Without axles race cars can’t even leave the pits, let alone go fast. The same goes for any street cars. Just like engines and tires, axles need love too, and they need maintenance. Especially axles on front wheel drive and rear wheel drive independent rear suspension cars. These vehicles have constant velocity (CV) joints. And as the name implies, unlike universal joints, the speed at which they rotate does not change as it moves through its range of motion. While the CV joints are sturdy, CV joint boots, well, not so much. But we’re here to help.
In my opinion, CV joints are a thing of miracle. They take all of the abuse of acceleration, deceleration, and are able to articulate during steering and suspension movement. These things keep the car going forward while putting power to the wheels, even after relentless 3,000 rpm clutch dumps during standing starts. Protecting these marvelous devices are rubber boots, which keep damagine dirt and grit out and hold the grease in place so the CV joint doesn’t weld itself together in under half a lap. With all of that constant velocity and suspension undulation there are a lot of moving parts in a CV joint and they need grease to survive.
Since we have established that race cars need axles to move, and we have determined that these axles need grease to survive, and we know that all of that grease is held in place by a rubber boot then we can surmise that these rubber boots are pretty important, and trust me they are. When a boot fails, and an axle is rotating at 130 miles an hour, physics takes over and the grease is rapidly ejected via centrifugal force. Simple explanation: the grease flies out of the boot, leaving the CV joint dry, which leads quickly to a failure.
Should you spot a torn boot, replacing it is easy and inexpensive. We will walk through the steps here and show you just how easy it is, using our 1990-1993 Acura Integra race car as an example, though the steps are essentially the same for any front wheel drive car. First step: yank the axle out of the car.
If you have a spare, well built, road racing axle you can simply swap the entire new axle assembly into your race car and repair the boot on the other damaged axle later. If you don’t have that resource, you aren’t out of luck. You can replace the a CV joint boot fairly simply and quickly, even at the race track. There is nothing technical about this process, it just takes a couple of specific tools to make the job easier and some spare parts. An inner axle CV joint boot cannot be replaced while the axle is still in vehicle. The axle assembly has to be disassembled in order to replace a boot. Pull the axle out of the car and find a nice flat, well lit, clean place to work.
These types of tears on a CV joint boot can be caused by a driver leaving the racing surface and off-roading through rocks and other sharp objects in the dirt at the exit of a corner. Be careful as to the spare boot you carry with you as we have found that not all boots are created equally. We try to get the thickest ones available on the market for use in road racing.
To complete the CV boot repair you will need the following tools and parts:
TOOLS: small screw driver, cutting pliers, c-clamp pliers, band strap tool.
PARTS: new CV boot, grease, two band straps (one small diameter, one large diameter).
Insane Shafts sells a slick little CV Boot Kit that has everything you need to repair both sides of an axle and comes with the perfect sized grease tubes. Our CV Joint Boot Repair Kit box in our race trailer has a number of these repair kits inside it along with the specific tools to replace a boot quickly. We don’t always have a lot of time at the track between practice, qualifying, or race sessions to get projects done. Being organized has ensured we can always get back on track even if we find a torn boot.
The first step is disassembly. Use medical gloves and have some throw-away rags ready because this is going to be a messy process. And change out of your driver’s suit before commencing a repair. CV grease is nasty stuff and it gets everywhere. Simply cut the two band clamps that hold the small diameter and the large diameter of the CV boot on the axle. Now the cup section (outer part) of the CV joint will come away from the tripod section (inner part).
For many people, there is a bit of a mystery about what is inside these CV joints. It is a very simple design. This inner CV is a tripod that has a cup (or cage) around it. There are bearings throughout to keep things rolling along. It allows for articulation at an even speed as the axle is putting power down to the track.
Having the right tools for the job always makes things easier. C-clip pliers will make quick work of the C-clip that holds the tripod assembly on the end of the axle. Once this is removed then the small diameter of the boot can be slid off the end of the axle.
Our road racing axles are built by Mike Evans, owner of Insane Shafts. Mike builds extremely strong axles for 500 horsepower front wheel drive Honda drag race cars, and builds blue printed, long lasting, strong axles for road racers, too. Before I ever attempted to replace a boot on one of his custom built spec axles I called him up to ensure I did it correctly. He walked me through the correct steps (which you are reading here) and gave me some insider tips on installing the boots. “Air expands when things get hot,” said Mike. “When the axle gets hot the air expands and that can balloon the boot. You need to purge some of the air out of the boot before you tighten the band clamps.” Mike suggests using a small screw driver between the axle and the boot to let some air out. I asked Mike, “So, you want me to burp the boot?” and he replied, “Exactly, I want you to burp it.”
What grease to use in a CV joint is a driver’s choice. Every racer I have ever met has extremely strong opinions about the perfect grease for CV joints or wheel bearings. We can all agree on one thing: some kind of grease is important. And we call all agree that the grease that NAPA Auto Parts or Autozone uses in their re-manufactured axles is the cheapest grease they can find (not what race car drivers are looking for). Our team, DNN Motorsports, uses the little individual easy to use tubes from Insane Shafts. Mike Evans has some super secret sauce grease he builds his axles with and it hasn’t failed us yet.
Like most things automotive repair related, assembly is the opposite of disassembly. Take the time to clean the old grease off of the CV parts and inspect for wear or damage. You will use the C-clip pliers to replace the C-clip on the end of the axle which holds the tripod assembly in place. The order of operations is as follows: first slide on new small diameter band clamp, then slide on the small end of the new CV boot, slide on the tripod assembly, and then install the C-clip.
Now that you see the design of how these axles are assembled, and realize how the rubber boot with little band clamps is what actually holds the two pieces of the CV joint together, you will be more careful next time you are trying to rip an axle out of a transmission. It is better to use a small pry bar between the transmission casing and the cup of the CV joint.
A band tool for installing the band clamps is a life saver for getting just the right amount of tension on the bands. The trick, according to Mike Evans from Insane Shafts, is not to deform the boot at its mating point with the cup or the axle. As the band tool holds the tension, you roll up the tool to bend the band (a little crease here is good), and then the tool cuts the excess band away. You press down the two small wings on the band clamp to hold the little piece of band left over and your boot is permanently in place.
Once the axle is completely assembled Mike Evans suggests using your hands to articulate the axle back and forth a bunch to move the grease around the bearings before installing the axle back into the race car.
We go the extra step of driving the car in circle eights in the paddock to ensure the grease is sufficiently in the correct places on the CV joint before we put any racing loads on the axle. We check the new CV boot for any leaks at the band ends or new tears before heading out for an important race.
CV joints are amazing components and they are abused heavily under racing conditions. All they want to continue to live is some grease and a healthy CV joint boot to keep everything together. Take the time to inspect your boots to ensure your axles can get you to the finish line.