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Discussion Starter #1
So, I showed off my car and bounced some questions off my wife's uncle regarding suspension and alignment. As any of you who have viewed/participated in my wobble threads may remember, I have had a persistant wobble in the right front even though I have replaced every suspension part. Well, the uncle (who owns a chain of Firestone tire dealers) listened to my stories and just chuckled. He said it sounds to him like the rear alignment is the source of all my angst and that shimming it straight should knock out the wobble, which he believes is just being transmitted to the front. I may pursue this tomorrow, even if I can't make it the 1.5 hrs. to one of his stores/shops.

I tried to quiz him more on how this was possible but he just held up his hand and said "See it every day."

Oh well...:lol: :eek:
 

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So maybe there is hope for your wobble yet...:D If shimming the rear wheels can fix it, please post... I know that half-shims were sometimes used to correct bad tire wear on older fwd cars with trailing arms. Mostly on cars that have seen too many potholes.

As far as I know, the rear alignment can be checked, but there is no adjustment for it. If the rear alignment is bad enough to cause a wobble in the front, I would seriously worry...
 

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Is the "wobble" the same as a shimmy, generally due to rotating forces out of balance ??

I view a wobble as something that that can be seen, such as a seriously bent wheel, or mangled suspension.. and this will shake the whole car, most any car

No way can I see a rear misalignment causing vibrations that can be felt in the steering (shimmy); but this does cause excessive tire wear and wandering on the road..

Brian, did anyone ever do a "on the car" dynamic wheel balance ??? On all four wheels...
 

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Discussion Starter #4
No, there is no adjustment for the rear alignment, but it can be shimmed. The toe is seriously off. As for the fronts, the camber is off. The fronts were the inside edge down regardless of the alignment. My car tracks as straight as an arrow...

As for the rears, They are feathered on about the inner third and have high spots associated w/ this feathering about every 10 inches or so. When on the rear, you don't notice a thing (unless they truly are causing the front shimmy/wobble). But I put them on the front, trying to preserve the insides of my last fronts before I got 2 new tires yesterday, and wow! Wobbly city. It's so bad it takes a strong grip from me (and I am a good sized guy) to hold the wheel steady. When I slow down to 15 mph, it practically sounds like the wheels are sideways-like some serious scrubbing is going on.
 

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The feathering and high spots sound like rims that have been messed up in one way or another. I have had a total of four bent rims on this car. Two pounded out, two new (used) rims and a new set of tires later, the tire problems and related vibrations are gone, but there is still a vibration felt in the steering wheel now and then.

After all the potholes, I would not be surprised if my rear alignment were off, it has not been checked in years. I may have to take the entire back apart all the way to the axle (or pay someone to do it), so I am really curious to hear how this turns out!
 

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Abbott in the UK have known about this for years.
Boxman poly bushed his rear axle and it did wonders for the car. Infact after he had done it he said it made more of an improvement than all the front polys on in one go.

So shimming and polys would be great.

See below for the Abbott page.

(price based on receiving good exchange unit)


The standard rear axle is a rather simple unit which is supplied from the factory with a broad tolerance for its geometry limits.

Tracking

Factory units - 1mm Toe-out to 3mm Toe-In (Based on 16" wheel)

This in practice can permit a 4mm tracking variation between vehicles. (4mm equals 35' minutes or 0.15 inch)

Cambers

Factory units can be -2.1 degrees to -1.1 degrees.

Again a tolerance of an entire degree, which in vehicle geometry terms is a lot.

A front wheel drive car is very sensitive to rear geometry. Racing the 900 during 1994 and 1995 taught us just how important it was.

In reality, to achieve the correct balance for the car, we spent more time altering rear tracking and cambers (using shims) than altering the front.

We also learnt that the rear suspension deflected under extreme loads and that stiffening the key weak points of the axle gave us considerable improvements in roadholding and handling.

Six years of tuning experience on the new 900 and now the 9-3 (which still uses the same axle you'd find on the rear of all new 900 models as far back as 1994), coupled with driving thousands of miles in customers and our own cars has led us to the following conclusions:

1. The ideal tracking should be 2mm Toe-In (20' minutes).

2. The ideal camber should be -1.0 (1 Degree negative).

These parameters give the best high speed stability, steering precision, turn-in feel, cornering ability and linear tyre wear across the entire width of the tyre.

3. The difference between a good and bad handling 900 or 9-3 can often be traced to a distorted rear axle or a bad production item having the widest spectrum of geometry limits.

The standard rear axle is not a serviceable item and requires major modification on a custom built jig (see below) to align it to our exacting limits.



We have designed and built our own jig to produce axles to our proven specification of strength and alignment, this significantly improves roadholding. A substantial fabricated strengthening section is added after realignment, to prevent future distortions and geometry changes - this is marked in white lines on the picture below.



You can now experience far more focused roadholding, handling and stability, by fitting our sports rear axle.

Dead
 

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Discussion Starter #7
PMI: Yeah, my rear right wheel IS bent a tad around the very outside edge, but the wear I get is on both wheels. So I wonder if that is the cause or not.

Dead: Yeah, I have enviously glanced at those Abbott rear axles...

I'm going to see if I can break away today and find someone who'll take a look.
 

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Raggy has also had trouble with a full wheel alignment.

He was unable to get a perfect job done due to fluctuations in the rear axle.
The company told him that the rears needed shimming to get a perfect setup.

Over at Yankton he welded up the rear with heavy plates so when that gets shimmed it will stay.

Dead.
 

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Dead, Thank You!!! I always questioned the wide tracking tolerance in the factory spec. That is exactly what I have been wondering for a long time! I looked at the Abbott web site before, but obviously not far enough.
 

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Still, having read about this rear alignment and improvements, and I accept the improvements in handling and tire wear - yet not a word about "wobble"..

Has an "on the car" wheel balance ever been done ?
BTW, weak hydraulics(shocks) can also cause a wheel shimmy - from what I have read.
 

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earthworm said:
Still, having read about this rear alignment and improvements, and I accept the improvements in handling and tire wear - yet not a word about "wobble"...
Well, I think I learned something new that I can try myself, until now I did not hear much about anyone using shims on the car.

I look forward to hearing about the wobble being fixed with shims in the back... :cheesy:
 

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Discussion Starter #12
Sorry earthy, but my shocks are fine. You should know from my many suspension threads that I've replaced pretty much everything. The rear toe is off, thereby causing a severe fethering of the wheels and irregular wear, which seems to be causing the wobble.

PMI, as for the shims, this is a pretty common practice for semi independent/soild rear cars.

I swapped the new tires to the front yesterday and I still get the wobble. With the smooth new fronts, you can definately tell now that the wobble/shimmey/WTF ever is coming from the rear now. This had been hard to tell previously b/c I had purchased all new tires at once.

Now my next concern is, what to do about the severe inner wear I get on my fronts. It's regular and forms slowly, but is there. It's as if I have some serious camber dialed in.


Now, has anyone tried to correct camber on the front??? I know it's not supposed to be adjustable either...
 

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Discussion Starter #14
I still haven't done anything! The wobble is definately in the rear now, though! It's a little more obvious! I've been having to play Mr. Mom a lot and not had a free moment to get it to a shop I trust.
 

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bkrell said:
I still haven't done anything! The wobble is definitely in the rear now, though! It's a little more obvious! I've been having to play Mr. Mom a lot and not had a free moment to get it to a shop I trust.
The children are the single most important thing in a successful family - so keep up the good work, Brian..

Is that bent rim still on the back axle ??
This will cause the car, maybe the seats to shake and vibrate, but not necessarily the steering, as a front imbalance would do..

I would post this on another good car forum (GardenWeb for one) , since this can happen with most any make of car... and they have far greater numbers...

The best way to find and correct these rotating forces is to use an on the car wheel balancer, but maybe no-one does this anymore ??
 

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Discussion Starter #16
No I know. The bent rim may definately be a problem, but the wear is on both rear wheels. Additionally, I suffer excessive inner wear on my fronts. I had a great deal going on 4 Viking wheels on eBay until someone sniped them at the last second.:evil: I think a good shop will be able to tell me what's wrong anyway, I just haven't gone.


As for the kids, they are great! Wouldn't trade them for the world! If someone would just pay for daycare...:cheesy:
 
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