cv gasket

wit61 · 10-07-2003, 05:58 PM

After a weekend spent replacing cv axles, I have to ask :

What is the purpose of the CV axle gasket ? It sits outside the mating surface and I can't figure out why they didn't go with a full gasket between flat surfaces.....

Al S · 10-07-2003, 06:28 PM

A full gasket would compress over time, and you wouldn't want the CV joints getting loose.

wit61 · 10-08-2003, 04:29 AM

Al S,

How is the concern about compression any different from say a head gasket ? Plus, the cv gasket goes around the perimeter where the bolts pass through. I'm still puzzled as to its' function.

Eugene at Pelican Parts · 10-08-2003, 08:24 AM

I understand your question, but I don't agree that they are ineffective (perhaps your joints are slightly different that mine). On my SC, the gaskets adhere onto a seat around the bolts (like you said) on the flanges. They are thick enough to bridge the space between the seat and the joint, sealing in the grease.

Now, regarding your question about the gasket not being between the mating surfaces, the comparison to a head gasket is inapplicable. The forces that act on a cylinder head try to push the head off the block linearly outward. In this example, the head studs secure the head in this direction, and a gasket that completely covers the mating surface is very effective.

On a CV joint, the load is perpendicular to the orientation of the securing bolts. The torque from the axle is trying to shear the bolts instead of stretching them out. With this in mind, we want the bolts to provide a VERY solid connection between the joint and flange. Since these parts cannot be welded together, zero clearance can only be achieved by the lack of a gasket, or by giving the gasket its own seat. Imagine if we used a full gasket, but it deteriorated over time. That would effectively cause the joint to loosen up on the flange. Not a pretty scenario.

I hope this answered your question, wit. Let us know!

wit61 · 10-08-2003, 03:57 PM

First of all, thanks for the explanations, and the patience.

I think my confusion is that if gasket deterioration is a concern, what happens with the existing design when the gasket goes south? I ask this because the ones I removed were in pieces or entirely missing on one of the inners. The grease did not escape because the surfaces are mated directly by the inner flange, which made me wonder what the outer gasket (and its' seat) is for.

Regardless, thanks to this board I am once again a little smarter ! Thanks

Jim Sims · 10-08-2003, 04:27 PM

The drive shaft torque in a properly tightened CV joint flange is not transferred through the screws in shear. The screws work in tension providing a clamping force (normal force) across the joint. The product of this normal force and the friction between the gasket and the metal flange surfaces produces a "traction" which carries the torque across the joint. The gasket is there to keep the joint sealed from the outside environment; a metal to metal joint of reasonable tolerance and surface finish wouldn't seal out water. An o-ring seal system would be better but is more expensive to make and the o-rings are a pain to keep in place without a special dovetail o-ring groove (even more expensive to make). Cheers, Jim