Omega Owners Forum
Chat Area => General Car Chat => Topic started by: feeutfo on 25 March 2013, 10:44:22
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After some experimentation with basic poly alternatives, IMO, it's becoming clear that a proper poly ball joint is needed.
Having discussed this with Powerflex regarding their range of rearward wishbone bushes, it's also clear that none have a centre hole that meats the omegas 14mm diameter to accept the omega bolt size. I don't think a smaller bolt is wise. So while some designs could be modified slightly by fitting sleeves to space out the bush outer dia to 49mm. It's a non starter if the bolt won't fit through the hole.
Any ideas on a poly replacement?
Here are the oe dimensions from the Meyle web site.
Meyle rear wishbone bush
614 035 0010
Height 46 (to space out the subframe)
Inner diameter 14 (to take the bolt)
Outer diameter 49 (to press fit into the wishbone)
To add, from memory, the wishbone metal is 26mm deap.
Thanks to numerous members with various projects that have tried various lumps of poly solutions, but these don't offer enough control, giving odd steering sensations on the brakes at best.
It seems it really does need to be a ball joint design. But to find one that fits.... :-\
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Something like this, some engineering may be required: http://cad.aurorabearing.com/viewitems/products-commercial-spherical-bearing-metric-units/s-spherical-bearings-metric-ptfe-liners-available-?
Though I'm not sure 32º of suspension travel is enough, without measuring bump-to-droop.. There's one with a 14mm bore, what's the OD of the standard bush?
Ride might be a bit harsh with just a spherical bearing in there, mind.
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I'll watch this thread with interest.... But unless you can get someone to make something which can be easily and cheaply made (looking at the movement of the axis I think that's going to be difficult) and provide longetivity well in advance of the genuine GM article - ie lifetime like the front polys - then I think GM is the only sensible route.
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Something like this, some engineering may be required: http://cad.aurorabearing.com/viewitems/products-commercial-spherical-bearing-metric-units/s-spherical-bearings-metric-ptfe-liners-available-?
Though I'm not sure 32º of suspension travel is enough, without measuring bump-to-droop.. There's one with a 14mm bore, what's the OD of the standard bush?
Ride might be a bit harsh with just a spherical bearing in there, mind.
Nice idea, but nothing on that list that is even close to fitting :'( very limited compliance as well :-\
Adding a thick washer to the support bush of the Sierra bushes might help reduce the lateral give. Say a thickness of 4-6mm and a diameter of 30-32 mm.
The amount of lateral force that the rear bush has to deal with is quite impressive...
Just to add, this is clearly a trial and error process rather than a simple fix, so perhaps needs an structured testing regime.
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Yes Aaron that's the general idea. The outside diameter is 49mm. :)
The oe bush has roughly a 4mm thick surround of rubber as a damper between the globe centre spacer and the outer shell. Say 8mm total accross the entire width , for argument sake.
To utilise the items in the link, two spacers would be required to 46mm to space out the subframe bracket, then a circular poly collar fitted to the outer shell to provide damping, this would have to fit within the 49mm diameter shell.
The ball joint itself will have to take massive lateral load, like the entire weight of the car, and not stick.
A big ask.
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This is the closest design I can find. Sizes are off, bloody Amricans insist on using inches. And the centre bolts is drilled. Bugger that. Although lubrication is going to be needed.
http://www.4wheelparts.com/Fabrication-Tools/Flex-Joints.aspx?t_c=86&t_s=528&t_pt=101460&Manufacturer_PQ=Daystar
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Plus, as said, not sure 20degrees of articulation is enough. :(
Also, looking at the diag,not sure but I think I'd like to see the red material/poly surround the ball further to stop it popping out. But that would restrict articulation further. :-\
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From the link for clarity
(http://i344.photobucket.com/albums/p326/chrisgixer/6e2ebd8f68c1ce7b545fe23a9a329f72_zps1bcae77f.jpg)
(http://i344.photobucket.com/albums/p326/chrisgixer/6b7ef2e43985b593fbd54750ef37a810_zpsf929a0a0.jpg)
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I wonder if we could use the poly parts and make the rest to omega sizes...? :-\
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Ooh... I wonder what the tooling costs would be to get a set made :-\
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yes - have looked at this in some detail and have come to the conclusion that a new wishbone with longitudinal bushes at front and rear is the only solution worthy of merit, BUT
your "floppy" vertical bushes are giving you quite a lot of improved handling by allowing the wishbone to move inwards at the rear under cornering. This in turn gives you some toe-in on the outer wheel, which is good !
I'd really need to do some serious calculation work on replacement vertical bushes before being convinced of their safety.
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Hmmm, I presumed the only reason the rearward bush is vertical is to give yaw movement given the excessive play the front oe bush can give throughout its life?
Plus, if fitting a vertical rear poly bush, I wonder if the depth of bush needed to keep it from popping out, will physically fit between the subframe brackets without striking the subframe on full extension and compression...?
The wishbone metal is only 26mm deep. A ball joint poly bush may well need to protrude either side. Full extension may well see the bush outer diameter meat the subframe. :(
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My next to steps are...
1. Replace the yellow bushes with the black ones. If negative performance then onto step 2.
2. If the black ones are supportive enough laterally, but too stiff to allow the arm to move vertically, then I will remove the flanges from the black bushes and replace with the flanges from the yellow bush. This would give a composite bush with the upper and lower 10mm being the softer yellow compound, whilst the central 26mm within the arm being the much harder black compound. This should allow adequate suspension travel whilst restricting the horizontal movement which is causing the toe changes under load and the subsequent tyre scrub.
3. If all else fails, refit the GM rears.
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An old thread but these work. £50 a wishbone from Volvo. Half hour a side to fit. Piece of Pee.
Ride is very firm on the c70 though. Mostly spring rates, but the the rubber bush depth around the circumference was about 3mm iirc.
http://oldsite.omegaowners.com/forum/YaBB.pl?num=1232197401/0
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The situation is different on a
shopping front wheel drive car, though. You have the forces from the driven axle to control so there isn't the luxury of allowing some "give" in the bushes to compensate for cornering, etc. or it'll torque steer all over the place.
What problem are we trying to solve with the original bushes? IME they have very much less "give" in them than the front bushes and, again IME, they don't seem to fail as quickly. :-\
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Longterm replacement for the rear bush together with better steering response :y
I know Chris is not convinced, but with poly fronts fitted, pattern rears only last about 20k. Once bolted on, balljoints are a doddle to change, with no set up required. :y
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The situation is different on a shopping front wheel drive car, though. You have the forces from the driven axle to control so there isn't the luxury of allowing some "give" in the bushes to compensate for cornering, etc. or it'll torque steer all over the place.
What problem are we trying to solve with the original bushes? IME they have very much less "give" in them than the front bushes and, again IME, they don't seem to fail as quickly. :-\
A bit more accuracy, although a vast majority if that problem can be removed by fitting tyres that actually work, and life span.
My lemforders rears are two years old and no splits or seperation, but whilst removed for some poly experiments, I clamped the bush In a vice and tested the resistance by levering/pulling the wishbone. Far from scientific but they are quite loose.
So some improvement in longevity would be nice.
But I've just purchased a 10 ton press, so no worries here really. I just would be nice to fit and forget. :)
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Note that ten ton is borderline for pressing out the front bushes :y
More than enough for the rears, a good vice will do those.
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Note that ten ton is borderline for pressing out the front bushes :y
More than enough for the rears, a good vice will do those.
Yes iirc I've seen 11 ton on this press, if the gauge is akawut. :-\
Or cut the fe@kers out is probably just as easy now. :)
... Got press me. :) :y
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Hmmm, I presumed the only reason the rearward bush is vertical is to give yaw movement given the excessive play the front oe bush can give throughout its life?
No - I'm sure its part NVH and part handling.......
Lots of NVH research points to a loose wishbone front-to-rear being the most important thing for comfort. Well, actually the hub centre being free to move a bit rearwards under bump deflection. That's part of what GM will have been trying to achieve.
From the handling side, what you really need is some automatic toe-in when cornering. This has the effect of gaining more turn than the driver thinks he needs ( or better handling to put it another way ). This is achieved as follows .......
under cornering, the outside wheel is more loaded than the inside one. The floppy vertical bush allows the wishbone to move rearwards ( see above ) It also allows the wishbone to move inwards at the back. Now think of what's happened to the outer ball joint - its moved both rearwards and inwards. Compare this to the steering tie-rod, which doesn't flex at all - you get bottem ball joint in and rearwards and steering knuckle unchanged, hence the wheel toes in slightly.
( don't even think that I came up with this one - it was down to a good mate of mine who just happens to be chief suspension designer for xxx )
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If the rear bush is too soft or worn, then the front wheels toe in at the first sign of ANY load ::)
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On TBE, I've been struggling to get GM rear wishbone bushes to last more than 12-15 months - which is next to frak all in mileage terms (5 or 6k max)
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On TBE, I've been struggling to get GM rear wishbone bushes to last more than 12-15 months - which is next to frak all in mileage terms (5 or 6k max)
Just wondering if bigger wheels with lower profile tyres and stiffer springs is accelerating the failure timescale?
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Possibly, Silver Bullet's have been in ages now (about 6 months before the homemade press got broken at Newent)... ...although TBE has had front polys in for longer...
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undoubtedly
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Stiffer suspension= less suspension travel=less wishbone movement= less stress on bushes to my mind. Poly giving less yaw too.
The rear bushes fitted at Newent where Meyle heavy duty. NOT Gm. NOT lemforder. Iirc...?
TB where Rusty Bullets bushes Meyle or Defo Gm..?
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...and how long did the failed bushes spend on Elite suspension? ...with an enthusiastic driving style...? :)
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For example, TBE doesn't roll around like this particular Elite any more ;D
(http://i344.photobucket.com/albums/p326/chrisgixer/2159db629610983ca510022e2d230f1b_zpsd06462c1.jpg)
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That front seat passenger looks about as impressed as Mrs TB ;D
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For example, TBE doesn't roll around like this particular Elite any more ;D
(http://i344.photobucket.com/albums/p326/chrisgixer/2159db629610983ca510022e2d230f1b_zpsd06462c1.jpg)
What? Even when full of salad-dodging journalists? ;)
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MV6 - genuine GM. Got receipt, dig out when I get home.
TBE - Mr DTM supplied, so guess GM. That car hasn't really been driven really enthusiastically that much.