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Author Topic: Suspension, handling, tram lining & tyre wear  (Read 8508 times)

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feeutfo

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Suspension, handling, tram lining & tyre wear
« on: 30 August 2010, 00:32:12 »

Some symptoms.

Inner edge tyre wear, outer edge tyre wear (less common), tram lining (car reacts and pulls to road surface irregularities ESP the "tram lines" or grooves made by lorries in lane one of the motorway or similar), pulling on the steering wheel, wondering, constant adjustment at the steering wheel, failed mot due to wishbone bush failure or rear subframe (donut) bush failure, and the comical-car steers left on the brakes while the steering wheel turns right or vice versa.

The quick answer to all this.
1. Inspect the car for steering and suspension faults.

2 Rectify

3 Full geometric set up

4 fit new tyres

The longer more detailed answer.

There are a whole range of odd symptoms and handling issues that can appear on the omega. Most of these are due to bush failure, link/track rod play, poor set up due worn or failed parts or tyres and how they wear as a result .

Not helped by the lack of set up knowledge generally in the motor trade. All too often we hear that the tracking (toe) has been set and it's made no difference. Or that suspension parts have been replaced but not set correctly after re fitting with a pair of ruined tyres as result, or worse a blowout due to maximum camber unknowingly dialled in.. Most back street garages, and some dealers I suspect, are unaware the omega has a camber setting much less how to set it correctly.

Set up is important on the omega, namely, "full geometric set up" at the likes of Wheels in Motion based in Chesham. Without doubt the most trusted set up company on the forum, and now with various franchises around the country. Highly recommended. Why? Well the omega has a range of settings. Even from the factory, as with so many Marques these days, the car set up will be fairly appalling. Some top end dealers, Aston Martin of note, will send their cars for full set up before delivery to the customer. Vauxhall settings by the way, are so wide as to be little short of useless, ESP on cars of this age and mileage. Many an owner has posted on the forum after set up with a spec sheet all in the green, only to find their tyres have still worn prematurely on the inside edge. Wheels in motion, WIM, have come up with settings that work well on the omega with well run in suspension and a few miles on the clock.

These settings include (in simple terms to the best of my knowledge) 
Front
Castor angle, the amount the front axle sits forward of the top suspension mount, not officially adjustable but the correct setting can be achieved by moving the subframe via the bolts to chassis.
Camber angle, the amount the wheel leans in from the vertical, adjusted via the ovalised holes and two bolts in the clamp at the bottom of the shock body.
Toe, or tracking, the amount the front wheels toe in from parallel, adjusted via the track rods to hub.

Rear
Toe only, also affects camber, adjusted via rear track rod adjustors.

Obviously it's not possible to set the omega correctly via the chalk and a piece of string methods some use for tracking given the settings needed. 


So, some diagnosis, pointers and tips on what to look for when finding faults affecting handling.


Front end.
Jack both sides and place car on stands securely. Helps if the ignition steering lock is not engaged.

Wheel play tests.

Wheel baring check.
Hold the wheel at the 12 and 6 o'clock position and rock up and down, this will show any wheel baring play. These will pass the mot with up to 0.5 mill of play at the rim edge ime. May get an advisory up 1.0mm of play. Any more will fail. Depends on the tester. Some play,0.5 at the most, can be taken out by nipping up the centre hub nut on the baring. Needs a long beaker bar and a big grunt though.

Track rod play check.
Hold the wheel at 3 and 9 o'clock and rock side to side, any knocking or play means there is wear in the linkages to the steering box pitman arm and can give a clonk over bumps. There are two track rod joints per side, inner and outer, linked by locking adjustors with left and right hand threads, turning this lengthens or shortens the track rod to give the toe setting each side. But be aware that wheel baring play will also play apart with this test if present, so take into account accordingly.

Wishbone play tests.
Not so straightforward this one. Hold the wheel at 3 and 9 o'clock again and pull the wheel side ways/for and aft, as opposed to in and out. There should be some movement as the bushes are made of rubber, but there should be no slop or uncontrolled movement or play.

Turn the road wheels to full lock in order to visually check the rear wishbone bush for splits and tears. With the car jacked the wishbone will be fully extended down stretching/extending the rear bush. When looking from the wheel arch gap between wheel and door any splits will be visible. Gat in there best you can and examine carefully.

Shocks and springs inspection
Visually inspect shocks for leaks around the oil seal, and springs for breakages on the ends of the coils, both are mot fail if spotted. However broken springs are difficult to spot and may mean wheel removal to view fully.
 
« Last Edit: 15 September 2010, 14:56:03 by jimbob »
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feeutfo

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Re: Suspension, handling, tram lining, tyre wear
« Reply #1 on: 30 August 2010, 00:33:26 »

Tests from under the car.

Continue with the front wishbone bush exam from underneath with a pry bar or similar and a torch. Lever the front wishbone joint around on both sides, do they feel the same? When the wishbone is levered away from the subframe are there any crack or splits in the rubber? Any slop or loose movement, cracks or splits, they are shot. But as said, the bush itself is rubber filled with gel in some cases so they are designed to move and absorb some road noise and harshness. Do not expect them to be rock solid.

In some cases a plastic insert is set into the centre of the front bush to take out the extra force and movement exerted when breaking. This action results in the front bush outer being forced outboard as the road wheels try to toe out as the car body momentum is forced forward relative to the road wheels. These can take a hammering and break.

Grab the rear arm of the wishbone and push pull it up and down, it should be firm but give controlled movement. If its loose, sloppy and allows the wishbone to rub or grind on the subframe bracket they are shot.

While your under the car play with the streering action while the wheels are unloaded. Grab a wheel or both wheels and pull through the range of steering movement from lock to lock. Any play should have been noted by the track rod test above. This test should help you identify which part is at fault.

 There are two ball joints per track rod on each side. Working inboard on drivers side is the steering box with with pitman arm joint to centre tie rod, the pitman arm side is fairly bullet proof. Pasenger side opposite is the steering idler and joint to center tie rod. The idler can be troublesome on the omega. Examin all these points as they move one by one for play. Usually play is most obvious when pushed up against full lock, lean on full lock repeatedly while watcihng and feeling each ball joint in turn. Or grab both road wheels and pull in and out against each other. Movement is usually most obvious at the top of the ball joint/lock nut end and felt in your hands as you pull and push.

Drop link test.

These have no ill affect on handling as they produce an infuiriating rattle and get replaced. Its not possible to test these when only jacking one side due to the way the roll bar works, so with both sides unloaded and the roll bar unstressed now is a good time to jiggle them. Grab each roll bar next to the wish bone as close to the drop link as possible. Pull up and down. Any play can be felt.

Check roll bar bushes as well, follow the roll bar in board and the bush can be found attached to chassis. The roll bar should be firmly held by the rubber bush.


Rear end inspection.
Jack and place on stands. Having inspected the front of the car you'll get the general idea of what to look for with wheel play. But pray that you don't have a failed rear wheel baring as these are a total nightmare to replace. In fact there is a good case for replacing the entire trailing arm with another known good from a breakers as it's an easier job. But the most common failures are easier to fix and are covered in the appropriate guide. Rear donut bushes and broken springs are most common.
Springs again may well mean wheel off to view fully.
Rear donut bushes need a look from underneath. Approach these by looking from the direction of the dif to get the best view of the opening between triangular plate and arm. Your looking for separation of the rubber bush from it's internal metal cup.push the rubber bump stops on the nearest edge inwards, if they stay put their ok. If they move and reveal a rusty metal cup replace. Mot fail.


Replacement.
Most of the individual jobs involved with this are covered elsewhere in the maintenance section. However there are other important factors to take into account as an overview to a good handling car, and these are the main reason for writing this little guide. Wishbone, shock and spring, track rod replacement on the front, and track rod(usually due to seized adjusters) and donut bush replacement on the rear(to a lesser extent, a crab, or of set rear axle is possible) all have a major affect on the car set up. So.....

BEFORE STARTING WORK

Take some measurements and notes with a view to setting the car up to something appraching the original settings, after the work, before you drive the car directly to a wim. This is to avoid scrubbing the tyres  excessively on the journey there, and its good practice anyway. Even better if the car has been set correctly previously as these methods merely replicate the original settings. But you should be able to set it no worse than before at least. With practice its possible to get it almost spot on, the socket method is quite accurate as whem wim re checked the camber they where unable to improve on thier previose settings.
Note the position of the steering wheel, is it straight or a fraction off center, and how the car drives.(i dont mean like a water bed)
Note the gap from shock body to vertical edge of the wheel rim of the front wheels. I use an appropriate size socket as a feeler gauge for this and it may not be the same on both sides.
Note the camber angle with the appropriate size spirit level. I do this by holding the spirit level vertical with it touching the bottom of the rim and measuring the gap to the rim at the top.
Rifle site the front wheels for alignment with the rear for the toe setting. Much like using a straight edge on the side of the wheel for alignment with the rear. Obviously its important to park the car car with the steering straight and not with wheels pinched as its just been dropped of the jack, drive the car at least a few yards back and forth to let the suspension settle to the correct track.

« Last Edit: 30 August 2010, 00:35:26 by chrisgixer »
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feeutfo

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Re: Suspension, handling, tram lining, tyre wear
« Reply #2 on: 30 August 2010, 00:34:53 »

Any upgrades?
Ideally decide at this stage how far you want go with your car as well as what needs repairing. You may want to fit lowered or sports suspension, lowered sports chassis from face lift mv6 or sport are worth while especially if you have the rather soft and wollowy suspension of an Elite which can be a little wayward when "making progress" depends what you want from your omega, some are quite happy with the stock set up and comfort it provides. More enthusiastic drivers find the same set up most uncomfortable at speed. Also consider irmscher, stienmetz or bilstein suspension upgrades, or kyb for oe replacement springs. Up to you of course. Gm springs are rather expensive for some reason, but shocks seem reasonable. I would not consider anything cheaper than gm shocks personally. A trade club card also help a lot with gm prices. See the bottom of any of my posts for the abs card link.

The idea here is to do as much work as possible to insure long term enjoyment of your car with as little outlay as possible. For instance it can be expensive to do a bit at a time. Fitting wishbones then set up. Then find the shocks fail the mot a couple of months later and needs set up again. Then find you would like better suspension and handling which needs set up again. Or not set up at all and find the car eats tyres which really is expensive as tyres worth fitting start at 400 a set these days, this really is a false economy. However a large bill all at once can result, but it's the cheeper way to do it in the long term if you can afford it purely because of set up costs each time an important component is disturbed.

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