What to use, stock, polygraphite or polyurethane?
Vehicle is not original.

Tony, rubber might be the way to go, if you consider the thickness of the metal and the area that actually touches the rubber, some of that poly is pretty hard.

Then you can stop and think about what is riding on that rubber or harder poly mount.

Big problem with 35 year old cars, window glass and regulators, jammed and broken, why not give that stuff a little bit of cushion if you can

A little extra cushion for that paint, filler, fasteners, radiator mounts, light bulbs, heavy window glass, door hinges, and panel separation in the trunk along the wheel wells

Would the rubber actually be better, I don't know, I'm guessing, but I'll take that little bit of an edge, and put mine in rubber.

Rob

Rob;

Thank you for the input. Your anaology makes sense and I agree.

Thanks again;

Tony

I bought rubber mounts, but installed polyurethane mounts instead based on recommendations from experienced rebuilders. The tip that sold me was that the poly mounts would last longer than rubber. I did notice more rattles the first time I drove the car after changing the mounts, probably due to the new mounts more than their material composition.

Experienced rebuilders recommend poly, well, if it breaks quicker, then thats good job insurance. Some off roaders and dirt trackers will tell you you should watch where you use the poly, more prone to breakage.

What about poly under a radiator support, a lot of these radiators don't last that long mounted in rubber.

A few years ago I use to fix a lot of cars, and heres something I noticed in regard to cushioning something.

My dad would buy a new pickup, and keep it a long time. He would always have the original battery in it when he sold it, where we lived in the cold area, batterys didn't last that many years, but his always did.

I always wondered why he got such long life out ot them.

I think the reason he did is because of the way he drove it, always slowed down over any bumps, didn't go down rough roads, and if he did it would be real carefull, he really babied his pickup, eventually they would rust out, but still had the original battery in it.

I think the lack of jarring and pounding was one ot the biggest reasons they lasted that long, no plate separation, does this extra cushion of rubber body mounts help any of this?

Rob

How long do you want them to last?
The original mounts lasted 35 years OK.

How long do you want them to last?
The original mounts lasted 35 years OK.

I do think the rubber GM used when the cars were assembled was vastly superior to the rubber cushions available today. I put reproduction bushings on my coupe when I restored it and given the years that have passed and the very limited use the car has seen I'm not entirely impressed with how well they are holding up.

I would think there designed to flatten out some, that would give it more area of support. Rich, are they cracked or just flattened out?

Rob

Rob (Rubadub), the recommendations I received were from people that would not gain from me using poly or rubber. I agree with your point about a preference for less vibration and jarring. If I had the spare time I could certainly do a material study and dynamic loading analysis to arrive at my own conclusions. I took the easy way out and, considering I have no experience with body mounts, relied on the advise of people with years of specific experience. I wonder if it really makes a difference? Right now I'm more concerned with tweaking my suspension to reduce vibration and jarring. Anyway, the poly kit I bought (and I've heard this from others) was incomplete ... no bolts or those smaller internal washers. Good thing I had the rubber kit to steal from, as I wanted to use all new parts (mounts, washers, bolts). So that's the only advise I can offer: make sure the body mount kit you buy, whether rubber or poly, has everything you want.

I would think there designed to flatten out some, that would give it more area of support. Rich, are they cracked or just flattened out?

Rob

They are beginning to crack.

Poly bushings won't really transfer much vibration to the interior, but they will make the car feel more solid since they greatly reduce the flex between the body and frame. Personally, I prefer a little more "feel" and more solid riding body.

I haven't yet found a poly bushing kit that includes the steel sleeves and washers. You either have to buy a rubber mount kit or use your old ones. I also haven't seen a hardware kit that includes all the sleeves and washers. The hardware kits I've seen contain just the bolts and some of the washers, what's really important, the sleeves, don't seem to be available separately for some reason.

Good point Mike, but heres a little more.

I wrote up a little thread two days ago on sheet metal thickness. I only got one comment, and he did it because he felt sorry for me that I didn't get any feed back.

I worked as a tool and die maker for quite a few years, and we had our own heat treating facility. So I learned a lot about metals, different types, how to harden and anneal different metals, so I just pay more attention to the type of metal and what its purpose is.

I have looked at several body mounts on 69 and 70 chevelles and the thickness of the metal around the body mount.

I have seen some minor indentations around a rubber body mount, and it makes me think if they had used a more rigid mount, it would have pounded the metal around it to the point that it might have cracked it.

I pointed out a couple of different thickness's in the metal around the rocker, compared to the floor pans.

All this metal thickness probably doesn't matter that much, but if you stop and look how they designed these cars, theres some things we probably need to pay a little more attention to.

Bodies and frames flex, and they tried to make the body panels as thin as they could in certain areas, probably trying to keep the overall weight down. This makes me believe that when we change something, are we really looking at the overall design of what the part is supposed to do.

Sorry about being long winded on this, but I really believe, if somebody uses poly for a body mount, that in time it will pound that metal down around the mount, and maybe eventually crack it, a rubber mount spreads out as it works, which gives it more area of support.

There is a lot of different companies doing suspension work for these muscle cars, but these 35 year old cars are not formula one racers, these cars have heavy glass, suspended by cheaply made window regulators, and chassis's designed to support all this weight.

They change the control arms, different shocks, etc. But it's still, spot welded sheet metal, leaded quarters, lots of rubber around the doors and windows. Bulbs that vibrate and blow out, radiators that fail in the spot welds along the side of them, hinge bushings that fail, doors are heavy, and the hinges hold them up, some might think that the latch supports it.

It's like trying to make a sled dog out of dachshund.

Anytime somebody makes a drastic change to anything on these old cars, they should stop and think. Can you justify a extra heavy duty sway bar, we need to take a look at what holds the ball joint in, where is the weakest link. those skimpy sway bar bushings, then change out those bushings and put poly in there.

This rant isn't directed at you, I'm just an ol guy blowing off a little steam, sorry.

Rob

Yeah, Rob, I also wonder about putting modern components in a tired metal car. Can't reinforce everything, but I'm trying to consider the impact of my changes from an engineering viewpoint. I also don't push my 42 yr old car. And that right window didn't rattle before I put in the new body mounts :)

Mike, my sons 70 with a 540 and nitros, the inside area in the trunk, next to the wheel well, had a quarter inch gap where the sheet metal pulled the spot welds loose from the torque.

All he was ever concerned with, was being able to make it hook up a little better, and I helped him get this going, we never thought about anything like this?

Rob

The guy rebuilding my chevelle talked me out of the poly bushings. He said he's seen it done and it causes the car to rattle and squeak more. I decided to go with the rubber.

Herbie, I was on another forum yesterday, and the question about putting them on a 70 gto convertible, poly or rubber, and I told him about the upper door gap can change by how much you tighten up a body mount, so I went out this afternoon and looked at my body on the rotisserie.

The body mount around the door area is in a floor pan support, Hard to get a micrometer or caliper in there, but I think under 60 thousands or close to it.

You can see where the old rubber mount was flattened out and how big of an area it actually was.

That rubber mount covers a lot more area after its squeezed down then a poly mount, there is no way I would ever even think about putting a poly mount in there after seeing that, that metal is just to thin to take it very long, somethings is going to suffer some place and it might be that floor support.

All of the 35 year old cars I have worked on all had flattened and cracked body mounts, but they were still doing what they were intended to do, cushion the body and all the componets in it, even after 35 years they don't look good but there giving it some cushion.

Another thing, I don't if I mentioned on here or another forum, is cracked control arms, it seems they are starting to show up, I don't know, but when you put poly in different places on a chassis, things like this could happen.

Another thing I've noticed on these cars, is when they restore them and don't take the body off, which is only a half restoration, they will leave the front mounts in because they were to hard to get out.

Anyway these are observations, and merely an opinion.

Rob

You can see where the old rubber mount was flattened out and how big of an area it actually was.

That rubber mount covers a lot more area after its squeezed down then a poly mount, there is no way I would ever even think about putting a poly mount in there after seeing that, that metal is just to thin to take it very long, somethings is going to suffer some place and it might be that floor support.

New rubber mounts should NEVER be tightened down so much that the rubber disc is crushed out to a larger diameter than they start out to be when not compressed. The surface area of a rubber mount that contacts the body is the same as the surface area of a poly mount that contacts the body.

Anything that stiffens up the body/frame relationship is a good thing that will make the whole contraption last longer. By stiffening the body/frame combo the suspension is forced to do the work of absorbing road imperfections. The more the body and frame are allowed to flex, the more metal fatigue is eventually going to cause something to fail. If the body and/or frame have been weaken by fatigue and/or rust they need to be restored to decent condition regardless of any other work to be done.

Well Rich, I guess if they had poly back in 1970 they would probably have used it.
But, it's a pretty good bet they would have engineered those floor pan supports and window regulators a little different then they do now.

When dream car garage on tv tightened the body mounts on a 1970 gto convertible, they could move the upper door gap in and out according to the tightness of the body mount.

They said you should adjust accordingly, I would think as the door gap moves, the rubber support would flatten out as you torque it down.

Do you think you can flatten that poly mount out enough to move that door gap, not.

You said stiffening up the body frame combination is a good thing, that will make everything last longer.

I don't know how old you were in the late 60's, but I was 28 years old, and I drove those cars right out of the showroom, and they rode and drove really nice.

They aren't race cars and they aren't luxury cars, but I know one thing, you don't take spot welded thin sheet metal with crimps in it to keep it from folding, and take out any of the rubber support it was designed for.

Actually, I probably should be an advocate of poly mounts, thats where I make my money, theres pretty good money in welding up control arms and fixing window regulators, oh, and since the poly came out, the spot welded supports on radiators, lots of them.

A little common sense can go a long way here, I'm just looking at what has been breaking on these 40 year old cars.

Rob

Adjusting the door gap based on tightening the body mounts? I sure wouldn't do it that way on any car I owned. I also doubt that method would be very likely to work on a coupe or sedan body.

These cars are or are pushing 40 years old, it can't be expected for them to be in perfect shape, especially considering how poorly so many of them have been cared for. American cars tend to be over engineered which allows folks to keep driving them even with serious mechanical problems present which leads to further and more serious damage. Asking too much of a tired old chassis by adding performance parts and then pushing it to the limits will always bring the weaknesses that have accumulated over 40 years to the surface. But then, that's why you restore it and repair any issues and augment things as needed to make it able to perform as you want.

Yes, these car drove great when they were new (and can again today if properly restored and/or maintained), in context of the times they were from. That doesn't mean they can't be made to be more than they were originally, it's been done by hot rodders for a much longer time than even these cars have been around.

Well, Rich I just went out and looked at my 69 on the rotisserie, I looked at all the body mounts, except the trunk, those are new.

You can see where the metal around it is indented where the rubber mount set. It looks like about a 1/16'' deep.

These are thirty five years old, I would bet anything, if that would have been poly in there, it would have pounded that metal right up in there a lot more then a 1/16.

Rob

Depends on what you wanna do with your car.
Poly...Cars handle better...... Turns rear control arms into traction bars..even though I've changed mine...performance baby for performance nuts.
If you have a cruiser, go rubber. Soft like charmine.
later

Chris, thats pretty much a true statement, but you can still have performance with the rubber bushings, also less chance for breakage with the rubber.

My sons consistent 11.2 in the quarter with a 70 chevell SS, all rubber suspension, he would drive it to the track, run 11.2's and drive it home, about 40 miles each way.

He never broke anything, but he had to rebuild a couple turbo 400's.

Rob

Depends on what you wanna do with your car.
Poly...Cars handle better...... Turns rear control arms into traction bars..even though I've changed mine...performance baby for performance nuts.
If you have a cruiser, go rubber. Soft like charmine.
later

I really can't see that the body mounts would have much of an impact on how a car handles.
I'd say the choice would be made more on how much of a rough ride one might be willing to put up with or maybe a comparison of how long they might last sorta thing.

A few years back with original rubber rear Lower&Upper bushings wheel hop was nuts on my 69 butternut chevelle....
LS6 13.2 e.t, change all bushings.... big job car.... turned hard & went bone straight & I did groove on the solid feel. Went back to the track,car hooked and did a best 12.05.
It's was a luv affair with bushings back then. Had a chevelle 25 years ago and wheel hop was not as easily fixed..... Hated those visual track bars.
For anything under 500HP solid bushings for your stock rear lower & uppers is a good thing....and cheap.... if your gonna punch it.
Things change... LS6 gone..... on different motors (more power) and I haven't done any damage around the bushings.
Son's car sounds cool Rob. Makes me think..... I trailer mine....More comfortable ride for sure.
Car makes some Jam

A few years back with original rubber rear Lower&Upper bushings wheel hop was nuts on my 69 butternut chevelle....
LS6 13.2 e.t, change all bushings.... big job car.... turned hard & went bone straight & I did groove on the solid feel. Went back to the track,car hooked and did a best 12.05.
It's was a luv affair with bushings back then. Had a chevelle 25 years ago and wheel hop was not as easily fixed..... Hated those visual track bars.
For anything under 500HP solid bushings for your stock rear lower & uppers is a good thing....and cheap.... if your gonna punch it.
Things change... LS6 gone..... on different motors (more power) and I haven't done any damage around the bushings.
Son's car sounds cool Rob. Makes me think..... I trailer mine....More comfortable ride for sure.
Car makes some Jam

BUT, I believe this thread is about body mounting bushings not suspension bushings.

Dean, another thing here, you were about 32 years old and I was about 28, in 1970. I owned and rode in quite a few muscle cars, rode in a new 70 Ls6, green 4 speed. That car rode and drove and handled really nice, I know I really wanted one, but with four children and my wife didn't work, there was no way I could ever get one.

I'm sure you either owned or rode in them also.

We were not young teenagers, and why anyone would do a frame off and put poly body bushings in a car like that is beyond me, they were beautifull riding driving and handling cars.

Rob

A more solid body/frame connection is a very desirable effect. It aids in the prevention of the "body roll" and it also always the suspension to do the work, rather then the softer rubber bushings. With Poly bushings, you have a more solid object (frame & body) that act as a whole, where with rubber you have two separate pieces (frame & body), allowing each to do their own thing, often contradicting one another.

For "cruising", rubber is better then poly, simply because it dulls a minuet amount of road harshness. But for a performance orientation, poly simply can't be beat.

-Todd

Thanx Todd, you said it better than I did. It is all about what you want out of your chevelle.
Cheers all
chris

Hey Dean,
Did realize it was about body bushings, was just commenting on the benefits of having things tighter performance wize on a chasis. There is commonality.
cheers bud
chris
69 butternut chevelle

A more solid body/frame connection is a very desirable effect. It aids in the prevention of the "body roll" and it also always the suspension to do the work, rather then the softer rubber bushings. With Poly bushings, you have a more solid object (frame & body) that act as a whole, where with rubber you have two separate pieces (frame & body), allowing each to do their own thing, often contradicting one another.

For "cruising", rubber is better then poly, simply because it dulls a minuet amount of road harshness. But for a performance orientation, poly simply can't be beat.

-Todd

So according to that, lets say you're going around a curve where the "body roll" causes the body to lean.
You would want the body to take the frame with it, lifting weight off of the tires on one side???

It just logically seems to me that would be the oposite of what you would want (but then what do I know). :)

Of course this is a pretty exaggerated example, I doubt that the body would actually "roll" independetely hardly any at all with either type of bushings unless we were running our Chevelles in a road course race maybe.

So according to that, lets say you're going around a curve where the "body roll" causes the body to lean.
You would want the body to take the frame with it, lifting weight off of the tires on one side???

It just logically seems to me that would be the oposite of what you would want (but then what do I know). :)

Of course this is a pretty exaggerated example, I doubt that the body would actually "roll" independetely hardly any at all with either type of bushings unless we were running our Chevelles in a road course race maybe.

For anything other then a run on a road course or highly spirited backroads driving, the reduced body roll will more then likely be undetectable. Taking into account the sidewall flex often associated with running 14"/15" rims, and a soft street suspension, running poly bushings would basically be a null point, it would still help-- but only a little.

As far as reducing the weight on the inside wheels, this would be true with rubber or poly. But with rubber, even more weight is being lifted off of the inside wheels when the whole body "shifts" over onto the outside wheels. Where with Poly, it will keep the body flatter, thus more weight on the insides.

:beers:
-Todd

I have to laugh at guys that say 60's & 70's cars handled great from the factory. I guess if all you had driven is 60's & 70's cars. If you grew up on todays cars, you would think old cars were built by Bayliner. Yeah, I said it.
Even if you went back to brand new everything on an original car, they are aweful for handling. Now, as far as ride, you guys might have a winner. Rubber is always a softer ride. Myself (only 34) love a nice firm car. No body roll. I love the fact that my Chevelle sits flat like a plate when I slide her sideways around a corner. The second you stop sliding it is completely under control & you can point her where you need to go. Yes, there is a sacrifice in the smooth factor, but I think that is more important when hemorroids are the issue.
I have to say it all depends on your experience & what you enjoy. The race car is a blast, but the minivan is nice on trips. Get it. There is no wrong answer. To each his own.

I replaced mine with rubber repops and within a year and a half noticed cracks..Now Im putting some polys in. One thing I noticed is I have to use rubber on the core support for some reason, the thickness is wrong on the ply bushing and sat up too high, couldnt get the sheetmetal to line up right?!?!?

For anything other then a run on a road course or highly spirited backroads driving, the reduced body roll will more then likely be undetectable. Taking into account the sidewall flex often associated with running 14"/15" rims, and a soft street suspension, running poly bushings would basically be a null point, it would still help-- but only a little.

As far as reducing the weight on the inside wheels, this would be true with rubber or poly. But with rubber, even more weight is being lifted off of the inside wheels when the whole body "shifts" over onto the outside wheels. Where with Poly, it will keep the body flatter, thus more weight on the insides.

:beers:
-Todd

OK, if you say so :)

I think you said the key word - "undetectable"

Without bringing suspension or tires or newer cars into the comparison though, I'll never believe that the difference in handeling between poly or ruber BODY bushings on our Chevelles would amount to a hill of beans.

Without bringing suspension or tires or newer cars into the comparison though, I'll never believe that the difference in handeling between poly or ruber BODY bushings on our Chevelles would amount to a hill of beans.

Without an upgraded suspension or wheel combo, I'll have to agree with 'ya.

-Todd

OK, if you say so :)

I think you said the key word - "undetectable"

Without bringing suspension or tires or newer cars into the comparison though, I'll never believe that the difference in handeling between poly or ruber BODY bushings on our Chevelles would amount to a hill of beans.

Without an upgraded suspension or wheel combo, I'll have to agree with 'ya.

-Todd

Make that 3. I always thought the same thing myself. Although I will say some makes and models may actually be more suseptible(sp) to body flex in race situations. But dont quote me on that.

Hey, you guys all have great answers and great ideas. At 66 I am still a hotrodder at heart, lucky I am not at the hemorroid stage of my life. But, have to agree with that thought. Like today, in the 60's and 70's the stress was on horse power and comfort. However, today the industry offers the horsepower with handling, ie Corvette, Viper etc.
I had the same experience with replacing the core support bushings, in three months they were cracking and deteriorating. Found this out because I went to a 572 crate engine and needed more clearance for the air cleaner. Since I didn't want to cut the hood or go to a high rise hood, after claculating how much I would need to get the desired clearance, I decided to raise the front by 5/16 of an inch. I also increased the next mount by 1/4 of an inch and left the rest at the stock height. I did use a polly kit.
As for the sheet metal, the factory spec allows for almost 3/4 of an inch in variation before alignment cannot be achieved. In my case the front fenders changed a little, had to add a shim at the bottom to bring the fender in to align with the door.
To compliment the new changes, I did change all of the suspension, Hotchkiss and appropriate springs, shocks and swaybars.
In these old cars, and even the new ones, when adding horsepower the rest of the car has to be updated to handle those changes.

Great information on this site, I have learned a lot in the past few months.

Thanks;

Tony