Omega Owners Forum
Chat Area => General Car Chat => Topic started by: chrisgixer on 21 June 2014, 00:04:18
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I'm reasonably happy with mine currently so no biggies here, but I was wondering, not wandering ;D, in the car today....
We know the steering link rods, tre's and centre tie bar, and the wishbones need to work very closely together without play or movement in their parallel planes (ish) to give a normal sensation of feel at the steering wheel. Trust me, we do. So that's all fine, we have polys to take out play there, we know a solid idler is key, no ball joint play, rear bushes sound etc. That all works as a unit. Mounted on the subframe. It's all fairly independent from there.
But then we have the steering box and column. These are mounted to the body. Now you may or may not have noticed, but when you jack one corner of the car, the drivers door doesn't close as well as it would normally. So obviously there is an element of body flex there, probably understandably though.
So, question 1
... is it reasonable to assume that if there is an element of flex in the body, and the body has the box mounted to it, that body flex could pull the steering box slightly over giving a slight pull? One corner of the car would need to be higher or lower for this to happen. Think table with a short leg and a flexible top. So to speak.
Further up the system there's often talk of a dead spot in the steering box in the straight ahead position. Re this I often think there's an element of delay in slight steering adjustments that's not present when more steering lock is dialled in. Actually I'm not sure about that but certainly dead ahead is a bit vague. Only a bit mind if all else is as it should be.
But, question 2
... If you accept the dead spot theory exists, how could a delay in steering input occur? The dead spot as its often described. An example of this, dead straight, motorway speeds, no dramas. Wiggle the steering half inch either way, very little response. But steer a half inch one way, and the car does eventually respond. But it's not instant.
Is it the steering box?
Is it the possible body flex?
Is it servo tronic?
Or... What about the the flexi joint at the base of the column, that connects the column to the box. It's quite a hard piece of rubber, but could it develop play with age. Or go soft(er) over time. Might allow the delay sensation to occur, as the shaft turns but the damping effect of the rubber takes a fraction longer to actually turn the steering box.
Just some ramblings. Any RELEVANT thoughts? :-\
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I'll play, but I do think you're rambling. These are opinions.
Flex in the body: it's inevitable, as your door example shows. But I doubt it affects the steering box if you consider the part of the body it's bolted to. The join of the bulkhead, inner wings, strut towers and chassis rails are further braced by the subframe and have got to be the most rigid area of the structure. The steering linkage is designed to accommodate the suspension movement, which is vast compared to any likely flex.
Your 'delay' in the steering is common to ALL boxes, powered or not. The cause is interesting at 02:00 until I get to sleep. I think it's just something you have to accept as a characteristic, and learn to live with.
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The only way to remove slack from the steering box is to pack the balls in a liquid poly, so that they have no slop.
If you turn the wheel one turn to the left, then a quarter turn to the right, then a quarter turn to the left, there will be slack in the steering feel at each change of direction. As Nick says, this is a natural characteristic of the design.
You either accept it, or you fit a rack... although a worn rack will give the same feel/symptons :-\
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Your door hinges are bent and worn ::) ;D
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I'll play, but I do think you're rambling. These are opinions.
Flex in the body: it's inevitable, as your door example shows. But I doubt it affects the steering box if you consider the part of the body it's bolted to. The join of the bulkhead, inner wings, strut towers and chassis rails are further braced by the subframe and have got to be the most rigid area of the structure. The steering linkage is designed to accommodate the suspension movement, which is vast compared to any likely flex.
Your 'delay' in the steering is common to ALL boxes, powered or not. The cause is interesting at 02:00 until I get to sleep. I think it's just something you have to accept as a characteristic, and learn to live with.
Take your point on suspension movement in relation to the wobbly table. But as you say flex is inevitable. But what to do about it?
Don't get me wrong there's no big issue, I 'd quite happily live with it as is, but why wouldn't we want to improve it? If possible?
Thinking head on cross section, we have the two triangular shapes made by the the pivot points of the suspension, ie top mounts, wishbone pivot point, and wishbone ball joint.
/|engine|\
Wheel/_| void |_\wheel
______
There's a massive structure at the bottom bracing the engine, a subframe.
So the only thing I can think of to help would be one of those nasty chavy strut brace things. That should get that chav TB going ;D
But to be fair the ones I've seen involve drilling the metalwork around the top mounts. Opps that :o
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The only way to remove slack from the steering box is to pack the balls in a liquid poly, so that they have no slop.
If you turn the wheel one turn to the left, then a quarter turn to the right, then a quarter turn to the left, there will be slack in the steering feel at each change of direction. As Nick says, this is a natural characteristic of the design.
You either accept it, or you fit a rack... although a worn rack will give the same feel/symptons :-\
Steering box is all metal parts. What's damping out the harshness? Hydrolics maybe? Or the rubber block in the rack to box connection?
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If you want to remove the flex
fully seam Weld the shell, put reinforcement plates on the crumble panels, then fit a fully triangulation cage,made from t45, and as its a road car,fill the hollow chassis legs with expanding foam. Then any thing that is rubber mounted or bushed, use a poly bush or a spherical joint. :)
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If you want to remove the flex
fully seam Weld the shell, put reinforcement plates on the crumble panels, then fit a fully triangulation cage,made from t45, and as its a road car,fill the hollow chassis legs with expanding foam. Then any thing that is rubber mounted or bushed, use a poly bush or a spherical joint. :)
No I don't want to remove all the flex.
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My MV6 just feels 'right'......and far nicer to drive than my CLS 500. :y
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Strut braces work when the struts are fitted in the middle of an unsupported panel. Ford were good at this, just look at a Capri or Escort. Extra bracing on those is easy to do, and effective. I lashed up a Capri strut brace out of an old school-desk one Sunday afternoon, which eliminated the wobble the car always had. A similar brace across the anti-rollbar mounts is even easier to make, and also makes a noticeable improvement.
Bracing the Omega is much harder due to the method of attaching the strut and the engine being in the way. And if you look at the strut tower, it's already reasonably well braced against the bulkhead, so any improvement is likely to be minimal.
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While I think about it, the much vaunted steering rack is hardly a paragon of stiffness either. How can it be? A metre long assembly of tubes, sliding and\or articulated joints, gears and bushes that are only attached in a couple of places is going to be a pretty floppy thing.
I improved the steering feel on my Avenger by machining a solid clamp for the 'floating' passenger side out 1" aluminium square bar. Rally cars use a much longer part that wraps around the rack tube to prevent it splitting!
Some slack in the steering is a necessary component for a comfortable, easy to drive roadcar. The gokart like steering on Seven type car, or quick-rack equipped car gets tiresome very quickly.
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The only way to remove slack from the steering box is to pack the balls in a liquid poly, so that they have no slop.
If you turn the wheel one turn to the left, then a quarter turn to the right, then a quarter turn to the left, there will be slack in the steering feel at each change of direction. As Nick says, this is a natural characteristic of the design.
You either accept it, or you fit a rack... although a worn rack will give the same feel/symptons :-\
Steering box is all metal parts. What's damping out the harshness? Hydrolics maybe? Or the rubber block in the rack to box connection?
The hydraulics mostly :y don't forget, the box is essentially part of the chassis, so any further damping is done by the tyres/ball joints/suspension...
The rubber connection is there for crash purposes, ie if you bend the car enough to move the box, the rubber will deform more effectively than a metal UJ. This means you're less likely to A) lose your lower legs, and B) end up with the steering column attached to your spine... both of which might otherwise be quite unpleasant...
This is summat that might be worthy of consideration when fitting a rack to the V8 :-\
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If you want to remove the flex
fully seam Weld the shell, put reinforcement plates on the crumble panels, then fit a fully triangulation cage,made from t45, and as its a road car,fill the hollow chassis legs with expanding foam. Then any thing that is rubber mounted or bushed, use a poly bush or a spherical joint. :)
No I don't want to remove all the flex.
Only filling all the box sections/cavaties with expanding foam could be a good compromise... you might find that it increases stress loads where the flat panels meet the boxes, so seam welding is probably a must. Without the bracing the shell will still have a degree of flex. It will change the crash dynamics of the car as well because the box sections won't deform at all, making any prang that much harder.
I don't know what basic crash testing costs, but you could buy a couple of scrap Omegas and fill the cavaties with foam and get them crash tested to compare the impact results.
Doesn't affect the steering though...
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Hmmm. ...I wonder could I get a govt grant? Might save in heating bills. Solar panels in the roof maybe? Hybrid power? Yeah, that'd work ::) ;D
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While I think about it, the much vaunted steering rack is hardly a paragon of stiffness either. How can it be? A metre long assembly of tubes, sliding and\or articulated joints, gears and bushes that are only attached in a couple of places is going to be a pretty floppy thing.
I improved the steering feel on my Avenger by machining a solid clamp for the 'floating' passenger side out 1" aluminium square bar. Rally cars use a much longer part that wraps around the rack tube to prevent it splitting!
Some slack in the steering is a necessary component for a comfortable, easy to drive roadcar. The gokart like steering on Seven type car, or quick-rack equipped car gets tiresome very quickly.
Getting warmer, as the rack would be mounted to the same structure of the subframe, rather than a separate structure of the body, in this example at least. Omega doesn't lend itself to a front axle mounted rack too well. So rear mounted is more likely, but that leads to quite an acute angle for the u.j. to negotiate. :( and then no need for this particular design of rubber block damper for crash protection as it will fold up naturally anyway.
Rack also eliminates the steering idler obviously, mounted to the other wing.
So two points of contact moved from the body to the subframe where all the business happens. Also removes the rearward arc of the idler and pitman arm. So thinking aloud, does that mean a rack needs to be mounted rear most point of that arc to get the lock angle on the hubs?
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Thinking about MotoGP bikes where they have found lack of frame flex decreases tyre adhesion over slight bumps, does the same apply under some conditions (like bumps with a loaded suspension) if you have too stiff a chassis on a car?
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Thinking about MotoGP bikes where they have found lack of frame flex decreases tyre adhesion over slight bumps, does the same apply under some conditions (like bumps with a loaded suspension) if you have too stiff a chassis on a car?
Not sure that applies to cars in the same way, because, as I understand it, the frame flex required in bikes is related to lean angle. And they are reaching some massive lean angles these days. 64/5 degrees in cases.
So a bikes suspension works in a vertical plane, same as cars, but, as the bike leans over there's a sliding scale of decreasing travel verses an increasing scale on bump height. By that I mean, the more the bike leans over the higher the bump becomes along the new ANGLED plane of bikes suspension travel as its leant over.
Effectively. Lean the bike over far enough, approaching 90degrees say (hopefully not or the rider has binned it ;D ) and there will be zero suspension travel in relation to bump height of the roads in perfections, and your then looking at frame flex to absorb the bumps.
At the rear they look at swing arm flex to achieve this. Massively braced up and down, but thinner side to side when viewed with the bike vertical. The idea is that its incredibly stiff in the direction of suspension travel, with slight flex in the side view to help with lean angle. Up front the frame sections forward of the engine mounts do the job there.
....afaik anyway.
Apart from anything else, cars lean the wrong way in a corner. Where as bikes lean in obviously. Much better. Forcing the tyre and suspension into the floor, increasing grip level as it goes. (Ignoring the all important direction of gravity for a minute, which is most inconvenient) It's not really something road riders will encounter, until they get into competition and slicks that generate serious grip levels, and the lean angles go up. Or down, depending on your point of view.
The way round it, to a point, is for the rider to,pick the bike up in the corner while maintains body position. It's often described as hanging off. Hence the knee and elbow down styles we see these days. If they kept bike, head and body in line with lean angle, they'd ride off the edge of the tyre first off, and second the suspension would become less effective over bigger bumps, and frame flex plays more of a part. It's also another reason why a higher tyre profile/smaller wheel sixes are used, so it can deflect and absorb bumps a bit more. Tyre being the first point of suspension :)
That's my understanding of it anyway. Not saying its correct mind. Just how I understand it. :-\ :)
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Is there an assumption, WRT racks, that the subframe is massively more rigid that what its bolted to? I thought they worked together, as a chassis, to give the rigidity?
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Is there an assumption, WRT racks, that the subframe is massively more rigid that what its bolted to? I thought they worked together, as a chassis, to give the rigidity?
Er, not sure I understand.
So far, my thoughts relate to the comparison of a steering box and idler bolted to a body, that's controlling wheels that are bolted to subframe(, via wishbones.)
Versus a rack that bolted to the same subframe that controls the wheels. This eliminates any possible flex in the body. Unless flex in the body is transfers to the subframe as well.
The reason for comparison is eliminating the "possible" flex in the body. As in when jacked on one corner....etc.
Or have I misunderstood? :-\
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More ramblings. Along the same lines...
Put another way.
The box and idler are bolted at a height x amount above the level of the steering linkage, on the side of the frame rails/inner wing, for want of a better description. Call it body for now.
If the body flexes then the flex might mean movement on a plane equivalent to the suspension strut towers moving in and out. Slightly. If accepting that as possible, which is arguable obviously, then a chavy item such as a strut brace might help. Just to give another way of explaining it.
But, if the box and idler bracket are removed, then the only possibility for that body flex to affect handling is for tower flex to affect camber. A minimal or, less off a consideration given the flexible top mount and and lower ball joint, and the give in those anyway.
In sort, a rack would remove that possibility of body flex affecting steering, of you accept it as possible in the first place of course. Failing that, a strut brace. Ignoring the nasty design floor of drilling holes in the strut tower and causing fatigue cracks and failure of course.
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You really need to measure the flex that you're concerned about. That will be a fun job, and I bet you'll be surprised by any figures that you come up with.
Actually, I think you're massively over-thinking this and should get out more! ;)
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You really need to measure the flex that you're concerned about. That will be a fun job, and I bet you'll be surprised by any figures that you come up with.
Actually, I think you're massively over-thinking this and should get out more! ;)
Its a good job I don't give a flying shit what you think then. Isn't it. ;) ;D :P
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The subframe is no more rigid than the body it's attached to, (don't forget it's C shaped...).
The box, bolted securely will only move very slightly as it's only attached to a small area on one chassis leg...
Whereas the subframe will flex across the car, and any rack attached to it will flex at both ends during cornering, by virtue of being attached to opposite sides of the car.
A strut brace will stop the turrets from flexing inboard and outboard under suspension load, (this is minimal anyway because the turrets are mounted against the bulkhead), but won't prevent chassis twist during cornering. Better off fitting diagonal bracing across the radiator aperture.
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As a thought, assuming the V8 is roughly in postion, is there any room across the car to mount the rack directly to the car, approximately where the tie rod currently sits :-\
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The subframe is no more rigid than the body it's attached to, (don't forget it's C shaped...).
The box, bolted securely will only move very slightly as it's only attached to a small area on one chassis leg...
Whereas the subframe will flex across the car, and any rack attached to it will flex at both ends during cornering, by virtue of being attached to opposite sides of the car.
A strut brace will stop the turrets from flexing inboard and outboard under suspension load, (this is minimal anyway because the turrets are mounted against the bulkhead), but won't prevent chassis twist during cornering. Better off fitting diagonal bracing across the radiator aperture.
Viewed that way, Mmmmyeah sort of agree. But viewed the other way, as presented?
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As a thought, assuming the V8 is roughly in postion, is there any room across the car to mount the rack directly to the car, approximately where the tie rod currently sits :-\
Position of the tie rod is deceiving. As its u shaped. To clear the sump. The ball joints are higher that the lowest point of the centre tie rod.
So to fit a rack, the lowest part of the tie rid will mean the rack will need to be 50mm higher. The jury is out as to weather the bonnet will shut ;D throttle body is the highest point and is a common problem on the monaro and r8's as the throttle body often rubs the bonnet lining.
A bonnet bulge will work, with a bit of Sammy. But the more serious concern is the height if the transmission tunnel. :-\
There is a bridge shape to the sump from the original design of the donor car. But even so, some of the webbing may need a nibble.
The rack Rats used, from an Almera, appears to be a fraction long though. It seems they may not have allowed for the fact that the wishbone pivot points toe out. They are not parallel.
....Or I have the wrong Almera rack which sounds more likely. ;D
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I would not use expanding foam anywhere......having experienced its use on Mk2 coaching stock it is BRILLIANT at holding water and NEVER dries out again.