Inliners International Forums General Discussion Drive Train rear end too low

Hi

My 56 gmc longbed (farmers truck) has rear end gears that are very low. I don't use first gear to start because of the gear ratio, and you can't get any decent speed on the highway either. My question, can you get replacement gears, or do you have to swap out the whole rear end. What ratio would I have, and what would be ideal for a driver.

Is your truck a 1/2, 3/4, or 1 ton? If it is a 4spd on the floor, even if you regear, I doubt you will use first unless you're hauling a load of hay up a hill or something. Your trans might be the SM420 I think which has a first gear of 7.something crazy low gear. But sure, I think you can regear the rear you have. Check Jim Carter's truck parts from the ads on this site. They sell all different ratios. If your truck is a 1 ton, you might have a 5.14 rear like mine.

It is a 1/2 ton with 4 on the floor as you suspected. How can I find out what the current gear ratio is, and what would be the ideal ratio for a driver. Not having to change the whole rear end would be a whole lot simpler to do.

56GMC, Like John wrote,you can change the gears in your diff w/o changing out the whole rear end.If you don't ever need to start out in 1st you've got a "granny" gear in there.The way I found out my rear end ratio was to raise up the back of the truck on jack stands, put a mark on the drive shaft,and another on a rear tire.Then,with the tranny in neutral,turn the driveshaft by hand while watching the chalk mark on the tire.Count how many times your driveshaft turns once you complete one full turn of the tire.That is your rear end ratio.Example:Drveshaft makes 3 1/2 revolutions once the mark on the tire has returned to original position.Rear end ratio= 3:55.When you do this make sure you chock the front wheels so the truck won't roll off the jackstands. God bless,Frank

'69 Chevy C-20
292 3spd.

Thanks for your help on this. Do you know what the gear ratio is on the most common 1/2 ton truck of this era, so I can try and source it.

Hey 56, according to what I've seen advertised, the 1/2 ton ratio is usually 3.90 which can be changed to 3.38, 3.07, or even 2.78. I see 3.07 being more common and will probably work well for you if you plan on using it as a work truck still and should see you having no problems starting off with a load with 3.07s since you got a granny gear. This is what I remember seeing advertised for your type of truck, I looked it up again. http://www.oldchevytrucks.biz/catalog2/0054.html