Are There Better Gears for a 1948 3600 Chevrolet Pickup?

By Classic Car Restoration Club Editors

Chevrolet Gears

Q.

I have a 1948 3/4 ton Chevy truck that has all of the original parts, which is why the top speed is around 45 miles per hour. I would like to increase the speed to at least 55 miles per hour to be able to drive it on the freeway more safely. I was told that I can achieve this by changing the rear axle with another vehicle’s rear axle. Is this true? and if so, which vehicle’s rear axle will allow me to do this? If this is not true, how can I achieve the increased speed without changing too much? I would like to keep it as original as possible.

A.

I am probably not the first to tell you but many who own early pickups share your problem. Let’s face it early haulers were designed to do just that. HAUL. Low gears were needed to haul heavy loads with relatively small displacement engines. Common gear ratios for 1948 Chevrolet ¾ ton pickups were 4.57:1 and 5.13:1, and while these low gear ratios did the job serving as a torque multiplier they did sacrifice top speed in doing so.

You mentioned wanting to keep the vehicle as original as possible, so we’ll rule out the possibility of upgrading to a more modern overdrive transmission and focus on the least invasive upgrade.

Your truck shares the same rear differential as the 1967-1972 ¾ ton Chevrolet truck. And automatic transmissions versions of this truck came equipped with 4.10:1 gears, and a few of my sources claim 3.90:1 gears were available. In either case the upgrade should easily get you to your target top-speeds and the rear differential can be swapped out without having to remove your rear axle housing, or even the need to jack it up, given its floating axle design. While personally I have never made this upgrade my sources claim the entire process can be completed within a couple of hours.

Best of luck with your project!

Wrench Safe.

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16 Responses to “Are There Better Gears for a 1948 3600 Chevrolet Pickup?”

  1. Dennis

    How much will this gear change affect the amount this 48 Truck can haul?

  2. Dan

    I have a 52 Chevy 5 window truck . The 235 6cly is trashed . I have a Chevy C10 350 and trans I what to install. I need to replace the old tubed rear end preferably something with 6 bolt hubs. Thanks for any info.

  3. Ricktherik

    Patricks truck parts in arizona?..thru have all your chevy parts.. an more about those gears an 6 cylinder motors thanmost places..gear upgrades..hiway gears..denise will point you in the right direction..

  4. Mark milton

    Hi iv got a 1948 chevi pick up and it's got an original diff I'm running a 305 camari 4 letre engine with a 4 speed muncie which I'll change to a 700r4 box can you tell me what diff ratio I can change too to make it go 70 at low revs as it's a shocking 45 mph thanks don't care what I'll change to make it better many thanks mark.m.

  5. Don Albert

    You mentioned that the rear differential on a 1948 3600 Chevy is the same as a 67-72 3/4 ton. Is this the same for a 1952 3600 Chevy differential? Thanks Don Albert

  6. Ray Darwin

    Does your answer apply to the 1947 Chevy 3600 truck? And what would be a good replacement 4 speed trans for truck

  7. William T

    I have a 1951 Chevy 3600. Looking to get rid of the rear end and the original engine and transmission.

  8. Kip wilhelms

    Will this fix work on a 48 1ton 3800 pickup?

  9. Danny

    What the heck, up until '54 the rear ends in those trucks were torque tube differentials and are NOT the same as later rear ends, especially the '67 to '72 modes stated in the article.

  10. Jim Weese

    Have a 1964 chevy pickup and want to know how hard it would be to switch from column to floor and bypass 3 on tree only because I cant find parts for linkage under hood. What is the best conversion shift to use?