Once again I am confused ...
This time about the how the A arms work

The bushing is pressed in to the a arm
and so the outer part rotates with
movement of the a arm.

My confusion is whether the whole bushing
outer sleeve, urethane bushing, inner sleeve
are all supposed to rotate together.


If this is true then the bolt is an axle and the
inner sleeve is a bearing surface.

Several things bug me about this...

1. The factory bolts seem wrong...
- They are considerably smaller than the ID
of the inner sleeve. This would seem to allow
both unrestricted motion and uneven loading
on the bearing surface.

- they are threaded over some of the length
of the inner bushing. This would distribute
the load unevenly and produce wierd
wear patterns.

2. The inner sleeve goes right to the end
of the bushing and so will see "binding"
forces ast the bolts are tightened

3. the urethane portion of the bushing
extends all the way to the end of the bushing
and so will see the same binding forces.

Sooo....
It either doesn't work this way...

Hmmm... one way it might work is
if the inner sleeve is supposed to be
bound and the urethane is supposed to
spin around the inner sleeve...

Anyway I need a hand thinking this through...

I just changed mine and the bolts are the point of movement. My bolts fix good through the bushings without much play. The bushings are a bear to press out of the arms.I used a ball joint press to remove and replace them with an impact gun. I put some lube on the bolts when I put them back on. Good luck. I would not try to hammer them out.

... or you could slowly drill out the old bushing material with a drill bit, going around the bushing until it just falls out.

But urbman, why are you concerned about it so much? They seem to work fine, except for the fact that GM used rubber instead of poly.

The new bushings I used are poly and came with new steel bushings .I had to drive out everthing not just the rubber part. The rubber bushing are fine for a street car. I hope to drag race and auto cross with mine when I am done. I will try to post a shot of the passengers side arm which is not done yet so you can see it out of the car.

No need, I know what you mean, I was just suggesting something that I saw in the How-To video that I got with the PST bushing kit. Thats what they did and both sleeves came out quite easily once the bushing was drilled out. I'd imagine that a pipe or race washer of that exact diameter would help as well.

Well...
In the late seventies we went through a lot
of Mickey F***ing around trying to sort out
what were then called "superbikes".

In those days we fiddled with trying to get
the chassis to do predictable things.

We fooled with replacing the swing arm bushings with stiffer material. eventually needle bearings.

Sooo....
Going to the trouble to replace these things
is a bit of work. Getting it right is not much
additional work.

The id of the inner sleeve of the GM bushing
is aprox 0.484 inches

The gm bolt is 0.464 inches

The PST bushing contains an inner sleeve
with an id of 0.515 inches

While fooling around I found a "Steve Spohn"
supplied bolt that seems to match nicely with
the PST bushing. It has an OD 0.495 inches

So...
My guess is that careful attention to detail
might have a benefit...

So why didn't PST just design their bushing to have an ID closer the stock bolt? Are they trying to do something that GM didn't think of? The video that came with the kit says to inspect the bolt carefully to make sure its not pitting, rusting and threads aren't distorted. Where would I go about finding a better matching bolt though? I understand where you're coming from and it would be a good idea to do it right the first time as I DON'T want to do this twice.

I believe that the inner sleeve is supposed to (does) remain stationary. Tightening the bolt pinches the frame bracket between the bolt head/nut and the inner sleeve. The inner sleeve cannot turn, and neither does the bolt. All arm movement is the result of deformation of the rubber bushing - you are sorta twisting it.

With urethane bushings, I believe that the same is true with regard to the bolts and inner sleeves. The difference is that instead of twisting the urethane, it slides around the inner sleeve. This makes for a freer movement, but presents the possibility of squeaks.

This explains why threads are included in the shear plane on one end of the bolts. They don't move and aren't really loaded in shear, so it doesn't matter. I would still prefer to use bolts with a longer plain shank so that the threads are outside the frame bracket. You have to use washers when doing this to make sure you don't bottom out on the threads before getting the clamping force you need.

This is my theory, and I'm sticking to it.

When I changed mine I thought about changing the bolts.I sandblasted them and they had no real wear or anything. I saw the step down in size on the bolts and figured GM did it for a reason and stuck with stock bolts and went poly bushings, however the bushing kit says to grease the bolts before you install them.I talked to the guys at Guldtrand Motorsports and they say that the bushings with grease fittings the grease goes to the bolt not the poly bushing and thats what stops the nosies. They also said if you use a high quality lube you will not need the bushings with grease fittings.

I finally got through to Kevin at PST...
(apparantly a supervisor at PST)
He seemed knowledgable about his products...

1. He indicated that the inner sleeve is not
"tightly bound" to the "Polygraphite" bushing
it is simply a press fit and not glued.

2. He indicated that they reccomend lubricating
the bolt, inner sleeve, and ends of the bushing
( I forgot to ask what the lubricant is )

3. He indicated that the A-arm will move freely
about the bolt

4. He indicated that the bushing should not
bind against the frame brackets.

5. He indicated that these surfaces should be smooth
and well lubricated.

6. He stressed the importance of staying precisely
within the torque specification for tightening
the bolts so as to "not" unduly bind the inner sleeve
too tightly. The idea is to "locate" the inner sleeve
as opposed to "fix it" as an axle.
He indicated that binding can occur but is
not intended. He speculated that this may be why
some squeak and some don't.

He indicated that this is indeed a different
approach than that of the stock configuration ...

So....
My guess is that there is some benefit to going
to a "bigger" bolt....

My guess is that the benefit will show up
in how long an alignment will hold up

Semi conclusion...
After talking to Kevin it dawned on me
how to check this...

1. I took one of the old bushings (rubber)
and reinstalled it. then I took a pipe wrench an tried to turn
it. It worked just like a spring....
So factory bushings work just like P J Moran says it does

However...

2. I installed one of the new bushings per "Kevin of PST"
instructions (smooth sides, plenty of lube)
It rotates "freely" that is when you rotate the bushing
it stays where you rotate it. it does not try to return
to its original position.

At the moment I am not sure if I am rotating
about the bolt or the inner sleeve...

The only way the inner sleeve can turn is if the bolt is actually "loose". Also, if the iner sleeve turns, you will quickly wear out the frame brackets and the sleeves (and to some extent the bolts). Especially if it is tightened at all. No grease is good enough to resist this for any length of time. So, I again assert that the inner sleeve is not supposed to turn. The bushing turns about the sleeve.

Yes, it's a press fit, but it's not that tight. You can press it out easily enough (knock it out with a hammer and a socket). You can often press it out by just pushing on it "by hand". You should do so and liberally grease it before reinserting it.

This is why you must first loosen the bolts before trying to remove the springs, and why you must not tighten them until the suspension is loaded. This is more important with the rubber bushings, but important with either.

Thanks PJ
Some of the problem I had with this is...

1. How tight is 90Nm
For you it was obvious that this would in fact
clamp the inner sleeve between the frame brackets

For me I wasn't sure the brackets could be deflected
with 90Nm on the bolts

PST say to use this spec (factory recomendation for this bolt)
but I could not get them to tell me why...
( The folks on the phone appear to answer questions from
a list. If you ask them something not on their list they seem
to take a guess at one of the prepared answers and repeat
it. )

What I was looking for was whether this was to insure that the
bolt does not become loose or to specifically "lock down" the
inner sleeve.

The other thing is that they mentioned over and over the importance of lubricating the bolt. I still don't get this...


2. When I read your post I thought you felt not quite sure about
it or more to the point not quite sure about what PST was doing.

I think you're on to something here...

Quote:
What I was looking for was whether this was to insure that the
bolt does not become loose or to specifically "lock down" the
inner sleeve.

The other thing is that they mentioned over and over the importance of lubricating the bolt. I still don't get this...

I'm confident this does lock the sleeve. It better! As I said before, the sleeve will rub on the frame bracket and cause problems. I always lubricate at least the threads of any bolt. Usually with anti-sieze. You never know when you might have to remove it again.

Quote:
2. When I read your post I thought you felt not quite sure about
it or more to the point not quite sure about what PST was doing.

I'm a structural engineer and was trying to not sound like a know-it-all. I've given this a fair amount of thought, having replaced control arm bushings (with both rubber and urethane) in a few vehicles. I've even seen knurled ends on the sleeves to prevent just such movement! See above about reading from a list...