70-80 mph vibration - update

Recap - a few weeks ago, while on my way to BRBS, I noticed a vibration in the seat and steering wheel of my 2005 Boxster (987) at 80mph. The vibration occurred in one second intervals.

Having first noticed it after replacing the front tires, I then got all four wheels/tires rebalanced on a Hunter RF machine. The rears were out significantly.

Initially, on a quick run, I though the problem had been remedied, but I was wrong. It continued.

New rear tires (PS2's) went on about 2500 miles later, carefully balanced, with no improvement. In fact, towards the end of my 4000 mile trip, I noticed that the vibration now starts at a lower speed (70 mph) and continues, though a bit less noticeable at 90 mph.

I took the car into the dealer for an alignment last week, and asked them to check all suspension/steering components. They discovered that, with the car jacked up and the wheel off the ground, the right front strut shaft can be made to wiggle (back and forth) where it goes into the strut tube, by shaking the front tire. The wheel/strut on the other side is sound - no wiggling. I can't help but think this is, at a minimum, contributing to the vibration problem.

I've not seen this type of wear before. It is clear (to both the tech and me) the strut must be replaced.The tech said the strut mount is fine and needn't be replaced.

Interestingly, he didn't suggest the driver's side strut be replaced. Each strut is $485, with 2 hours labour at $120 per hour to replace each. With taxes, and after PCA 10 % discount, that's $750 per side.

I'd always read/understood that struts should be replaced in pairs. However, in view of the fact the tech didn't suggest I replace the left side, and not being eager to spend an additional $750 if it's not necessary, I figured I'd get some input here. The car has just under 59k miles on it.

I don't know long the service life is of Boxster struts. No doubt, it's affected by the type of roads and driving. I can't help but wonder if the one side is gone, can the other be far behind, and will there be different compression/rebound from side to side, if I replace only one.

BTW, these are PASM struts which, I'd guess, are pricier.

R

... or, IMNSHO, in 4s.

Certainly a suspension component that allows movement can contribute first to vibration and then to resulting uneven tire wear. However, the hub is located by the control arms, and to a degree by the spring, sitting on the perch, connected to the top mount, with 800 lbs of car on it. The strut piston should not locate anything, and, in fact, significant load on it could *cause* the play ( and its eventual failure). So i wonder if the loose piston is the effect of the vibration, not the cause.

The service manual clearly states to replace them in pairs. Otherwise you ill have different damping and even to some degree roll stiffness in the two directions.

I have seen play in the strut with it unloaded. Remember that when unloaded, it has no structural integrity. I would be more concerned abotu a worn mount\ than play when things are in effect taken apart.

Have you really checked for OOR wheels?; tires? (visually, not "it balanced" - i can balance a square tire with enough work)?

Good luck, these things are annoying.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Grant's comment about replacing struts in pairs makes sense; besides the different damping abilities between a new shock and one that has a lot of miles on it, you have to wonder how long it will be before the other rear strut needs to be replaced.