I have NO major projects for the vette for this summer, was just planning on enjoying it for a radical change (and I AM, knock on wood)...


But I am planing for this winter. I am saving up for a TKO-500, as I don't think a WC T-5 will be able to handle the torque of a 383 I plan to build. Someday. Anyway...in the mean time, I have decided that without overdrive, I'm not going to be cruising on the highway much regardless of rear gear ratio...so why suffer with the 3.08 I have?

Here are some questions, and some info...



TKO-500 /// 3.27, 1.98, 1.34 ,1.00, 0.68 Tranny I will have
ST-10 /// 2.64, 1.75, 1.34, 1.00 Tranny I have now
3.08 rear end
Stock radius tires


Current motor makes most of it's power in the low end range, such as it is..."probably" 275hp, 300tq, from 1,700rpm up to 4,500rpm.

What I'm wondering is, which rear gear would be ideal? 3.55? 3.37, or whatever the exact number is?

My second question is, how big of a job is replacing the gears in a rear end? Any special tools, special knowledge, etc? Is this a job your standard backyard mechanic can handle?

And last, the ol' "while I'm at it"...would it be a good time to replace/upgrade the diff? I was looking at richmond Lock Right, in my summit mag. But there are so many...any advice on any of this is greatly appreciated! Thanks guys!


Oh, yeah, and HAPPY 4TH!!!

 

With that 5-speed trans, a 3.08 is perfect because the total torque multiplication is 10:1. Any more than this and first gear becomes nearly useless for performance because it won't hook up at full throttle.

 

According to a speed calculator, I would need to travel at LEAST 80mph with an over drive of .68, rear tire radius of 18, just to keep engine rpms UP to 1,500. I think that is a bit too much. What are the options for rear end gears for these cars?

 

You don't really mean tire radius of 18 inches do you? That would make the diameter 36 inches. I haven't checked your math otherwise but, I have a C5 with the 6 speed manual. Sixth gear is .5 to 1. Tires are about 27" dia. and 1,500 rpm puts me at about 70 mph. That's in 6th, at .5 to 1.
Changing ring and pinion gears is not a job for a do it yourselfer. You need a dial indicator, micrometer, a bunch of shims for trial and error setup. Gaps, backlash and wear patterns need to be checked and adjusted numerous times, usually. You have to deal with a pinion crush sleeve. I sent my diff to Bair's. They did a nice job.
That being said, if you switch transmissions, you should stick with the 3.08s.

 

OK, the speed calc I was using provided wrong info, or I put something in wrong. Went to another one, and here is what I got...

With what I have now, in first gear, 2.64, with 3.08 final drive, I can get to 47 mph @ 5000rpms. That's why my car is a dog. BUT, in 4th gear, my 2000-3000rpm cruise speed is 49 - 74mph. Not bad...but not really good, either. I'd prefer to not have to "cruise" at 3,000rpms, to keep up with (barely) traffic. With this, I don't plan on doing any long road trips, though I desperately want to start making trips to Limerock and Watkins Glen.

Change to 3.55, in the meantime, nets me a first gear that redlines at 40mph...so, really, not much better, huh? And 75mph comes at 3,500rpms. No cruising there.

With the TKO, my 1st gear speed at 5000rpm with 3.55 rear gears is 33...should be MUCH better for acceleration...so long, as mentioned before, I can put the torque (goal is 400) to use. 5th gear, at 2,500rpms is 80mph. Great cruising. With 3.08s still in place for the TKO, first get's a little longer, but probably easier to drive, but 5th, at 2,000rpms, is doing 73mph. That's seems pretty good, actually.


So, not to waist all of your time...my conclusion, I guess, is that the problem isn't my 3.08 rear end, but my current 2.64 first gear.

So, here's a question...just this one little question...to the bulging brains (ex brains?) at GM...WHO in the name of Christ decided that a 76' L48, making 170hp, and something like 240tq on a COLD day, should need, or even be able to USE, a 2.64 1st gear, no matter WHAT rear end it has?

 

Way back in 1976 (I'm old enough to remember), no domestic cars had more than a 2.6 to 1 first gear manual. The old Muncies had 2.5 in the wide ratio and only 2.2 to 1 in the close ratio. Ford and Chrysler were no different. Nobody had overdrive transmisions either. This is just one example of how cars have improved over the years.

 

I have installed a bunch of the TKO transmissions in C3 cars. The best rear gear is a 3.55 or a 3.70. The 3.08 ypu will never use 5th gear. First gear is a little short but the car moves out very quickly. So you shift out of first quickly, it works. I have never had anyone come back and want it changed. I have a 3.55 in my garage waiting for the next TKO trans change I do.

 

What I want is the best of both worlds...

I want fast 1st, 2nd, and 3rd gears, for autocross and occasional trips to Limerock or the Glen...BUT, I want decent mileage in 5th, because Limerock is a 2 1/2 hour drive, and Watkins Glen is 3 hours away. And I don't plan on buying a truck with a trailer to haul the old girl there.

 

I have the TKO and 3.08's. It is an excellent combination with my 331 inch motor.

A good solution is to move up here to Litchfield County. I'm 20 minutes from Lime Rock.

Of course, we're hours from everywhere else......

 

Why not a Richmond 4+1? That what I have with a 3:08 and I like it. A close ratio 5 spd with 1:1 5th.

Not my car but this tells it all.
http://www.computersupport.ca/Restoration/Richmond.htm

 

Your best gas mileage is also with something near 3.73. I drove aeound in my vette for over 20 years with 4.11 and OD. It's a good ratio and I believe that 3.90 is a good choice.

I now have a 3.55 just to make my first 4 gears more usable and my .64 is my freeway gear. But I also have a little moe TQ than you. My little 383 loved the 4.11 and TK0 600

 

I'm using the same transmission and 3.08 rear gears with a pretty decent roller motor in front of it (~400HP). I get along OK, but will likely swap to 3.55 at some point because first and reverse are a bit tall for my taste.

~2150 at 70 MPH is nice though.

 

Noting that ~10:1 multiplication in 1st is typically a good rule of thumb, thought I'd paste this info from my gearing spreadsheet...

TKO-500 - 3.27 - 1.98 - 1.34 - 1.00 - 0.68
w/3.08:1 - 10.07 - 6.10 - 4.13 - 3.08 - 2.09
w/3.55:1 - 11.61 - 7.03 - 4.76 - 3.55 - 2.41
steps - 39% - 32% - 25% - 32%

TKO-600 - 2.87 - 1.89 - 1.28 - 1.00 - 0.64
w/3.08:1 - 8.84 - 5.82 - 3.94 - 3.08 - 1.97
w/3.55:1 - 10.19 - 6.71 - 4.54 - 3.55 - 2.27
steps - 34% - 32% - 22% - 36%

TKO-600RR - 2.87 - 1.89 - 1.28 - 1.00 - 0.82
w/3.08:1 - 8.84 - 5.82 - 3.94 - 3.08 - 2.53
w/3.55:1 - 10.19 - 6.71 - 4.54 - 3.55 - 2.91
steps - 34% - 32% - 22% - 18%

Richmond SS - 2.89 - 1.85 - 1.31 - 1.00 - 0.77
w/3.08:1 - 8.90 - 5.70 - 4.03 - 3.08 - 2.37
w/3.55:1 - 10.26 - 6.57 - 4.65 - 3.55 - 2.73
steps - 36% - 29% - 24% - 23%

Richmond 4+1 - 3.27 - 2.13 - 1.57 - 1.23 - 1.00
w/3.08:1 - 10.07 - 6.56 - 4.84 - 3.79 - 3.08
w/3.55:1 - 11.61 - 7.56 - 5.57 - 4.37 - 3.55
steps - 35% - 26% - 22% - 19%


FWIW, top end performance would definitely be better with the 0.82 or 0.77 5ths of the TKO-600RR or Richmond SS 5/OD than taller OD's. Hope that helps.

 

RichmondSS 3.36 rear gearing. 2.58 overdrive. 9.71 low gear. Best percentage drop between gears RichmondSS. Or TKO600 with 3.70 rear.

TKO500, 3.08 rear 2.09 overdrive to extreme. 3.55 now 11.61 low gear now its to extreme.