[Shotimes] vibration: what is wrong?

[cmichaelo@optonline.net]

> re: shims and alingment. I thought that it was odd but
> I think the shop was trying to go the extra step to
> get my car aligned as perfectly as possible. They did
> notch something out at the LCA to SF mounting point to
> adjust camber since it was way out on the driver's
> side.
This could indicate that your subframe is too far to the left. If so, the way to solve this is obviously NOT to move the LCA further to the right, but rather to move the SF to the right. The alignment "specialist" in the shop most likely never do this or may not even be aware of it.

> I have not had that bolt out so I can't really
> see what they did. It is possible that the bolt is
> slipping. 
If the LCA-SF bolt is loose, you'll definately get vibration.  Suppose they tightened this bolt at first and then it slowly worked itself loose. That would explain how your vibration slowly started to get worse after the alignment.

> If that is the case, I have Mark Levy's old
> 1990 subframe to install in my car for when I do the
> motor swap. I was planning on dumping the tension
> strut rod shims and using the Ingalls adjustable
> tension rods. I never really liked the idea of the
> shims.
You shouldn't need to replace the SF in case the LCA-SF bolt is loose.

> It's interesting what you said about the bushing
> compressing but I don't really understand. I believe
> the shims are in between the bushing and the metal tab
> on the strut rod that the bushing normally sits
> against. Why would the addition of the shim alter the
> bushing compression?
OK. Here's why.  The way that the tension strut nuts are tightened is by turning the nut until it gets to the end of the thread on the tension strut.  As you can see, this guarantees a certain "spacing between the nut and the standoff on the tension strut and between which two you squeeze the bushings.

In between the bushings you have the SF which takes up a little bit of the space between the nut and the standoff.

Now suppose that you add shims in between the nut and the standoff, e.g., in an attempt to push the tension strut further backwards.  The presence of such shims will reduce the effective space for the two bushings.  Thus, when you tighten the nut, you'll be compressing them more than before.  Not unlikely, this may cause the bushings to eventually tear open and break apart.

Btw, if your SF is too far ahead, that in itself would make the caster too large.  The way to bring back the caster to spec is obviously not to insert spacers, but to realign the SF.

> By the way, this started after the alignment but the
> car was aligned months ago and this problem is fairly
> recent (though it was getting worse with time).
Alignment problems have a tendency to evolve over time. See my earlier remark about the possibility of the LCA-SF bolt working itself loose.

However, I will tell you this.  9 out of 10 alignment specialists don't really know what they are doing.  Furthermore, they rely heavily on the alignment rack and the measuring equipment.  If the rack is not up to par or the measuring equipment is not attached properly to the car or you have a bent rim, well then you're asking for trouble.

I do all alignment by myself.  And it's quite possible to do so.  At first I thought aligning a car was some sort of magic.  Let me tell you, it is so f*cking easy once you get started. Anybody can do it.  And it makes you feel so much peace to know that your car is aligned properly.

Not to get off on a tangent, but briefly speaking, you need to make sure that all four wheels are leveled (so a garage helps here), some knowledge about trigonometry (we all have that), the fabrication of a special device for measuring toe (involves a 2x4 stud cut to proper length and two swivel arms at the ends), a heavy object (e.g., an axle nut) hanging in a thin wire to measure camber and finally you need a slide caliber. I'll write it up some day. 

I've been doing my own alignment for the last two years now. And my [summer] tires  wear slower and more evenly than ever before.

> I think the CV joint failed because the subframe was
> moving up and down and extending the boot. SF bolt was
> loose which was causing that mishap.
If the other three SF bolts were tight AND the fact that you have ALU bushings, I can't imagine you subframe moving up and down much in the driver side corner. And even if it is moving up and down, I would think that should be very little AND ONLY occur when you're driving on an uneven surface.

IOW, I doubt the loose SF bolt has anything to do with your CV joint failing. More likely it's related to some of the other things that might be wrong with your alignment, e.g., a misaligned subframe.
 
> I hope this was coherent. I just took some Tylenol 3
> so I am on cloud 9 at the moment. :)
Enjoy the little buzz...:)

Michael
94MTX,green,BOS+,Koni/Intrax,Baer,Corbeau
SHO items for sale: http://hometown.aol.com/cmichaelo/for_sale.html