68C3er

OK Guys, I am 58 and I have just traded my 36 Ford Coupe for a 1968 Vette. I have never owned a Vette and thought it was about time to have something different. I have never had anything but Street Rods. (MY Wife Likes Vettes). It's a gas to drive, it is a frame off resto. I would give the mechanical and interior a 9.5 of 10. The paint is a 7 of 10 but then I am (my wife says) ****....I like particular better. Any way it's a 427/4 speed car but it's been punched out to around 469 (still waiting on all the documentation). This car will pin your ears back, but on the interstate it's tongue is hanging out at over 50 MPH and the tack reads half of the speedo. 50MPH = 2500 RPM's, and reads half the MPH's at any speed. A local Vette guy said it had a 373 gear ratio (I think it's lower?) He wanted to sell me a set of 336 gears he had. Anyone out there been through this? I am not worried about losing bottom end, this car will never see a drag strip, it doesn't matter anyway as strong as the motor is. I just want to be able to drive it on the interstate without it sounding like it's running 100 when it's running 60! ANY help would be appreciated on a good gear ratio for the 68. Thanks from a FNG!

TheSkunkWorks

Rather than change the ring and pinion, IMHO it's time for a Richmond SS 5-speed w/2.89 1st and 0.77 OD 5th. With 3.73:1 FDR and 255/60R15's, you'd only be turning ~2000 rpm at 55 mph and ~3000 at 85, while having 10.78:1 total first gear. Or, maybe a TKO w/0.64 OD if you want to drop cruising rpm still further. My $.02...


TSW

mikey

sounds like the ratio is somewhere between 3.73 and 4.11
can't know for sure without knowing tire diameter.

you can count it yourself - just jack the rear end up so both rear tires are off the ground.. then with the car in neutral, rotate the rear tire and count the diff input pinion rotations vs tire complete rotations. i like to do 5 tire rotations and then divide by 5, it helps ensure you can tell the difference between 3.73, 3.90 or 4.11

a 5 speed trans as mentioned above is certainly a good option these days. i just installed a tremec tko600 from classic chevy 5 speed with .64 5th gear on my 3.90 rear gear.. should make for some pleasant cruising..

Fishndude

Welcome to the 68 club, I just bought my first vette (a 68 too) about 4 weeks ago

Ganey

Yes, 3.36 is good compromise for BB 4spd.


PS I tried to buy a Deuce coupe w/ a 350 as a first car. A neighbor had it in his front yard. He wouldn't drive it (said it was an evil handling outfit) or sell it. Looked stock outside except modern steel wheels. Did get his 57 Chevy.

roscobbc

My '68 now has 528 hp/565 ft lb 489 with c/r M21 and 3.08 rear end. With 27" tall tyres this cruises at approx 2600 rpm at 70 mph. 1st gear is also good for 70 mph! Like you I won't be seeing too any drag strips with the car so this gearing (for me) is perfect - not too low a ratio for issue with traction pulling way yet a semi-reasonable cruise rpm

Rally68

I have read a lot on this subject on this & other forums; seems like 3.70/3.73 is a pretty popular gear across the spectrum, so you are not alone in your high-rpm highway experience.

I had a 3.08 in my '68 small block w/thm400, and have just started disassembly of my diff to install a Richmond 3.73 set. I have modern but not wide (225/70) tires and the 3.08 was a bit too anemic from a stop. I'm guessing if I had the horses you have, I would've been fine with it, but keep in mind she won't "pin your ears back" the same way if you switch to lower gears.

That said, I agree with the other posters, to have your cake and eat it too, a transmission upgrade with a low overdrive (.67:1 ?) would be the best thing. It's a few thousand, vs. a few hundred for a new ring & pinion of course.

My 3.08 ring & pinion are in great shape, if you decide to go that way

PRNDL

To answer your question. 3.70 is the gear ratio that would produce approximately "mph equal to double the rpm" as you described... 3000 rpm would give you 60 (or 62) mph. 3.70 was an optional ration in 68. A 3.36 rear gear would give you the same mph at 2700 rpm. I have a 3.36 in my 68 L-36 and it is a pretty nice compromise but if I were going to do a lot of highway driving rather than spend money on a swap from 3.70 to 3.36 I would invest in an overdrive trans to get the best at both ends.

capevettes

I've got the stock 3:08 rear in my 68 L36 automatic/Turbo 400. I love it. The big block makes so much low end grunt, even with the 3:08's it's still a blast to drive. It really loves to cruise on the highway. 70 mph is about 2600 RPM's. I would just put a 3:08 rear in if you want to take it on trips.

TheSkunkWorks

I'd get in touch with CF member GTR1999 if you want a quality diff rebuild. Gary seems to know C2/C3 diffs as good as anyone you'll find. (Wonder if I ought to ask for a commission, as often as I mention him.)

7T1vette

You didn't mention it, but I suspect that you would like to keep the car reasonably 'original'...which means no overdrive tranny. If that's the case, put a 3.08 gear in back and enjoy the highway. The ideal combo for your engine [for street and highway use] would be a 3.36 diffy with the overdrive transmission, however.

carriljc

read the numbers on the underside. Code should tell you what gear ratio is in there.

...then you can look it up here.
http://www.corvettec3.ca/axle.htm

Mine is labeled 2AP22968W; which according to previous deciphering meant:
2-don't know
AP- 4.11 positraction
2- Feb
29- 29
68- 1968
W-Warren
http://www.corvettec3.ca/axle.htm

7T1vette

3.36 will reduce the highway revs considerably from the 4.11 diffy. That might be enough of a change for you and still allow good 'take-off' performance.

GTR1999

What gear would you recommend for the 63-79 vette?

Staylor63

So digging in to my new purchase of a 68 with a 327, i found my rear end has an LR code...so with the date it is a 3:36 from a 1972. How do I know that is is a posi?

Steve

GUSTO14

Steve, the easiest way to determine if your rear is a posi or not is to pick the back of the car up in the air. (Support the control arms with jack stands to keep the half-shafts close to horizontal.) Put the car in neutral and try to rotate the drive shaft by hand. The drive shaft should turn fairly easily. If both tires turn in the same direction it is very likely a posi. If they try to turn in opposite directions (or only one turns), it is definitely an open rear.

You do realize that this is a 6 1/2 year old thread don't you? It might be worthwhile to start a new one with your question in the subject line. Since this subject line is about gear ratio's, observers may not read through to your question regarding posi or not.

Good luck... GUSTO

toobroketoretire

A "diffy"? What in the hell is a diffy?

7T1vette

pumpkin; screw; rear gear; differential (diffy).

The rear gear goes by different slang names in different parts of the US.

c6silver

I'd toss 2.73s at it with a Muncie M-20 wide ratio if you're going to do a lot of highway driving...and never see the drag strip.

Ironcross

But it's one that always appears...My Yellow Vette is a 4.11 gear and the tach reads exactly 1/2 speedometer.....60 mph is 3000 rpm, and 70 mph is 3500 ect ect.....however 70 mph reads 4000 with a 4.56......Most of my toys has one or the other