The Stovebolt Site Forums The Parking Lot Big Bolts gearing

Hi, guys
What are my options for getting slower rpm's at cruising speed?

Engine? Trans? Truck size? Routine use? Disc brakes?

In general:

- lower-ratio rear end
- lower high-gear ratio transmission
- larger diameter tires
- drive downhill as much as possible

Post anwers to EdPruss's questions - people will post opinions/options.

My truck has a 235 ( I think) 4 speed transmission, general use, no hills in southwest kansas so downhill is not an option!

Engine? = 235 (or, maybe 216) - what is the engine serial number?

Trans? = 4-speed - 1949 4-speed SM420 - open or closed driveshaft?

Truck size? - ?

Routine use? - general use, no hills in southwest kansas so downhill is not an option

Disc brakes?- original 1949-style brake system?

Dont know the serial#. Original 4 speed open drive shaft. Truck size is 4100. Original brake system

Getting them to go faster can be accomplished in a number of ways, and many folks on the board have used various methods with success. It must be remembered that once you start making modifications for speed, upgrades to the braking system should be strongly considered. Also, the power requirement to maintain higher speeds goes up dramatically and you might find your stock engine struggling. All that said, there are a number of options. Although I'm not that familiar with the 4100 size: There are several 5 speed transmissions with an overdrive that can be installed, with varying amounts of modification needed. The rear axle can be changed with one from a more modern truck to obtain a better axle ratio. It might also be possible to add an auxiliary transmission or overdrive unit to the truck between the stock transmission and the rear axle. I'll leave the model numbers to another member with swap experience. I don't always have luck with the search feature, but there are past posts available covering many options.

Someone will chime in with more options and some specifics about how to accomplish the various mods.

Like said above, disc brakes might be nice for increased speed.

Some Saginaw 4 speeds with side shifter arms also come with an OD on the rear. I don't know the MN, someone here will no doubt chime in.

Get everything in good shape first before modifying a bunch of stuff. My 46 2-ton will run on the interstate at 55. I have seen it above 60 but the engine was not sounding good. The only modifications I have made are to the brake system. As said above, you must be able to stop if you plan to go faster.

I've just never been in that much of a hurry to where I had to push an old truck. If I get in that much of a hurry, I failed to plan

The old '48 GMC and '51 F8 I drove when I was a kid, I don't think I ever got em up over about 35. No need to. Besides, if I broke it with too much speed, I'd have to answer to Dad! (That lesson stuck)

They were designed to go 40-50 miles an hour, tops, and go forever that way. They do a great job at it, too!