The Stovebolt Site Forums The Parking Lot Big Bolts Can you speed up a BIG BOLT?

Since I am relatively new to this site, and to the larger trucks, I need some advice. I have 1951 GMC 1 1/2 ton with a two speed rear. I love this old truck the way it is, but I was wondering if there would be a way to get her up to maybe around 65 or more? I have no idea what kind of tranny would be a good idea to use or if this is even possible. I want to keep the original engine, the 270 because I know they hardly ever die. Can someone offer some help? Thanks!

Well,one way is to find a brownie 3 speed box. There have been several posts on this topic. You might find some more info if you do a search. The brownie/spicer's are difficult to find. I saw one at the Portland swap meet for about $300, but it was frozen. Most go for about $1,000. Then you have to have the drive shafts, and linkage, and shifter. I thought of doing it, but I'm putting that on the back burner for now. If I saw a nice unit with all the mounts etc... I would consider it, but it sure isn't a priority.

Someone may be able to confirm this, but I think there are some 5 speeds around from some 50-60's big bolts with Overdrive in 5th gear. Seems to me that would be the easiest way to get some more speed. I know I saw an old road tractor with a 5 speed for sale claiming that the 5 speed was an OD and I know where a transmission out of a firetruck is that is the same model number....so I've been eyeballing it for the same reason.

An NV4500 transmission is probably a good swap to gain one faster gear, 0.73 OD (about).
Swapping the rear axle for a single speed from a 1.5 ton may be cheaper and accomplish the same goal?

I've seen plenty of small auxiliary transmissions for sale, and I think $1,000 would be way to much for one even with mounts and a shifter. I sold one without any extras for a whole lot less than that and it took a while to sell.

Calculate gear ratios and speeds here
http://www.onlineconversion.com/bigger_tires.htm

At some point you either don't have enough engine to pull the truck along at the speed you desire, and or you don't have safe enough or large enough brakes to be going that fast in it any how.

In my mind that cutoff point is around 60 mph, and if you want to go faster start with better brakes, a dual circuit MC will be a good start. Then at probably 65-70 you'll run out of HP and just waste fuel trying to go fast.. again, just my guesses on that.

Grigg

i can attest to all of this. grigg is right on with his statements . what i'll add to this is that at those speeds your looking to obtain, handleing becomes an issue also. just yesterday i had issues with brakes and handling and i was only doing 50 in my 350 on a trip i was returning from.

some say you run these trucks as fast as you can all day long. i disagree because i have two of them that i drive regularly. for the safety and what the trucks like to run at the way they are is any where from 45-53 mph contstantly

We ran 2 tons all they would go back in the 50's which might even be 70 down hill and almost walking up the next hill. Running them at 70 was dangerous, but those were different days. Wrecks were common and thats just how it was. If a driver had a wreck a year, that wasn't considered too bad. Today we live in a different world. Past 55 or 60 two tons become unsafe and beside that, due to the fact that they are not at all aerodynamic, they don't have enough HP to break the wind at those speeds on level ground. Unless a 2 ton had a larger engine installed, every part of the suspension rebuilt, every part of the steering rebuilt or retrofitted with newer components and the brakes completely rebuilt, I don't think of running two tons over 55 or so. 50 years ago I would kick them out of gear on a long down hill and they might get up to 80 which gave me a better run at the next hill. But as I stated before, those days are long gone. It doesn't hurt the engines to run 55 all day and gearing them any faster accomplishes nothing in my opinion.

I love just going the back roads, even in my modern vehicles that can go a lot faster.

Maybe try a Spicer 3053A from an M35A2 (deuce-and-a-half) military truck. They are a "big truck" 5-speed transmission with overdrive. I believe they can be made to match up to an SAE bellhousing. I have no idea if it would fit, but you can find them pretty cheap and they are basically bullet-proof.

If you're not hauling/pulling, a single speed rear end with a closer ratio will do what you want. The 270 will turn decent RPMs, if I can get my monster up to 60 you should be able to take a smaller truck just as fast.

BUT! My numbr one rule on building vehicles: Moving is optional, stopping is mandatory.
These old brake systems aren't the best, tey definately weren;t made for the speeds we drive these days so make sure you keep up on your inspection & adjustments.
Something that big with brakes that weak,... If you plan on driving it like a new truck, equip it with better brakes. Like Grigg said, a dual circut master cylender is a solid investment in your longevity.

All the info is greatly appreciated. I don't know that I will be changing anything out just yet, but knowing that there are options gives me something to look at. I really don't want this to be a fast mover, just maybe a quicker work truck. I grew up with the smaller version of these and always had fond memories of those long dusty roads we'd drive up and down.
Thank you for all the advice.