The Stovebolt Site Forums The Shop Area Engine Shop Driveline help

I've been reading in some earlier posts about the best driveline combos. i have a stock 59 3800 1-ton with a 283, 4speed bulldog and 10 bolt 5.14 rear, and weighs 4100 lbs. i want to replace the 283 with a sbc 350 and th350 tranny from my 82 c-10. Will this combo with the stock rear get me to highway speeds, 60-70 and not kill me on gas? The rear as only 47,000 miles on it. I can get to 55 quick with the stock setup now, ( with eldelbrock intake and 4barrel carb)but i think it's running to hard to keep it going any faster. Any ideas?

Nothing in what you describe changes how fast the motor has to turn to make a given speed.

It takes horsepower to go fast, and you are most likely adding horsepower with the 350. However if you have to turn 4000 RPM to make 70 with the 283 you will still need to turn 4000 RPM with the 350 to make 70.

Both the stock 4-speed and the TH350 have a 1:1 ratio in the top gear.

Your 5.14 rear is usually called an Eaton rather than a 10-bolt. I haven't counted the bolts holding the cover in place, but the size of the ring gear has much more significance than the bolts holding the cover.

Many GM rears the ring gear diameter is relative to the number of bolts in the cover, but even then the difference varies.

I understand that i have a 5.14 Eaton rear and that 4000 rpm is the same with a 350 or 283. My question is what gearing in the rear will make me go faster easier. This thing was made to pull trailers and haul water to fires. My motor and tranny combo is time tested, but i don't know about a 5.14 gearing. I can make the 350 go faster but it aint worth nothing if the rear is to low. i haven't seen any ring and pinion sets for 1 tons either. Maybe i'm just not lookin in the right place

I would recommend either a 3.42 or 3.73 rear if you do not haul much. If you haul a fair amount, then a 3.90 or 4.11 gear set. This will bring your RPM's down from the 5.14 gears that you have now.

The short answer is the RPM that the engine makes its peak torque is the RPM, or just faster, that you want to run at when cruising on the highway in high gear. This makes for a drivable vehicle, and good fuel economy.

Several things factor into this calculation, including HP and torque available (what engine). Also what does the truck weigh, and how much air does it push out of the way? And how fast do you cruise, 95 mph needs a fair amount more HP, and therefore more RPM than 55 mph does.
These last few things are hard to put a value on, but you can learn from others. If someone else has a similar setup, has it geared reasonably well, and is pleased with it, plenty of get up and go, and decent economy, then you are pretty safe with that engne and vehicle to calculate for the peak torque rpm at cruising speed, as this is near ideal in most cases.

If you don't have the HP, have a heavy vehicle, and/or drive really fast, then you will have to compromise on one of those variables, or run more RPM and sacrifice fuel economy.

This is a good Tech tip: http://www.stovebolt.com/techtips/calculate_rpm_tire_axle.htm

And I really like this calculator for figuring speeds and RPM.
http://www.onlineconversion.com/bigger_tires.htm

Grigg

That same rear was used in 3/4- and 1-ton trucks as late as 1972. It was offered with at least three different gear sets and there are persistent rumors of a fourth option.

The 5.14 was used in 1-tons and was an option at least some years in 3/4-ton trucks.

The standard ratio in 3/4-tons '47 to '54 was 4.57. In some later years some 3/4-ton trucks had 4.11 gears.

Those are the three gear sets available for your rear that seem not too hard to find. The fourth option is 3.something but while I hear talk of it, I don't think anyone here has ever claimed to actually have one. I've begun to suspect the 3.something ratio option was not available in the Eaton, but rather in the Dana that was available in the early 70's trucks.

Randy's Ring and Pinion lists some parts for the Eaton rear but may no longer list any gears for it. This rear was popular with the rock crawler crowd at one time, but it appears to me people are moving on to newer rears with more readily available parts. As the market shrinks interest in providing parts for it is shrinking too.

Some time ago I bought a 1-ton that had 3.42 gears. But that rear was a GM 14-bolt from a newer truck. I plan to use that rear under my 1-ton project truck. I expect to get away with the gears while still pulling a load because I intend to run either a Chevy 454 or a Cadillac 500.

Years ago I ran 3/4 ton 4.57 rears with 7.50x17 tires behind a 302. It was a good combination for power and running 70. And the 4.57 gears will bolt right in. What size tires do you have now?

I got a 4.11 assembly for my '62 one ton. I found it in a 1968 GMC 3/4 ton suburban with a smallblock and auto. trans. Pull both axle shafts,the nuts off the front of the carrier and drop the driveline and the carrier assembly will come right out. Be ready-it's damned heavy. Reverse the operation for installation. I cleaned the housing out and washed the mating surfaces with brake cleaner and put a decent skin of hi-temp copper gasket silicone on the face of the housing just before putting the carrier in. I ended up using a small floor jack chained tightly to the carrier to lift it into place. Pick the best two axle shafts and do the same clean up and glue trick on them. Be careful not to over-do it on the glue,it'll screw things up if much of it gets into the bearings.
A 4.10 or 4.11 ratio should give you about 3,500 rpm at 70 mph or about 3,200 at 60 mph,as near as I can remember. Didn't seem to affect my mileage a bit,but it sure felt better on the highway. I suspect with the taller gearing my engine wasn't revving as high,but it was pulling a little harder,and thus was getting quite a bit less vacuum,so having to drive with a little more throttle offset the lower rpms.
Speed

Hey crenwelge, i'm running the stock 8-17.5 wheels ans bias tires