Check here for specific information on manual transmissions: Manual Transmission Information.

Check here for specific information on automatic transmissions: Automatic Transmission Information.

Transfer Case Discussion:

Transfer cases come in several different flavors and styles.

Some have two shift levers, some have one, some have electrical switches instead. Those with two shift levers from the factory have one lever for four-wheel-drive/two-wheel drive, and one for high range/low range. Aftermarket dual-lever setups may provide different combinations.

One trait that sometimes confuses people is the "divorced/married" mounting of transfer cases. The most common is the "married" type, where the transmission is bolted solidly onto an adapter housing that's bolted on solidly to the transmission. Divorced transfer cases are more common in long-wheelbase trucks, and have a short driveshaft that connects their input to the output of the transmission.

Some transfer cases have the rear output directly behind the front output. This used to be fairly common, but seems to have gone away in the last 20 or so years.

From what I've seen, in general, most Chevy/GM solid axle trucks, Dodge solid axle trucks, small Jeeps, and International trucks all used to have a right-hand drop front transfer case. Starting with the YJ's, the small Jeeps moved to a left-hand drop. Somewhere along the line, the Wagoneers also moved from a right-hand drop to a left-hand drop. Chevy/GM trucks with independent front suspension also used a left-hand drop. For has used the left-hand drop all along.

Check here for a quick chart on transfer cases: Transfer Case Information.

Check here for more detailed information on transfer cases: Detailed Transfer Case Information.

Axle Discussion:

I'll handle some general axle information here. For more specifics, see Detailed Axle Information.

There are several axle design styles, but the two most commonly found today are the "Hotchkiss" and "Salisbury" styles.

The Hotchkiss style has a removable third member, which contains the ring gear, pinion gear, and differential. This design is also called the "third member style" or the "banjo" design. Some examples of this are the Ford 9", Chrysler 8-3/4", and the Toyota truck axles.

The Salisbury design is much more common. In this design, the cast (usually iron, but sometimes aluminum) center housing contains the gears and differential and has a bolt on cover. Steel axle tubes are pressed into the sides of the housing. Examples of these axles are the GM axles (10, 12, and 14 bolt), AMC Model 20, Ford 8.8", Ford 10.25", and all Dana axles that I've ever seen.

There is a lot of discussions that go on about which axle is strongest. Here's the final answer:

There is no answer unless you define what you mean by "strongest".

For example, the ring and pinion gears on the Ford 9" are beefier than the Dana 60 or the AMC model 20, while the latter two have a larger diameter ring gear. If you cut a cross section from the inside to the outside of the ring gear, the Ford 9" has a larger cross sectional area. This means that there's more "meat" in the Ford gear than there is in the other makes. The Ford's low pinion has two benefits; one, it allows for a third bearing on the pinion, which Ford located at the inside end. This is a really nice, strong setup that helps keep the pinion gear from "walking" up the ring gear during high-torque situations and thus flexing/weakening the pinion shaft. Also, the low pinion position allows for more teeth to be in contact between the ring and pinion gears at all times as compared to the Dana and AMC axles.

However, since the "hole" inside the 9"'s ring gear is smaller than the Dana 60 or AMC 20, and thus the differential isn't as big as it is in the Dana 60 or AMC 20. The bigger the differential, the more metal there is in it, and thus the stronger it is. The Dana 60 wins this round.

This is just an example of how confusing the whole thing is, and as to why you can't just globally say one axle is stronger than another. And in the above discussion, I didn't even touch on things like axle shaft diameter, spline count, tubing wall thickness, or full floating/semi-floating outer ends.

There is one point in favor of Dana axles in general. Dana Spicer Corporation makes some of the best gears ever, not only in their axles, but also in their transmissions and transfer cases. I don't know if it's in their design formulas, or in their metalurgy, but they make great, tough gears. If I ever need to buy a new set of gears for a Dana axle, I'll be looking only for Dana branded ones.

Most axles have the pinion located lower than the centerline of the axle shafts/differential. This is fine on cars, but on lifted trucks, this causes the angle of the driveshafts to be steeper than if the pinion was located higher. The only OEM axles that I'm aware of that ever had this higher pinion are from Dana. In the late 1960's, Ford requested a high pinion axle from Dana to use in the front of their trucks. Seeing how well that worked for Ford, some other makes also used high pinion Dana axles. High pinion models include the 30, 44, and 60. Sometimes these axles are refered to as "reverse cut", due to the fact that the angle of the teeth in the gear sets is cut in reverse of the gears in the standard axles. (Some folks also call these "reverse rotation", which really isn't accurate, as any axle used in the front of a vehicle is running in "reverse rotation" as compared with if that axle were in the rear of the vehicle.) One added plus of these axles is that when a standard axle is run backwards (like, flipped around for the front of the truck), the gears are considered to be running in their weakest direction; Dana says this makes them about 30% weaker. The reverse cut gears are stronger, since they run in the "forward" direction.

Here's a question that keeps coming up regarding pinion placement on axles:

"Why don't you just flip the axle upside down, then you could raise the pinion and reduce your driveshaft angle."

Some folks even claim to have seen or spoken with someone who's done this. As a matter of fact, I even saw this suggestion in a hot rod magazine once, as a suggestion to get the driveshaft up out of the wind stream passing under the car.

No one has actually done this and made it work right. Period. Everyone that's claimed you could do this and has been pressed on the issue has either backed down, "sold the truck several years ago" or "heard about it from someone else".

You can't turn an axle upside down and get it to work.

Lots of folks claim it's because of oiling issues in the gears. While that may be a factor, there's still one big problem. If you turn a rear axle upside down, and put it back in the rear of the vehicle, the wheels will turn in the wrong direction. Period. There's no way around it; no different gear sets, no turning the ring gear around (yeah, I've actually heard that one a few times; the poor guys really didn't know anything at all about how the internals of an axle work to have suggested that one), nothing. If you want a high pinion on a Ford 9", you'll need a different third member, and thus different gears too, as the angle of the teeth on the gears is set by how the pinion gear and ring gear meet (both the angle and center line-to-center line distance). Currently, the only outfit I know of that makes a unit like this is Currie. It's some big $$$, but it's a cool solution.

If you order a replacment differential for your axle, you might be asked to provide the gear ratio that you're going to be using. This is because of something known as the "carrier break point". It's a confusing sounding term, but the concept is pretty simple. There's a big flange on all differentials, whether they be OEM or aftermarket. This flange is provided for the ring gear to bolt onto. Since a lower numerically gear ratio will have a larger overall diameter pinion gear, the toothed side of the ring gear will need to be further from the pinion centerline the lower the gear ratio, and closer the higher the ratio goes (as the pinion gear gets smaller in overall diameter). Sometimes this can cause the ring gear to be too thick, or too thin. To combat this problem, the axle designer will design a different "carrier" for the differential, that will move the ring gear flange closer or further from the pinion.

The end result is that you'll see differentials listed with a range of gear ratios that will work with them. Now, mind you, not all axles have a "break point" (break point being where the differential changes for the next range of gear ratios). For example, the Ford 9" has no break point, while the Dana 44 has a break point between the 3.73:1 and 3.92:1 gear ratios. Thus, on the Ford 9", you can change gear ratios without having to get a different differential carrier. On the Dana 44, one carrier will work for gear ratios of 2.72:1 to 3.73:1, but requires a different carrier for gears in the range of 3.92:1 to 5.89:1.

Check here for information on break points for various popular axles: Axle Carrier Break Point Information.

There's one more question that I've been asked several times that I'd like to address here. That question is:

"What's with the weird numbers on axle ratios?"

This is actually a pretty good question. It seems like all axle ratios have two digits after the decimal point, doesn't it? They're not nice whole numbers, like 4:1, but something like 4.09:1.

The reason actually comes from a pretty good engineering practice. First, however, let's get into a bit of math. The gear ratio is calculated by taking the number of teeth on the ring gear and dividing it by the number of teeth on the pinion. The result is how many times the pinion gear rotates for one full rotation of the ring gear. Thus, if the ring gear has 45 teeth, and the pinion has 11, the ratio (rounded off to the nearest hundredth) is 4.09:1. Another common ratio that's close to this is 4.11:1, which comes from there being 37 teeth on the ring gear and 9 on the pinion.

Okay, now that we have the ratio math under our belts, let's look at those raw numbers again. Both gear sets listed above have one gear with a prime number (11 and 37). Those prime numbers are what gave us the messy math, but the prime numbers also have an interesting effect on the gears as they run. It causes every indvidual tooth on the pinion to mate with every tooth of the ring gear. (The technical term for this is a "hunting gear set.") In the case of our 4.09:1 ratio, every 11 rotations of the ring gear sees each tooth of the ring gear be touched by each tooth of the pinion. What this does is promote a very even wear pattern on the gear teeth, which greatly extends the life of the gears.

Now, there are some exceptions to this prime-number design practice. On some smaller, lighter axles, like the old Ford Salisbury-style thing that was in my old 6-cylinder Mustang, the tooth counts were 35 and 10, giving 3.50:1 gearing. This was considered okay for the supposed light-duty use of that axle. I'd be surprised to ever find a medium-duty or heavy-duty axle without at least one of the gears having a prime number of teeth on it.

As a side point, think for a moment about transmission and transfer case gear ratios. Other than a 1.00:1 gear, all the other gears are weird numbers, going off into the decimal places too, aren't they? It's for the same reason as we just talked about; it's an engineering practice that makes the gears wear evenly and last longer.

For details on specific axles, see: Detailed Axle Information.

Ackerman Geometry Discussion:

Please understand that the changes of my selection of grammar and spelling in the following discussion is on purpose. This information is taken directly from an email conversation I was having (thus the grammar) with some Canadian buddies of mine (thus the spelling).

"The whole idea of the Ackerman geometry is to move the inside wheel further than the outside wheel in a turn. Now, mind you, the rest of this is the book theory. We all know about theories and how they apply to the real world... The Ackerman geometry is based on a line that goes from the centre of the pivot point (ball joints, in this case), and thru the centre of the rear axle. (For now, let's put aside the fact that those of us that swap to axles of different widths, and fart around with the wheelbase screw up this last part.) The connection for the tie rod should ideally be someplace along this line. On two-wheel-drive stuff, this is frequently behind the axle, while 4x4's have to have that point in front (so as not to hit the pinion and driveshaft of the front axle). If you drill the holes for the tie rod closer to the centre line of the ball joints, AND you keep in on this "Ackerman line", you won't have changed anything. If the arms on the steering knuckle are straight you've got a good chance at the hole falling on this line. If the arms are curved, well, then you might have a problem. Really, though, the OEM may be a bit off anyhow. (For example, my 1984 Bronco uses the same knuckles as the 1984 longbed F150. Obviously, the wheelbase is different.) If your Ackerman is off too far, you'll get a kind of chattering from one of your front tires when you corner slowly (been there, done that), as one of the tires tries to drag around the corner instead of rolling (which one chatters is based on your speed)."

General Engine Discussion:

Please understand that following may have changes in my selection of grammar and/or spelling and a few typos. Any information in quotes is taken directly from an email conversations I was having (thus the grammar and typos) with buddies of mine. Sometimes, these are on Canadian lists (thus the spelling).

Also, I'm not planning on going as in-depth into engines as I have for transmissions and axles; putting together engine data would be at least as involved as the transmission and axle sections were, and I'm not feeling that I've got a very complete listing of those.

"Hey All! Catching up on a few threads here; and I noticed the discussion on how a 4.0L V-6 won't lug as well as an 4.0L I-6. Another comparison I've seen (and experienced) is the Ford inline 300cid versus the Ford V-8 302. The reason the V-6/V-8 dies easier when lugged down is is 'cause of the V-shaped cylinder arrangement. When building engines for torque and extended low RPM usage, we always used to use the heaviest flywheel we could find. Yeah, this kills the ability to rev up quickly, but the more rotating mass, the better the engine runs at low RPM. How this translates into everything, is that when you think about it, an inline engine has a longer crankshaft than a V engine. Right there, a lot more mass. At really low RPM, an engine's crankshaft rotation tends to pulse just a bit; it speeds up after each cylinder firing, and slows down on each compression stroke (think of the wacky sounding idle of the odd-fire Buick V-6's, as they take this to an extreme). The more rotating mass there is, the less there is of this effect. In other words, the engine continues to rotate into the next compression stroke and to the next cylinder firing. My personal experience has been more with the Ford 300 and 302 than with anything else. For a low-RPM farm truck, the 300 I-6 kept running when lugged down a whole lot better than the 302's did. (Of course, the 302 does have the advantages of being able to rev higher and faster, *much* lighter weight, shorter length, better mileage, and slightly easier-to-find parts.) Now, I'm still a fan of V-8's, so that's what'll be going into my Jeep. "

When you're building an engine, think about the application of the engine before you get started. A good, slow-running torquer buildup (good for a rock crawler 4x4) takes a different build than a quick-revver (drag racing car). For lots of torque, use as much rotating mass as you can; in other words, use a heavy flywheel, and if possible, a heavy crankshaft and vibration dampner. For quick revving, you want as little rotating mass as possible; so go for light components. Some drag racers take this to the extreme by using aluminum flywheels.

A lighter rotating mass has less "drag", and thus can change speed quicker, but at idle or low (engine lugging) speed, there's less mass (and thus less inertia) to keep the engine rotating over to the next power stroke. Thus, at low engine RPM, a lighter engine may idle rougher, or lug down and die easier than the heavy engine. Since straight-six engines by design have more rotating mass than a V-shaped engine of comparable size, they do quite well in low-RPM work and produce some of the best torque-per-cubic-inch numbers.

However, there are some very definite advantages to V-shaped engines. For a comparable displacement, a V-6 or V-8 is lighter than a straight-six. Also, the V engines aren't much wider than the straight engines (less the exhaust), and are quite a bit shorter. This makes them a whole lot easier to fit into the short engine bays of pre-1972 CJ's. While there are some performance parts for straight-six engines, there's nowhere near the huge variety of parts available for small block V-8's. Since the V design is more efficient (shorter and more equal length intake runners, for example), the horsepower-per-cubic-inch ratio is higher. Also, block weight for a comparable displacement is less with a V-designed engine. (If I remember right, the last set of numbers I saw showed that a Ford 300 cid straight-six weighed about 160 pounds more than a Ford 302 V-8. That difference is equivalent to a couple of big winches on the front bumper.)

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