Anatomy of a Jeep control arm, and why it’s time to upgrade

This tech article is dedicated to all you XJ/MJ, ZJ, and TJ/LJ owners out there.  In my time I’ve owned a small fleet of Jeeps.  If you count the ones my immediate family has owned that number all but doubles.  The majority of Jeeps the driveway here at the house has been home to have all been from the mid-to-late 90’s and early 00’s.  Most of you probably know this, but in case you didn’t, they all share the same control arms.  That means they’ve all shared the same problems.

The old front lower control arms off my 1997 Grand Cherokee
160,000 miles that weren’t exactly “easy” miles

In this article I’ll go over the basic anatomy of the stock OEM Jeep control arm found on XJ’s, MJ’s, TJ’s, LJ’s, and of course ZJ’s.  After that I’ll cover the drawbacks and flaws in these arms and why it’s time to upgrade to new arms.

What do they do?

The control arm on your Jeep does the job of locating the axle front-to-back.  Consequently the track-bar is what locates the axle side-to-side.  Together the four arms (two upper and two lower) along with the track-bar keep the axle under your Jeep where it should be.  That not only means they have an important job to do but it also means they are on the front lines of taking some pretty nasty abuse. Every bump, pot hole, rock, tree stump, and curb you hit while driving is felt by your control arms.

Basic blowout of a stock Jeep front suspension

Anatomy of a control arm

You’re probably asking, “okay, so how do they work then?”  A control arm is basically a fixed link with two pivot points.  One attaches to the body and one attaches to the axle.  These points allow the suspension to cycle up and down.  For ride quality these pivot points are comprised of a rubber bushing that is pressed into a sleeve that is tack welded to the control arm.

New OEM arms are available through Mopar Parts
You can see the rubber bushings on either end
You can also see how the shape is dictated by the stamped sheetmetal

The arm itself is nothing more than a “U” shape stamped piece of sheet metal.  This shape is relatively strong but also light weight.  It’s also open which prevents water and debris from building up and rusting it from the inside out.  More importantly it’s cheap.  Think of how many Jeeps are on the road.  Every TJ, LJ, and ZJ have four lowers and four uppers.  Every XJ and MJ  run a pair of each.  That’s 100’s of 1,000’s of control arms.

Common sources of failure

The first point of failure on the OEM control arm is no fault of it’s own.  The enemy of the rubber bushings at either end of the control arm is time.  The simple passage of time will cause the rubber in those bushings to break down.  Even if someone found a brand new virgin 1997 Wrangler TJ with 3 miles on the clock the rubber bushings in those control arms would be 20 years old.   Rubber is natural.  When exposed to the elements and temperature cycles is slowly breaks down.  It’s just how it is.

Now, take a similar vintage Jeep and driving it for 20 years and you’ll find the next source of failure.  Impacts are the next source of failure of the OEM control arm.  This comes about in three different ways.

  • First, impact on the rubber bushings eventually breaks them down.  Coupled with age the rubber just looses it’s give and take over time.  Think about a rubber band.  How many times can you stretch a rubber band before it just snaps?  Same goes for the rubber bushings in your control arms.  They can only take so many impacts before they snap, or more accurately collapse.
Degraded stock rubber bushing
  • Second, impact on the control arm can cause the tack welds holding the bushing in place to fail just allowing the bushing to “float” in the control arm.  This can cause vibrations in steering or even the dreaded DEATH WOBBLE.
Yeah, the bushings just fell out when I removed the arms.
You can’t even see the tack welds any more.

Okay… so maybe I hit a few too many rocks.

  •  Third, impact on the control arm can cause it to buckle.  Let’s be honest, most of are doing things with our Jeeps that would make even the most seasoned of automotive engineers cringe. Hit one too many rocks, curbs, or stumps and eventually the thing metal of the control arm will give up the ghost and go from straight to bent with relative ease.  This is compounded by the factor above of time.

Buckled upper control arms from my ’97 ZJTop: Passenger side
Bottom: Driver side
Yeah, pertty bad.
Top: Passenger side
Bottom: Driver side

Top: Passenger side
Bottom: Driver side

Buckled passenger side lower control arm on my ’04 LJ
I blame Moab

Why it’s time to upgrade

If you’re reading this chances are you’re not driving a mall crawling pavement princess.  You are also the type to not give up on your Jeep just yet.  So I’m telling you right here right now if you’re running stock control arms you better save your pennies and upgrade them ASAP!

“But why?” You ask.  “Why not just replace the bushings or buy new reproduction arms?”

Here’s the deal, replacing bushings is an option.  I did that on my 1997 ZJ shortly after I got it.  I got the Jeep for a pretty good price so it wasn’t surprising it needed a little work here and there. The arms were still straight but the rubber bushings were just over 10 years old at the time with around 130,000 miles on them.   With that in mind I opted to just replace the worn out rubber bushings with polyurethane ones.  I did the work myself to save time and after a long day in the shop All but four bushings (rear uppers) had been replaced (and they were skipped because the torch ran out of fuel).

Now, before you think, “Awesome.  That’s what I’ll do. I’ll just replace the bushings.”  Check out these photos:

The thin sheetmetal fatigued enough to tear
(Sorry for the out of focus shot)
New bushings won’t prevent this kind of fatigue
The axle end of the stock arms are very vulnerable.
Most aftermarket arms are smaller and do not hang down past the mount.

As you can see even with new bushings the weaknesses inherent in the OEM design reared their ugly heads a few years later.  I was chasing a nasty case of death-wobble and a very persistent  steering shimmy even when I wasn’t screaming the “OH MY GOD WE’RE ALL GOING TO DIE” death wobble chant.  I had told myself, “Oh, it can’t be the arms. I already replaced the bushings.”  Sure enough when I finally decided to get new arms the bushings literally FELL OUT OF THE ARMS.  Can’t make this shit up even if I tried.  So yeah, you’re due for new arms.

My own personal take on suspensions and why you get what you pay for

Now, let’s jump back in time just a little.  I picked up the LJ in the fall of 2014.  Having learned from past mistakes I knew I wasn’t going to bother replacing just the bushings.  I knew a full set of upper and lower arms were in my near future.  However, despite being 10 years old with 140,000 miles on it the Jeep drove really well.  No death wobble.  No shimmy. No vibrations.  The arms were all straight.  Seeing as the Jeep appeared to be an off-road virgin I figured I’d be good for a year or two before I would “need” new arms.  I also opted to leave the suspension alone for the 2015 trip (and we know how well that worked out).

While doing the JKS JSpec lift earlier this year I gave the arms another once over.  They were all straight and the bushings felt tight.  I again procrastinated replacing the arms thinking they’d be a nice upgrade to do before the 2017 trip.  Then Moab happened.  Yes, I blame Moab.  I can’t say it was ‘Top of the World’, ‘Kokopelli’s Trail’, or ‘Elephant Hill Trail’ but somewhere along the line my front lower control arm on the passenger side buckled.  The whole way from Moab to Flagstaff for Overland Expo and the whole way home from Expo I fought death wobble and a nasty steering shimmy.  And that, my friends, is why there are eight new control arms under the LJ now.

That’s also why you should be putting all new control arms on your Jeep as soon as possible.  By now the rubber bushings in your stock arms are aged out and due to be replaced.  By now the weak tack-welds holding those bushings in place are probably busted.  By now the weak stamped steel arms are ready for retirement.

Since the very first XJ hit the trails in the mid-80’s equipped with the new fancy coil-spring front suspension there have been companies improving upon the design and coming up with new ways to overcome the shortcomings of the OEM components.  New control arms, new track-bars, upgraded bushings, slick trick joins like heims and “Johnny Joints.”  People have boxed stock arms, build their own arms from square tube, built them out of round tube, and even gone with longer arms.

Color me biased but one company that has been at the forefront of these advancements has been JKS Manufacturing.  Founded in 1989 shortly after the XJ hit the market they hit the aftermarket with their revolutionary sway-bar disconnects.  Ever since they have been making Jeeps ride better both on road and off.  When it came time to find a suspension system for the ECOA/NHT Wrangler I knew one way or another I’d be running JKS components.  Now, with a full set of springs, shocks, control arms, and track-bars I can honestly say the LJ is the best handling Jeep I’ve ever owned or even ridden in.

So yeah, color be biased but I’ve “been there; done that “and “seen it done” when it comes to suspensions.  I’ve run the el-cheapo budget boost spacers. They blew out on me after Camp Jeep in 2005.  I’ve run the discount off-brand 2″ coils and shocks.  Sure they were better than my old worn out springs and shocks but only by a small margin.  I’ve had countless friends run every brand imaginable and the one mistake I see made time and time again is the piece-meal approach.  They by springs from this manufacture, shocks from this manufacturer, arms from that manufacturer, and track bars from this other manufacturer.  In the end they think they have the “best of the best” but in reality they have a bunch of components that were never meant to work together and have no R&D time behind them.  It’s no wonder the ride is harsh and the Jeep doesn’t handle right.

In contrast, by running a full comprehensive suspension system by one manufacture, in my case JKS Mfg, I have a suspension that has been be designed to work together.  Everything from the valving in the shocks to the length of the control arms, the spring rates in the springs, to the joints in the track-bars has been meticulously R&D’d to work together.  That’s the price you pay when you go with a full system.

A comprehensive system.
Springs, shocks, control arms, and a track-bar all designed to play nice with each other
Also all made in the USA!

So, a word of caution.  Before you run out and buy a cheap set of control arms think about what you’re buying and why you’re buying it.  If you’re Jeep is a daily driver that spends 99% of it’s time on the road you’ll honestly be fine replacing the arms with some reproduction arms.  However, if you’re building your Jeep to be a dual-purpose trail rig in addition to being a daily driver, or if you’re like me trying to build a Jeep that can handle pavement, overlanding, and technical terrain then you’re not going to want to skimp out on your suspension.  You don’t need a winch (at least not right away and not if you travel with a group).  You don’t need a snorkel (I’m still not running one and I’m doing fine).  Unless you’re pre-running the Baja 1000 you certainly don’t need a 50″ LED light bar (seriously, you don’t. No one needs one of those. Remember, more light isn’t always better light).  So take all of that money you could have spent on stuff you don’t need and put it into something you do need: a good suspension system.

As of right now my only regret is the same one I mentioned before.  I wish I would have done the arms when I did the springs and shocks.  I should have just pulled the trigger on everything all at once.  Probably would have saved myself some headache dealing with blown bushings and a bad arm.  I also would have had a much better riding and handling Jeep for both of my No Highways Tour book trips.  At least I know the 2017 trip will be the best one yet in that respect.