# Sticky  Definitive Definition Of Gto Suspension Concerns



## dms (Jun 27, 2005)

*FRONT SUSPENSION PART 1​*
last year, I posted a similiar post that defines the concerns of the GTO suspension and offered solution to the concerns. i was asked to do this by moderators. Somehow, an error occured, and one of the moderators deleted the post. I spent a serious amount of time on this and left this forum. Today I decided to visit the forum again because Rob at Wretched Motorsports is a Pedders sponsor here. So i decided to revisit and will repost an updated definition/solution base for the GTO. Wretched Motors can offer you support to resolve any issues listed below. If allowed I will assist you as well.

I am well known in the GTO community and go by DMS, which stands for "Doing Mike's ****" I have dedicated a very serious amount of time, energy and conflict on the GTO and will pass on knowledge that I have on it. This forum has very little information on the GTO, and I feel this community can benefit by this info, just if it generates questions. So here we go!

*The Definitive Explanation of GTO Suspension Concerns and Permanent Resolution Part One *​
This document was prepared to give the novice GTO owner a list of concerns common to the GTO suspension, and offer solutions to each problem.

*FRONT SUSPENSION ISSUES*​1. STRUT RUB
2. INSIDE TIRE WEAR AND CUPPING
3. NOISES
4. RIDE HEIGHT CONCERNS
5. BRAKING ISSUES
6 EXCESS SUSPENSION TRAVEL
7. EXCESS BODY ROLE
8. INSUFFICIENT NEGATIVE FRONT CAMBERS
9. POOR STRAIGHT LINE STABILITY
10. LOOSE STEERING FEEL
11. FRONT END NOT CENTERED TO THE BODY

*REAR SUSPENSION ISSUES*​1. INNER TIRE WEAR AND CUPPING
2. RIDE HEIGHT CONCERNS
3. POOR LAUNCHING AND EXCESS SUSPENSION TRAVEL
4. EXCESS WHEEL HOP
5. EXCESS TOE AND CAMBER CHANGE
6. EXCESS LATERAL SUSPENSION MOVEMENT

*
FRONT SUSPENSION SOLUTIONS
*​*1. STRUT RUB*. There are 2 kinds of strut rub on the GTO. When the GTO first came out, it was common to have strut rub, (tire to strut contact). In 2004 and early 2005, this was due to aggressive alignment settings for negative camber. Why was this a issue in the USA and not in Australia? Simple. GM added approximately 400lbs of structural support to the GTO so it would meed Federal criteria. Due to this, GM needed a larger capacity tire than the 235/45R17 used in Au. To try and increase tire life, GM went to a 245/45R17 tire which has a larger capacity rating, but is 10mm wider. The 235 has a load range of 1433lbs @ 44psi, and the 245 has a load range of 1521 @ 44psiWe initially saw strut to tire contact at the first rotation. GM was/is aware of this problem since the beginning but did not publish anything. If you called GM Technical assistance, they would tell you to put the front cambers to the positive end of specs, .2 camber. This strut rub would only cause a cosmetic issue, and is/was not destructive. This fixes the first style of strut contact, but severely reduced the handling. We have come up with a general spec to go negative on the cambers to the -.3 to -.4 range. At this range, you should be able to have at least a pencil width clearance between the tire and the strut. With that said, it is also CRITICAL to have your tire pressures at 35psi cold!!!. This fixes the first kind of strut rub, at least temporarily.

How many of you had not issues at at at the first tire rotation at 6,000 miles and the second one at 12,000 miles, but at the 3rd rotation at 18,000 miles the inner tire tread is destroyed, and there was evidence of strut to tire contact? You took it to the dealer and they said you must have hit something and knocked the front end out of alignment? Does this ring a bell to many of you?? Now i is true that you could have wacked something and knocked the front end out of alignment. But you also could have driven the GTO like a little old gramma going to Sunday school, and never hit a leaf in the road, and will still have the problem. Why? The strut bushing is damaged the moment it gets off the boat. To protect the front end, Holden installed front coil spacers to eliminate all front coil movement. Then they chained and cinched the car down really tight. The GTO was this way for over a month. This collapses the front strut bushing. But collapsing strut bushings is just the first issue, and by itself, is not that severe of a problem. But when collapsed, it weakens the rubber, and therefore the center of the bushing cannot stay centered in the bushing. This causes 2 issues. First it causes the strut shaft to migrate to towards the engine compartment, seriously increasing negative camber, as well as it will cause the camber to seriously change. The center of the strut bush, thus the strut shaft, will move all over the place, causing serious camber change, which ultimately causes serious toe change, which always screws up your tires. 

Now for some controversy: When the strut shaft moves in and out with respect to the engine, this movement is rapid. It will also cause the tires to have excess sidewall flex. Add the normal sidewall flex of turning, and you now have a lot of sidewall movement: enough sidewall movement to cause the tires to kiss the strut. I have seen and documented a severely worn strut bush, causing major inner tire wear, and strut contact, with 1/2 inch clearance from the strut to the tire. The strut contact issue, however, is again primarily cosmetic and not destructive. The tire wearm however, is severe and is often interpreted as contact wear from the strut

So the primary fix will be to replace the strut bush, and bearing, which will most likely come apart once the strut is dissassembled, then re-align the front end to get -.3 to -.4 negative camber. This usually will give you the pencil thickness clearance.

All of us have seen the reallllllly serious strut rub that destroys tires. It is my opinion that this strut rub is only caused by major impacts and bent parts. 

*2. INSIDE TIRE WEAR AND CUPPING*. The primary reason for inside tire wear is wear as a direct result of the strut bushing as previously mentioned. But there is another concern. You can see it by drivng your GTO 7-8mph then seriously jam on the brakes on. Observe the front wheels. It is not uncommon to see the front wheels kick back 2 inches. What this movement does is reduce braking action and brake pedal feel, but mostly causes major caster change, which again causes toe change. Toe gets toed out a lot. This again causes major tire wear, primarily on the inside and is a major contributor to tire cupping, which again is a major problem with the GTO. The cause of the excess movement is primarily the front OEM radius rod bushings that are fluid filled and often leaks, thus increasing the movement. The rear radius rod bushing also gets damaged and the washers bent due to the excess movement caused by the front radius rod bushing. the fix is to replace the front radius rod bushing with a firm urethane bushing like the Pedders EP9166. The other advantage using this bushing is your ability to get an addition 1.25 degrees caster. More on this later. The Pedders EP9019 inner radius rod bushing will add serious support for reducing caster and toe change, and reducing tire wear. There are other benefits that will be discussed later

*3.NOISES*. There have been a number of noise issues found on the GTO. Here is a list of things that I have seen at least 10 times or more: 
a. Front coil contact on parking lot manuevers creating a clicking noise. The repair to this is to reverse the OEM coils. There is a bulletin on this
b. Sway bar end link bushings and links get torn and bent easily. end links bend very easily with aftermarket sway bars. Replacing them with Pedders HD end links is a practical way of fixing this concern. The OEm bushings wear extremely rapidly. If it is just the bushings and the end link is not bent, then the end link bushes can be replaced. Note that the end link washers are dished, and the dish, if you will always goes away from the bushing. This is different than most vehicles.
c. Torn strut bushings, especially when the ferrule delaminates to the bush, can cause a knocking noise, on top of all kinds of other tire wear
d. Strut bearings can get lumpy and create a popping noise
e. 95% of all GTOs on the road that have OEm suspension have damaged front bump stops. They get torn due to excess suspension travel. This can create a knocking noise on a heavy jounce (compression of suspension)
f. Loose tie rod ends. The OEM tie rod ends are very prone to wear and can knock
g. Loose lower control arm bushing nuts and torn lower control arm bushings can easily cause a knocking or clicking type noise in the front
h. Front tires contacting the inner fender wells, especially the right front. You can either remove the portion of the inner fender well, or drill a couple of holes and use a large nylon tie strap and pull the fenderwell forward

*4. RIDE HEIGHT CONCERNS*. it is normal to have the front end 10 to 15mm low. This is primarily a function of collapsed and damaged strut bushings, and collapsing, under-sprung coils. Our Pedders coils are designed for performance and still maintain a very fine ride quality. Our coils, on average, have a 50% increase in sprung weight. Plus each is bench tested to 2MM tolerance. Also the GTO is a old body design and the acceptable tolerances of the body are significant. It is not uncommon to have as much as 1/2 inch height variation in the body totally due to the assembly and tolerance variations in the body. 5mm variations are more common and there is little you can do unless you have adjustable coil overs

*5. BRAKING ISSUES.* With the exception of the 2004 brakes, the 05-06 work pretty well, However, there seems to be a detectable lag time in the brake application. To understand the solution, you need to understand the cause. When you jam on the brakes, if there is any looseness or softness in the suspension. Before you actually stop, the looseness must be absorbed first. This is primarily an excessively loose or soft bushing concern. Replacing the radius rod bushings seriously reduces the fore/aft suspension travel, thus causing the brakes to react faster. Also the coils are way too soft. Jam on the brakes hard, the front suspension collapses and the rear suspension grows, this reduces the effectiveness of the rear brakes and adds additional weight and stress to the front brakes, Adding upgraded coils and dampers seriously reduces this affect

*6. EXCESS SUSPENSION TRAVEL*. This is a function of collapsed and damaged coils, and weak shocks, especially the front oil only struts. Going with a Pedders coil and any one of the 6 or so damper options that Pedders offers will control this concern. The rear is the biggest concern. Watch a OEM GTO take off. Notice how the back end collapses, this also seriously increases negative camber, thus promoting tire wear as well as other negative handling issues.

One of the other issues with excess suspension travel is movement of the strut bushing, even on a new one. A great way to improve the control of the strut bushing is to install a Pedders strut tower brace.. Putting on th animal strut tower brace, I feel, does little but improve "impression ratio". He with the biggest, baddest strut tower brace wins" to be honest the OEM unit works just fine. So how why is the Pedders unit special and different? Pick up your GTO and look at the strut plate to see what it does, It moves down approximately 1/4 to 1/2 inch depending on the condition of the strut bush. Our Pedders strut tower brace eliminate this movement by the positioning of the mounting plate. It goes between the strut mount plate and the inner fender well. Thus eliminating the gap, and eliminating the movement. This makes the spring/strut more responsive and adds life to the strut mount bushing.

*7. EXCESS BODY ROLE*. Once shocks and coils and critical bushes are updated the sway bars are still under-rated. Now by replacing the sway bar end link bushes, and mounting bushes with our Pedders urethane bushes, will add approximately 10-15% improvements to the OEM controls. This is due to the poly bushes being more responsive. But also Pedders offers a very HD front and rear multi adjustable sway bar assembly that comes with HD end links and rear end link bushes. No other sway bar kit, like Hotchkis, comes with these components. The Pedders HD sway bar kit will offer more control improvement than all the other sway bar kits on the market

*8. INSUFFICIENT NEGATIVE FRONT CAMBERS.* This is a function of not having sufficient tire clearances and tires being very close to the strut. There are several ways to resolve or reduce this concern. One is to install our soon to be available eXtreme Xa Monotube 30 way adjustable coil overs, install upper strut adjustable mount bushings, or relocate the lower control arm, decrease wheel offsets. Pedders has tested and elected not to have an adjustable strut mount bushing due to what they feel is serious reliability issues especially in the strut upper shock seal. There is a serious increase in strut seal leakages due to this style of strut mount. Pedders has come up with an adjustable lower control arm bushing, that can add approximately .75 to 1 degree of additional negative camber without getting the tire any closer to the strut. Changes in offset wheels really add a lot of strut to tire clearances. There are very few wheels actually made for the GTO. Most are designed for a BMW, and relabeled for a GTO. 


*9. POOR STRAIGHT LINE STABILITY*. There is lots of looseness in the OEM front end, but eliminating the looseness, and increasing spring and damping rates is not enough. Increasing caster is required. Installing the Pedders EP9166 front radius rod bushing not only seriously reduces the caster/toe change by keeping the tire from kicking back to the rear, but it also allows you to add up to 1.25 degrees of positive caster. You can get the front caster to the 10.5 to 11.5 range. The GTO can handle this without any negative affects, as long as your power steering is functioning. Adding caster seriously adds straight line stability and adds steering feel to the driver.

*10. LOOSE STEERING FEEL*. Once all the excess looseness is eliminated by bushings, springs/dampers, and making sure the tie rods are OK, which are a real pattern failing component, the steering can still feel loose, slow, and lacking feel. Adding front caster improves the feel, but may not be enough for all performance drivers. The OEM gear has a 3 turn lock to lock ratio for the GTO. The Z06 has a 2.6 turn ratio. Pedders offers a very limited supply fast ratio steering gear that has a 2.4 turning ratio. That is more than a 1/2 turn difference from the OEM gear. This also gives you substantial feel improvements, It is most noticeable during aggressive mountain type driving. It feels really great

*11. FRONT END NOT CENTERED TO THE BODY*. The Monaro in Au requires a front and rear cradle alignment process and supply their Holden dealers with alignment fixtures. In the USA for the GTO, Pontiac only supplies its dealers with a rear cradle alignment tool and does not supply, like Holden, a front alignment tool. Pedders dealers are the only ones that have a front cradle tool. Pedders dealers also align the trans mount to have all 3 cradles perfectly in line


Most of the parts and problems described above, especially strut bushings, can be viewed by checking out my webshots site listed below

Hope this gives all of you some room for thought and explanation of why your GTO is the way it is.

thanks
mike
dms


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## dms (Jun 27, 2005)

*Part 2, Rear Suspension*

*
REAR SUSPENSION PART 2​*1. INNER TIRE WEAR AND CUPPING
2. RIDE HEIGHT CONCERNS
3. POOR LAUNCHING AND EXCESS SUSPENSION TRAVEL
4. EXCESS WHEEL HOP
5. EXCESS TOE AND CAMBER CHANGE
6. EXCESS LATERAL SUSPENSION MOVEMENT

*REAR SUSPENSION SOLUTIONS*​
*1. INNER TIRE WEAR AND CUPPING*. This concern has multiple causes and resolutions for each cause. They are as follows:
a. collapsed rear coil springs as a direct result of the shipping process. I checked 30 brand new GTOs on the lot one day and literally had 100% of them showing collapsed rear springs. In fact, the best way to tell a GTO if it has OEM suspension or not is to look and see if the rear is lower than the front. Once the GTOs left the USA port in Benicia, Ca. to the dealers, all the rear springs were collapsed. When the GTO left Australia, the back end was higher than the front. It is very normal to have the rear coils collapsed 1 inch. When the coils collapse, negative camber increases. So with a low coil which has lost its rate, when you take off, you literally can bottom out the back end if you have some sticky tires. This causes 2 wears, inside tire wear due to excess negative cambers, and cupping, caused by excessive changes in camber, which changes toe, which causes inner tire wear and cupping. 
b. Excessive rear control arm bushing looseness. The outer lower control arm bushings are solid rubber bushings and can be improved, but are not a problem. it is the inner control arm bushing that is the problem. The voids in the bushing. Look at the left rear inner bushing. The majority of the OEM bushings have a problem with the left inner. Look at the bushing and you will see the bolt is not in the center of the bushing. This means that the bushing is so weak it cannot keep the bolt in the center of the bushing. Plus, when in a torque situation, it will allow the inner bushing to move back and forth, thus changing camber again, which will again cause changing toe and thus potential tire cupping and inner tire wear again. These bushes are also a major contributor to wheel hop. More on that later.
c. Rear shocks are far better than the fronts but still have barely enough control for the weak, and severely under-sprung and damaged OEM rear coils. Even our entry level Pedders comfort Gas rear shocks are light years ahead of the OEM rear shocks. the OEM rear shocks again allow way too much suspension travel for a lot of GTOs. Excess suspension travel causes excess changes in camber, which causes excess changes in toe, which causes inner tire wear and cupping

*2. RIDE HEIGHT CONCERNS*. This was covered in the review of tire wear in 1.a. But again the rear coils are damaged in shipment. The coils are made out of a lightweight alloy, and once collapsed, they loose a serious amount of spring weight capability. 99% of all GTOs in the USA with OEM suspension will have collapsed coils. If your back end is lower than your front, then your rear coils are collapsed

*3. POOR LAUNCHING AND EXCESS SUSPENSION TRAVEL*. This is a big concern for a lot of GTOs in OEM configuration. The solutions are covered in the above with the reasons in depth. The poor launching and high 60 foot times is a result of lack of ability to transfer torque. There is a lot of time wasted in "loading up" all the suspension components first, before torque can get transferred to the rear wheels. Weak rear coils and dampers, and the weak and excess moving lower control arm bushings really add to a lot of wasted energy and delayed transfer of torque. But there are 2 other components that add to this. The OEM rear cradle or Xmember bushings allow a lot of movement in the rear cradle, that supports the rear cradle assembly, which supports the entire rear suspension. The rear differential mount is the 3rd of 3 mounts that support and transfer torque to the body. The mount is bolted to the rear differential and the body itself. the issue with this bushing, is the massive amount of voids in this bushing. Having excess movement and weak 3 part contact bushings, transfering torque is slow and lots of torque s lost. 

The repair for the rear cradle is simple. PEDDERS and some other Au companies offer much harder dura solid bushings for the rear cradle or Xmember bushings. Pedders on some other Au companies offer inserts that press into the massive voids of the rear differential mount, seriously increasing the strength of this bushing. 

So to summarize, update weak bushings, improve the damping, and increase the spring rates.

There are 2 other issues and potential concerns that can be addressed. Due to irregularities in body tolerances, we can have a large variance in rear camber, and tracking. Rear camber is not adjustable on the GTO. But installing our Pedders 5403 or some other Australian bushings in the outer rear lower control arm bushing will allow you an approximate +/-.7 degrees camber change. Also the rear cradle can be mis-postioned into the body, There is a cradle alignment procedure for the rear cradle to body, that is extremely sensitive. . A fixture that attaches to 4 datum holes, 2 in the control arms and 2 in the body, when all are attached to the rear to the cradle fixture tool, will gaurantee extreme accuracy of the rear cradle to the body.


*4. EXCESS WHEEL HOP*. Again, partially covered. But wheel hop is caused by looseness and a frequency generated in the chassis. the fix is to either remove the looseness and/or adding dampening. The looseness is improved by updating the rear cradle mount bushing, rear differential mount insert bushing, replacing lower control arm bushings, especially the inner, adding more rear damper control, increasing rear spring rate. These are the common areas to improve looseness. For 100hp at the wheel increases you may have to eliminate the 2 piece driveshaft to reduce flutter in the driveshaft by installing a 1 piece driveshaft. Other ways of reducing wheel hop is to add air bags in the coils. This does not eliminate any looseness but acts as a damper. There are negative effects of air bags. Traditionally they are connected to a single air supply port. Adding air to the bag, will lift the back end, dampen the wheel hop movement, bus also will act as a reverse sway bar in the rear. Not a good thing to have when going thru the twisties.


*5. EXCESS TOE AND CAMBER CHANGE. *Already covered but a problem non the less. Excess toe and camber change is a function weak and collapsed coils, under controlling dampers, , excess movement in the lower control arm bushings. 



*6. EXCESS LATERAL SUSPENSION MOVEMENT.* What this means is the body moves a certain amount when turning, but the rear suspension moves laterally even more than the body. This is a function of the cradle moving separately from the body. To repeat, there are 3 contact areas that mount the rear cradle to the body. There are 2 front cradle mount bushings, and a rear differential mount bushing. The OEM bushings allow a very large amount of movement laterally and up and down. Installing Pedders or other aftermarket cradle bushings will seriously improve this movement. Adding a Pedders differential insert bush is the 3rd part of a 3 part fixture that seriously supports the rear cradle in all directions. 

Most of the parts and problems described above, especially strut bushings, can be viewed by checking out my webshots site listed below

Hope this gives all of you some room for thought and explanation of why your GTO is the way it is.

thanks
mike
dms


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