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Manual vs. Auto Jeep Transmission

Posted in How To: Transmission Drivetrain on May 1, 2011 Comment (0)
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Manual vs. Auto Jeep Transmission

We have all been down this road. Whether in your buddy's garage, out on the trail, or over a pint down at the local watering hole, the question of manual versus automatic is an argument that has been raging since before the first Powerglide was swapped into a Jeep.

The pros and cons are pretty well known by now. A manual transmission offers anvil-like reliability that doesn't care what angle you run it at, compression braking that no automatic can match, and a much more involved driving experience. The automatic, on the other hand, makes rock wheeling so much easier and makes driving on the street a nice and relaxing cruise.

Despite knowing all of the pros and cons, we all still have our preferences. Your three favorite monkeys like to think that we base our preferences on facts, but the only irrefutable fact is that everyone's preferences have just as much basis in experience as they do in cold, hard facts. We are sure that Joe Friday is rolling over in his grave for this one, but enjoy our poo-flinging gearbox session anyway.

Trasborg Weighs In
Let me start by the one statement that usually makes people think I'm the old dog that can't be taught any new tricks: "My favorite transmission is the SM465." Then my bonus follow-up statement that further puts me out with the lunatic fringe is, "I just don't trust automatic transmissions and I try to avoid putting them in my Jeeps if at all possible."

Look, I know that an automatic can be built to withstand the abuse we put them through, but I've had so many die on me over the years and a few leave me stranded that I just don't trust them. So unless there are outside factors, I try to avoid them. About the only one I do trust is the AW4, which I have in my '98 Cherokee, and even then I will tend to take a manual-equipped Jeep out into the desert if I know I am going to be far away from civilization.

SM465

On the manual side of the fence, I have a lot of first hand driving experience with the SM465, AX15, AX5, NV3550, T-150, BA10/5 and T-176. I've had two Wranglers with the infamous Peugeot BA10/5 and managed to rack up over 100,000 miles on them without blowing a single one up. So personally, I've not had any problems with the transmission. The internal hydraulic slave cylinder is another story, though. That said, I've had enough friends and acquaintances blow them up with some regularity and have been involved in plenty of transmission swaps because of them that I wouldn't recommend the BA10/5 to anyone, but I wouldn't hesitate to buy a Jeep just because of it.

The T-150, while I've never blown one up, has such a stupid-high First gear that it is near useless in the rocks or really anywhere off-road. The T-176 is another one that has gotten a less than stellar wrap over the years, and while First gear is nothing spectacular, I still had no problems with it in my V-8-powered CJ-7 rolling on 35s for somewhere around 40,000 hard miles. I've blown up more AX5s than I can remember and the only thing I have to say about that is that if you have one and kill it, you should definitely look into swapping in an AX15.

AW4

The SM465 has a great granny gear, I've run a couple of them with no oil accidentally, and they just take abuse. Sure, very abused ones can pop out of gear and almost all of them are rough to get into gear-but they are reliable. The AX15 and NV3550 are just about interchangeable to me. The NV3550 is probably the stronger of the two and has a better First gear, but I've got somewhere north of 500,000 miles on only three different AX15s and that seat time gives me a lot of confidence in them. The NV3550 always makes noise even in Neutral (which can't be good), and it takes expensive gear oil. Sure, I have about 40,000 trouble-free miles under the belt with one, but for the premium price they command over the AX15 I have trouble sending people that direction. I'll always say, "Well, find an AX15 or an NV3550." The external slave-cylinder-equipped models use all the same bellhousing and clutch stuff, and even the internal hydraulic throwout bearing versions can be easily converted. So to me the real questions are "What condition?" and "How much money?"

Hazel's Harpings
When do I want an automatic transmission? Well, my mom has bad knees. So if she's coming into town I like to have a vehicle with an auto for her to drive. Otherwise, make mine manual. I could play devil's advocate and find reasons and excuses to justify an automatic transmission, but in the end it basically comes down to you're either too lazy or feeble to work a clutch and toggle the shifter of a manual gearbox.

NV4500

That said, I do own vehicles with auto trannies. My Dodge Cummins diesel pickup has an auto. Why? Because I don't want to work a clutch in stop-and-go traffic or worry about stalling when backing a trailer up my snaking, inclined driveway. See? Laziness and feebleness. My Cherokee (Project JR), TJ (Project Steal-J), and Commando (Project Comman D'oh) all had autos, but that's only because they already had a slushbox tranny when I bought them. At one point in time while driving each of those vehicles on- or off-road I found myself thinking, "I'm gonna put a manual transmission in this thing." Conversely, I've never once thought, "Hey, this Jeep needs an automatic!" while driving one of my manual-transmission Jeeps.

With an auto you have to worry about torque converter flash rpm, stall rpm, shift point rpm and vehicle speed, vacuum and cooling lines, tranny pan leaks, loss of fluid, overheating, plugged coolers, uncovered sump pickups, burned fluid, and so much else. In an emergency maneuver you have to worry about how quickly you can toggle the shifter into Neutral or Reverse and then whether or not the tranny will be sucking air or if it'll actually grab and save your bacon before you roll off a million-foot-tall cliff and die. Sure, autos can shift faster than a manual, but we're talking off-roading in Jeeps here, not 1/4-mile drag racing. Besides, I can bang-shift an NP435 or AX15 surprisingly fast

AX15

With a manual you only worry about: does it shift and does it go. A slipping clutch, worn synchros, growling bearings, or even loss of fluid will rarely if ever prevent you from getting home. You can pour engine oil into your manual tranny, pound wooden wedges between your clutch and flywheel, or just grind gears with no disengagement to get home in a pinch. With an auto, to get home in a pinch you call a tow truck. Let's put it this way: in the two- or three-dozen vehicles I've owned during the 25 years I've been driving I've beat shoe leather five times because of an auto transmission that died for some reason or another. I've never whanged a manual transmission so bad that it couldn't get me back.

Cappa Shifts
You're a wuss if your Jeep has an automatic transmission. The only exceptions are if you purposely run an automatic to keep your 500hp V-8 from tearing up the rest of your drivetrain, or your Jeep has 20-inches of wheel travel and races across the desert at 120 mph.

Most people consider Jeeps to be enthusiast vehicles. They are driver's vehicles that are meant to be fun to drive and manipulate, much like a sports car. And who buys a sports car with an automatic? That's right, Christian's mom. Taking away the manual transmission shifter on a Jeep is like neutering a cage fighter and dressing him up in pink Hello Kitty garb.

32RH

Manual transmissions can improve fuel economy, they generally last longer, require less maintenance, create less heat, sap less horsepower, and are typically less expensive and easier to repair and rebuild than their automatic counterparts. You can sink a manual tranny in the swamp and it will still work for quite a while if filled with water. An automatic instantly stops working when the oil becomes contaminated. On steep hills the oil pickup on many automatics will starve for oil, halting forward movement. As long as the gears and bearings get a splash of oil now and then, the manual tranny can run upside down all day long if need be.

Like Trasborg, I've smoked several heavy-duty automatic transmissions, and a couple of them have left me stranded. However, I literally wore the synchros out of an ultra-high-mileage, 50-year-old GM SM420 truck four-speed (I had to pull the large twisted brass bits out through the PTO plate), but I could still drive the Jeep and shift. On another occasion I broke the case of a Saginaw four-speed nearly in half and all the gear oil leaked out. I was still able to limp it back to camp several miles through the sand dunes. Try that with an automatic.

The only place I'm sort of on the fence with the auto versus manual debate is in a tow rig. But in my case that's generally not a Jeep anyway, so I'll save that for another time.

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