Whether you’ve got a long-travel go-fast rig or a showroom stock truck, A-arm IFS front suspensions are a fact of off-road life these days. Within an A-arm 4x4 system, CV-equipped drive axles are a key component.
Despite external appearances, all CV axle assemblies aren’t the same once you look underneath. Here’s what’s behind the boots.
01. Here’s what you’ll find at the outer end of virtually every CV shaft assembly. It’s a standard or “fixed” CV joint. There’s also a “plunging” CV joint, which we’ll get to later. You probably know that “CV” stands for constant velocity. This means that no matter what the axleshaft’s angle, the axleshaft and the outer CV joint housing (and thus the wheel) will turn at the same rate. By contrast, U-joints tend to “pulse” by accelerating and decelerating when turned to extreme steering angles.
05. Here’s the same plunging CV joint at the opposite end of its travel. As the suspension cycles up and down, the distance between the differential and the wheel hub will change. This change in distance means a non-fixed inboard CV (tripod type or plunging six-ball) is necessary because it can compensate for the changing distance.
06. Up close, you can see the angled ball grooves in the outer housing of a plunging CV joint. The center star and cage are also designed around the angled grooves, and the total package allows the center star (with its attached axleshaft) to move in and out while maintaining perfect constant velocity. Plunging CVs are capable of operating at much greater angles compared to tripod joints. To save money, most OEMs choose to use tripod joints instead of plunging CVs.
10. Here’s a newer Toyota axle-and-hub assembly. This design is typical for all vehicle brands these days. The outer CV bell has a splined shaft that indexes into a unit bearing hub. There’s an outer nut that holds it all together, including the unit bearing hub. On the inner side, the tripod joint’s splines slide straight into the differential. You’ve got to have an outer CV bell and an inner tripod bell both attached in order to drive the vehicle. Break a CV joint or axleshaft, and you’ll have to replace it with a good one before you drive any further. In an emergency, you can run the outer CV and tripod bells by themselves (no guts or axle shaft) in order to make it home. The good news is that the newer Toyota CV joints are actually bigger and stronger than their older counterparts, so you’re less likely to break in the first place.
11. All CV joints aren’t of equal quality or size. Kartek Off Road stocks many models and options to fit a variety of needs and budgets. Porsche CV joints (both fixed and plunging) are commonly adapted to other applications. That’s a 934/935 model on the left, and a 930 model on the right. The dollar bill is for both size and cost comparison. The bigger stuff is stronger as well as more expensive. Also note that the 934/935 CV is polished. The polishing allows smoother, cooler operation, but of course it adds to the price.