Here, the pinion loads are applied to the complete axle housing during a hard-acceleration event. If you look underneath a lifted truck when it takes off from a stop, you can see the pinion portion of axle twist under load. As this depicts, the forces twist the axle from front to back. Since your goal is to attain maximum efficiency, you must understand all these forces to counteract and remedy these forces. After all, the goal is to maintain the driveshaft and axle alignment to transmit maximum power. (Dana Holding Corporation/Joe Palazzolo)
This pinion-to-stationary ring gear reaction actually rotates the entire axle housing counterclockwise, as viewed from the right side of the vehicle. The result is inefficient transfer of torque. This is why traction bars and pinion snubber-style devices came into existence, and were added to many vehicles. It was recognized that if this upward rotation tendency were not resisted, then the suspension would have a difficult time trying to counteract the event. The issue comes into play when this rotation of the axle is finally resisted, and the axle returns back to the correct state—back to its original, near-horizontal position. As the axle rotates downward quickly, it applies an additional rotation load on the wheels. This is very common with traditional leaf-spring-style suspension setups. In this situation, the leaf springs temporarily deform from their normal bow shape into an “S” shape and this event can be seen from the side of the vehicle. As the spring releases this stored energy, the wheels may momentarily lift off the ground with some vehicles. This is more evident on pickup trucks but can happen on cars as well.
There are many other events that can cause wheel hop. Even non-beam-style-axle vehicles can exhibit wheel hop based on the suspension geometry and overall axle drive system stiffness. The worst thing that you can do during a wheel hop condition is to stay on the throttle. As the wheels lose traction and regain traction quickly, enormous spike loads travel through the drivetrain. These impact loads can cause drivetrain components to fail quickly.
Finding the Right Parts and Service
Now that I have covered the fundamentals that apply to all rear axles, let’s review how to find a good shop for parts and service.
Let’s face it; at some point, you will need to find a place to purchase parts. After reading this text, you may even decide that you do not want to tackle the work yourself. What are some important items to consider when deciding where to buy your parts? Price is very important, and most places are competitive. However, you may want to get some technical assistance, and that costs money too. Larger businesses commonly have free tech lines or email assistance. Some very reputable places may not have the best prices, but can help you make the best-informed decision. You definitely want to get your parts from a place that moves sufficient inventory to actually have the parts on hand. Some of the smaller shops cannot afford to have stock on hand, and you could be waiting quite some time to get your parts. Not to say that the smaller shops are bad, especially if you are working on a longer-term project and have the time to wait a few weeks for the right parts. If it is your daily driver and weekend race machine, you probably want, and need, your parts quickly.
This is just one of the inventory stock aisles at Drivetrain Systems (DTS). DTS and several other drivetrain vendors offer a complete line of axle and driveline components. DTS has an entire section of the building dedicated exclusively to inventory. It stocks a wide range of drivetrain parts, and they purchase more common items in bulk. I was amazed to find pallets of Eaton posi units. (Randall Shafer)
Now, with the relative ease of shipping and the Internet, you may want to buy complete parts, a complete axle, or even send yours to a reputable shop to get it rebuilt. Some places just sell parts and do not work on the axles themselves. You want to be careful with these places. They are great to get parts from, but be cautious of any advice that they give, as they do not have daily hands-on experience with the parts and vehicles. A lot of these words of caution pertain to any work that you are having performed.
Here is a tiny sample of the quantity of hardware on hand at a great specialty shop like DTS. This amount of inventory allows the shop to service just about any product that comes in the front door. (Randall Shafer)
Here you can see the ever helpful counter person at DTS is actually the sales and service manager. Rob Gutowski takes the time to explain the intricacies of the hardware and function to help the customer make the correct decision. (Randall Shafer)
You may decide that you do not have the time to work on your axle this time around, and just want a competent shop to handle it for you. Unfortunately, there have been, and still are, many automobile repair shops that are corrupt and incompetent. The more specialized the repair becomes, the more difficult it is to find a trustworthy, competent shop and mechanic. Most general repair facilities do not like working on axles. Axles are at times more of an art than a science, and some mechanics get frustrated trying to repair them correctly.
It is not always the mechanic’s fault. They are trying to fix an item that, at times, they have not been properly trained to repair. It is difficult to get good training on axles; shop manuals are not always good sources of information, and even your local dealership may not have an axle expert on hand to correct the problems. Realistically, axle problems are not that common, and therefore the mechanics cannot stay up to speed on all the latest items. There are good reputable shops in about every state, but you may need to drive a little further to get to them. We have found that the hassle of driving further to find a good axle repair facility far outweighs the hassle of dealing with a nearby, marginal shop.
This specialty driveline shop concentrates on axles of all types. Notice that they not only repair and service but, just as important, they sell parts. This means that they stock plenty of parts and are familiar with what works and what doesn’t. (Randall Shafer)
As you look around for a shop, the facility does not have to be spotless in order to be reputable. Busy shops work through a lot of drivelines, so many are not “operating room” clean. Here is a great selection of hard-to-find parts. Every good axle shop should have this available. (Randall Shafer)
This selection of used parts helps keep stock vehicles in good repair. Some of these parts are actually take-off parts with less than 1,000 miles on them.
At times, shops that do not work on axles often do not have some of those hard-to-find parts at their fingertips. Your axle may need a new adjuster nut for the differential case support and the shop does not have one available. If they are in a hurry to get the car back to you, they may improvise. Axle support takes up valuable shop space, but it’s well worth it when when it comes time to repair or replace some of the less-common axle internal components.
There are even times when you need a good axle shop to work on your normal daily driver. At DTS, they even have good, lightly used parts that work great for your daily driver. Some of these parts have very low miles, while others are open-box customer returns. With options available, there is no need to explore around the local scrap yards in your quest for good used parts.
Here are some good questions to ask:
• How many axles do they work on per week?