11-19-2006, 09:38 AM
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Poly Bushing Question and Debate
Before I posted this query I read almost all of the threads related to installing in the rear axle, polyurethane bushings. There doesn't seem to be a solid concensus one way or the other. So I thought I would toss this out and see what comes back.
I have 2 sets of trailing arms that I have accumulated over the years. Last week I had a tool made to remove both the large and small bushings. Works like a million dollars as it easily removed the bushings with out damaging the arms.
Now I am faced with the task of reinstalling front and rear bushings. I have both replacement rubber bushings and poly bushings that I can install.
I plan on installing the trunnion bushing to center the rear axle. I had this on my 89 spider it was one of the best mods I ever put in a car. It tightened up the rear axle but didn't effect the ride quality.
I need to know if I should use rubber in the rear and poly in the front of the arms or the other way around? I don't want to effect ride quality so I was thinking of rubber in the front and poly in the back. Or can I go poly all the way around? Previous posts say that the rear axle would be to stiff if I went poly all around and make the car twitchy (oversteer?) and lift the rear wheels going around the corner.
The car already has red Koni's installed.
Thank you in advance for your advice.
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11-19-2006, 09:47 AM
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Darth Slacker
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Join Date: Mar 2006
Location: Northern NY, USA
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I've got poly on the trunion to pumpkin and both ends of the arms.
One end is blue, the other red making for a difference in durometers or whatever the hardness measure is on those things.
Haven't had any issues with oversteer or tricycling and it felt pretty much the same as it did with the rubber bushes in there, except it no longer dog tracked or got rear steer through axle displacement :shrug:
One thing I wish I would have done while it was apart would have been to weld a plate the length of the open side of the arms to get a bit more rigidity and overall strength out of them.
Not that they are noticably floppy or anything, but certainly it should/would help reduce any flex and/or fatigue they may be subject too.
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11-19-2006, 10:06 AM
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 Quote:
Originally Posted by Tifosi
I've got poly on the trunion to pumpkin and both ends of the arms.
One end is blue, the other red making for a difference in durometers or whatever the hardness measure is on those things.
Haven't had any issues with oversteer or tricycling and it felt pretty much the same as it did with the rubber bushes in there, except it no longer dog tracked or got rear steer through axle displacement :shrug:
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I have a set of red bushings for the big end and a set of front/rear in blue.
Which would be the best way to go here? The safe way would be to go blue all the way around.
Next question would be how to tighten these bushings up. The best way I read is to put the car on the ground and tighten. My question is...how tight is tight? Factory torque specs?
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11-19-2006, 03:04 PM
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Darth Slacker
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Join Date: Mar 2006
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Quote:
Originally Posted by velocedoc
I haven't heard of anyone twisting the rear arms before, but that doesn't mean it hasn't happened.
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Loosely it had to do with stiffness rather than failure, but apparently in outright competition use, they can wad themselves up. (the words used were 'boxing the trailing arms is a must')
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Which would be the best way to go here? The safe way would be to go blue all the way around.
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I didn't have the option, or at least the patience to wait weeks for a matched set, (middle of the summer 'ain't nobody got nuthin in stock blues'), so my excuse is 'it's ok because the softer poly is closer to the rubber AFA hardness, so it's less likely to be over stiff but still acts as an improvement' (again, an excuse, not a reason  )
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Next question would be how to tighten these bushings up. The best way I read is to put the car on the ground and tighten.
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Definitely, though somewhat difficult to accomplish, particularly on the body to arm end unless the car is on a lift held up by the wheels or up on jackstands at the front jack points, under the axle tubes at the rear, and the chassis relatively level.
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My question is...how tight is tight? Factory torque specs?
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At the arm to diff it was 79-98 ft lbs on the nut side, (dry, and with an additionally uncalled for tiny drop of loctite), but I never did find the spec for the trailing arm to body end and sorta split the difference while trying to make sure it wasn't so much that those thinner mount points were crushed/deformed.
Last edited by Tifosi; 11-19-2006 at 03:07 PM.
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11-19-2006, 06:48 PM
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Join Date: Jan 2004
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If Alfa Romeo thought it would work....
Picture this: Putting in solid or poly bushings, why didn't Alfa Romeo or Auto Delta do it??
Putting in poly bushings make the car SEEM faster because the inside tire starts to lift, loosing grip, and you get oversteer, Whee, I must be faster since I can now slide the rear end around a corner!
Auto Delta used rod ends on both ends of the trailing arm to allow the axle to comply to the road/track surface in the corners. Ever wonder why?
Why in the hxxx would you want to turn a set of pivots into a solid, so that the trailing arm now becomes a torsion arm is beyond me. (Or a trunion pivot). When you see a trailing arm fatigue and break on a car at the track, you "might" get the idea how a suspension works.
Just because they are for sale, doesn't mean it we NEED it.
Many have passed on this message to those that want to BUY something, like poly bushings, Please use the search engines, that the ALFABB has so nicely maintained and given us for free, to find these pearls of wisdom.
Am I getting cranky, or have I seen and weighed in on these same questions asked SOOO many times over the years?
__________________
George Willet
willet@q.com 520-374-2220: please do not use PM, email me direct, saves us both time.
Note: I prefer to offer parts to the AlfaBB members first, and eBay second.
THESE are the good old days!
There are no easy answers to complex problems.
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11-19-2006, 07:49 PM
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As George says, suspension systems are designed to MOVE.
IMO anybody that uses poly bushes on the rear of an Alfa Romeo has simply not thought it through properly.
Traction is everything, suspension must move freely to achieve this ... and BTW: as George said, nothing does this free'er than a rose joint. Anything that impeds suspension travel is a negative to traction. The only thing that should control the axles movement is the springs and shocks, the links should just ensure that the axle is COMPLETELY free to move as the springs and shocks want it to.
If you use poly bushes you are adding another restriction to this movement that (again as George said) makes the trailing arms into torsion bar springs ... thus you will have to stiffen your shocks to compensate ... further stiffening the traction end of the car that should be as soft as possible, unless you like getting blown away out of corners.
IMO there are only 2 options, rubber as per original (everywhere) or rose joints. Poly bushes are only usuable on leaf spring rear axles where the leaf spring has to twist to provide any single wheel movement ... and why leaf sprung cars are a step backwards in the handling department (ie. MGB rear will improve as the hard poly bushes will help sideways location ... as there is none other than the leafs).
I naively used poly bushes on an Alfa Sud that I classic raced many years ago ... I then bounced from bump to bump with a now extremely nervous car. Worst thing I ever did to it ... other than crashing it a couple of times  
BTW: Many will say after a poly conversion that there car has improved in feel, etc. They are misunderstanding a now over nervous car that feels faster because the poor driver has to constantly correct, etc. ... it will not be faster!
Pete
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Last edited by PSk; 11-19-2006 at 07:52 PM.
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11-19-2006, 08:25 PM
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The advantage to having an extra set of trailing arms is that if you don't like em you can swap em out. I don't plan on racing or pushing this car hard at all, so a trip down the highway with some poly bushings isn't going to hurt anything. This is going to be the wife's car and not mine. She is conservative where I would be the one to push it to some limits.
If one considers the Duron or what ever rating it is called, softer and closer to stock is obviously going to be better. I have no intentions of stiffening up the car to the point where things bend or have restricted movement.
Why didn't Alfa put in poly or solid bushings? Was poly available when these were made? Solids would make the car so you couldn't ride in it it would be so rough. Solids would also tend to rip out mounting brackets. It would have been Alfa wisdom to choose a rubber that is hard enough but flexible enough to retain flexible motion over a long time span. Red poly has got to be alot harder than the blues, so I am going to go with the blue ones and see how it goes. If they are not so hot, I will just put in my other trailing arms with the new bushings and let it go at that.
I am tired, so if my words come across as harsh, I apoligize for being a grumpy ol guy. |
11-19-2006, 09:11 PM
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Quote:
Originally Posted by George Willet
Picture this: Putting in solid or poly bushings, why didn't Alfa Romeo or Auto Delta do it??
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While I won't argue with your theory one bit, I think equating Polyurethane with "Solid" is a mistake. Poly comes in a huge range of durometers, some of it is like hard plastic and others can be softer than the natural rubber used in most bushings.
For example, most of the Poly bushings we sell at Centerline are only 15-20% stiffer than the stock rubber they replace. That firms up the suspension a bit but is nowhere near "Solid".
Joe
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11-19-2006, 09:12 PM
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interesting.. just bought some poly bushing from a alfa shop on the bay area, berkleey.. they sent me both front and rear trailing arm bushings, red pair for the rear and blue pair for the front....hum...
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11-19-2006, 09:21 PM
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Quote:
Originally Posted by JoeCab
George,
While I won't argue with your theory one bit, I think equating Polyurethane with "Solid" is a mistake. Poly comes in a huge range of durometers, some of it is like hard plastic and others can be softer than the natural rubber used in most bushings.
For example, most of the Poly bushings we sell at Centerline are only 15-20% stiffer than the stock rubber they replace. That firms up the suspension a bit but is nowhere near "Solid".
Joe
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11-19-2006, 09:22 PM
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Velocedoc,
Would you describe the tool that you had made(pics would be even better!)? Since there seems to be a chance of bending the trailing arms (I guess having 2 sets really eliminated any worries there) with the usual pound-it-out-with-the-proper-sized-pipe, it sounds like your tool is a pretty good design.
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La vita e troppo corta per non guidare Italiano! (Life's too short not to drive Italian!)
You're traveling through another dimension, a dimension not only of sight and sound but of mind. A journey into a wondrous land whose boundries are those of imagination. That's the sign post up ahead. Your next stop: [COLOR=Red]The ALFA Zone[/COLOR].
Ron Linhart 
'76 Spider Veloce(tucked away in my garage)
'76 Spider Veloce(a roller)
'79 Spider Veloce(parts-donor lawn ornament)
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11-19-2006, 10:02 PM
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Darth Slacker
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Join Date: Mar 2006
Location: Northern NY, USA
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Quote:
Originally Posted by JoeCab
I think equating Polyurethane with "Solid" is a mistake.
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Even at full and proper torque on poly stuff, you can still move the arms up and down by hand with relative ease (when the diff is disconnected or the springs are out obviously) which IMO is pretty far from 'torsional arm springs' but certainly does reduce the amount of linear twist they may get.
Loosely, it just stops some of the twist the arms have in relation to each other, but by then you're on the bump stops anyway and need or deserve all the punishment you get. (and goes a long way toward getting rid of that god awful dog tracking/rear steer crap, unless you consider that 'normal' or 'proper')
I've not experienced any tricycling/inside tire lift nor even any extra or overt slide/loose since the install.
I'd hazard if someone is experiencing that, they either went way to hard, screwed up the install, or have something significantly more wrong than what the bushings could have done on their own. :shrug:
*(probably) unlike velocedoc right now, I'm half in the bag and don't really care what I come off sounding like.
I know what they did for me and ain't compelling anyone to follow suit or not based strictly on what if's relative to what they designed or decided late last century. (hey, if that's the case for reference, then damnit, you'd better weigh 165 lbs and your full time, every time passenger better too, otherwise you're screwing up the overall trim as described by the manuals and therefore are outside design specs to begin with)
I know what they did and didn't do for me and am content with that. If anyone else wants to follow suit, cool. If not, well, it ain't no skin off my sack and more power to ya 
Last edited by Tifosi; 11-19-2006 at 11:14 PM.
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11-19-2006, 10:09 PM
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Quote:
Originally Posted by spider76
Velocedoc,
Would you describe the tool that you had made(pics would be even better!)? Since there seems to be a chance of bending the trailing arms (I guess having 2 sets really eliminated any worries there) with the usual pound-it-out-with-the-proper-sized-pipe, it sounds like your tool is a pretty good design.
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JoeCab and Velocedoc,
Don't you think it is interesting that NEW cars still come with rubber bushes ... not this so wonderful poly stuff?
The only advantage (and this is from the manufacturers if I remember right) of the poly bushes is that they do not perish like rubber ones ... funny thing is my Toyota Tarago, for example, is now 13 years old and those rubber bushes are doing fine. I think replacing a rubber bush that costs < $20 every 10 years or so is no big deal, definitely not worth the change to a product that car manufacturers STILL don't use.
Pete
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ps: Remember it's all just opinions
'71 1750 Series 2 GTV: http://www.alfabb.com/bb/forums/showthread.php?p=208078
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11-19-2006, 10:22 PM
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Yep, its all opinions...
I went to my local machine shop around the corner where I work and made a request with some ideas through out as to what I was looking for and the next day I had a fixture for the small and big ends plus a mandrel to push the bushings in and out. Works like a charm on the 20 ton press.
I was thinking of offering this as a service if anyone was interested of pressing in new bushings...besides I got to pay for my hobby somehow. |
11-19-2006, 11:09 PM
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Darth Slacker
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Join Date: Mar 2006
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Quote:
Originally Posted by PSk
The only advantage (and this is from the manufacturers if I remember right) of the poly bushes is that they do not perish like rubber ones ... funny thing is my Toyota Tarago, for example, is now 13 years old and those rubber bushes are doing fine. I think replacing a rubber bush that costs < $20 every 10 years or so is no big deal
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You've answered yourself
Manufacturers don't use it because it cost more than rubber to produce, especially when you're getting into many various models with slightly different components.
You don't mind dropping around $20 to replace rubber bits every 10 years (though I'd hazard that's prolly 5 years too long) but manufacturers certainly aren't even going to pop for an extra $10 per car going out the door to swap to the more expensive poly.
They are going to pocket that $10 per unit and pocket the millions they saved in what they call the 'profit margin'.
Conversely, some cars just don't need it, so there'd have to be a sort of dual market thing going on that produces poly for performance vehicles and rubber for more luxury or lower line cars. This in turn would drive up manufacturing costs across the board and cut even more deeply into that profit margin.
Car companies and thier stock holders like to make money, not lose it on what they as investors feel are un-neccisary expenses.
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