Best Things to Modify After Buying a Used 4×4
Written By: Jerrod Jones
There are a lot of quality used rigs out there just waiting to be loved by someone who can appreciate
their worth. Buying a used truck, Jeep, or other 4×4 is a great way to save a chunk of change for
customizing your ride the way you want it to be! And with the addition of some carefully chosen mods,
you can make that rig work better than new and built to your liking.
We’re going to assume that “used” means that you purchased a truck or 4×4 with at least 15,000 miles
on the odometer, in which case there is already some wear on the vehicles and you could already be
making some “maintenance modifications” (make sure to call them that so you can tell your significant
other that you’re performing necessary “maintenance”). But what do you do first? Adding a custom
cold-air intake hood isn’t going to do much for the way it drives, but changing the tires or improving the
suspension—that could make a world of difference. Stick to mods that will improve the way your 4×4
works for you before you start adding a bunch of additional mods that you want (We know; That really
cool air compressor is calling your name). That’s why we put together a batch of some of the best things
to modify first when you buy a used rig.
You’d think we’d say tires and wheels, huh? And wheel-and-tire packages are often some of the first
things changed because nothing personalizes a vehicle like wheels and tires…but chances are that the
wheels on your newly-acquired truck are still in good working condition! Therefore, money would be
better spent on other modifications if you’re trying to get the most out of your 4×4. But unless your tires
are brand new, there is always room for improvement. As tires get older, the rubber can start to break
down due to age and UV exposure and this can affect the performance of any tire. Even if the tread is
still “almost new,” we’d recommend replacing any tire that has been on a vehicle for more than six
If you are planning on changing the wheels for style preferences (or to upgrade to beadlocks!), then find
the extra cash and do it now because you’ll save yourself some money on mounting/dismounting by
changing the whole wheel-and-tire package at the same time.
If you’re driving your truck or 4×4 every day and not looking to change to winter tires (assuming you live
in a snowy area), you’re likely an all-terrain customer. Ninety-five percent of the time an all-terrain will
not let you down in the dirt/snow/ice, plus it’ll give a smooth ride with good on-road manners and
minimal tire noise.
If your job puts you on a lot of dirt/muddy roads or you just like to spend a lot of time on them with your
truck or 4×4, you will probably benefit from a mud-terrain tire. While it may not have the road manners
of its all-terrain brethren, new mud-terrains are made with impressive compounds and designs that
allow many tens of thousands of miles of use. Expect fuel economy to dip a mile or two—it’s the price
you pay for such a heavy-duty tire.
Suspension and Steering
Now is the time for some performance improvements! If your ride is even a little bit used, then there
has already been stress put on those bushings, ball joints, and tie rod ends. A new suspension system
will often replace many of the worn items, and give you a chance to easily replace other worn parts (like
steering) when installing your new suspension. If you purchased a truck with an upgraded suspension
already on it, many brands have rebuild kits available that will renew that aftermarket suspension for
you. We can certainly help you find the correct pieces to renew your ride.
Another key component of your vehicle’s handling is the steering system. If it feels like there is too much
play in the steering wheel then you may want to look into a new steering linkage kit.
An entire suspension system upgrade is going to make your rig feel new. Not only do you often replace
links and arms, but new shocks and springs that are better suited for off-road use.
Shocks are going to play a big part in the way your vehicle rides. Even if you have an existing suspension
kit, a new set of shocks or rebuilding them (if possible) is going to get you a better and more controlled
If your bushings or joints wear out, there can be some sloppy driving performance. Unfortunately, a lot
of the times the signs don’t exhibit themselves unless you’re already pushing your vehicle past a cruising
condition—like when you need to react quickly and your truck takes a second more to react than you do
because there is so much play in everything.
New steering linkage can help fix sloppiness and beef up a weak point in your 4×4’s moving parts.
If you’re rolling with a clutch and a real gear selector, then you’re probably set for now…assuming the
clutch is still biting. If not, now is the time to put some of that saved money into an HD clutch!
For all of the automatic guys out there, you know the drill: Besides the tranny fluid and the filter, you
probably want to look into a shift kit if there is one available or tune your transmission electronically
using a programmer to change shift points and shift firmness. The changes will help the transmission
better survive and perform with a larger tire package and when hauling heavier loads.
If you feel some slipping, an HD torque converter or aftermarket clutch is definitely going to help put
power to the ground, but if you don’t feel anything wrong then remain patient, save your money, and
wait until something starts to go—it’ll probably be soon enough if you’re having fun with your truck!
A deep transmission pan is going to add some extra fluid capacity and help alleviate some of that heat
coming off that transmission. You can help add some life to your tranny by adding some extra fluid
Axles and Brakes
If you made the lucky purchase of a 4×4 with some bent axles, ditch those old dogs so we can set you up
with some custom axles that can be built the way you want! But if your housings are okay, then you
should probably concentrate on upgrading any wearable parts. Check the U-joints, the ball joints, the
brakes, the bearings, and the seals. Add synthetic fluid because you rarely change the gear oil.
If there is a little clunking or banging when you hit the gas, there’s a good chance you’ve got some worn
U-joints. If they’re worn, replace them with some extreme aftermarket U-joints. If they’re good, give
them a little grease for good measure.
Unless you see catastrophic failure, you probably don’t need to replace your gears unless you change
your tire size. If you added larger tires, then you’ll want to think about a different gear ratio in the axles.
If your new purchase has some higher numbers on the odometer, there’s a good chance your unit
bearings or wheel bearings have seen some good wear. Check all four corners and make sure everything
Whether you add larger tires or not, upgrading your brakes will not be something you regret. A
complete disc brake upgrade or conversion can be great, but just a simple performance pad and rotor
can make a big difference.
Technically, you could consider ball joints part of the suspension, but no matter what they are, you don’t
want them wearing out or breaking. And if they do have some play, now the time you can beef up those
ball joints with some heavier duty pieces. There are even rebuildable HD ball joints for certain axle
Assuming you didn’t buy something too modified by previous owners, your electrical system should be
functioning all right if the vehicle is running. Many auto shops are happy to run a quick test using a
battery analyzer to check amperage and voltage on the existing battery. If it is on its last legs, this would
be a great time to upgrade to a sealed battery designed for more severe electrical duty.
A “dry cell” or sealed battery can often add a larger reserve capacity and be able to better feed high-
You may also want to think about upgrading the headlights. Lighting technology has come a long way
and there are many HID and LED aftermarket upgrades that you can choose from to replace your old
Hopefully, the stock interior in your new used ride hasn’t been messed with too much, but this is one of
the things you have to worry about with a used vehicle purchase. The driver’s seat will be the first to
show wear, but that’s nothing a good upholsterer couldn’t fix if you’re not ready to add full-race seats in
your truck yet. For now, we’d recommend leaving your interior largely alone while you concentrated on
other things first with your newly-acquired used 4×4. And when you’re ready, we have lots of tuners,
switch kits, and accessory mounts available!
Check/Replace All Fluids and Filters and Plugs
When we say check all fluids, we mean “all” fluids. Top off that windshield washer fluid even—you’ll be
thankful when the going gets muddy! But besides that, we’re talking about the vital fluids to keep your
4×4 running smoothly. Doing an engine oil change on a newly-purchased used gem is a no-brainer, but
what about flushing the cooling system? How about the condition of the fuel filter? Did you remember
to buy fully synthetic gear oil for the axles since you’ll likely never change that fluid again? And make
sure the transmission gets new juice (if it’s an automatic); Fluid can often be burn, resulting in
premature wear and decreased performance. Here’s a quick checklist of the fluids/filters you want to
Engine—Engine oil, oil filter, air cleaner, coolant/antifreeze, fuel filter, water/fuel separator (if
Transmission—Filter, transmission fluid
Axles/Differentials—Change to synthetic gear oil, add LSD fluid if running a clutch-type limited slip
DEF Tank—If you have a newer diesel, top off the Diesel Exhaust Fluid tank
Engine Plugs (if applicable)—Petroleum (gas) engine has spark plugs, and older diesel engines have glow
plugs that are replaceable