Rear gear Ratio Opinions/Suggestions

[custom10nut]

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)
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

[LockDoc]

-
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.

[pjmoreland]

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.

[BRL]

Originally Posted by pjmoreland

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.

That's exactly what I had and exactly what I did and I couldn't be happier!
As far as a sluggish 1st gear goes I have what I consider to be a rather healthy low end torque engine and I don't drag race the truck.
This pickup has plenty of pick-up!
God I'm witty.

[MikeB]

Originally Posted by pjmoreland

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.

My truck has a 3.08 posi behind a mild 350, and will spin the tires for 50 ft if I stomp on it in first gear. PJ, you must be one of them there hotrodders with a big cam and 850 double pumper.

[pjmoreland]

Originally Posted by MikeB

My truck has a 3.08 posi behind a mild 350, and will spin the tires for 50 ft if I stomp on it in first gear. PJ, you must be one of them there hotrodders with a big cam and 850 double pumper.

I did that swap 27 years ago, and I'll admit the gas pedal spent a decent amount of time mashed to the floor back then. I had a 70s smogger 350 with a stock cam, so it was nothing too crazy. With the 4:10 gears it would squeal the rear tires effortlessly. Not so much with the 3.08 gears.

A few years later I swapped in a 300HP crate 350 to liven things up. The younger brother of an ex-girlfriend asked to borrow my truck for a high school day at the local drag strip. My truck did quite poorly that day, getting 17 second quarter mile. I ended up installing 3.73 gears after that, but once again it was miserable on the highway.

[geezer#99]

Just drive slower.
60 mph is about 2700 rpm.

[dmjlambert]

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.

[Already Gone]

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.

[custom10nut]

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.

[MikeB]

Originally Posted by dmjlambert

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.

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.

[Luke87gt]

Transmission with OD out of the question?

Best of both worlds

[pjmoreland]

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.

[jocko]

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.

[MikeB]

Originally Posted by jocko

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.

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.

[Accelo]

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.

[HO455]

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.

[MikeB]

Originally Posted by HO455

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.

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.

[custom10nut]

Originally Posted by HO455

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.

275/60/15 BF Goodrich T/A Radials.
I think they’re 29 or 30 inches tall
Is realist here.
I never going to chase the dream of 18-20mpg (right now I get about 15 Hwy)
My concern is the constant running at 32-3300 rpm at 70-75.
Oh the truck will easily do it, but I don’t want to abuse the engine.

[Already Gone]

Originally Posted by custom10nut

275/60/15 BF Goodrich T/A Radials.
I think they’re 29 or 30 inches tall
Is realist here.
I never going to chase the dream of 18-20mpg (right now I get about 15 Hwy)
My concern is the constant running at 32-3300 rpm at 70-75.
Oh the truck will easily do it, but I don’t want to abuse the engine.

Your 275/60 15's are 28 inches tall.

[jocko]

the actual RPM your truck is experiencing in the upper left red box - along with various trans and gearing combos that have been mentioned in the thread. Obviously you won't want to do BOTH an O/D and 3.08 gearing - they're just listed for reference only. It shows why 3.73/700R4 is such a popular option (and why GM built zillions of modern 1/2 ton trucks this way) - it improves 1st gear acceleration and also reduces your cruising rpm more than a 3.08 does. But, several options can get you closer to what you're trying to achieve. Hope this helps!

[KQQL IT]

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.

[chris mc bride]

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.

[geezer#99]

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.

[MikeB]

Originally Posted by geezer#99

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.