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Poly vs. Rubber
https://slantsix.org/forum/viewtopic.php?t=10485		 Page 2 of 3
Author:  Matt Cramer [ Fri Oct 01, 2004 10:45 am ]
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One of the reasons the factory didn't use polyurethane is that some of the lubricants they've developed for poly bushings were not around when they built new A-bodies. When polyurethane bushings first came out, they were notorious for squeaking. I've rebuilt my front suspension using an Energy Suspension poly kit and have not noted any problems with it so far. It's not harsher, not squeaky, although I can't really tell how well they will work in an autocross or other extreme handling test. I want to get my EFI conversion working before I try that.

However, some polyurethane kits appear to have definite issues. I was once looking to buy a CRX race car from OMP Performance, a well known Honda shop. They commented that they never use any polyurethane bushings on their cars because the ones available would always bind and ruin the handling. Some of the issues they had do not really apply to A-bodies - evidently Honda bushings do not use inner or outer shells - but it appears that when polyurethane bushings are made wrong, they're very wrong.

Polyurethane is as much as 100 times stiffer than rubber. Delrin is 10 times stiffer than polyurethane. However, Delrin is slippery, almost like Teflon. Precision bored Delrin bearings will not squeak or bind unless the bolt running through them somehow goes off-axis (not a big issue on Mopars, but don't even think of using them for a Fox-body Mustang rear suspension!). The drawback is their extreme stiffness - short of replacing your bushings with needle bearings or spherical rod ends, they aren't really meant for the street. If you're building a hardcore race car, though, I'd suggest using Delrin or metal bearings depending on your class rules.
Author:  argentina-slantsixer [ Fri Oct 01, 2004 11:16 am ]
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I machined idler arm bushings in delrin cuz I was sick of replacing them like 3 or 4 times per year and so far I'm very happy.
Author:  Dennis Weaver [ Fri Oct 01, 2004 12:01 pm ]
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Quote:
Precision bored Delrin bearings will not squeak or bind unless the bolt running through them somehow goes off-axis (not a big issue on Mopars.
Matt, all good points, but think very carefully as to how an A/B body upper control arm is adjusted to provide the proper camber/caster. If memory serves me correctly, the fore and aft bushings are on the same center line. once they are installed and adjusted to spec (or the racer's specs) the adjusting bolts running thru them are not likely to be on the exact same axis... This is taken up in a stock suspension by slight deformation of the rubber bushings - not possible with hard bushings which slide rather than twist, as does the rubber, so they end up binding which eventually wears even the polyurethane.

D/W
Author:  sandy in BC [ Fri Oct 01, 2004 2:18 pm ]
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I now understand why poly bushings wont work for you. They need to be installed properly.
Author:  Dennis Weaver [ Fri Oct 01, 2004 2:46 pm ]
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Quote:
I now understand why poly bushings wont work for you. They need to be installed properly.
That's quite a shot, sandyinBC. Now kindly back it up by explaining what you mean.

D/W
Author:  72swing [ Fri Oct 01, 2004 4:08 pm ]
Post subject:  Hot Topic!
Well, It looks like I need to buy some rubber, some poly for my application. I'd like the silence and compliance of rubber for some components, while others would definitely benifit from the stiffer poly bushings :? . I'll do some more research and see what the local SCCA guys are using on the cuda.

JRC


PS: We are all a community of friends here :) . Friendly banter and occasional "one-upmanship" is expected, but I hope I haven't started a flame war because I am trying to find information :shock: . The most important thing I've learned in 20 years of working on cars and 8 years working on big, ugly, old cars... is that I don't know ANYTHING. I appreciate everyone elses opinions because they give me a perspective I am sorely lacking.
Author:  Dennis Weaver [ Fri Oct 01, 2004 5:08 pm ]
Post subject:  Re: Hot Topic!
Quote:
The most important thing I've learned in 20 years of working on cars and 8 years working on big, ugly, old cars... is that I don't know ANYTHING. I appreciate everyone elses opinions because they give me a perspective I am sorely lacking.
Great attitude. I learn something new every day as well, (and I have regular "doh's!" and serious brain-farts to deal with on a regular basis) and have learned quite a bit at this particular forum. Of course there's nothing wrong with a lively debate, but it doesn't need to get personal. I state my opinions as just that - opinions, perhaps they are "truths" in my mind, and I always try to add supporting arguments for why I hold a particular opinion. I didn't just get up one day and decide that "poly" sucked. Of course if it works well for someone else, I truly am happy for them. As with most things, there is more than one way to skin a cat. Slant sixers by nature are an unusual breed, it seems we all tend to march to our own drummer to some degree, which I think is fantastic!

D/W
Author:  1969ron [ Fri Oct 01, 2004 7:17 pm ]
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for racing+hi-performance handling+ long service life use poly. for going slow or for original apperance , short product life,<i have had to redo more RUBBER front ends on my customers cars and trucks because of deterioration and noise> and the handling/cornering of a mushy boat, use rubber. hey sandy, don't worry about dennis. i have also used poly on customer's cars and trucks/plow trucks for years and NEVER had any problems with noise. why would i take the chance of having to redo a job for free, especially for a customer, because of complaints like noise or short service life? ron
Author:  Dennis Weaver [ Fri Oct 01, 2004 7:45 pm ]
Post subject: 
Quote:
for racing+hi-performance handling+ long service life use poly. for going slow or for original apperance , short product life,<i have had to redo more RUBBER front ends on my customers cars and trucks because of deterioration and noise> and the handling/cornering of a mushy boat, use rubber. hey sandy, don't worry about dennis. i have also used poly on customer's cars and trucks/plow trucks for years and NEVER had any problems with noise. why would i take the chance of having to redo a job for free, especially for a customer, because of complaints like noise or short service life? ron
Why the hell should either of you be worried about me? I agree rubber sucks, too, until someone designs something in polyurethane that will work well (to my standards) in a Chrysler front end, I will stick with it, thank you, and continue to point out the bad points about polyurethane if someone asks.

D/W
Author:  Matt Cramer [ Fri Oct 01, 2004 9:15 pm ]
Post subject: 
Quote:
Matt, all good points, but think very carefully as to how an A/B body upper control arm is adjusted to provide the proper camber/caster. If memory serves me correctly, the fore and aft bushings are on the same center line. once they are installed and adjusted to spec (or the racer's specs) the adjusting bolts running thru them are not likely to be on the exact same axis... This is taken up in a stock suspension by slight deformation of the rubber bushings - not possible with hard bushings which slide rather than twist, as does the rubber, so they end up binding which eventually wears even the polyurethane.

D/W
That is possible, but I'm not sure exactly how the bolts behave when tightened. IIRC, there is no mechanism on an A-body to hold the centerline of the bolts to a particular angle. If you are using stiffer bushings, the bolts may align themselves to the center line of the control arm, so the bolt isn't off-axis at all. I'll have to take a closer look. In any case, the geometry issues aren't nearly as attrocious as what the 5.0 Mustang crowd has to deal with when they want to make a Fox body corner.
Author:  Jeb [ Fri Oct 01, 2004 9:30 pm ]
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I installed poly leaf spring bushings in my Duster about a year ago. They haven't started to squeak yet. Sez on the box they are self lubricating.
Author:  sandy in BC [ Fri Oct 01, 2004 9:35 pm ]
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You are right Matt. Any misalignment that causes binding is evidence of improper installation or a bent A-arm. Part of UCA installation is making sure the arm swings through its arc without binding. The same holds true for the LCA. I usually check these components separately before bolting up the ball joints. The lower is tougher because of the strut rod and bushing. I like Lou's LCA/strut rod setup ,,,,seems to me a more precise way to locate the LCA and create an "A" without binding.

We did the UCA bushings on our Roadmaster last week....I used rubber because I am happy enough that it is a quiet, ill handling pig.....wouldn t do it on a real car though....
Author:  Dennis Weaver [ Fri Oct 01, 2004 9:46 pm ]
Post subject: 
Quote:
You are right Matt. Any misalignment that causes binding is evidence of improper installation or a bent A-arm. Part of UCA installation is making sure the arm swings through its arc without binding. The same holds true for the LCA. I usually check these components separately before bolting up the ball joints. The lower is tougher because of the strut rod and bushing. I like Lou's LCA/strut rod setup ,,,,seems to me a more precise way to locate the LCA and create an "A" without binding.

We did the UCA bushings on our Roadmaster last week....I used rubber because I am happy enough that it is a quiet, ill handling pig.....wouldn t do it on a real car though....
sandy, please look more closely at mopar upper control arm geometry next time you deal with a front end on one. I am not doing anything improper, the design is as it is. I happen to be a very experienced mechanic as well, by the way. If the roadmaster is like most GM stuff I've dealt with, the upper control arm bushings are on the same shaft, on the same centerline. When I said "poly" sucked, I'm specifically referring to the type cars in question here, mostly Mopar A and B-bodies, not other makes with different front suspension layouts. For them, polyurethane might just be the ticket, although I'd prefer the type with zerks fittings that can be lubed, as I've seen for some shivvy (GM) applications...

D/W
Author:  MileHighDart [ Mon Oct 04, 2004 1:06 pm ]
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Just thought I'd throw in my 2 cents.
I rebuilt the front end on my 71 Scamp with the PolyGraphite bushings cause I wanted it to handle better than original.
After getting the car running and driving it a while, I feel that the poly bushings make the car ride a bit harsh,,, however it handles fantastic !
I do have a problem with the lower control arm poly bushing.
After installing the lower control arm, I started tightening the strut rod nuts,, and at the same time I could see the poly bushing being pulled or forced out of its home in the lower control arm. Only a little bit, but it made me nervous.
I have had a little trouble getting a good alignment done since the rebuild. Its been done twice by different shops and its still not quite right. Dont know if the movement in the lower control arm has anything to do with it or not. It handles great in the corners but its a little "twitchy" in a straight line.
As far as the "harshness" of the ride, I can only compare it to a 72 scamp I used to have since this car wasn't running before I rebuilt the engine and front end.

Anyway, I just ordered a rubber front end kit from PST for my 68 Dart.
The dart will be my daily driver and does not need to have "g-machine" handling. Rubber may not be the best for handling but i'm sure the car will handle much better with a completely new front end than it does with 35 year old components. Some of us would be satisfied with haveing our cars handle like they did when new. I will be adding a front sway bar as well since it doesn't even have one right now. I'm sure that it will feel like a different car when its done. All i'm saying is buy whats right for your intended use.

Scott
Author:  vynn3 [ Mon Oct 04, 2004 1:40 pm ]
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Quote:
Rubber may not be the best for handling but i'm sure the car will handle much better with a completely new front end than it does with 35 year old components. Some of us would be satisfied with haveing our cars handle like they did when new. Scott
I can confirm that. I used all rubber components (Moog) except for the strut rod bushings (Energy Suspensions) when I rebuilt my front end last spring, and was STUNNED by how much better it handled and drove, even without poly everywhere. I have stiffer torsion bars and KYB shocks as well, and I know it would've been too harsh for my tastes if I'd gone all poly. But then I'm getting old...

VM
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