The Stovebolt Site Forums The Parking Lot Big Bolts How fast will my truck go?

Im currently bringing a 48 2 ton back to life.
It has the 248 with a 4 speed and two speed rear.
I was just wondering if someone could enlighten me on how fast this truck will go once its up and running. Thanks!

1948 GMC 350 (2-ton) with SM-420 4speed and 2-speed rear.

Without knowing the gearing on the 2-speed rear, I'll venture a guess of 45 mph comfortably on a straight/level road, and 55 mph would be an exciting ride.

Do you have good tires.
Do you have good brakes (and a good hydrovac), all properly bled and adjusted?

How long will it take to stop is a good question too ;-). I'm hoping for 55-60

More important is how fast will it stop. Get that in order before anything else. I just sold my 46 2-ton to a guy in Arizona. Tophat is his user name on here. Look him up and if he is close to you, ask for a ride. I updated the front brakes to disc and it will STOP.

I have a 1942 1.5 ton duelly with a 235 4 speed (compound) Wide open I had it topped out at a whopping 42 MPH...Thought the thing was going to explode lol Comfortably I can drive it 35-37 mph as she seems to be happy there. These larger Big Bolts dont stop very well so use caution.

Gregg

Alright, thanks for all the help. Is there a transmission swap i could do to go 55-60 comfortably? Maybe i have to lose the two speed rear? im new to all of this! Im obviously not looking to set any land speed records but id like to be able to make the 20 mile drive into town without making too many people unhappy haha.

Are you going to haul heavy loads or just a cooler and lawn chairs?

The factory transmission and rear were engineered to work with the power the engine has to offer, are you planning an engine swap as well?

Mike B

Getting that rig up to 55-60 is a pipe dream, and no, it won't be comfortable. It will be all over the road, and if anybody else is on the road with you, you'll be a deadly hazard to navigation. Be absolutely sure you rebuild the brakes, steering, and suspension to "factory new" condition before you even consider any sort of gearing upgrade. 2 speed rear axles have two basic operating modes - - - -"slow" and "slower". The 248 with the 2-speed should top out around 45, no matter what you do to it other than swapping to a higher ratio single speed rear end. Then you'll have a really big "Cowboy Cadillac" that will be worthless for carrying the kinds of loads it was designed to haul.
Jerry

My 46 2-ton that was still running the splash lubricated babbited rod bearings. It could run up to 55 comfortably on the interstate. I had it 63-65 a few times, but it didn't feel right! 55 wasn't bad. I had rebuilt the engine with .030 over pistons. Everything else was stock internal and only upgrade to a Bosch blue coil externally. Stock induction and a 2 1/4" exhaust pipe on the stock manifold. 8.25 tires in the back with a single speed rear end.

Gotta make sure the thing stops and steer's as it should first. If you want a faster driving truck, consider a chassis swap. I'm not a big fan of that, but it would be an easier way to go to just put your cab on another chassis!

I also routinely had the bed loaded with 8,000-12,000 pounds worth of steel. It was comfortable at that, but would only reach about 40...

Decide what you want the truck to do and plan the build.

Oops, hit the wrong button there. Can anyone share the secret formula to estimate top speed if the gear ratios are known? I ain't that bright can push buttons on a calculator. Thanks.

Top speed is whatever you think your truck can reach.

Here are ways to determine top speed are various RPM for various "equipment".
http://www.csgnetwork.com/multirpmcalc.html

An important factor is what maximum RPM you want (or, what RPM you think your engine can safely maintain/sustain).

My 52 Two Ton runs comfortably at about 45 and that's it. I don't try to push it any faster because the engine is wound very tight if I do.

Kevin

Thanks for all the help. Sounds like ill have to put a new drivetrain in it if i want it to be a practical truck for me to use.

A few eons ago a buddy bought an a old '50's dodge panel truck and we added an overdrive unit from a similar year car. With that he could get that old flat head really cruising on the highway, with an electric shift he worked it like a 2 speed rear end. Has anyone ever done something similar with a big bolt? Is a there an overdrive made that's tough enough? Would be a cool solution to keep all the low range power but "slide it on down into overdrive" for highway travel. Just a thought from a restless mind...