The Jeep Geek

The Jeep Geek's Blog
Nov 2010

Steering the Course

All modern Jeeps have power steering. This has caused havoc on the trail. OK, maybe havoc is a bit overstated, but manual steering is preferred for off road. Huh, has The Jeep Geek lost his mind? No my friend, enhance your calm and The Jeep Geek will explain.

This is a cautionary tale, you can destroy your steering system on the trail. When we were all in driver’s education, we learned the correct way to steer the vehicle, but then we promptly adopted the wrong approach for the rest of our lives.

The Jeep Geek can still hear the old football coach (who was also the driver’s ed teacher) admonishing him to only turn the steering wheel when the vehicle was moving. The rationale given was that to turn the steering wheel with the vehicle stationary would put flat spots on the tires. Well, The Jeep Geek would like you to know that the most important reason to not turn the wheel on a stationary vehicle off road is to save the steering system.

What often happens is that one of the wheels is against an obstacle...see the last article. If you are stopped, then the obstacle may prevent the wheel from shifting right or left. If you have a power steering equipped vehicle and decide to just turn the wheel in that condition, damage will occur...almost guaranteed. Maybe you will be lucky and only destroy the wheel...but you could easily damage the steering gear as well. Here’s how that happens...in a non-power steering system, when we turn the wheel and get a significant amount of resistance we stop to see what is wrong...in a power steering equipped vehicle we don’t get this feedback and the system generates so much power that things can go snap without further warning.

If the vehicle is moving (even slowly) and the steering wheel is turned into an obstacle, the Jeep will attempt to climb the obstacle and you will get feedback when a corner of the Jeep rises...humm, something is over there.

So back to coach (whatever his name was). Only turn the steering wheel when you are moving...or face the repair bills if you have power steering. And, yes, non-power steering is better for off road...but more work in town. So The Jeep Geek is glad The Hummer Recovery Vehicle is equipped with power steering as he spends more time driving in town than on the trails...but he is cautious with the steering wheel off road.
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Rocks on the Trail

On the subject of trail damage...how did we get to trail damage? The Jeep Geek has no idea, just kinda came to him today. He was meditating on some rocks and was inspired to write this article.

There are so many ways to damage a Jeep out on the trail. Most people think of body damage, fender damage, drive line damage, but one of the most common is tire damage. This type of damage is usually caused by those damned rocks. The good news is this damage can largely be avoided if you know what to look for on the trail.

Finding a line is the key to successfully navigating any obstacle on the trail. Looking for that path that prevents scraping the bottom of the body, suspension components, differential covers, or dragging off the muffler involves looking for large protrusions. Once found, the careful driver will make sure he places his wheels over the center of these. If the careful driver’s Jeep has rock rails, then very little damage is likely. Slowly crawling up the rock and slowly moving back down is the key to success here.

Danger does wait out on the trail. It usually is accompanied with warning signs...if you can just read them. Scroll up to the picture at the top of this page and the arrows will show you those signs. What you are looking for is black marks on the rocks where other Jeepers have lost sidewall rubber, or white streaks were they have lost the rims of their wheels. Either bit of damage may require the replacement of the wheel or tire.

Now for the really bad news. If you scrape the side wall of your tire, it could be damaged to the point that it will go flat. You get to enjoy the exercise of replacing a tire out on the trail. Now if you have been doing 5 tire rotations on a regular basis, then the spare tire will be almost the same diameter at the ones on the axles...you can just replace the flat tire and move on in 4 wheel drive mode.

If you have not been doing 5 tire rotations and your spare is brand new and the tires on your axle are worn down significantly, then you have a lot more work to do...you will have to make sure that the oversized tire is placed on the front axle and you will have to limp home in 2 wheel drive mode. Having two different sized tires on a driven axle will place considerable strain on the axle and transfer case.

Here’s the really bad news...it is usually the back tire that scrapes these evil rocks...your spotter usually gets the line correct for your front tire, but often they neglect to watch the rear wheels.

Keep your eyes peeled, look for those low rocks with black marks and make sure you place the wheel directly on top of these, or steer completely around them if possible.

Remember this, if you damage a tire and have to replace it, the cost will be between $200 and $300...most of the time, you will have to buy 4 or 5 tires at this time to make sure they are all the same diameter...so multiply the tire cost by 4 or 5.

The plastic fenders on your Jeep cost between $200 and $300...and don’t have to be replace if they are scraped...you can just live with the Colorado Pin-striping. So, it is better to take a line that might scrape the fender then the wheel.

Any way, that’s The Jeep Geek’s two cents.

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Different Differentials

The Jeep Geek is often asked what the differences are between the Sport and Rubicon (they both look similar). When he tries to answer the question it becomes clear that often the questioner doesn’t have a fundamental understanding of four wheel drive systems. So The Jeep Geek thought it would be good to lay out the different differentials that one encounters in 4 by 4 systems.

First, the differential is the pumpkin sized bubble roughly in the middle of the axle. In the case of a four wheel drive vehicle, there is one differential on the front axle and one on the rear. These connect to the transfer case which splits the engine power (from the transmission) to each axle.

The job of the differential is to enable the wheels on an axle to turn at different speeds. Yup, different speeds. The Jeep Geek will explain. When a vehicle turns around a corner, the wheels on the outside of the corner turn at a faster speed than the wheels on the inside. (The radius of the turn is shorter on the inside of the turn by the width of the car. This makes the outside wheels travel a greater distance in the same amount of time...hence faster.)

If there was no differential it would take two men and a strong boy to turn the steering wheel, and the vehicle would buck violently as it makes the turn.

The power going to the axle moves to the outside wheel (which is turning faster) whenever the vehicle makes a turn. This is an “Open Differential”.

Open Differential

Most 4 wheel drive vehicles have open differentials. This improves drivability on paved roads. It also makes steering easier and reduces stresses on the steering system, tires, front suspension and driver’s nerves. All-in-all an elegant solution with only one drawback.

The trouble with open differentials is when one wheel loses traction (such as off-road or snow) then all the power on the axle goes to the wheel that has lost traction. If the transfer case is also an open transfer case, then all the engine power goes to the wheel that is slipping uselessly...and you are stuck.

Now there are ways of dealing with this situation if you have open differentials and are stuck. One method is to apply the brakes (lightly) which will slow the spinning wheel. At the same time apply gas to the engine and the differential will “think” that the formerly slipping wheel now has traction and move some of the power back to the other wheel(s) which hopefully do have traction. This effect is at the heart of all modern traction control systems. They automatically apply some brake pressure to a spinning wheel to make sure that all the power doesn’t “leak out” of the axle.

So what if someone designed a differential that only transferred some of the power to the wheel that was slipping...say 60% of the power and retained 40% on the wheel that had traction (or in the case of going around a corner, only transferred 60% of the power to the outside wheel)? That might be called a “Limited Slip Differential”. How would that be?

Limited Slip Differential

A limited slip differential does just what the name suggests. It limits the slip of the power from the wheel that has traction to the wheel that lost traction. In fact it keeps 40% of the power with the wheel that has traction and only allows 60% of the power to slip. This enables enough slip to make it easy to navigate a turn on dry pavement and still leaves enough power in each wheel so that if you are off-roading you won’t lose as much traction and momentum.

Most manufacturers offer limited slip differentials on the rear axle only, leaving the front axle open. This is done to improve steering and ride quality while still giving some ability to get out of a difficult situation. It’s not perfect, but offers good performance in snow and normal off-road conditions.

On the subject of limited slip differentials not being perfect, here is a story about one of The Jeep Geek’s friends. He was driving his large 4 wheel drive pickup trucks in farm country. After passing the road he wanted to take, he tried to do a u-turn and ended up in a deep drainage ditch, nose first...rear end sticking up in the air...rear wheels off the ground. Since his truck had an open differential and limited slip differential in the rear, he was stuck. One of his front wheels was slipping and all the power was sent to this wheel, no traction at all in the rear (air has low co-efficient of traction). He had to be pulled out of the ditch by a friendly farmer and his truck was no worse for wear.

While the story above is an extreme example of what could happen to defeat the power of a limited slip differential, most people will find that this type of differential works best for their needs. If it doesn’t, wouldn’t it be nice to throw a switch and turn off the slip and lock up the differential when needed? That’s possible.

Locking Differential

The third type of differential that we will look at is the Locking Differential. This differential is normally open. So as you drive around with this vehicle you find that it drives normally. But when you approach an obstacle (in low range please) you can throw a couple of switches and a relay (or air supply) causes an extra gear to engage in the differential that locks the two wheels on the axle to turn together at exactly the same speed. No power is transferred across the differential...it is locked 50%/50%.

This setup is ideal for rock crawling where one wheel may be hanging in space when the other wheel is crawling up a large rock. This setup allows the maximum mechanical energy to be left with the wheel that has traction. No traction control braking to slow down momentum. No power slipping out the spinning wheel, just a slow steady crawl up a boulder strewn path.

The only downside of this solution is that the Jeep is very difficult to turn while the axles are locked...again two men and a strong boy are needed. Some Jeepers just lock the rear axle and leave the front axle unlocked when they approach an obstacle that may require some maneuvering to avoid things that can’t be crawled over. This at least provides optimum traction in the back, ok traction in the front and the ability to turn. Then when the path ahead is clear of the need to steer, the front axle can again be locked.

So the type of differential that you need depends on the conditions that you expect to encounter. The Jeep Geek loves the locking differentials that came in his Rubicon...but they are not perfect for every condition and perhaps a Limited Slip Differential is a better choice for you.

The Jeep Geek is willing to provide a free consultation to any of you who would like his advise, just drop a note on the Contact Us page and he will respond.
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Hemi Powered Wrangler

The Jeep Geek has written articles on improving the horsepower of the Wrangler engine...this one involves discarding the engine altogether and replacing it with a 5.7Liter Hemi...probably the most extreme modification in this area.

The Jeep store where The Jeep Geek works has such a modified 2011 Wrangler Unlimited with a Hemi engine and The Jeep Geek took it out for a short test drive (short for The Jeep Geek...also known as “The King of the Long Test Drives”).

First impressions were that this unit develops enough torque to give you a wonderful head snap when the accelerator is stomped on. The acceleration was smooth (as one would expect from the Hemi). There was the slightest torque steer to the right when The Jeep Geek stomped on the pedal while traveling at 45 miles per hour...nothing that can’t be dealt with, just a bit of a surprise.

It is expected that this unit produces 400 Hp because a cold air intake and cat-back exhaust was also added. The Jeep Geek has not dyno-tested this one.

The modifications were made in town here (Boulder Colorado) and Pollard Jeep provided the new Hemi engine, as well as the Wrangler.

So what is involved in this modification...well quite alot. The engine is replaced (obviously). The new engine is significantly more powerful than the previous engine, so the transmission must also be upgraded. Pollard Jeep used a Dodge Truck Heavy Duty Transmission (an automatic...see The Jeep Geek’s last post). The radiator must also be upgraded since this engine occupies more space in this smaller engine compartment. Pollard Jeep used a Griffin Radiator as well as some custom fabrication. Finally, the conversion requires a kit of stuff like Wiring harness, Pollution control module (PCM), mounting hardware, fuel lines, steering shaft relocation bracket, power steering high pressure hose, exhaust kit, A/C lines, basically bits-and-bobs as it were to make it all work. The Kit used here was the Burnsville Off-road (BOR) Conversion Kit. Simple right? Well, not really, but it is a wonderful result.

This conversion will set you back about $20,000...and Pollard Jeep keeps your old 3.8Liter engine and transmission. However the cost doesn’t end here...it will also cost you your warranty. Chrysler will not stand behind any of this. So once these modifications are performed, the warranty on the power-train is voided. Warranty should still cover basic stuff like power windows, radios and the like. But for those who don’t care about warranty, and have the need for speed...this may be the answer you have been looking for in the Wrangler.

So if you desire a large aggressive lift, 37” tires, and don’t want to pay the performance hit that you will take by making these mods, then consider the advantages of a Hemi conversion.
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Manual vs. Automatic

The battle lines have been drawn for decades and now The Jeep Geek wades into the fray. Many beginning Jeepers have asked The Jeep Geek if they should purchase a Wrangler with automatic transmission manual transmission. The answer he gives is:...well it depends.

If you want to roar down city (or country) roads like a bat-out-of-hell, then the Jeep Geek recommends a corvette (ok...just kidding The Jeep Geek wanted to see if you were paying attention). The Jeep Geek recommends a manual transmission. This is because you can pick shift points that are at the top of the torque curve. In addition most of the power boosting engine mods available for the Wrangler only work well on manual transmissions. Apparently the automatic transmission computer tends to de-tune the engine performance a bit which wipes out any gains made by opening up the breathing of the engine.

The Jeep Geek recommends the automatic transmission if the new Jeeper wants to do some off-roading with their new Wrangler. Huh? Automatic is better for off-road? Yup. The rumbling sound you hear is old Jeepers turning over in their graves.

The key issue on off-road use is control. Slow and easy, carefully executed maneuvers yield the desired result, getting over an obstacle with a minimum of damage to the Jeep (and the ego of the driver).

So given slow is good when rock crawling, lets examine what that looks like on the trail. When you start going over a rock you are going to be moving slow as you climb it...however once your wheel gets to the upper portion of a large rock (or small boulder) it will pick up speed if you aren’t using your brake. Going down the back side of a rock requires just as much slow going as the front side. If you allow the Jeep to lurch forward as you transition to the back side of a rock, you will allow the Jeep to slam down on the rock and this is a potential cause of damage to your Jeep. So rock crawling requires one foot on the gas pedal and one on the brake. In a manual transmission you will also need one on the clutch. (not really, The Jeep Geek will explain in a few moments).

It is just a lot easier to rock-crawl with one foot on the brake and one on the gas. Then you can control speed on obstacles a lot easier. Yes, you do have a hand brake, but that activates only rear wheels, and your hands are going to be busy on the steering wheel as you are crawling...don’t use the hand brake unless you stall and need to restart the engine.

So is it even possible to rock-crawl with a manual...yes. The technique is similar to crawling with an automatic, one foot on the gas and one foot on the brake. It is a bit more difficult to do this without stalling, but stalling your Jeep is not the end of the world. If you do stall, just apply the parking brake (so you don’t slip off the rock), take your left foot off the brake and put it on the clutch and restart the engine...let the clutch out slowly as you release the hand brake...then get that left foot back on the brake.

So what about heel-toe technique with the brake and gas pedal? Leave that for your roadsters out on country roads. It is just too dangerous on the trail. You need to concentrate on keeping the vehicle moving (slowly) and riding the brake is the best way to keep things from getting out of control. (Things can get away from you fast on the trail.)

So what do you do if you bought a manual transmission Wrangler and you want to go off-road? Learn the technique above and have a ball out there. Don’t beat yourself up if you find you are restarting the Jeep often as you learn the technique.

Which transmission is right for you? The one you enjoy driving most. Both choices are good, personal preferences should dictate. Just don’t think that with an automatic you are somehow impaired off-road.
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