Rear gear Ratio Opinions/Suggestions
 

Just throwing this out there for the masses.
My C-10 (350/TH350) currently has the factory 3.73 rear gear.
My goal is to get better drivability on the Highway (65-75mph).
I know mpg is a pipe dream.
Currently it’ll run around 32-3300 rpm around 70mph.
It’s ok for shorter trips, but currently, longer trips are kinda out of the question.
What I’d like ist to get the rpm down around 25-2800 range.
I don’t tow anything, and other than occasionally running to the Lumber yard, it’s really in semi-retirement (like me:lol:)
I’m not ready to “upgrade” to a 700r or 4l60,
Would a ratio in the 3.23- 3.35 range help any?
I just wanted to ask

Re: Rear gear Ratio Opinions/Suggestions
 

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My '68 was a little different, but not really. It had a 327/TH400 but it had a 4.11 rear gear. I put a Dana 3.54 in it and it made all the difference in the world, as far as driveability. The 3.54's are kind of hard to find but they are out there. You didn't mention if your truck has coils or leaf springs.

Re: Rear gear Ratio Opinions/Suggestions
 

I had a '67 C10 that was ordered originally with 4:10 gears. I put a 350/350 combo in it, and it was miserable on the highway. I swapped in 3.08 gears, which made it great for highway cruising. I drove that truck between California, Colorado and Oregon many times over the years I owned it. A set of 3.08 gears would drop you from 3300 down to 2700. The down side, of course, is that you will end up with a very sluggish first gear.

Re: Rear gear Ratio Opinions/Suggestions
 

Just drive slower.
60 mph is about 2700 rpm.

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The economy gear is 3.08 and that's what came stock on my 69 with a 350 and TH400 transmission. 3.08 sounds ideal for your situation IMO.

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I'd wait till u were ready to upgrade to the 700R4 and do that. Did that with mine and with the 350 V8 and 3:73's and 29 inch tires i'm at 21/2200 at 70 MPH.

Re: Rear gear Ratio Opinions/Suggestions
 

Thank you to all for your input.
Now to comment:
My C-10 is LWB with the Trailing Arm/Coil Spring rear suspension.
Speed wise: I generally do just tootle around the area, running errands, to the Hardware/Lumber Store, but occasionally I go out on the Interstate to go pickup things for the Boss-Lady.
Driving 60 on the interstate here (I-40/I-81 East Tennessee) is sometimes more dangerous than exceeding the limit.
I know that the 3.08 gear will have an impact on first gear (I had a 69 Impala with them. It wasn’t much off the line, but it would cruise at 80mph without issue).

All that being said, I’m leaning towards something in the 3.30 - 3.35 range.
This will kinda give me what I’m wanting without hurting 1st gear.:smoke:

Re: Rear gear Ratio Opinions/Suggestions
 

Transmission with OD out of the question?

Best of both worlds

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A set of 3.31 gears will drop you from 3300 to a little over 2900.

A 700R4 with your current gears would drop you to 2300.

Re: Rear gear Ratio Opinions/Suggestions
 

if you're od trans averse and don't want to crack open the rear end, a gear verndors overdrive is another option. It's not the cheapest, but unless you're doing the rear end work yourself, it's not "that" much more than paying a reputable driveline shop to install your rear gears. With no other changes, a GV unit would make 3200 rpm drop to 2500 rpm (i.e. almost twice the reduction of going to a 3.31). A GV unit can be used as an overdrive only, or can be used to split gears, essentially giving you a 6-speed automatic, but there's almost zero point in the latter for the type of use you describe. Anyway, just another option so you have them all on the table.

Btw, what's your tire diameter?

I feel your pain - my C20 has a 4.56.. I haven't decided which way to go yet, and I may do nothing. I like geezer's approach too - but true statement above that driving too slow can be as dangerous as speeding on today's crazy highways. Some states have 80 mph speed limits in some areas - and I like to keep up with the flow, but that wouldn't happen in my C20.

The other thing to keep in mind is that while 3200 rpm may "seem" loud, annoying, or worse yet, damaging to the engine - only the first two may be reality - and that's probably mostly because of how our perceptions of what "should be" have changed over the last few decades with od transmissions becoming standard on everything. This old era of trucks was never designed with od transmissions in mind and a 3.73 isn't that radical - you could opt to just do nothing - cruise, sit back, and enjoy the fine whine.

Re: Rear gear Ratio Opinions/Suggestions
 

With an Overdrive transmission, you will drop the RPM by 33%. 3300-rpm to 2300-rpm nominally.
3.73 to 3.08 is a 17.5% decrease in RPM.
To get the equivalent RPM drop using only rear-end gearing, it would require 2.61 gears.

When comparing costs and benefits, it's easy to see how transmission change may be the better option for some.

• Low gear is much lower than the THM 350 ratio for better power off the line.
• The lower rpm, in overdrive, typically adds 30% to your highway mileage.
• Has the additional benefit of a quieter cab.
• In my experience, you can do nothing that quiets a cab more than dripping motor rpm.
• The lower RPM also changes the amount of engine wear and the hydrocarbons released per mile of travel.
• All OD transmissions also have lock-up converters that will reduce highway RPM by another 200-300 rpm at highway speeds over a none-lock-up 350.

The cost to change the transmission varies, as does the rear-end gear change.
Only you can know what's best for you.

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3.08 is what my 69 C10 has had for 55 years. And even then, I wish I had another gear at 70mph and above. And that's with 29" tall tires. Back in the day of "55 saves lives" it was perfect at 60mph.

Engine/trans is a mild 350/TH350.

Re: Rear gear Ratio Opinions/Suggestions
 

Od or 3.08 - 3.36

I just did a 4l80 in my 73 and love it.
But near 5k all in.
$2200 rebuild
$1100 convertor
$1200 controller
$400 driveshaft
Atf x 3 gallons

And it has opened a new can of worms.
As 3k rpm is nearly 90mph, now the brakes are entirely inadequate.

Re: Rear gear Ratio Opinions/Suggestions
 

Or think about adding some sound deadening material to the floor, doors, and behind the gas tank, and maybe even under the hood. In my case, I'm less concerned about the revs than the cab noise. And that's with new door seals and no open holes in the firewall.

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You haven't mentioned what size rear tires your running. For my GTO with a T400 3.55's with a 26" tall tire was perfect for me. But I wouldn't have been happy with 28" tires.

In my Burban I run 3.73's with a Gearvendor (Which I got off Craigslist for $600. It was the 3rd one I've bought used.) on 28" tall tires.

Re: Rear gear Ratio Opinions/Suggestions
 

Will have to dbl check but think my 69 panel with factory 3 on tree has a 3.08 gear. Mileage not terrible and that's with 454 and medium cam.Heck it isa better than my 2016 Silverado 2500.

I have a 4l60e ready to go in but need standalone computer to make it work. When it goes in 3.73 or 3.90;s are going in rear along with posi unit. Better milage and tire frying first and second and maybe 3rd.LOL

If original is not issue I would go with over drive transmission. There is reason late model stuff has 6 and 8 speed transmissions. I 700r4 had a over drive of .75:1 so 25% reduction right there.

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I must be a wuss, because I can't image driving at anything above 55-60mph with a 3.55 and 26" tires. And back in the 90s a buddy of mine with a 71 or 72 C10 went from a 3.08 to a 3.73. I was thinking about doing the same, but he told me no way should I do it. And that was probably with 235- or 225-75x15 tires.

Funny, but in my teens and 20s I had a few 55-57 cars with 3.55 axles, and even a 3.70, and drove those cars on highways quite a lot. Of course 60-65mph was the norm. I never once thought the revs were too high.

Finally, I had a co-worker 10-12 years ago, who back in the day had a brand new early 60s Corvette with a solid lifter 327 and 4.11 gears. He said he drove that car from Dallas to Houston a couple times/month to see his sweetie, but didn't remember the revs bothering him. However, his latest car--a mid-70s Nova--had a 3.42 and he was planning to go back to a 3.08.

So, I salute you guys with 3.55-3.73 axles!;)

As for Gear Vendors, that's got to be a great way to go if you have the budget or can find a deal on a used one.

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Rpm, what’s a little rpm.
You guys should try 400 miles in a 56 sb with a bbc (468) m22 and 5.13 gear. Big block just singing at 4200 rpm.
Made that trip 3 times that summer.

Re: Rear gear Ratio Opinions/Suggestions
 

:eek::eek::eek:

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:lol: And it burned rubber in all 4 gears, too, I'll bet! Fact of the matter is, it would probably burn rubber in all 4 gears with a 4.11!

As for me, I run the truck at 55 MPH with my setup. That shell blocks a lot of wind, but I'm retired, and not in any real hurry.

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My 70 was changed to 3.08, makes big difference on the highway.

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Do you have a 350 motor and a tach?

Just curious what your rpm is on the highway. I"ve never bothered trying to connect my clunky bench tach (for tuning) for a test drive...

Re: Rear gear Ratio Opinions/Suggestions
 

Assuming a 28 inch tall tire it would be about 2600rpm.


I have this calculator saved.


http://www.advanced-ev.com/Calculators/TireSize/

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^^^^^Cool, thanks Geezer!

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350 yes, Tach yes, 3 speed manual, so at highway it would be sam as T350. Rpms are about 2300 at 70MPH, 60 is a hair over 2K. 265/70x16 tires or about 30.5 in high