- If there ever is a Mount Rushmore of off-road vehicles,
on the list has gotta be the Jeep Wrangler.
The Wrangler was built for the off-road.
Yeah, you can drive it on the streets,
but what this American four-wheeler wants most
is to taste the dirt.
You want to go trail riding?
Oh yeah, it does that.
You want to crawl up some rocks?
Oh, of course it does that.
You want to do a little mud boggin'?
You bet your muddy buns a Wrangler can do it.
The Wrangler was designed and engineered
to beat the Germans in World War II.
It's got Adolf-whoopin' DNA under the hood,
but what makes it so good?
Well, today we're gonna look at some of the engineering
that goes into one of the most popular
and most capable off-roaders ever built.
We're gonna be talking about coilovers.
We're going to be talking about suspension geometry.
We're talking heavy-duty, Dana 44 axles.
If you know, you know.
Wrangle up some breakfast or a late night snack,
depending on where you're at and what time it is,
let's get some B2B going.
(chill music)
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to bring you this episode of "Bumper2Bumper".
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Now, in my opinion, the TJ is peak Wrangler.
It's the favorite child of the family.
It brought back the famous round headlights
that were on the CJ.
It was the last Wrangler to use AMC parts
and it was the first Jeep
to feature the oh-so popular Rubicon package.
Now the goal of the engineers, on the TJ program,
was to make the Wrangler more comfortable
and usable on a daily basis while also building up
its off-road capabilities at the same time.
And one of the ways they did that
was in the suspension department.
They went from leaf springs to coil springs.
Mm, coil me, baby, like a snake.
(hissing)
If you take a gander under the majority of trucks
out there on the road,
you'll see that they're fitted with leaf springs,
and leaf springs, man, them things have been around
since the medieval times
when they were called carriage springs.
Little horse and pony and a little carriage.
Now these springs are made up of arc shaped pieces of steel
that are stacked up on top of each other
and then sandwiched together.
And the two ends of the leafs
are then attached to the frame of the truck
and the center is where the leaf attaches to the axle.
They can either be on top of the axle
in what's called spring over axle
or below, which is called spring under axle.
And regardless of where the leaf is located
relative to the axle,
it's the leaf that provides the support
and the weight of the vehicle
and any other weight added to it.
It's also used to locate the axle
and control the height of the truck or the SUV.
Now the upside of leaf springs
is that they can take a large amount of vertical load
being pushed down on them,
which is why heavy-duty trucks still use them to this day.
And this vertical load is also distributed
through the entire length of the spring.
Now, if a leaf breaks, for example,
you still have enough support in the other leafs
that you can actually make it back home.
They're also simpler in design.
At the end of the day, it's just steel strips
bolted to the axle and the chassis,
but one of the main disadvantages of leaf spring setups
is that they ride rough.
I mean, the springs can carry heavy loads
but when they're not loaded, they bounce around, like,
I don't know, let me think, bounce around like,
I don't know my eyebrows, apparently.
Now did you know that eyebrows
keep moisture away from your eyeballs
so that your vision stays clear?
Okay?
And there are also essential in nonverbal communication.
Anyways, you also can't tune leaf springs.
Now you can add leafs and you can take away leafs,
but that's pretty much it.
And maybe most importantly, in the off-road game,
they also don't offer as much flexibility and movement.
Now in nasty terrain, a leaf spring suspension
doesn't have the flexibility
to keep the wheels in contact with the ground as easy as,
mm, I don't know, a coil system would.
(upbeat music)
So in 1997, when the Jeep team released
their new TJ Wrangler,
they ditched the leaf spring setup from the previous model
and used coil springs on all four corners.
They called it the Quadra-Coil 4-Link System.
Now Quadra-Coil means four coils, we got that
and four links relates to how the frame
connects to the axles.
And we're going to get to that in a second
but first let's figure out why the TJ
updated its suspension with coil springs.
Now, instead of having long, heavy plates of steel
to act as your spring, the steel is coiled
and there's some obvious benefits to this one beam way.
You use less material to make the spring
so your suspension setup is lighter.
But the Wrangler engineers,
they weren't after necessarily weight savings,
as much as they were interested in
better ride quality on the pavement
and better off-road capabilities on the trail.
Now let's imagine a coil spring
is just a really stiff slinky
but even if they're stiff,
they're still more flexible than leaf springs
and this greater flexibility
allows more movement in the suspension system.
Now coil springs ability to flex
and bend, help it absorb potholes
and terribly paved bumpy roads
compared to its leaf counterpart.
But if you bought a Wrangler,
chances are you bought it to take it off-road.
So what are the off-road benefits?
Well you get a lot more articulation with the coil spring.
If you look at images of Jeeps, crawling up rock faces,
they look more like some Cirque du Soleil performer
than they do a freaking SUV, it's wild.
Leaf springs stick out in the front
and the rear of the vehicle
and they inhibit the approach and depart angle.
That's approach, going up a rock.
Depart, going down a rock.
Now with coil springs setups, you avoid that.
With the switch from leaf to coils,
the Wrangler got seven more inches of wheel travel,
that's the distance the wheel can move vertically
without bottoming out
either at the top or the bottom of its stroke.
And we talked about not being able to tune your suspension
with leaf springs moments ago.
Well, with coil springs,
you can choose your spring application
to match the terrain that you're driving over.
Let's go on a little field trip.
I'm going to hop in the old Jerry bus
and let's take a short trip.
We don't got to go far.
We're gonna go right over there to the back of my garage.
(upbeat music)
Welcome to the back portion of my garage
and behind me, I have a bunch of different types of springs.
And the first spring I want to talk about
is what's called a linear spring.
And I know it's a linear spring
because if I look at the spacing in between the coils,
they're all the same.
That tells you that the rate of compression
is the same throughout the entire length of the spring.
Now this is a 5.4 kilogram per millimeter spring.
That is the spring rate
and that tells you, in a linear spring,
that that compressive force,
that spring rate, is the exact same
throughout the entire stroke or length of the spring
as it's going through its travel.
Now, this spring isn't that the only type of spring.
There's also what's called a progressive spring,
and a progressive spring gets progressively stiffer
as you compress it.
And if you look at the spacing in between the coils
on the top portion of the spring versus the bottom portion,
they're different.
And that's because when you go to compress it,
the top portion soaks up that initial force
and then as you get stronger into there,
or you apply more force,
the bottom spring rate comes into play.
Now, that's not the only type of spring.
There's also what's called a dual rate spring.
And right here, I have a linear spring
and I have another linear spring.
This has one spring rate, this has a different spring rate.
Well, when they go to manufacturer a dual rate spring,
they take two springs, like this, with different rates
and they combine 'em into one continuous coil.
That's called a dual rate,
and also, I actually lied a little bit,
this is not actually a progressive spring,
this is a cup holder
and you put pens in it
and Fleabag gave it to me to use this as an example
and he wants me to give it back to him
but I'm probably not going to because I like it.
So those are all pretty solid reasons
to switch to coil springs.
But one reason the engineer's designed the TJ
to use coil springs
was that the previous generation Wrangler,
they had this problem and it was called axle wrap.
Now say you have an engine that's got a lot of torque.
Well, when you go to step on the gas,
that torque is transferred from the engine
to the drive shaft, to the axles, to the wheels.
In a leaf spring setup,
this causes the leaf to twist and bend into an S shape.
And the result of this is a loss of traction.
All that torque that could have been transferred
to the wheels is now being taken up
by the twisting of the leaf spring.
Not only that, it also causes the pinion angle to change.
Now that's the angle of the differentials pinion
in relation to the drive shaft.
And you don't want your pinion angle changing under load.
It creates a ton of drive line vibration
in the best of scenarios
and in the worst of scenarios, you can break stuff.
Not good, no thank you.
Now, the TJ and its Quadra-Coil suspension setup,
it helped improve the ride quality,
gave off-roaders the ability to tune their suspension
and it eliminated axle wrap.
Bing, bang, boom, jeepers creepers,
where'd you get those peepers?
(record scratching)
And when we talk about suspension,
there are three parts to focus on.
There's the weight support, that's your springs,
there's the dampening, that's your shocks
and then there's your axle location, that's your links
also called control arms.
So not only did the TJ use Quadra-Coil,
it used what's called a 4-link setup.
Now a 4-link setup means that your axles
are supported by four links.
Two upper arms connected to the top of the axle
and two lower arms connected to the bottom of the axle
with the other ends of the control arms
connected to the frame.
Now in general, when you hear the word link
that's anything that helps hold the axle in a certain place.
But when we say 4-link,
we're specifically talking about control arms,
and you need these control arms to locate the axle,
meaning, you want to keep the axle in a defined area.
The main function of the Wrangler's control arm
is to control the up and down movement of the suspension.
They support the vertical motion of the axles
while also keeping the axle center
from moving front to back.
Well, why would you want your axles
to not move from front to back?
Well, you don't want it moving around
in that direction, really, at all.
That's how you ended up breaking stuff.
Remember, we just talked about axle wrap.
That's a product of having an axle
being able to shift forward and back.
And there's another unwanted side effect
of not having links to support your axle,
and it's this nasty little phenomena called bump steer.
Bump steer is when you hit a bump on the trail
or road, wherever,
and it causes your car to want to change direction.
That bump causes your springs to compress,
which then causes some unwanted
articulation of your suspension
that ends up changing the steering angle of the wheels.
Your wheels are pointing in a direction
you didn't tell them to go.
So what did the Wrangler engineers do?
Well, they used a 4-link suspension setup
with control bars to control the fore and aft movement.
Fore and aft, that's just forward and back
it's just a fancy way of saying it.
But if you're sitting there thinking,
"Hey, Jerry, what about the side-to-side movement?"
Well, they used what's called a panhard bar
or track bar, mounted parallel to the axle
and that keeps it centered from side to side.
So by adding control arms,
they improve the TJ's directional stability,
its ability to put torque on the ground,
which improves traction
and it also prevents bump steer,
a common occurrence in older Jeeps.
Guys, you are now all masters in 4-link suspension.
You're officially certified B2B engineers.
We should make a sticker like that.
You guys want a B2B engineering sticker?
Drop a comment down below,
let me know if that's something you want.
I'll certify each sticker that goes out to you
and it is gonna be a lot cheaper
than actually going to college.
Also, a quick side note,
the engineers designed the Wrangler
so that the suspension geometry
prevented bump steer from occurring,
but in true Wrangler-boy and Wrangler-girl fashion
when you start modifying your Jeep,
throwing lift kits on there
and changing your control arm lengths,
your suspension geometry is now not the same
and you get into more dangerous areas of the Wrangler
such as death wobble.
You want to know what death wobble is, look at this.
It's definitely terrifying.
A part of what makes the Jeep Wrangler so good
from the open trail to the technical rock climbs
are its solid axles.
There are two types of axles.
There's solid, also called straight axles
and then you got your independent rear suspension
or independent front suspension.
Now I'll let you guys debate in the comments
which is better,
but we're going to talk about solid axles.
And the Wrangler, to this day, still uses solid axles,
no fancy independent suspension.
"But why Jerry?"
Well, because if Jeep did that,
the Wrangler crew would burn Chrysler down to the ground.
They love their straight axle and here is why.
Now straight axles are simple and they're strong
and it's just a system of gears
and axles contained within a metal housing,
which transmits power to the wheels.
And the Wrangler uses solid axles on both the front
and the rear.
Now compared to independent front suspension
or rear suspension, these axles have less moving pieces,
which makes them easier to work on or even swap out
if you end up damaging them.
You don't have CV joints to deal with.
If you ever need to get inside the differential,
the cover is right there,
it's not buried in between the frame rails.
And the housing, it's made of cast steel.
So yeah, they weigh a ton
but they're heavy-duty, which adds to protecting the gears
and axles inside that housing.
And from a performance standpoint,
solid axles can put more torque to the wheels
since there are fewer parts
that the power has to transfer through.
So when the TJ was released, Jeep equipped its Wrangler
with some of the toughest axles ever made, Dana axles.
Now Dana has been making axles since the early 1900's
and almost every big name manufacturer, at some point,
has stuffed some Dana's under their rigs.
And the TJ's got Dana 30's, 35's
and the very popular 44's in the Rubicon
and those numbers simply identify the different axles.
In general for Dana axles, the larger the ID number,
the bigger the axle housing, axle shafts,
and the ring and pinion diameter.
The only thing cooler
than having Dana 44's on your Wrangler?
I don't even know.
Should I show 'em, should I Fleabag, should I show 'em?
We can put some fricking sweet donuts stickers on it.
(loud beep)
The great thing about the Wrangler
is that through its 33 year run,
they share a lot of the same stuff.
Now we've had four generations of the Jeep recipe
and that recipe has barely changed.
See, actually, did I say Jeep?
Shoot.
See, ah I did, see what I did there?
I said Jeep.
I know, but I meant Wrangler
and that actually leads me to my next point.
It's such the brand's identity.
Jeep would be nothing without the Wrangler.
It's really important
and if you want to know more about that story,
you should actually watch this episode of "Up to Speed",
it's a really good one.
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Bye for now.