Are 2WD and 4WD Transmissions Really the Same? The Truth Will Surprise You!
The main difference between a 2WD transmission and a 4WD transmission is The 4WD transmission is designed to mate up with a transfer case to engage 4WD and Lo-range (4L). Also, The Output shaft of a 4WD is shorter than a 2WD version.
After owning a variety of 4x4s with over 20 years of offroad experience, I’ve often wondered what makes a 2WD transmission different from that of a 4WD. I was also curious to know if a 2WD transmission can be customized to function as a 4WD transmission with a few modifications.
Later in this article, I cover the differences as well as the process of converting a 2WD transmission to a 4WD version and what components you’ll need to successfully pull it off.
But first, let’s look at what the core differences are in more detail between the two transmissions.
If I look at the basic shape, structure, and internals of a 2WD transmission compared to a 4WD derivative then i would say they look very similar in many ways. As stated at the outset, the main 2 differences are the output shaft length as well as the ability to mate with a transfer case.
These are 2 key differences to take note of. But have you ever wondered if a 2WD transmission can be converted to work in a 4WD truck?
Let’s find out…
Will A 2WD Transmission Work In A 4-Wheel Drive Truck?
NB: This is quite a major job and some specialized transmission expertise are required to pull this off.
So, the first thing you want to do is remove the entire transmission to give you easier access to the internals. Once out, set yourself up nicely so we can remove the tail-shaft housing. There are usually about 6 high tensile bolts you will need to remove to get the cover off. Save those bolts for reuse later.
You can remove and get rid of the tail-shaft housing since it won’t fit anymore once the modification is complete. The rubber O-ring that seals the housing can be discarded as well. You’ll need a new one.
- Remove the sleeve that is seated on the tail shaft.
- Remove and discard that as well.
- You’ll notice 2 holes and the opening around the output shaft.
- The seal that sits around the output shaft needs to be replaced with a 4WD shaft seal.
- Make sure that the seal is well-seated and secure.
- Give it a few good poundings to ensure it’s sitting 100% secure and flush.
- Next, you want to close up the 2x holes on the transmission case.
- You’ll need to find a pin or fabricate a pin to close those holes.
- Take extra care not to allow any metal shavings to fall into the transmission case.
- The best way is to tap a thread into those holes and then plug it.
Next, you’ll need to size the output shaft and cut it shorter. You can measure the correct length by using your 4WD adapter plate. Mark the length and cut the shaft.
Converting a 2WD to 4WD transmission summary:
- Strip and remove transmission from truck
- Remove tail-shaft housing
- Discard the rubber O-Ring
- Remove the tail-shaft sleeve and discard
- Replace the tail-shaft sleeve with a 4WD version
- Secure seal properly
- Tap threads into the 2x open holes in the transmission housing
- Plug all holes
- Measure the output shaft length with your adapter plate
- Cut the tail-shaft
Next, let’s look at the 2WD vs 4WD differences in more detail…
2WD vs 4WD Differences
The main difference of a 2WD is that it only propels 2x wheels, which is either the 2 front or the 2 rear wheels. 2WDs have no transfer case or extra front driveshaft. You also won’t have a low range due to a lack of a transfer case with lower gearing. Alternatively, A part-time 4WD can drive in 4WD or 2WD mode by deactivating 4H to engage 2H Which propels the rear wheels only.
Conversely, a part-time 4WD when driven in 4H is propelled by all four wheels. A 4WD can either be a permanent 4WD or a part-time 4WD. Permanent 4WD are always in 4H and do not have the 2H option.
A permanent 4WD means the engine propels all 4 wheels forward. One way It accomplishes this is by employing a viscous coupling between the front and rear driveshafts. This is necessary to allow the front and rear drive-shafts to rotate at dissimilar t speeds, which is necessary when cornering on a high traction surface to prevent drivetrain “binding” or “windup”
Drivetrain “binding” occurs when you are driving a part-time 4WD on a high traction surface like pavement and there is not enough slippage to allow the front and rear driveshafts to rotate at dissimilar speeds while cornering. THis is necessary since the inner wheels closest to the corner side will rotate slower than the two outer wheels. This is because the turning radius is larger on the outside than on the inside.
Next, let’s look at the conversion process for a 2WD truck to a 4WD truck. We’ll use the Toyota Tacoma as an example since it’s one of the most popular pickups that were produced in both 4×2 and 4×4 versions.
Converting Your 2WD to A 4WD (Components & Customizations Needed)
Converting a 2WD to a 4WD used to be viewed as sorcery and wizardry in previous years, however, it’s becoming more and more popular with companies fine-tuning this craft by specializing in these conversions.
Why would you consider a 4×2 to 4×4 conversion?
- Emotional or Sentimental value
- You’ve overcapitalized on accessories
- Fun project to take on
Notice, that cost-saving is not mentioned as an option since selling your 4×2 and buying a 4WD Tacoma is always going to be a faster and cheaper alternative. If it’s a cost-saving you’re after then a 2WD to 4WD conversion is not the way to go. Whatever the reason, the good news is this conversion is possible and becoming more popular.
Conversion process basics and components needed:
YOU WILL NEED:
- A 4WD transmission from an FJ Cruiser with a rear adapter to mate up with the transfer case
- Cut open your floor to allow the transfer case shifter up into the cabin
- A custom cross-member fabricated up since the original or 4WD from a Taco won’t fit.
- New front drivetrain components
- New Front diff
- New Front CV axles along with all the 4wd front hubs, seals, and appropriate dust covers
- A RST ADD harness so you can activate your front diff
- 2x Custom front half-shafts
- Custom exhaust work to accommodate the new transfer case
There’s a link below to the guys at Rocksolidtoys who are pioneers and specialize in this type of 4WD magic.
REAL-WORLD FORUM Opinions & Experiences
All the internals and the cases are the same with the exception of the tail shafts and the tail shaft housings (A45DF has a stubby shaft and housing to facilitate mounting of the transfer case). So technically you could swap these parts but it would require almost a complete tear-down of both transmissions to do so.
https://www.toyotavantech.com/forum/showthread.php?633-are-2wd-4wd-transmissions-interchangeable
The tail shaft of the transmission would be different, but I don’t see why you couldn’t hang the 4wd trans and t-case in it if you modify the driveshaft. I think they’re the same U-joints. It would just be a useless transfer case. Personally, you’d be better off selling the good 4wd one with the t-case and buying a 2wd trans. you’d probably come out ahead.
https://www.gmt400.com/threads/4wd-trans-and-transfer-in-2wd-truck.56749/
Helpful Resources
- https://www.gmt400.com/threads/4wd-trans-and-transfer-in-2wd-truck.56749/
- https://www.toyotavantech.com/forum/showthread.php?633-are-2wd-4wd-transmissions-interchangeable
Final Thoughts
Hopefully, by the end of this article, you’ve learned what the differences are between a 2WD and a 4WD transmission. We also touched on what is involved in converting a 2WD transmission to a 4WD and lastly, we looked at converting a 2WD to 4WD and which components you’ll need.