#621532 - 11/11/08 09:14 PM
Re: body bushings
[Re: MattsMonte]
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Joined: May 2002
Posts: 4,237
MAP
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15+ Year
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Yuma, AZ
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Hi MM,
We've been trading some PM's on this topic via this site - and now is probably the time to broaden the readership.
The best characteristics of body bushings from an NVH perspective are very low stiffness, and high loss factor.
The best characteristic of body bushings in terms of deriving maximum benefit from the body in order stiffen the part of the car the suspension is attached to, namely, the frame, is to use the highest stiffness possible. High loss factor helps here too.
As tire and spring designs are trending stiffer and stiffer with the passing years, the lack of stiffness in the A/G body frame (designed in 1975 as essentially a carry-over from designs of decades prior,) is generally becoming more apparent to the driver. This increases the motivation to use the stiffest body bushings possible. Again, high loss factor is always a benefit.
So you can see we are left with a profound conflict: do we want high stiffness for good handling and a feeling of chassis "tightness," or do we want low stiffness for a comfortable ride with good NVH properties. Further, material properties generally vary so that high stiffness comes with low loss factor, and vice-versa.
(One note about PU: polyurethane can be tweaked to have a huge range of material properties. The kind used for most aftermarket body bushing applications is very stiff and has low loss. But I've worked with very soft variants (E=1MPa, tan(delta)=0.25,) that would better match OEM rubber. N.B.: most modern body bushings are made from butyl rubber, as opposed to natural rubber in the "old days." I'm not sure when the "old days" ended, so A/G body bushing material composition is unknown to me; 1975-1988 could have been in a transition period for all I know.)
The "either/or" bushing dilemma can only be solved by radical changes to the fundamental structure of the car, such as radically increasing frame stiffness, or by eliminating them altogether by converting the car to a unibody design.
One further comment for now: I've found the best overall compromise for my taste, to be to use stiff bushings at the four corners of the car, combined with soft OEM rubber everywhere else. It's not a very good compromise, but it's probably the best that can be hoped for short of radical surgery, to achieve the mutually-exclusive aims I spoke of.
Best, MAP
Last edited by MAP; 11/11/08 09:25 PM.
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#621551 - 11/11/08 10:29 PM
Re: body bushings
[Re: MAP]
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Joined: May 2007
Posts: 1,626
MattsMonte
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Johnston, Iowa
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Thanks Mark,
Mark's postings on this subject are some of the best around. As he has stated, these results must also be combined with what you do on front and rear suspension as well as what tires you run.
Finally, it depends on what you are using the car for and how much you care about Noise, Vibration, and Handling (NVH).
I am working on finding a source for replacements for OEM. If anyone has a source, it would be welcome.
![[Linked Image]](http://i575.photobucket.com/albums/ss193/mattsmonte/4fbfdc7d-7bb2-4ba4-a908-e19b9971cacb_zpss2ppjjx7.jpg) 1988 MCSS T-Tops. Frame off restoration, 330HP 350 crate engine, 700R4 transmission.
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#621653 - 11/12/08 02:56 AM
Re: body bushings
[Re: pazzo1969]
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Joined: Mar 2006
Posts: 1,770
85t5mcss
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Member

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Posts: 1,770
Indpls.,IN
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1985 Monte Carlo SS, T-Tops, 355cid w/ AFR 195s 409HP/429TQ, C5 Front Brakes, T5 5 Speed, QA1 Adjustable shocks/springs Front and Rear blah, blah, blah.......... Silly "Ricers", useless wings are for penguins!
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#621707 - 11/12/08 05:37 AM
Re: body bushings
[Re: MattsMonte]
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Joined: May 2007
Posts: 4,931
Buick Runner
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Dharma station 1 the Hydra
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In general Regals and Monte Carlos are slightly different body mounts for the uppers.
Mount Cutlass Regal Monte Cutlass Regal Monte LocationUpper Upper Upper Lower Lower Lower 2 356561 330986 10005267 457915 457915 457941 3 330942 348080 330951 377801 377801 377801 4 348080 348080 330951 457915 457915 457915 5 556755 None 488610 None None None 6 330951 330942 488610 377801 377801 377801 7 25500592 1242754 14032560 377801 377801 377801
Perhaps the GNational was different. I am not sure. Perhaps the Regal is close enough. In general, Buicks were set up to be a softer ride than the Chevy.
I will try contacting them to see if they will tell me the part numbers in the kit. All Gbody Buicks except GNXs did not get all the body mount bushings like the MCs did. The first handling upgrade for a Gbody Buick is to install the missing body bushings that GM did not install. Buick claimed that not installing some of the bushings gave their cars a softer ride. So a stock body bushing set for a Regal probably won't be complete for a MC.
Last edited by Buick Runner; 11/12/08 05:39 AM.
SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.
2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.
Never argue with an idiot. They will just drag you down to their level and beat you with experience.
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#621744 - 11/12/08 11:41 AM
Re: body bushings
[Re: MattsMonte]
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Joined: Nov 2008
Posts: 1,087
novaderrik
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Ashby, MN
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the only Buick that got all the bushings was the 1987 GNX.. the regular Regals and GN's had a bunch of missing bushings- my 84 T Type (essentially a GN with blue paint and no spoiler on the trunk) actually has a few spots where there is an upper bushing but no lower bushing.
Last edited by novaderrik; 11/12/08 11:42 AM.
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#621823 - 11/12/08 04:33 PM
Re: body bushings
[Re: novaderrik]
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Joined: May 2007
Posts: 4,931
Buick Runner
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10+ Year
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Joined: May 2007
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Dharma station 1 the Hydra
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Most of the Gbody Buicks, even GNs either had 4 to 6 lower body bushings not installed, my n/a Regal Limited had 4 missing lower body bushings, but I installed those 4 lower bushings which did improve the handling.
SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.
2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.
Never argue with an idiot. They will just drag you down to their level and beat you with experience.
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#621838 - 11/12/08 05:59 PM
Re: body bushings
[Re: Buick Runner]
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Joined: May 2002
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MAP
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Hi Folks, Here's something of a primer about selecting materials for bushings: http://machinedesign.com/ContentItem/61978/Shockaweandvibration.aspxA bushing has two important properties: stiffness and dampening. Assuming the translational modes are the only ones that count (which is true for body bushings,) then the bushing behaves as a spring shunted by a viscous loss dampener (i.e., a shock absorber,) in x,y,z. That's why if the bushing is made from a single piece of material, then the material should be viscoelastic. For best mechanical isolation, the lowest possible stiffness, combined with high loss factor, are important. (That's why some of the non-MCSS G-bodies have missing bushings - there's no cheaper way to decrease stiffness than to delete bushings!) But as previously stated, what's good for mechanical isolation is bad for chassis dynamic behavior, and vice-versa - that's because for most body-on-frame cars, such as our G bodies, most of the chassis stiffness is derived from the body, and not the frame. If the frame "floats" with respect to the body, then the suspension doesn't act as it should, and the result is vague, uncontrolled, "weird" handling. In short, our G body frames desperately need stiff coupling with the body so that the modern tendency toward stiff tires/springs/shocks/swaybars can work at least passably well with our cars. But you ultimately need to make the judgment call between good handling and bad NVH (Noise, Vibration, Harshness,) or its converse. Your mileage may vary: NVH perception is notoriously subjective, but it can probably be said that many enthusiasts reading here would most likely veer in the direction of poorer NVH but better handling, as opposed to the original factory design. This would indicate stiffer bushings than stock; but again, stiff or not stiff, we want high loss factor. Exactly 100% of the aftermarket PU body bushings I've seen fail miserably in this regard. Best, MAP
Last edited by MAP; 11/12/08 08:51 PM.
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#622202 - 11/13/08 08:46 PM
Re: body bushings
[Re: MattsMonte]
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Joined: May 2002
Posts: 4,237
MAP
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Yuma, AZ
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Hi MM, I found one location where I wrote about these bushings in detail: http://www.montecarloss.com/community/ub...true#Post486863I'm unaware of anyone that manufactures these bushings, so you'd have to make your own. Plus - read the full text of this thread, since it describes one of the potential pitfalls of using stiff bushings at the corners of the car. I like Delrin (acetal) for this bushing since it has attractive material properties for this application: reasonable modulus, low creep, low moisture absorption, and low mass density. It's also an electrical insulator, which avoids the galvanic action problems of using dissimilar metals in close contact. A disadvantage of Delrin is that it's one of the pricier plastics out there, so you might want to consider an alternative (possibly Nylon, but this is mostly uncharted territory for me. I wouldn't use HDPE, but that's opinion more than fact. Someone claimed success here several years ago using plain PVC.) Best, MAP
Last edited by MAP; 11/13/08 11:35 PM.
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