at 60 to 65 mph, watching the Hyundai's pass me by. I bought my car to drive and enjoy, so I can justify the cost. I'm saving my pennies.

jb78L-82

I might be able to help you. I can tell you for sure that my 3.70 gears with the 4 speed on the highway in 4th 1:1, with the stock diameter 27 inch tire is 3,500 RPM on the tach @ 70 mph. I do suspect though that my tach reads slightly high (about 300 RPM meaning that 3,500 is actually 3,200 from dyno runs RPM readout on the dynojet and other sources). I can also tell you that car magazine in the day for my combo reported 2860 RPM @ 60 mph with the 4 speed and the stock 27.1 diameter tire.

I suspect that you have the 3.70 gears.

jb78L-82

Totally! The justification for an OD tranny can never be justified by the outrageous cost from the aftermarket. Its all about being more pleasurable to drive and you will never recover the cost of the conversion. Your comment about the grunt with your engine is spot on. I chuckle when folks say that their 500 hp engine will REQUIRE the .82 OD ratio since the .64 OD will lug the engine...give me a break..not a chance if your engine has even moderate mid range torque that any V8 will have: BB, SB, moderate HP, big Hp. Total nonsense!

I roll into the throttle now with the 4 speed because I don't want to break the trans/rear end and don't need to spin the tires rolling in 2nd or 3 rd....

With my 355 L-82 with 450 Gross HP with tons of mid range torque and the 3.70 gears, I would love to have the .64 OD. A 5 speed would be great but as long as the vendors insist price gouging, not happening any time soon for me.

jb78L-82

As much as the price gouging on the OD trans burn me, I too, may some day bite the bullet but with 2 kids in college, I may be waiting a bit......