Driveshafts are nothing new, but they are a critical part of your vehicle. If yours is a 2×4, it has one; if it’s a 4×4, it has two; and if it’s AWD, well, it has one or two, depending on what make you’re talking about. But what goes into them? And how do they do their job?
These and other questions were on our minds lately, and we knew who to turn to on our quest to find out more – Jim Reel, founder and owner of J.E. Reel Driveline in Pomona, California. Jim has been tinkering on these drivetrain components for most of his life, and his products can be found in everything from daily drivers to UTVs to Trophy Trucks.
Through our discussion with Jim, we got into the nitty-gritty of driveshafts. From material make-up to balancing to upgrade considerations, our topics ran the gamut of these parts and their importance in four-wheeling. Without further ado, let’s dive in.
The Foundation And Basic Materials Of Driveshafts
Driveshafts trace their history back to the mid-19th century, and while designs have changed, their underlying purpose has not. “In a given rear-wheel-drive vehicle, it’s going to deliver the power of the engine and transmission to the rear wheels,” said Jim. “It helps push the vehicle forward or backward.”
These days, driveshafts are made of one of three basic materials – steel, aluminum, or carbon fiber. Steel is the most common, and in the off-road market, the predominate choice. “In off-road, it’s tougher than aluminum or carbon fiber,” commented Jim. “It resists bending and being bashed on rocks better than the other two.”
Aluminum, meanwhile, is similar to steel in a lot of ways, but its resilience to abuse is not quite as strong. “It’ll bend a lot quicker than steel, and doesn’t deal with side load as well,” said Jim. “If you hit a rock or hang it up on something, it will bend more easily than steel. But in drag cars, aluminum has the torsional strength required to do the job and it holds up fine.”
Lastly, there’s carbon fiber. “There’s really no application for carbon fiber driveshafts in off-road,” commented Jim. “You nick it, and it comes undone like a ball of yarn. It’s better suited to hot rods and drag racers.”
What Do The Numbers Mean?
When searching for a driveshaft, you might find a four-digit number along the lines of 1310, 1350, 1410, and so on. But what exactly do these numbers entail? As it turns out, they derive from Spicer’s numbering of their U-joints, which became the dominant standard over the years. J.E. Reel has also taken this route with labeling its driveshafts.
“1310 is the most common size,” said Jim. “It’s used on passenger cars and light trucks, and is naturally the most common U-joint size found on Jeeps. Going up to 1330, it’s the same size cap and trunnion, so the bearing is the same size as the 1310, but it’s a wider body. Then it goes to 1350, which is a much bigger trunnion, bearing, and body.”
Following 1350 is 1410, 1450, and 1480. These all go up in terms of body width, caps, bearings, and trunnions. “1480 is where you’re getting into Trophy Trucks and big drag cars,” said Jim. “Anywhere there’s big power, you want a big U-joint there to back it up.”
Beyond these are 1550, 1610, 1810, and then Spicer Life U-joints like the SPL140 and SPL190, which are “lubed for life,” and require less maintenance. This is the territory of big rigs, 2.5-ton stake bed trucks, box vans, and the like.
The Importance Of Being Balanced
Balancing a driveshaft is something that yours truly learned about firsthand a couple of years ago, also thanks to J.E. Reel. Back then, it was from a yoke going bad on a near-200,000-mile Toyota 4Runner. Today, it’s about relearning why driveshaft balancing is so important in the first place, and why neglecting it can only lead to heartache.
“The importance of driveshaft balancing is that it eliminates vibrations,” explained Jim. “Vibrations can wear out bearings and cause lots of premature wear on the rear axle, front axle, and transfer case.”
Entropy affects all things, as we know, and truck and Jeep drivelines are no different. Given the nature of their operation – delivering power from an engine or transfer case to a drive axle – driveshafts are subject to torsional stress, and going out of balance is a natural progression over time. “The tube wears and fatigues, and instead of running at 10 thousandths of an inch, it will move to 30 thousandths out of spec,” said Jim. “It will ‘bow,’ so to speak. At that point, it will cause a vibration. It’s not just spinning at that point; it’s also oscillating, similar to a crankshaft.”
When it gets to that level, balancing is required, and this is something J.E. Reel specializes in. With the proper tools at their shop, chiefly a balancing machine, the driveshaft can get back within specifications. “With our balancing machine and a dial indicator, we can locate where to add weight,” said Jim. “It’s similar to how they balance wheels and tires. We have a formula we use that tells us if it’s 10 thousandths this way, there is a set mount of grams of weight that will counteract that movement on the opposing side.”
Out With The Old, In With The New
There are some cases where a driveshaft can be so unbalanced that it is essentially a lost cause. “Definitely, there are times when you have enough fatigue in the tube,” said Jim. “The yokes can get stretched, and the eyes where the U-joints go can get loose. The tube can be fatigued enough to where we can straighten it and balance it out, but a week or two later, it’s back to its vibrating. Just like taking a piece of sheet metal and bending it back and forth will weaken it and eventually break it, the same can happen to a driveshaft.
If a customer needs a new driveshaft, J.E. Reel goes through the process of making one. “First, we look for what we can salvage,” said Jim. “If it’s a transmission yoke or something like that, we’ll reuse it on the next one.”
New ends would be pressed into the driveshaft tube, and the two would be phased to each other to remain straight and parallel. “We would dial it in true, weld it up, and then true it again to account for heat warping,” said Jim. “Next, we would take it to the balancer. Oftentimes, it will be minor imperfections in the yoke, or a light spot versus a heavy spot. The balancer will tell us where to put weight to offset the high spot. Once that’s done, the driveshaft is good to go.
The Clientele At J.E. Reel And Parting Advice
With so many applications needing attention to their drivelines, J.E. Reel is never short of customers. “We do a lot of Jeep, a lot of desert racing trucks, a lot of Ultra4 cars, and quite a bit of general repair for local mechanics and diesel repair shops,” commented Jim.
But the work at J.E. Reel isn’t always repairs. There are folks looking to upgrade, too; for example, people who are taking their truck to a prerunner stage, or a prerunner onto a full-blown racing truck. To that end, Jim has honed his skill over the years and always knows when to recommend an upgrade.
“These folks, when they’re ready for an upgrade, have signs that I can see it makes sense,” said Jim. “Usually, it’s because they’ve altered the suspension, going from stock to long-travel. Or, they might have adjusted the slip joint up and down to get more travel. Or, they might be going to bigger tires, and need bigger yokes and U-joints to accommodate the extra stress that comes from that.”
If there’s one thing to take away from all of this, it’s that driveshafts, while hidden from view, should not be kept hidden from memory. As a vehicle starts to increase in weight or height, it’s going to undergo additional stress to the drivelines, and taking care of these components will pay dividends in the long run.
Even right now, as you peer over at your truck or Jeep sitting on the driveway or in the garage, consider Jim’s parting advice: “Most of the U-joints now are tending toward non-serviceable, but they last longer than the greaseable ones. The big maintenance issue is greasing the slip yoke on a Jeep that sees water. It’s one of the biggest wear problems we see in our shop. They get rusty, freeze up, and break a transfer case, or they grind out and get loose and vibrating. It’s going to be sooner rather than later, so we recommend you check on the slip yoke.”