mallie

I like the torque/acceleration, but cruising on the highway at 60mph and 3500rpm is not fun! Getting around 10mpg though, that pretty good I think

Not sure if my car came originally with 4.56 rear axle or if it was added later on for racing. Anyone knows how many 1965 coupe L76 were came with 4.56 from the factory?

Vet65te

Sounds like you've already done the math on it to determine the ratio but have you gone underneath to read the stamping on the diff for date codes? That might narrow it down as to whether your Coupe came originally with 4.56's.
In the NCRS Spec Guide, it lists 789 1965 Corvettes had 4.56 differentials but that is a total number and isn't broken down by smallblock or Bigblocks.
Mike T.

mallie

Good point, date code would give me a good indication if car came with 4.56. Will have the car up on the lift this week, so will be able to check.

Thanks,
-Matt

Matt Gruber

i had a 4.56 in a Duster for 2 weeks. it was NOT faster in the 1/4 so the 3.23 went back in.
so while it is up, swap it!
EDIT
a 370 or 411 is popular with the L76. But the whole idea behind the l76 is totally obsolete. New combos make more power and pull strong off idle. So an L76 sounds like a lost 60's race car to many people with a newer car.
That said, i have a 4.11 in my 61, and it is fun. But i stay off i95!

65GGvert

If they swapped the 3:36 for a 4:56, they swapped the carrier too. I'm not so sure the date code will tell you much if it's been swapped. But maybe they'll all match up.

mallie

Right, the date code won't guarantee car came with 4.56, but will give an indication as if it may have come with it at least. I think 3.70 was default (or at least the most common) rear diff for the L76 365hp (dont think you could get the 3.55).

63Corvette

Donny Brass has an L79 with 4.56 gears. He knows what it'll do in a quarter

Donny Brass

it looks like you have a 4.56, which will definately be faster in the 1/4 mile than a 3.23 and it will fit in ANY case

I have a 4.56 gear in a 3.08 stamped case

mallie

the casting code on the read diff only tell you what case it is? inside, you cud have any gear?

MikeM

A 327/365 Corvette with close ratio and any rear gear in the 3's will be a complete dog in the 1/4 mile compared to one with a close ratio and a 4.56 rear gear.

Dusters (most of 'em) aren't fast with any gear in them.

Vet65te

Matt - No and Yes. The code will typically indicate the gear ratio inside (and whether posi or not) but since these cars have been around for a lot of years, someone could have done a gear swap.
You might want to pick up that NCRS 53-67 Spec Guide (pocket book sized) because it will have all the various codes listed. When you get a chance to inspect the stamped code on the bottom of your differential, the two codes used for 4.56 were AQ for smallblocks and FC for Bigblocks.
Mike T.

mallie

Right, that's what I meant: code could day 3.70 b/c that cud be the original rear diff, but then the actual gear inside would have been swapped for a 4.56. If code is AQ, then either car came with 4.56 from the factory or the entire diff (case+gear) was changed later on, correct?

I thought that cases were different for 3.70 and 4.11/4.56?

Thanks!
-Matt

Vet65te

Matt - Long ago, less people got hung up on dates and codes and it was probably more common, and cheaper, for someone to replace a differential with another usable diff from another Corvette and not worry about correct codes. The diff in my 300 horse, 4 speed 65 Coupe was already replaced before I bought the car in '85 and it's an AT code 3.08 out of a '68 Vette.
Mike T.

Donny Brass

Correct. But by math it's a 4.56. Assuming a standard 26.7 or so tire height

mallie

Correct, I know the rear diff is 4.56. Just trying to figure out if it could have come stock. Best case if that diff date code is around March 65. Anything else will tell me car did not come with 4.56 from the factory.

Thanks
-Matt

Donny Brass

The case is the same. The carrier is the posi or non posi inner workings the ring gear is bolted to. Seems to be a trend of calling the case the carrier. The carrier is gear set dependent, unless you buy Richmond gears are designed to fit where they shouldn't

mallie

ok, got it. Thanks Donny Brass.

Now, back to my original question: who actually has L76 with 4.56 rear gear??

MikeM

The "case" is what the ring gear bolts to. The "carrier" is what has the code stamped on it.

As has been mentioned many times before, engines like yours run best when they can run up around 3000 rpm or more. That's why the factory geared them that way and released gear ratios the way they did.

Your car could still run well if you used the 3.36 rear and wide ratio four speed but you probably would like it's performance at lower speeds in high hear.

Big mistake when some here think they are cutting a hog in the ... when they put a 5 speed OD in front of one of these engines and just choke it down where it won't run in high gear.

TCracingCA

One of those Hone Overdrive units (aka Baldwin Motion used to sell them) just for this type of problem! It was expensive, but you would definitely have bragging rights!

00fxd

I remember those. Not too strong I recall ...