Subscribe to a magazine

Nuts & Bolts - March 2014

4 7l Highoutput V8
Trenton McGee | Writer
Posted January 21, 2014
Photographers: Staff

Your 4x4 Tech Questions Answered

Which Tranny?
Q So here I am finishing the YJ spring-over-axle conversion lift to my ’881⁄2 Suzuki Samurai, and I am planning Phase 3 of the build, which is the powerplant. I plan on running a TBI 4.3L V-6, SM420, and Dana/Spicer 18 transfer case with the overdrive kit, but my confusion comes into play after I read the Ultimate Adventure 2013 attendees’ specs: automatics, automatics, and more automatics! Am I missing something going with a manual tranny? (Part of my desire for a manual is I flat-tow my rig.) Or is the automatic simply being used for the ease of throttle control? If so, where is the fun in that? This is a test of man and machine’s technical ability and skill. All kidding aside, I am confused. Auto or manual?
Joe Ortiz
Via nuts@4wheeloffroad.com

A It certainly sounds like you’re building a cool rig. While you pose a good question, it’s kind of like the Ford versus Chevy debate—you’ll get a lot of opinions that mostly go nowhere. The answer really boils down to personal preference. That said, I believe I can provide some insight on this, as I’ve spent a lot of time behind the wheel of both manuals and automatics off the pavement. There’s also a pretty clear cut choice for your build, but we’ll get to that in just a minute.

You are correct that more and more automatics are on the trail these days, partly because manuals are slowly disappearing as factory options (you can’t buy a new 1⁄2-ton fullsize truck with a stick these days), partly because the off-road learning curve is shorter with an automatic and partly because factory and aftermarket technological advances have made automatics much better behaved off the pavement than in years past.

Automatic?

And you are correct that automatics outnumbered manuals on this year’s UA. However, there were a few manuals on the trip: Ken Smith’s flattie, the Nitro Gear & Axle Toyota, Tim Hardy’s Suzuki, and my own rig (the Cummins-powered JK that Fred Williams let me borrow). All were equipped with sticks, and all of them had no problem keeping up with the group.

I was once a dyed-in-the-wool manual tranny guy; you were going to have to pry that stick shift out of my cold, dead hand. My first couple of rigs were manuals, and my current stable of four rigs includes only one automatic. A manual’s attributes include ultimate driver control for gear selection, a mechanical connection between the engine and the rest of the drivetrain, often lower gearing, good compression braking (using the engine to slow the vehicle during a descent), a generally simpler design (less stuff going on inside to go wrong), a more compact package, and often a stronger case that can withstand impacts with rocks (if the tranny has a cast iron case). Sure, using three pedals with two feet off-road takes some practice, especially in rockcrawling and other slow-speed situations, but once the skill is mastered, a properly geared manual is hard to beat on the trail.

An automatic, on the other hand, is a trickier proposition on paper. They generally have higher gearing, they’re physically longer, most of them are made of aluminum that shatters when hit hard enough, some offer virtually no compression braking, they get hot, they’re more complicated (more stuff to go wrong internally), and (this is a big one) they rely entirely on pressurized fluid to transfer power. If that fluid is lost or is no longer able to be pressurized for any reason, you’re dead in the water.

Manual?

However, automatics are not without their benefits. The torque converter acts as something of a buffer that can help prevent shock loads from being transferred to the rest of the drivetrain. Converter torque multiplication and slip can help compensate for an auto’s higher gearing as well as a vehicle that is geared a little too high in the axles or transfer case. They’re far easier for an inexperienced driver to control off-road. Plus, most of the drawbacks mentioned above have been addressed by the aftermarket and are easy to overcome, making automatics a very viable option in any form of off-roading.

These days, I really don’t have a preference for manual over automatic. What changed my mind? Several years ago I spent a lot of time behind the wheel of a YJ owned by a company I worked for that was equipped with a stock manual transmission. I even took it on an the Ultimate Adventure. It was a good Jeep—nothing special but fairly reliable other than occasionally popping a few locking hubs. One day the guys at the shop decided to put an automatic in it, and I was totally against it. They did it anyway, and it turned out the next year I ended up in the same Jeep, now equipped with a Torque Flite 999, on another Ultimate Adventure. No other changes had been made to the Jeep. By the end of the trip, I loved it! No more three-pedal dancing, compression braking was as good or better than with the manual, and thanks to the giant tranny cooler we installed, it never got over 190 degrees. I also never popped a hub in that Jeep again.

The biggest reason my mind changed was the ability to shift mid-climb. Imagine sitting at the bottom of a fairly long, sloppy hill that’s going to take a fair amount of wheel speed and momentum to tackle. With a manual, you’re committed to the gear you choose at the bottom because no matter how good you are, you won’t be able to shift fast enough to avoid losing nearly all the momentum and wheel speed you’ve gained. With an automatic, the shift is nearly instantaneous, and you have that much more wheel speed and power at your disposal. If the engine starts to bog down, you just slap the shifter and you’re back in a lower gear. With a manual, you’re done and usually sliding back down to the bottom of the hill by the time you downshift. Any time you need some sustained momentum or a little extra bump over an obstacle, an automatic will win out a lot of the time. In all other situations, one or the other might have slight advantages or disadvantages that wash each other out, but in this one type of situation, I feel an automatic has the advantage. If you study the UA 2013 video and watch hard-charging (and highly skilled) drivers like Chris Durham and Erik Miller, you’ll see why those guys have a slushbox in their rigs. It’s hard to argue against a rockcrawling champion and a KOH King. Even so, I still like manuals just fine and use them off-road all the time.

At the end of the day, both tranny types have their place in off-roading, but for your build, you might want to stick with your planned combination. Samurais have a very short wheelbase, which make them highly nimble off-road rigs, but it also means that driveline angles (especially rear driveline) are going to be problematic. Your spring-over-axle conversion makes driveshafts even more of a challenge, as that’s quite a bit of lift even with flat springs. Your SM420/Spicer 18 combo is among the shortest package available, and the shortest automatic combination we can think of is going to be at least 8-10 inches longer. Keep in mind the Spicer 18 is going to require front and rear axles with differentials offset to the passenger side (which you already have assuming you’re keeping the original Samurai axles), and we’d recommend high-pinion axles to alleviate driveline angles and to make the most use out of the flex on an SOA conversion. As for flat-towing, we’d recommend placing the 18 in neutral and the tranny in gear.

Mini Mud Tire Choices
Q I have an ’02 Chevy Tracker. It has been a solid, dependable SUV. Currently it sits on 235/75R15 Goodyear Radials with a bit more clearance from a 2-inch spacer lift. My only wish is that tire companies would make more aggressive tires in this size. I can’t afford to go bigger on the tires yet because I need more lift, new wheels, and regeared differentials. Nor do I have garage space to do all this stuff. Why don’t the tire companies make more aggressive tires in smaller sizes? We can’t all afford to go big all at once.
Jerry Sherred
Via nuts@4wheeloffroad.com

A I’m a big fan of nimble compact 4x4s and have always been impressed with their capability. The Tracker certainly falls into this category. Though we spend a lot of time in these pages talking about big tires and building suspensions to clear big tires, the fact is that you don’t need any of that stuff to have a good time on the trail. All you need is a 4x4 and a trail that matches your vehicle and skill level. The important part is actually getting out there and doing it.

I suspect you may have fallen victim to the limited selections available at your local tire store. The fact is there are several excellent aggressive tires available in your needed size. BFGoodrich (www.bfgoodrichtires.com) offers both the All-Terrain T/A and Mud-Terrain T/A KM2 in a 235/75R15. Goodyear (www.goodyear.com) offers its very cool-looking new Duratrac. General Tire (www.generaltire.com) has the Grabber AT2. Maxxis (www.maxxis.com) has both the Trepador and Bighorn. All of these are readily available in your size. We would encourage you to point this out to your local tire shop because they should have access to several of these brands, but if they still can’t help you, then any large mail-order company like Discount Tire (www.discounttiredirect.com) or 4Wheel Parts (www.4wheelparts.com) will be able to deliver the small knobby tires of your choice directly to your door. Both of these companies also have retail stores all over the country, and there may be one near you.

Nuts, I’m Confused
The Numbers Don’t Add Up
Q I am confused by the power and torque numbers I saw in your article on Grand Cherokee upgrades (“Sum of the Parts,” Dec. ’13). On page 35, the caption states the engine is rated at 265 hp and 325 lb-ft of torque. But when you started you had 188 hp and 227 lb-ft of torque, and after all the upgrades you still only have 220 hp and 253 lb-ft of torque? Am I missing something here?
Billy Ferguson
Via nuts@4wheeloffroad.com

A The discrepancy in the stated numbers has to do with the parasitic loss of the rest of the drivetrain components. The engine is rated from the factory with 265 hp and 325 lb-ft of torque at the crankshaft. Our baseline of 188 hp and 227 lb-ft of torque was measured at the rear tires. The significant difference reflects the fact that power from the engine is lost as it travels through the rest of the drivetrain. The transmission, transfer case, driveshaft, and rear axle all drain engine power due to internal friction and a variety of other factors. In this case, we measured about a 30 percent loss in horsepower at the rear tires compared to the factory rating. This is not at all surprising when you consider that the factory’s numbers tend to be a tad optimistic and represent a brand-new vehicle, whereas our tester had about 110,000 miles on the odometer at the time of the test. Plus, the test vehicle was equipped with full-time four-wheel drive, so the drivetrain losses are greater than a vehicle that could be shifted into 2-Hi. The factory rating we mentioned in the article is simply a reference; the numbers to pay attention to are those we measured at the wheels.

Load More Read Full Article

Comments

Advertisement