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Vehicle Modification - CV & DOJ Boot Protection
Protect Dem Boots !
One of the major causes of Constant Velocity (CV) or Double Offset Joint (DOJ) failures in Subarus is damage caused to the mechanism by loss of lubrication and/or ingestion of abrasive foreign matter, such as dirt or water - particularly salt water. The most obvious way for this to enter is through a crack or tear in the flexible rubber boot which is designed to keep the lubricant in and the abrasives out. The boot can crack through normal wear and tear as it hardens through old age, but for "off-road" Subarus, damage by contact with foreign objects - sticks or rocks - is usually the cause. Changing boots is a messy, though not difficult nor expensive task; but replacing a CV or DOJ (generally meaning a complete new driveshaft) is definitely expensive. Avoiding the need to replace boots or shafts by adding a little protection ahead of time (insurance) is therefore very worthwhile.
A Cracked CV Boot and the Enemy Front Boots Damage to the front boots, even when not provided with extra protection, is not a common occurrence. The inner boots sit up high and are inherently protected by exhaust pipes and the engine crossmember. The outer boots are generally protected by the driver picking a careful path over visible obstacles and the natural protection afforded by surrounding lower suspension arm, tie rod and torsion bar (on the L-series). The outer boot, does become vulnerable, however, when the wheel is turned outward and the boot becomes exposed to strikes from the front.
Unfortunately for L-series owners, this form of protection is not a practical solution, as the L-series, unlike the MY, is fitted with a fixed torsion bar which would foul the same type of protector attached to the moving tie rod arm. If any L-series owners know of any other solutions, please let us know; otherwise - drive carefully. MY Series Front Boot Protector
Rear Boots Rear boots are the ones that score the most hits as that end of the car is unsighted by the driver and just follows the rest of the car blindly into danger. Fortunately, both the inner and outer boots can be protected on all models. Again, some early Subaru models were delivered with small protective devices strategically attached to the torsion bar suspension in front of the boots. While these protectors provide a small degree of protection in deflecting small sticks and flying stones away from direct impact with the boots, they provide little or no protection against big obstacles that a vehicles may encounter when negotiating rough tracks or rock climbing. This is a particularly dangerous time for the boots, when the vehicle is prone to losing its footing and the rotating rubber boots come crashing down on hard ragged surfaces. To provide better protection for these boots, large, self made protectors can be fitted.
Standard Fit Rear Boot Protectors - MY Series (maybe some L-Series)
For the inner boots, curved T-shaped brackets can be fabricated from steel (approx 50mm x 4mm flat) and welded to the diff carrier behind the axles, such that they curve forward over the axles to provide a hanging point for rubber flaps in front of each inner boot. Ensure that the size and gape of each bracket is such that it provides clearance from the axle as it deflects up and down over rocky terrain, and that there is small, but adequate clearance from the standard fuel tank. Thick canvas reinforced rubber is used for each flap which is bolted to the bottom of the Tee. This provides enough strength and rigidity so that the rubber does not tear easily on rocks nor bend back in the slipstream and rub the boot during normal highway driving.
Inner Rear Boot Protector
Although the appearance of such large flaps hanging down does look rather ungainly, the seemingly excessive flap length is used to provide a protective envelope for the boot when driving over obstacles. If the vehicle comes down on top of an obstacle, the flap covers the underside of the boot to ensure that the boot enjoys only a rubber-to-rubber contact instead of a destructive rubber-to-rock engagement.
Inner Rear Boot Protector The outer boot can be protected by an even easier to fabricate bracket and flap. For this bracket a 170mm x 60mm x 3mm piece of flat steel is used. For flap attachment, 3 bolts and a reinforcing piece of steel is used. The bracket is then welded at an acute angle to the trailing arm ahead of the axle. In this application it is important to use fairly rigid rubber as it needs to self-maintain a swept back angle under the boot, rather than hang down limply and drag over obstacles. Again, the length of the flap ensures a protective envelope is formed when travelling over obstacles.
Outer Rear Boot Protector (Axle Omitted From View)
Front View ........ Outer Rear Boot Protector ........ Rear (side) View Tidying Up When selecting your rubber don’t forget that there will be times when you will be reversing back into obstacles that may tend to catch the flaps. For that reason it is important not to have too rigid a piece of rubber as you need some flex to prevent it tearing off. You might also want to round off the corners of the rubber to prevent it being caught up on obstacles. And don’t forget to slap a bit of paint around the brackets and welds for that day down the beach. Happy Rockclimbing !
Danny Williams SC412 Disclaimer: Technical information given or disclosed in this website is given with the best intent and is advisory only. No responsibility is taken by the the Subaru 4WDrive Club of Queensland or its members for any damage or injury caused by any vehicle modifications made, or by the use of any products or the adoption of any procedures mentioned in this website. |
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Some of the earlier (MY) Subaru models were delivered with small, rudimentary protectors bolted over the tie rod arm. These simple devices, rectangles
of reinforced rubber attached by U-bolts, add a good degree of protection to the boots but some club members have opted for adding or replacing them with larger versions of the same device; providing just that little more protection than the standard fit.
This protective measure is cheap and simple to install on MY models and can be made from readily available materials such as a piece of rubber; nuts, bolts and washers, and plumbing type U-brackets available at most hardware stores.
