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.
29 Responses to “Are There Better Gears for a 1948 3600 Chevrolet Pickup?”
How much will this gear change affect the amount this 48 Truck can haul?
Hi Dennis. Great question! The ‘Ask an Expert’ section is currently for members of our online community. By becoming a member, you will have access to our expert’s knowledge. With your membership you will also receive discounts on products and hundreds of hours of Premium content.
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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.
Hi Dan. There are a lot of options when replacing the 3100 rear axle. Of course the easiest is to simply replace the center section with one from a 1955 – 1959 Chevy truck… It’s a straight bolt-in, there are new gear sets available to get you decent gear ratios, and you keep the majority of your rear axle in place.
On the other end of the spectrum Currie enterprises will build you a new 9-inch Ford axle to the exact width you want with 6-lug axle shafts.
Most everything else will require some degree of adapting.
The stock axle is approximately 58.5-inches wide from wheel mounting surface to wheel mounting surface.
There are options like most Dana 44 rear axles in GMC trucks in the 1960s were 60-inches wide, had 6-lug axles and had gear ratios from 3:21 to 3:92.
Some prefer to use Chevrolet S10 4×4 rear axles but will require wheel adapters to get the 6-lug pattern you’re after.
Mark
Classic Car Restoration Club
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..
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.
Hi Mark,
If you’re planning to use a 700r4 transmission, it has an overdrive gear which will help, but you need to change out the rear axle gears.
If your truck is a 3100, it came with 4.11:1 gears or 4.57:1 gears. these low gears are great for pulling stumps but no match for today’s roads.
I would swap out the gears to 3.55:1 rear axle gears available from Chevs of the 40s (www.chevsofthe40s.com).
That should give you the driveability you are looking for.
Wrench Safe,
Mark
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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
Hi Don,
Yes, according to Hollander’s Interchange Manual the 1946-60 Chevrolet Non-4WD 3600, 3/4 to 1 ton rear differentials are the same.
Hope this helps,
Mark
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Does your answer apply to the 1947 Chevy 3600 truck? And what would be a good replacement 4 speed trans for truck
Hello Ray,
Could you please provide us with a little bit more information as to what answer you are referring to?
Thanks
Becky
Classic Car Restoration Club Video Membership
I have a 1951 Chevy 3600. Looking to get rid of the rear end and the original engine and transmission.
Will this fix work on a 48 1ton 3800 pickup?
Hello Kip,
The 3/4 ton and 1 ton Chevrolet trucks share the same rear differential but not all of the rear axle components are interchangeable.
Thanks,
Mark CCRC Video Membership
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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.
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?
Hello Jim,
There are many great shifter options… and ask enough people and you’ll hear pros and cons on each of them.
I have converted 3-speed trucks using the Hurst Mastershift shifter (3667271) and found it worked really well, although some guys prefer a longer shift handle, and with a little digging you can find one to suit your needs.
Thanks,
Mark CCRC Video Membership
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I have a 1949 Ford F1 (Hope I can sneak in a Ford question). I there a later differential with higher gear ratios to “speed” things up?
Hello Tom,
Low gears are a common issue for many early truck owners as most were used as tools to move stuff and rarely seen as a vehicle for general transportation. In 1949 Ford commonly used gear ratios of 4.27:1 and 3.92:1 on F1 pickups. These are gear ratios that can make modern highway driving difficult or even impossible.
Many convert these trucks over to a more modern 9-inch rear axle that offer a wider range of gear ratios. While the 1957 to 1972 F100 9-inch axle is a close fit, it will still require some modifications, which commonly include shock mounts and sometimes pinion yoke to reconnect the driveshaft.
Another option is to locate a 3:73 higher gear rear axle for the F-1 that was offered from 1948 to 1950. These are a little harder to locate but they’re out there.
Finally you could change the gears in your rear axle. Here is one source that offers a 3:54.1 rear axle ratio gear set for your truck. If you’ve never done this though I would encourage you to get the hands on assistance of someone who is familiar with these axles.
Wrench Safe,
Mark CCRC Video Membership
Is there a similar option for my ’52 Chevy half ton? Came with 4:11 and some swap gears for 3:55. A direct change as you describe sounds way better. Thanks.
Trucks of the 50s often had very low gears. Your 50 Chevy 3100 is no different. If you have a set of 3:55 gears, I suggest that you go that route! Even if you’re not familiar with setting up a rear differential, it will be money well spent to have it professionally changed.
Wrench Safe!
Pretty old discussion but I’m rather new to the community here. To solve questions like this without playing the guessing game, use a gear calculator. As long as you have the correct information, a gear calculator will spit out all the information you need with a +/- 1 MPH accuracy, which might be more accurate than your speedo. You’re welcome to use a gear calculator I created to be used in Excel or Excel-compatible software. Download link below.
https://drive.google.com/open?id=0B3iyR3ENvnVsTTdkQ2ZZenFkTlk
You now need to reset the whole thing. Did you keep the original shims for the pioinn. The big thing is getting the torch of the pioinn nut correct. I beleive the 35 uses a crush sleeve. You should do a complete rebuild, since you took it apart. Change all the bearings and seals.
It is amazing I have the same question as the guy did with the 1948 chevy pickup. I have a 1985 chevy 3/4 ton with 4.10 gears.Thanks Guys for answering my question. May be I will go with a 3.90:1 gears. If I can find them. Any help with that?
The reason that most cars have a trssnmisaion is because a internal combustion engine can only run efficiently over a narrow range of rpms while the wheels must turn at a wide range of rpms. An electric motor can efficiently run at any rpm so it can drive the wheels directly without a trssnmisaion. If a car does not have a trssnmisaion, it does not need a clutch.
I have a 1973 mustang 351 Posi rear end original that makes a noise when in reverse. At 60 MPH I am about 2500 rpm.
Is there any gear I can replace it with and stay positrack to get more speed with less rpm ? .
Thanks for the question, the ’73 Mustang is a great car and when equipped with a 351ci engine and Traction Lock rear end, they can be fun cars to drive as well.
I’ll try to answer your questions in order.
You mentioned your rear axle was making noise in reverse. Typically, my first question to you would be to describe the noise… It is not uncommon for the car to have a little whirring noise in reverse as the gears and wear on the gears occurs chiefly in the forward motion. Although if it is excessively loud or if it is more of a grinding sound, I would advise taking it to a mechanic and have them listen to it as well. It could be a bad bearing, rear axle clutch, or even severely worn/broken ring and pinion gears.
1971-1973 Mustangs shared a semi-floating hypoid rear axle. While most six- and eight-cylinder Mustangs used an eight-inch rear end, high-performance cars came with a nine-inch rear end.
You didn’t mention which rear axle was in your car, as Ford made two size ring gears and this is what is referred to when trying to figure out if you have an 8″ or a 9″ rear end. The housing for 8″ rear ends is more rectangular while the 9″ is more round.
A number of final drive ratios were available both in open and locking forms of rear axles; ratios available with the limited-slip Traction Lok or Detroit Locker rear end included 3.00:1 (most common), 3.25:1, 3.50:1, 3.91:1 and 4.11:1.
Additionally when trying to calculate what your car likely has for rear axle gears it is important to know if the car is equipped with a manual or automatic transmission. With automatic transmissions not all of the engines RPM’s are transferred to the drive shaft, (this is one reason modern automatic transmissions feature a “Lock Up” torque converter).
After making a few assumptions about your car (Tire Diameter and transmission) the fact you are at 2,500 RPMs at 60 MPH, and doing the math, it is very likely your car is equipped with 3.00:1 rear axle gears. Although doing the math is a lot easier with calculators like this one available from Richmond Gear (www.richmondgear.com/2.html<http://www.richmondgear.com/2.html>).
There is not many gear sets available with “higher ratio” than what you currently have and you may not be pleased with the results of moving to higher gears. If top end speed is your only concern, then yes, higher gears will help, although you will sacrifice lower speed performance, as the taller gears will make the engine work harder to get up to speed. If the majority of your driving is “In-town” you may not see any change in fuel mileage because of this.
I hope this helps!
Wrench Safe, Mark
It sounds to me you had to pull the ring gear to itasnll (fit) the lunchbox locker.If you did not do anything else like remove bearings or shims, you should be good to go.You didn’t really replace anything but the spyder gears, and the ring gear shouldaccurate enough to bolt back on with no changes.
While the torque crasacterihtics of an electric motor do not require a clutch or a transmission they are often not taken out of a vehicle prepared for conversion. The main reason the transmission is left is to keep a reverse gear. Typically a reverse gear is a different ratio making it easier to go slower and the electric motor will not have to be reversed electronically. The speedometer is also often connected to the transmission. Keeping the clutch may make connections easier but the inertia of an internal combustion engine is more than that of the replacement electric motor. In many instances shifting the manual transmission may not require the clutch. The conversion process typically removes the engine, exhaust and fuel systems. The transmission is left in place as well as the associated bell housing and/or clutch if a manual transmission. An adapter plate is installed over the housing. The electric motor is installed and anchored to the frame. Batteries are positioned and installed in series and a motor controller is connected to the former gas pedal. Most modern batteries will benefit from a battery management system. Some method has to be provided to charge the batteries. One battery is often isolated to operate the 12 Volt electronics of the car: lights, horn etc. This will need its own charging circuit.The only pump for an automatic transmission but external to it might be a cooling fluid pump. Electric pumps for power steering or power brakes may be added if necessary.