Click for Coverage
  • JP Magazine
  • Dirt Sports + Off-Road
  • 4-Wheel & Off-Road
  • Four Wheeler
Subscribe to the Free
Newsletter

Answers to All Your Jeep Questions

Posted in How To: Tech Qa on July 17, 2017
Share this

New Tread Dilemma

I just put new tires on my ’12 Wrangler JK that came with Goodyear P255/75R17 tires with a load rating of 2,523 pounds and a max air pressure of 44 psi. I switched to BFG T/A K02 LT255/75R17 tires with a load rating of 2,405 pounds and a max air pressure of 50 psi. These numbers look funny to me, but I got them off of the tires. Now, having thumbed through a story in an older issue of Jp (“Load Range and Max Air,” June ’15), should I start at 35 psi? This is what the old tires were at and the tread wore well. So how would I know how low I can go with the air pressure without damaging the tires on pavement and how would you be able to test it? Can I paint a line across the tread and look for wear?

Paul Brose
Via email

As you and many others have found, predicting the correct tire pressure on your Jeep can be very difficult after switching to larger diameter tires, or in your case, sticking with the same size and making the change from passenger car tires (designated by the “P” in the tire size) to light truck tires (designated by the “LT” in the tire size). Switching to a tire with a different load range letter can also require tire psi adjustment.

The best method of figuring out what tire pressure your Jeep needs is to find a smooth and level parking lot or quiet, deserted road. Run a chalk line across the tread of each tire. Be sure to note the initial tire pressure you are starting with. Drive the Jeep forward in a straight line for about 100 feet and then take a look at the chalk lines. If the lines are erased in the center only, you have too much air pressure for the weight of your Jeep and the tires are crowning. This will cause the tires to wear out prematurely in the centers, decrease traction, and provide an unnecessarily harsh ride. If the chalk lines are wearing away more quickly on the outer edges of the tread, you have too little tire pressure. This will wear the tires out prematurely on the edges of the tread, cause poor handling, and could lead to overheating and tire failure if the pressure is really low. Adjust the pressure and drive the 100 feet until you find that the chalk lines are worn uniformly across the treads. Also, you will likely find that the front and rear tires will require different pressures.

Depending on what pressure you end up with, you may need to reprogram the TPMS system to keep the low or high tire pressure alert from constantly going off. Companies such as AEV (aev-conversions.com) offer programmers that allow the threshold of the TPMS system to be reset to work with your new tires and altered tire psi.

TJ Oil Eater

No mechanic here can figure out my problem. I have an ’04 TJ with 43,000 miles on it. It’s new to me. An O2 sensor is causing the check engine light to trigger, even after being replaced twice. Also, the engine is using oil like crazy, but there are no leaks and no smoke. No one here has a clue. The outside of the engine is dry. I have no clue where the oil is going except it must be being burnt during driving. I need expert help.

Neil Hawkins
Via facebook.com/jpmag

Some vehicles go through oxygen sensors more quickly than others. Burned oil in the exhaust could be causing the problem you are having and it will also lead to catalytic converter overheating and failure. Of course, some oil use is normal. Typically, most OE vehicle manufacturers claim that up to 1 quart of burned oil for every 1,000 miles is acceptable, although to most automotive enthusiasts this is ridiculous. One quart of oil use for every 3,000–4,000 miles is pretty typical on older engines.

There are only a few ways that oil can leave the internals of an engine. If you see no external leaks, only two options remain. If the oil isn’t making its way into the coolant system via a blown head gasket or warped head, then it is being burned during the combustion process. Oil leaking into the coolant system is easy to spot. With the engine cool, remove the radiator cap and look at the coolant. If it looks milky or you see an oil slick in the coolant, you have a head or gasket issue.

An engine can burn quite a bit of oil without leaving a James Bond fog behind. There are three ways oil can enter the combustion process. The most likely culprit in your case is via a clogged or malfunctioning PCV valve. This is an easy component to test and clean and inexpensive to replace if need be.

Other possibilities include a bad valve stem seal or worn piston rings. Of course, both of these possibilities seem unlikely with only 43,000 miles on the Jeep, but since you are not the original owner, we have no idea what could have been done to this engine.

If the PCV valve checks out OK, then you should perform a basic compression test on each cylinder. If they vary more than 10 percent you will need to consider digging deeper into the engine.

Steering Straight

I have a ’77 CJ-5 with a 4-inch spring lift. I am running 31x10.50 tires. My kids are going to be driving this Jeep, mainly on the road and on the beach. Yes I know, but keeping them away from my toys isn't working and I’m not willing to get rid of it. The problem is that there is some bumpsteer, which was fine for me, but with my kids driving it I would like the Jeep to be as stable as possible on the road with the best road manners possible. I would like to keep the lift, although I will return it to stock height if I have to. Getting stuck at the beach is not a problem. Someone will always be there to pull them out. What do I need to do to the steering to improve the road handling and is there a tire size that will be more stable on the road? I have added 4 degrees of caster for a total reading of 6 degrees caster. This helped a lot but I would like to do better. Thanks for your help.

Vicki Mayfield
Via email

Fortunately, the ’76-’86 CJs are incredibly simple and there are still plenty of aftermarket parts available for them. Bumpsteer on a CJ is generally caused by lifting the suspension without addressing the geometry change to the steering draglink. In this case,s your Jeep should have a dropped pitman arm installed. A dropped pitman arm lowers the draglink the same amount that the suspension was lifted to correct the steering geometry. Dropped pitman arms are available for the CJ power and manual steering boxes. Be sure you order the correct arm for your application. Suspension lift companies such as Rough Country (roughcountry.com) and Skyjacker (skyjacker.com) offer a dropped pitman arm for your Jeep.

While you are working on the steering of your Jeep, it’s a good idea to inspect the entire steering system for slop. If anything looks worn or there is any unusual movement, it should be addressed. Another potential area for steering slop on a CJ is in the factory steering shaft that goes from the steering box to the bottom of the steering column. Borgeson (borgeson.com) offers a heavy-duty replacement that bolts in place of the failure-prone factory shaft. Ultimately, a solid and fresh steering system will be less likely to wander down the road.

As for tires, nearly any modern-day radial tire with the correct air pressure will keep your CJ steering straight on the road. Excessively wide tires and wheels have a tendency to follow grooves and dips in the road. A 31x10.50 sized tire on 15x7 or 15x8 wheels with around 3.5 inches of backspacing should be fine for your CJ.

Braking Bad

I am having an issue with the brakes on my ’99 Jeep Cherokee. It does this thing where occasionally the brake pedal will go almost to the floor before the brakes engage. It is very random and only seems to do it at very low speeds. I thought that this would be a worn master cylinder, so I replaced it. The Jeep still has the same issue.

I thought maybe I had a bad wheel cylinder in the rear since they were old, but they were not leaking. Rather than just replace the wheel cylinders, I went and did a disk brake conversion. It still has the same exact issue. Nothing changed.

Then I thought maybe I had a bad front caliper, since everything else had been replaced, including bleeding the brakes several times. I went ahead and replaced the front calipers, pads, and rotors. The same problem persists.

I’m not sure where to go from here. This is a simple braking system. There is no ABS, but I can't seem to fix this issue and everyone I ask has no idea what it can be. Again, this issue is random and only happens at low speed and low rpm. The Jeep still stops, but not until the pedal nearly reaches the floor. When it does this, the pedal has no resistance until almost at the floor. There is no brake fluid leaking anywhere.

Thank you for your help. Hopefully, someone will have an idea on what this is and how to fix it.

David Bergman
Via email

Inconsistent brake issues can be a real bummer and difficult to solve. It sounds as though you have replaced nearly everything, so I will assume that nothing is worn or leaking and that all of the air has been bled out of the system.

This may be a reach, but I once had a similar problem on a Jeep I performed a front disk brake swap on. Like you, I replaced the master cylinder, thinking it was intermittently failing. The problem persisted. I eventually found that when I turned the steering to full lock, one of the calipers was hitting a shock bolt, forcing the caliper piston back into the bore. When I went to hit the brakes after this, the pedal would go to the floor initially, and then function normally. Like your problem, it only happened at slow speeds and when I was turning sharp. Perhaps some axle or suspension modification you have made is causing contact with one or both of the front brake calipers or brake line bolts when turning. Check the calipers and lines for marks that would indicate contact with something and make any needed changes to eliminate the caliper contact.

Five Flattie Fenders

I have a ’74 CJ-5 and I have found that getting aftermarket parts is a challenge. I just received my August ’17 issue of Jp and saw the CJ-7 on the cover. I realize that the cover CJ is newer than mine, but I really like the front fenders on that Jeep! Do you know of any vendor that makes a flat tube fender that will fit the ’72-’75 CJ-5? Great magazine, keep up the good work.

Bob
Via email

Those particular front tube fenders are Smittybilt (smittybilt.com) XRC units, and although the company’s website doesn’t show them for the CJ-5, so many parts are interchangeable or adaptable between the 7 and 5, a call to the company’s tech support at 310/762-9944 could net you the answer to that question. If not, there are many different smaller companies that specialize in older CJ-5 aftermarket components. Companies such as Extreme Custom Parts (extremecustomparts.com) offer CJ tube fender conversion kits (requiring some fab and welding) that will provide the look you are going for.

No Filler

I'm building a ’51 CJ-3A. I’m going to sandblast it and fix a few problems with the sheetmetal. Should I use body filler to make the body perfect or should I just paint the massaged areas? I plan on painting it a metallic green like a ’71 Jeepster Commando I once had. It’s going to be ’wheeled as much as most JKs (just kidding), and is not going to be some “show queen” at all.

@skinny_fabrication
Via Instagram @cappaworks

This is really a personal preference question, but if you want my opinion, I’ll certainly hand it out. I have always looked at the flatfender bodylines as very simple, industrial, and utilitarian. Even on a brand new unmolested body, you can still see the spot welds in many places. I don’t believe it was designed to be a smoothed vehicle. So with that in mind, would you consider using body filler on a piece of heavy equipment like a dozer? I wouldn’t.

In my own experience, I hate finding body filler on my Jeeps. It always seems to get in the way, chip, catch fire, and make a huge mess when I’m welding near it or making other repairs. I'd rather have dents and dings than body filler on my flatfender sheetmetal. Now, if you’re painting your Jeep a dark glossy color, it will show all of the flaws in your bodywork, if that is a concern. Lighter color paints and flat paints will hide the flaws a lot better.

What's Trending

Connect With Us

Newsletter Sign Up

Subscribe to the Magazine

Browse Articles By Vehicle

See Results