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What is the most important tip you'd share with MJ owners?

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looking for those warnings or little gems of knowledge that you want every owner to know, but they'll likely not ask about until it's too late. Things like pulling up the carpet to check for moisture, or checking that your master clutch cylinder isn't leaking into your fuse box.


So what do you wish you knew when you got your first MJ? :brows:



--get yourself a headlight relay harness!  15 bucks and 15 minutes gets you brighter headlights and could save your truck from an electrical fire.  they are very popular and the sellers are always running out (so this particular one may be sold-out), but this is an example:  https://www.ebay.com/itm/1x-CERAMIC-H4-HEADLIGHT-RELAY-WIRING-HARNESS-2-HEADLAMP-LIGHT-BULB-SOCKET-PLUGS/290975680907?epid=25018508875&hash=item43bf80898b:g:YUMAAOSwxzBc2-B9



--Add your truck to the registry!  you'll get a build sheet and birthday for you baby as well as help us piece together all the missing bits of info from back in the day. :L: 




--do all of Cruiser's MJ tips.  should be the first link in here:


--When at all possible, do the work yourself! Tools and shop manuals are good investments. Handing over money to the shop guys only helps in their investments.


--Pull up your carpet! EVERY MJ owner should do it asap. I don't care what climate you live in or how little rust is on the outside of your truck, there must be a dozen ways for moisture to get under the carpet and once it's there, it's only a matter of time before the floor rots out from under you.


--Please do not ever spend any money on a Peugeot transmission (manual trans behind 87-89.5 4.0Ls) beyond new gear oil. It is a weak transmission with very expensive parts. Look into an AX-15 swap


--Please do not spend any money on a Dana 35 rear axle beyond gear oil and brakes (and if you're doing a complete overhaul, the ZJ disks are an easy swap). It is a weak axle and not worth upgrading or heavy repair. Look into an MJ/XJ Dana 44 or a Liberty 8.25 or 97+ Jeep XJ 8.25 or Explorer 8.8 swap if you want to upgrade. Or if you just need the truck running again, look for another Dana 35 or a 96-earlier 8.25. Don't forget to take this opportunity to get some better gearing. :thumbsup:


--Better gearing in your axles will give more kick-in-the-pants acceleration than any muffler/airbox could ever dream of.


--If you have a manual trans, check your fuse box with each oil change for any evidence of the clutch master cylinder leaking into the cab and dribbling down the firewall into the fuse box. Brake fluid will disintegrate the plastic.


--Lube you hood release mechanisms! Including inside the cable and the center pivot. With every oil change if not more often. If it breaks, look here: http://comancheclub.com/forums/viewtopic.php?f=2&t=872


--Use a hose to spray up in front or behind your rear wheel well to clean off that little shelf above the tire that collects dirt, which collects moisture, and rust is inevitable. There's a reason why our trucks rot there first and it's very preventable.


--Clean out the drain holes in the bottom of your doors. Dirt collects in that pinch seam and that attracts moisture, etc.


--Add rocker guards if you wheel. And do it before you smash your rockers. We have a long wheelbase and the rockers are extra susceptible to contact with rocks, logs, even simple mounds of dirt.


And lastly: Be careful when contemplating your first MJ purchase. These trucks have proven to be highly addictive to certain individuals!

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Do NOT use Fram oil filters. (they have a history or failures in Jeeps)


Check your battery box for cracks/breaks if the hold down is broken out all it takes is hitting a bump for the battery to come up and hit the hood, causing a severe short.


Check your CAD (central axle disconnect) b4 you go offroad for the first time, and lock it over if necessary . (or permanently bypass it and never worry about it again :thumbsup: )

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buy 2 or 3 the same if you can that way you have parts when needed.

Look over the frame realy well for cracks or signs of weld repairs.

look for broken wires under hood and dash or wires that have been taped or replaced

as stated before clean and keep clean to prevent rust.

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Know how to diagnose your jeep. Get a self-ranging multimeter. :thumbsup:


know the OHMs values for the CPS, the IAC, the TPS, the Ballast Resistor....don't pay money to shotgun fix it, TEST it before replacing it.


For the Renix owners, a lot of those values can be found using this site:

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm


learn how to clean the throttle body and IAC bore, and reset the TPS to spec . Understand an old MJ will REQUIRE you to clean the throttle body, or suffer.


learn how to clean the bulkhead connector.


Carry in the glovebox, 1 spare CPS, 1 spare fuel line quick connect kit (fuelrail to hose repair kit/MOPAR), 1 ignition switch, 5 feet of wire +/- and tape, and at the minimum 2 pipe connectors with straps.


USE IT- don't let it sit, and don't baby it. Let it sit too long, you will suffer the consequences....Jeep MJs hate to be left alone...you were warned.


understand the 4.0L, when properly used past 200,000 IS a carbon creating monster- accept blowby- its a fact of life.

and always remember, the volt gauge LIES.

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*Contrary to popular believe, some dana 35's have a metal plug opposed to the rubber plug most people identify them by.


*Invest in PB Blaster (a rust penetrant) and use it several times starting a few days before you plan on wrenching on your jeep. WD-40 is NOT the same thing.


*Use locktite on bolts.


*Know torque specs and do not over torque a bolt or use air tools on lug nuts.


*If you remove the bed on your Jeep, you must reground the wiring harness or it will not start.


*97-up front end is easily swappable to a Comanche.


*97-up doors will also fit on a Comanche.


*97-up mirrors will fit on 96-down doors with minor trimming.


*If you do a 97 up front end swap. upgrade your flashers to heavy duty jobs.


*Jeeps will potentially consume all of your excess money.


*Your wife/girlfriend will get pissed because you work on your Jeep to much.

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If your a city-slicker and like to wheel in the woods or ORV park always remember a spare door key...


If your a city-slicker and park on the street buy a steering wheel club and use it...


If you blow through ball joints switch to Moogs...


If you have the Renix cooling system get rid of it! it's easier to fix than a newbee would think!


for wheels and tires Discount tires has been good to me...


If your truck gets fender bendered and the person that hit you leaves a note get a written estimate for repair and see if the person that hit you will pay out of pocket... then do the the work your self and put the money elsewhere into your rig!

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No matter if you find no rust anywhere when you checkout the vehicle - you can count on having to do a restoration job on the rusted floor when you remove the carpeting.


If buying a 2.5L then look for a gear ratio of 4.1 or 4.56 you will thank yourself later


Replace the lower shock mount on the rear immediately with a axle universal mount $20 for the mounts and a little welding. Otherwise you'll be fighting bent mounting bolts every time you go out.

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If you are having taillight troubles, then check and most likely rework the ground connection inside the drivers side taillight pocket.


If you the fuel gauge doesn't work and the fuel pump is having trouble, check the chassis ground back at the tank. I have had to re-ground this on 3 different MJs' so far... :headpop: I just go to the frame rail, or bed, depending on which is closer to the break in the wire.

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  • 2 months later...

pull and inspect your clutch pedal.
there has been more than one report of the pedal failing at the welds.


I personally have experienced this. 
the weld was not completed and ended at the skinniest portion of the metal, the portion where it was drilled for the sleeve.

It ended up cracking, and eventually broke


quick visual, ensure there is adequate weld




may 27, 2019
check the welds on your brake pedal as well, i have just had a failure....



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  • 3 weeks later...

If your 4.0 is idling high or your constantly blipping the throttle to try and get it back down, try changing out your old single port fuel injectors for the 4 port high flow injectors, engine will idle very smooth plus increase in power and better fuel mileage I think this was one of the best mods I did.

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Certain parts are getting harder to find. If you get a chance to grab them, get them even if you don't need them right now.



Agreed had the chance to takes parts off a mj in a junkyard and didnt thinking i would need stuff went there a week later to get something and it was gone.


Make sure u replace the valve cover gasket once u get the truck they go bad and make sure ur friends arent trying to jump in thebed while u are driving away. Happened to me tailgate drop since one of them grab the handle and now the tailgate is all messed up

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  • 1 month later...

Proper gear ratios will make you think you have a v8.

Your Comanche will go just about anywhere you want to with lockers.


By all means collect every hard to find part off any MJ, I used to just look for taillights - now I look at the entire rear bed. I wished I had not passed on a couple of the those $500 comanches just because they had the 2.5

The cherokee fuel pump and sending unit is not the same as the comanche and will require fabrication to make it work properly no matter what the parts store clerk tells you.

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  • 3 weeks later...

"always carry a spare fuel pump ballast resistor and then a spare for your spare.

or carry a jumper wire to get you home"


This is so true! I owned 88 xj for 7 years and It only broke down one time and it was in the middle of a creek! I ran a wire from the battery to the fuel pump to get home only to find out it was the stupid f#cking resistor!

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  • 3 weeks later...

From my limited experience I've learned you should check:


1. Your clutch master cylinder for leaks. Check in the engine bay and above the fuse box. If it's leaking it will leak into your fuse box. Brake fluid and plastic do not play well together.


2. Under your carpet for rust. Unless you have a SoCal or Arizona vehicle it's there.


3. With the wife before dropping a couple a hundred on parts.


:cheers: Jeff

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  • 1 month later...

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