Ever wonder why the front axle is on the driver side?

psrivats

TJ Addict
Supporting Member
Jun 4, 2018
1,397
OR, USA
I was very curious and looked this up. Find the below in 4 wheeler network. Very interesting to me .. old timers on the forum may already know this.




Why do the front axles under most 4x4s have a driver-side differential?
@fsj_travis
Via Instagram @cappaworks


techline-jeep-wrangler-dana-44-rubicon-front-jl-axle-mopar.jpg


The reason for the differential location is actually a lot less glamorous than you might think. Interestingly enough, most front differentials didn’t start out on the driver side. Many older 4x4s such as Dodges, GMs, Jeeps, and Toyotas have a passenger-drop front axle. It wasn’t until later that they switched, matching the driver-side differential drop of the Ford 4x4s. It just so happens that the switch was around the same time as the industrywide changeover to chain-driven transfer cases in place of gear-driven units. In most cases, the differential location is dictated by packaging and available clearance in a chassis. In other cases, however, vehicle-manufacturing budgets appear to have come into play.

We reached out to retired Jeep old timers Phil Toney and Mike Smith to get a firsthand story. The reason for the differential location change that Jeep made from the passenger side on the CJ in 1986 to the driver side on the YJ Wrangler in 1987 might surprise you.

Phil Toney:
“With the left-side differential, the engine is offset slightly to the right, so there is better side-to-side weight balance with a driver behind the wheel than with the right-side differential. One problem we had with the right-side differential was with V-8 CJs, where under vigorous driving the right-side differential would hit the V-8 oil filter/pump, causing loss of oil pressure and possible engine failure. A cross-frame brace was added, which helped reduce engine movement. Other considerations were packaging, Quadra-Trac transfer case usage, and so on. Historically, differentials were on the right side, but the move to NP transfer cases with YJ drove the differential to the left side.”

Mike Smith:
“For the ’80 model year, there was a joint program to develop a new transfer case for the Jeep Wagoneer and Cherokee, plus develop the new AMC Eagle. The packaging of the front axle on the Eagle required the differential to be on the driver side. In order to justify the cost of developing the Eagle, it was decided to use a common NP transfer case. The NP119 model was used in the Eagle and the NP219 model with low range was used in the senior Jeep line. When they incorporated two-wheel drive in 1981, the numbers changed to the NP129 for the Eagle and NP229 for the Jeep. This forced the Jeep to change the differential to the left side. When the CJ went out of production in 1985 and the YJ went into production in 1987, the Dana model 300 transfer case used in the CJ with the right-side front axle was no longer available. The YJ was forced to use the New Process transfer case. Thus, the reason for the difference between the CJ and YJ front axles. It was purely for packaging.

As an aside, there were budget constraints during the time of the development of the Eagle. Jeep had a generous budget, but the passenger-car group had a lean budget. Therefore, in order to justify the Eagle, it was necessary to hide much of the cost in the Jeep budget. That of course included the new transfer case, which was the highest-cost item, and a change to the front axle on the Jeep to accommodate it. We could have developed an NP transfer case to accommodate the right-side front axle on the Jeep far cheaper than the tear-up required to change to a left-side front axle. That’s just how things work. So, the bottom line as to why the Wrangler has the differential on the left side is because of the AMC Eagle.”
 

TJ Hunnicutt

TJ Enthusiast
Supporting Member
Apr 5, 2018
628
Texas, USA
Seems to me that this all works in our favor because, as we pick our line, it is much easier to determine what to avoid, so as to keep from hitting the pumpkin, when it's (pretty much) directly under our butts than if it were under the passenger seat. Imma thinkin'
 
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Squatch

Master Thread Derailer
Supporting Member
Oct 25, 2017
4,554
Everett, Wash, United States
I was very curious and looked this up. Find the below in 4 wheeler network. Very interesting to me .. old timers on the forum may already know this.




Why do the front axles under most 4x4s have a driver-side differential?
@fsj_travis
Via Instagram @cappaworks


View attachment 77229

The reason for the differential location is actually a lot less glamorous than you might think. Interestingly enough, most front differentials didn’t start out on the driver side. Many older 4x4s such as Dodges, GMs, Jeeps, and Toyotas have a passenger-drop front axle. It wasn’t until later that they switched, matching the driver-side differential drop of the Ford 4x4s. It just so happens that the switch was around the same time as the industrywide changeover to chain-driven transfer cases in place of gear-driven units. In most cases, the differential location is dictated by packaging and available clearance in a chassis. In other cases, however, vehicle-manufacturing budgets appear to have come into play.

We reached out to retired Jeep old timers Phil Toney and Mike Smith to get a firsthand story. The reason for the differential location change that Jeep made from the passenger side on the CJ in 1986 to the driver side on the YJ Wrangler in 1987 might surprise you.

Phil Toney:
“With the left-side differential, the engine is offset slightly to the right, so there is better side-to-side weight balance with a driver behind the wheel than with the right-side differential. One problem we had with the right-side differential was with V-8 CJs, where under vigorous driving the right-side differential would hit the V-8 oil filter/pump, causing loss of oil pressure and possible engine failure. A cross-frame brace was added, which helped reduce engine movement. Other considerations were packaging, Quadra-Trac transfer case usage, and so on. Historically, differentials were on the right side, but the move to NP transfer cases with YJ drove the differential to the left side.”

Mike Smith:
“For the ’80 model year, there was a joint program to develop a new transfer case for the Jeep Wagoneer and Cherokee, plus develop the new AMC Eagle. The packaging of the front axle on the Eagle required the differential to be on the driver side. In order to justify the cost of developing the Eagle, it was decided to use a common NP transfer case. The NP119 model was used in the Eagle and the NP219 model with low range was used in the senior Jeep line. When they incorporated two-wheel drive in 1981, the numbers changed to the NP129 for the Eagle and NP229 for the Jeep. This forced the Jeep to change the differential to the left side. When the CJ went out of production in 1985 and the YJ went into production in 1987, the Dana model 300 transfer case used in the CJ with the right-side front axle was no longer available. The YJ was forced to use the New Process transfer case. Thus, the reason for the difference between the CJ and YJ front axles. It was purely for packaging.

As an aside, there were budget constraints during the time of the development of the Eagle. Jeep had a generous budget, but the passenger-car group had a lean budget. Therefore, in order to justify the Eagle, it was necessary to hide much of the cost in the Jeep budget. That of course included the new transfer case, which was the highest-cost item, and a change to the front axle on the Jeep to accommodate it. We could have developed an NP transfer case to accommodate the right-side front axle on the Jeep far cheaper than the tear-up required to change to a left-side front axle. That’s just how things work. So, the bottom line as to why the Wrangler has the differential on the left side is because of the AMC Eagle.”
Thanks for sharing that, @psrivats. I never knew why, and now I do! (y)
 
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JEEPCJTJ

TJ Enthusiast
Supporting Member
That is very interesting.

FWIW, just yesterday as we pulled up the driveway with my son driving, he said hey look at your Jeep with the pumpkin on the passenger side. With him being a diesel mechanic and seeing that CJ hundreds of times and us rarely riding together, I figure he was just trying to make some conversation to which I replied, You gotta have something over there to counter balance the driver.

Phil Toney may be right about offsetting the engine but I don't think his comments about the V8 applied to the YJ but he has inspired me to do some measuring of where the engine is in all three of our Jeeps if the weather ever gets better.