Jeep YJ Frequently Asked Questions

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Jeep YJ Frequently Asked Questions
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Frequently asked questions about the YJ


What size of tires fit without rubbing?

Older YJ (sagged springs on stock rims with lots of miles) - 235/75r15

Newer YJ (non-sagged springs on stock rims with few miles) - 30x9.5r15

Newer YJ (non-sagged springs on non-stock rims with few miles) - 31x10.5r15

2.5" lift on stock rims - 32x10.5r15

4" lift on stock rims - 33x12.5r15

Backspacing on the standard rim is 5.5".

Stock height of Jeep to rocker panels - 18"

Wheelbase length of the YJ - 93.5"

Wheelbase width of the YJ - 57"

Ground clearance - 9"

Towing capacity - 1,000lbs with proper hitch (officially) - 2500lbs with proper hitch (un-officially)

What kind of transmissions are in the YJ?

1987 - 1989

AX-5 - Aisin 5-speed behind the I4

BA-10/5 - Peugot 5-speed behind the I6

TF904 - TorqueFlight Automatic behind the I4

TF999 - TorqueFlight Automatic behind the I6

1989 - 1995

AX-5 - Aisin 5-speed behind the I4

AX-15 - Aisin5-speed behind the I6

TF904 - TorqueFlight Automatic behind the I4

TF999 - TorqueFlight Automatic behind the I6

How do I know what engine I have in my Jeep?

If you lift the hood you will be able to count either 4 or 6 spark plugs.

Early (pre 1991) 4-cyl engines were fuel injected via throttle body - 2.5L

Second gen (post 1992) 4-cyl engines are fuel injected via MPI (Multi-Port Injection) - 2.5L

Early (pre 1991) 6-cyl engines were carb'd - 4.2L

Second gen (post 1991) 6-cyl engines are fuel injected via MPI (Multi-Port Injection) - 4.0L

What gears do I have in my Jeep?

I4 Automatic - 3.73:1

I4 Standard - 4.10:1

I6 Automatic - 3.54:1 (normally)

I6 Standard - 3.07:1, 3.54:1 or 3.73:1 - must verify with the tag on the axle or by pulling the differential cover and reading the numbers stamped in the ring gear or by counting revolutions of wheel versus driveshaft.

What fluids do I use in my Jeep?

Axles - Gear oil - 80 weight for light duty and normally cooler climates - 90w120 weight for heavy duty and normally warmer climates Note: Some rear axles are equiped with factory posi - a limited slip additive must be put in with the gear oil to extend and protect the limited slip action

Engine - 10w30 for good general usage in most climates - 5w30 for those colder climates (when temps are below freezing for extended periods of time)

Transmission (standard) - 80 weight gear oil

Transmission (automatic) - Automatic Transmission Fluid (ATF) Dexron III

Transfer case - Automatic Transmission Fluid (ATF) Dexron III

What is the easiest way to gain room for larger tires? - Suspension lift. When the springs are sagged out from years of use or abuse, a 2" suspension lift gains more clearance (and flex) than a 2" body lift. The other easy way to gain room for larger tires is to install Bushwacker or TJ flares and trim the sheet-metal of the body to allow for more room.

Which is better, open diff, posi-diff, lock-diff or spool-diff in a set of stock axles? - The posi-diff situation is the easiest on the Jeep's axles with least chance of serious breakage. For more information regarding the different choices, try Randy's tech sheet. A locking diff is the strongest, and will carry you further down the road less travelled.

I want to put a winch on my Jeep, which one should I get? - The rule of thumb is that a winch must be rated at least 2-times the weight of the vehicle. For a stock YJ running no doors or top, no back seat and minimal tools/spares a 6000lb electric winch will do the job very nicely. Once you start adding in extra weight-inducing extras (hard-top, full hard-doors, tools, people, etc), an 8000lb electric winch gets the nod. If you are into hard-core mud or rocks, 9000lb winches and higher will become the recommended rated unit.

Can I swap my 4.2l engine for a 4.0l engine? - Yes you can. Its basically a bolt-together situation, but you will have to remember to remove all the wiring with the 4.2 and put in all the wiring for the 4.0 (all sensors, including O2 on the exhaust). While you are at it, install an electric fuel pump to provide the correct PSI and GPM for the 4.0. The guages on the dash should work properly once they are all hooked back up again.

How hard is it to swap in a V8? - The Chevy and Ford V8's are very easy to put in with lots of room under the hood. AMC/Dodge V8's can be mounted infront of the I6 transmissions with minor modifications to the bellhousing. Using the existing transmission may not be best, and is not recommended to use the I4 transmissions behind V8 power. Standard tools with a welder, grinder and angle-finder are all you would normally need.

If you are wishing to use all the stock power-train (transmission to the axles) with V8 power under the hood, check Advance Adapters to get their V8 swap book, their adapters and motor mounts to make the job real easy. Novak Adapters has a great knowledge base online about the V8 engine swap. It is an easy to understand article.

My carb'd Jeep keeps stalling when I hit the brakes - why!? - Welcome to the world of the early YJ. It is a well known problem and a complete PITA! To start, check all the vacuum lines around the carburetor. Any that are cracked or missing - replace. Once that is complete, if there is no change in the way the Jeep runs, try a simple repair as listed at If that doesn't work, then its time to visit a professional, or go the route of thousands of other Jeep owners and get rid of the Carter carb and replace it with a Weber carb .. you can find these carbs from E-bay (used) or new at many autoparts stores.

Which CB channel should I use when wheeling? - Channel 4 and Channel 16 are the two most used channels when 4x4'ing. If you are out alone, try both to see if there is someone nearby to join up with.

I want a softtop for my Jeep - what should I get? - Bestop has been in business since 1954 and has very high quality product and service. California Tops is fairly new to the aftermarket top scene, but their designs are cutting edge.

I want better sound in my Jeep - what should I do? - Pioneer, Sony, Panasonic and many others make great non-skip players and when combined with poly-speakers you don't need to worry about dunking them as much. Replace the front speakers on the driver's side by removing the bolts along the left side of the dash and prying the dash away from the body. You will have enough room to reach the nuts on the old speaker and replace with the new speaker. Passenger-side is easily done without first removing the torx-bolts. A sound bar with aftermarket speakers is great to have. Thor Sound Wedge is also a great product. You could also custom-build speaker-boxes and amp-boxes if you have the inclination.

What are the best mufflers to get? - Personal preference here - the cheapest ones won't hurt your wallet as bad when you bash them on the rocks, or rip them off on obsticles. A free-flow muffler and cat are good for a few more ponies. To check if a muffler and catalytic converter are free-flowing - look through it. If you can see your friend on the other side, its free flowing.

I want some headers - what should I use? - Clifford Performance has great headers for the I6 - even the ability to run true duel-exhaust (not considered legal in some states)

Gear Ratios?

Normal available gear ratios for YJ axles are:

# 3.07:1

# 3.54:1

# 3.73:1

# 4.10:1

@ 4.56:1

@ 4.88:1

@ 5.13:1

# = Stock available gears

@ = Aftermarket supplier like Randy's Ring and Pinion

I want to run 35" or larger tires, what should I do to reduce breakage? - The front Dana 30 axle is fairly strong, and can handle upto 37" tires if you aren't too hard on the gas-peddle. The rear Dana 35 is not as strong, and its maximum recommended tire-size is 33". To strengthen the rear axle, Superior Gear has the Super 35 kit to increase the strength of the stock rear axle, combine that with a truss and you will have less chance of breakage. Replacing the rear axle with a Ford 8.8" (out of a 1995 or newer Explorer), or a Dana 44 (Metric-tonne Commanche (MJ), Towing-package Cherokee (XJ)) are a direct bolt-in once the spring perches are welded into place. Also, some of the newer Toyota axles also have the same wheel-bolt-pattern as a stock YJ, and their width is just about perfect as well.

What is the best way to gain more flex from my Jeep? - Removing both the front and rear track-bars (bar from frame to axle, one mounting point on each side) will gain you alot of flex right from the start. Most are happy removing the rear track-bar and suffer no ill-effects. Removing (or temporairilly disabling) the sway bars on the front of the Jeep will be the icing on the cake for flex. Some find the ride horrible on the street with lots of body-lean in the corners. Others are happy without track-bars or swaybars. Try removing one at a time (starting with the rear track-bar) till you find the ride the easiest for your driving style without making you feel un-safe in corners.

Why does everyone hate body lifts? - Its not that we hate body lifts on our Jeeps, its that most find their looks as being ugly, and the higher body lifts can become dangerous - especially in accident situations. Many instances the body lift has busted through the body and caused the body to sag at one or more places - even to the point of the body lift pucks breaking through at all mounting points and the body coming to rest on the frame again.

Can I put a CJ-7 hardtop on my YJ? - Yes you can. There are a few things you must do in order to make it function properly with your tail-gate, but it will fit in place without any major issues. Look towards opening your rear-window before opening the tail-gate. You can also attempt to swap a YJ-style rear window onto the CJ's top.

I want different rims. What will fit? - Within the Jeep line of vehicles, you can use rims from any YJ, XJ, MJ, ZJ, WJ or KJ. Outside of the world of Jeep, you can get Ford Explorer and Ranger rims, Toyota pickup rims (certain newer models only). Of course, the Mazada B4000 rims will fit (It is a Ford - or is it vice-versa). Pontiac 6000 cars also use the same bolt-pattern, but their rims are 14" in diameter - so its not a perfect match.

You can also purchase brand-new aftermarket rims. All you need to specify is the bolt-pattern of 5-bolts on 4.5" diameter. The most popular after market rim for the YJ is the American Racing rim model 767.

Why do I have water pouring inside my Jeep when it rains? - That is a fairly common occurance. The grill on the top of your engine area (just in front of the windshield) allows fresh air into the Jeep for the heater. It also allows water and snow to collect. There is a drain-hose on the firewall about 1.75" in diameter that can get plugged. Pull off the hose, and tip it upside down. Wash it out with the garden hose in the backyard and then wash the grill-area down as well pouring as much water down as possible to wash all the trapped dirt out. Place the hose back in place and enjoy dry feet again.

You can also add a scoop to the grill area to limit the amount of water/dirt entering the fresh-air intake.

What is the best way to clean my soft-top? - You can use a baking-soda/water mix to clean the canvas tops and doors. Using a soft bristle brush, work the paste into the top. Once completed, rinse with clean water. If that doesn't remove all the stains, visit one of your local boat-supply stores and ask them for some canvas cleaner (many boats use a canvas cover). While a little more pricey than the baking-soda, it might just do a good job for you.

What should I look out for when purchasing a used YJ? - Depending on what you are looking for, any of the YJ's are great projects, wheelers, daily drivers, etc.

1987 - 1988 - Major Project Jeep

V8 swap with swapped in transmission and transfer case

SOA, trimmed body panels, exo-cage

Look for rusting in the floor near the roll-cage mounts

1989 - 1991 - Minor Project Jeep / wheeler

Lift kits/bigger tires

V8 swap for I4 (also change transmission and transfercase)

Look for rusting in the floor near the roll-cage mounts

1992 - 1995 - Daily driver / Minor Project Jeep / Wheeler

Lift kits/bigger tires

V8 swap for I4 (also change transmission and transfercase)

As with any vehicle, make sure that you know what you are getting. Check fluids, check bushings, check for rusting, check for accident damage, check for 4-wheel-drive (not just the light on the dash, but that is a good indicator) by "twisting" the suspension till you have one front and one rear tire spinning in the air, check for the doors closing properly (again, accident damage), check over any mods that may have been done (you don't want farmer mods on it - clean bolt-on's are great, or properly welded ones) .. and always get a saftey inspection done.

How much is this Jeep worth - or - how much is my Jeep worth? - Modifications to the Jeep do not increase or decrease the overall value of the Jeep. In general visiting Kelly Blue Book will give you a good starting point for buying or selling a Jeep.

by: Badfish0212



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