L76/3.08

[Jim Cear]

I was just checking the archieves on rear axel ratios as I had recently determined i had a 3.08 in my '63 L76. My car also has a wide ratio tranny, a combination that was not an original option as many will know. As many others have also commented in the past the L76 is stronger in the upper end of the RPM range. My cars combination seems to make it a bit more difficult to quickly climb the rpm range. Could anyone comment on the effect of changing the rear end to one of the standard mid 3 range gear sets with the current wide ratio tranny? I do mostly local driving and not really concerned with highway rpms. Fun factor is important

[Wayne M.]

That combo with a wide ratio is not that bad

Translates into about 3.55 ratio with a close ratio trans. Be warned that if you go with a 3.70 or 4.11 differential gearset, you'll need different trans speedo drive gear (on the output shaft inside the rear trans extension), as well as the correct colored plastic driven gear.

I learned to drive a Corvette with a '65 L79 and factory 3.08's. Lots of fun launching on hills.

[Joe C.]

Re: L76/3.08

Jim,

L76 was only available with close ratio, and tallest gear available was (I believe)3.08:1. Open diffs were not available with L76. Most popular gearset with L76/L84 was 4.11, with 3.70 being second choice. Some hardy souls opted for taller axles, and very few even chose 3.08:1. Since your car already has a wide ratio box, then consider it an advantage, with lower 1st gear ratio of 2.56 (?) instead of close ratio's 2.20 (?), this will help get the car launched, which is sometimes a problem for those (*****es) not used to driving the more high strung SHP smallblocks. Since you have the W/R gearbox, then I recommend a 3.55:1 axle. Better yet, install a 3.70, or 4.11:1 and go with the Tremec 5 speed with .6:1 overdrive. That combination will give you blinding fast holeshots, with excellent cruise RPM.

Joe

[Duke W.]

Re: L76/3.08

The standard axle with L-76/84 was 3.70 with an open diff. Of course Positraction was available, but if you wanted any of the five available axle ratio options, they could ONLY be had WITH Postitaction.

The overall drivetrain reduction is transmission ratio times axle ratio, so the base gearing overall first gear reduction is 2.2 x 3.7 = 8.14.

The equivalent axle ratio to achieve this with a 2.56 WR transmission is 8.14/2.56 = 3.18. So your 1-3 overall gearing is not that different from the standard drivetrain until you hit the huge 3-4 gap.

If you installed a 3.36 axle it would be about equivalent to the CR trans and a 4.11 axle in the first three gears.

Each axle represented about a 10 percent change in overall gearing, except 3.55, which split the 10 percent difference between 3.36 and 3.70.

Or put another way, a 3.55 with the OE 6.70-15 tires (760 revs/mi) is about the same as a 3.70 with 215/70R-15 tires (775 revs/mi) in terms of revs/true speed relationship.

The Richmond Super T-10 wide ratio set is 2.64, 1.75, 1.34, 1.00:1 compared to 2.56, 1.91, 1.51, 1.00:1 for the BW WR T-10. With the Super T-10 WR set the widest gap is 1-2, which is a much better setup for all around driving than three CR gears and a huge gap to fourth.

I don't know if it's possible, but if the Super T-10 WR gearset can be installed in a vintage BW T-10 case, it would be a good way to go with a low numerical axle on SHP/FI engines and would provide a decent combination for both in-town and highway driving.

The Super T-10 WR (and CR) were used on seventies vintage Corvettes, and is still available today from Richmond, and I believe a Super T-10 is pretty much a bolt-in replacement for a BW T-10.

Duke

[Joe L.]

Re: L76/3.08

Duke-----

As a complete unit, the current Richmond Super T-10 is almost, but not quite, a direct bolt-in for Corvettes originally equipped with a T-10, Super T-10, or Muncie. However, the mainshaft and extension housing are about 3/4" longer than the original T-10 or 63-70 Muncie. So, for these cars, the driveshaft needs to be shortened by a similar amount. Also, the size and spline configuration of the output shaft is different than any 63-70 Muncie or original T-10. So, a different transmission rear yoke must be used (the same one used for most 71-79 Corvettes) and either the driveshaft front yoke changed or a conversion u-joint utilized with the existing yoke.

The other difference is the spline count for the input shaft. The pre-71 Muncies and T-10's used a 10 spline input; the Super T-10 uses a 26 spline input. So, the clutch disc must be changed. That's no big deal, though, since if one is changing out a transmission, the clutch disc is easily changed at the same time.

For 71-74 Corvettes with Muncie, the T-10 is a direct bolt-in, although there may be some shifter linkage differences. As I vaguely recall, one or more of the shifter rods may need to be changed. This also applies to pre-71 Corvettes.

As far as changing the gearset in an original T-10 case to the Super T-10 "innerds", I do not know if it can be done, or not. I know that some of the internal parts between a T-10 and Super T-10 do interchange. However, I don't know if there is some internal difference in the cases which would make a complete gearset change not possible. The current Super T-10 is actually a "third generation" T-10. After Richmond Gear acquired the manufacturing rights for the Super T-10 from Doug Nash Company (which had earlier acquired them from Borg Warner), they made other substantial improvements which may or may not affect the interchangeability of even original Super T-10 parts with the currently manufactured Super T-10.