Here's what you do:
First time you get the acceleration vibration, swap cups side to side. Cost? Zero.
When you pit the new surface, install half-shaft spacers. Cost? About $169 for the pair.
Note that this will NOT prevent further pitting. Therefore, the third time the vibration happens, swap the CV cups once again. Cost is still zero.
Finally, the FOURTH time the vibration happens, you can either find a set of spacers with a different thickness, or replace the CV cups altogether. Replacement cost? $299 each list price. (Looks like the usual parts websites will sell them for $430 for the pair.)

So with the swap and spacer tricks up our sleeve, we can make the CV inboard joints last four times as long.

 

That might actually work.

Billman, what do you think?

I think I figured out what's bothering SpitfireS. Because our inner CV joint sits closer to the lower arm pivots than the upper arm pivots the spider is fully extended when the angles of the shaft and arms are most nearly equal. This is always the case, but the angle will be tilted down if the shaft pivot (the height of the spider) is lowered, and up if it's raised. That means our spider is farthest out with the arms angled down slightly.

Bill, do you have an easy way to measure the arm angles at stock ride height, full compression, and full extension? I think with SpitfireS's drawing and dimensions, and the three values, we can calculate the spider movement pretty accurately, and it would be interesting to compare the calculated values to the measured values.

As for myths being bustted, we've seen how the spider normally goes in and out as the outer CV joint goes in and out with the up and down movement of the suspension. Moving the cup outward doesn't change any of the angles, but merely shifts the working range to another part of the cup. It seems to me that the only time you'd want 10mm spacers on the differential flanges is if you increased the cars track by 20mm using longer wishbones, OR (possibly) if you were trying to get twice the life out of the inner joints.

Billman, how often to you replace inner CV joints on cars at stock ride height? Aren't most failures the result of boot damage and loss of lubrication?

 

Most failures are from the buckets pitting. I've done about 6 axle bucket swaps to fix them. Even then it's not really a "failure". Just a vibration under acceleration. All cars were stock height.

I have never seen one fail due to a bad boot or lubrication loss.

Even if the spacers DID do some kind of good, what would it be? S2k's are not experiencing premature wear due to lowering, they are getting a vibration from pitted buckets. You can bet your ass no spacer will fix that. In other words, they will not relocate the bucket to a spot that won't pit.

 

I am still confused about this.....I just had my03 lowered, on KW-V3's, and had the J's 10mm spacers installed.... I have never had vibration, or clicking noise. Car only has 20K on it...Is it going to hurt anything with the spacers installed...????

 

It's not going to hurt anything. I think what they've found out is that they just weren't needed in the first place (ie. a waste of money).

 

Thanks Rich...!!!!

 

Just a quick point to clarify - everyone has mentioned spider gears. This is referring to the tripod bearing? I've always known it as the tripod bearing, cos, well, there are three round things on the end of the shaft. I was 'taught' that the spider gears referred to gears inside the diff.

Another note from Saabworld - it's not uncommon to do the inner driver swap. Again necessitated by vibration under acceleration. On the old 99s and classic 900s, the inner drivers could be swapped to eliminate this problem as well. I guess my S2k isn't so different from the Saabs after all!

 

I usually analyze these types of things by extrapolating to extremes. One extreme is if the cup were as short as possible to barely allow unhindered ball movement through entire suspension travel. The other extreme is if the cup was long enough to extend past the wishbone pivot point on the frame. Which is preferable?

Why run the ball out further from the diff than absolutely necessary to avoid contact with the back of the cup? If the wishbone arms are indeed above horizontal at rest, then the only time the ball might bottom out against the back of the cup is under droop. Forces are limited to the weight of the unsprung components (much less than sprung weight) times the dynamic effect as they speed up.

As you move out to the open end, in general, more chance of things going wrong. Unsupported open end more likely to stretch, deform, crack, vibrate, etc. Easy to visual this statement, Confucious say 'all else equal, deep socket not as strong as short socket'. Someone could even test it too. I bet out of 10 drinking cups, at least 9 will break at the rim.

I have a feeling that the spacer is merely a generic bandaid, used to position the balls further back in the cup towards the base. All else being equal, this will be the strongest, most rigid area of the cup. Also, the highest natural frequency for reduced vibration. If this area has fresh wear faces, even better.

My big question is why the cup seems longer than it needs to be for the ball movement incurred during S2000 suspension travel. Was this part sourced from another vehicle with longer suspension travel? What is the better solution?

For the drag racers, would a billet cup, short as possible, with more thickness or reinforcement at the open end, and replaceable hardened wear faces be the ultimate answer?

I have zero vested interest in the spacers or their vendor, just curious. But I'm sure Driveshaft Shop is too.

 

"Spider bearings" is a new term for me. Based on my brief Googling, a "spider" can be used to describe something that goes on a shaft and has bits sticking straight out from it. So a spider bearing would have bearings at the end of those bits... (Note that this term is a bit different from "spider gears".)

I like the term "tripod bearing" - haven't heard that one until now either.

 

[QUOTE=snakeeater,Jun 6 2007, 11:28 AM]I have a feeling that the spacer is merely a generic bandaid, used to position the balls further back in the cup towards the base.