C2 body mount cushion change

[jkmhb]

Anyone have experience changing the body mount cushions without removing the body? Can you do one side at a time and lift high enough to get them out?

2. Pros and cons of using poly mount cushions instead of rubber? Will it really make the ride much more harsh?

[Michael W.]

Re: C2 body mount cushion change

Hi jkmhb,

How do you pronounce that?

I have heard of several people changing the mounts one at a time, according to them you undo ALL the mounts first then gingerly lift each body mounting point just enough to slip the old cushion out and the new one in. Go slowly and watch for any sort of resistance. Try to spread the lifting surface as much as possible to avoid local stress cracks. Might want to watch out for the steering column, disconnect it at the rag joint.Master cylinder brake lines also.

Poly mounts? They should be added (IMHO) to the growing list of 'snake oil' fixes. The makers tout 'longer life' as a benefit. I guess that's a good idea, after all the originals only lasted 33+ years.

Ottawa Carleton area?

Have a look at the link below.

Mike


Quebec NCRS Chapter

[Jon W.]

Re: C2 body mount cushion change

I'm in the process of replacing the corroded aluminum body mounts on my "70 coupe right now. I would expect the C2 to be basically similar. I will share what I've learned so far.... Yes, you can do this by lifting the body up just a bit and replacing the mounts. Besides the rag joint and brake lines previously mentioned, you should loosen the bumper bolts and bumper brackets, etc to avoid cracking the fiberglass in these areas. I don't know if the Mid-year radiator core support connects the body to frame like the Sharks, but if so, I would loosen the core support-to-frame bolts as well. The key to whether this will be a relatively "easy" swap, or turn into a bigger job is whether you can remove the body mount bolts without having them snap off or needing to cut them. These bolts are certainly in areas that are exposed to the elements. Some bolts/nuts have relatively easy access should they break, but others will require the body to be lifted *much* higher in order to access the caged nut on the frame that the bolt threads into. Good idea to liberally soak bolts for a couple weeks before trying. Bottom line...don't start cushion change unless you are prepared to deal with "worst-case" scenarios.

Regarding change to poly mounts.... I have heard that '63 had solid mounts and that GM changed to rubber cushions for '64-'67. The '68-'72 sharks had solid aluminum mounts which then changed to rubber cushions for'73 and later. I'm presently debating whether to switch to rubber or stay with the solid mounts on my '70. NDB contributor Jim Trekell made the switch to rubber years ago on his '70 and says the difference in ride is significant.(In fact Jim gave me lots of good info on swapping mounts by slightly lifting the body as he did) I'd be interested in comments (pros vs. cons) from others as well on this issue.

Good luck.

[Duke W.]

Re: C2 body mount cushion change

Sixty-threes, indeed, do have solidly mounted bodies. Rubber cushions were added in '64 to improve NVH (noise, vibration, and harshness) characteristcs along with variable rate springs and numerous other small changes, which continued through 1967. The solid mounted '63s are stiffer than later models because the bird cage and body reinforced frame stiffness in both bending and torsion, so the '63s have the potential to handle better, but the later cars are more refined.

The shark was a whole new body, so the engineers essentially started from ground zero on the mounting scheme. I'm not familiar with the aluminum mounts. Are they solid - essentially spacers? If they later switched to rubber cushions this would be an indication of further NVH engineering.

Keep in mind that mounts were developed with the OEM tires of the era. Modern radial tires have different attenuation characteristics that the various types of bias ply tires used through '72. The switch to radials in '73 was probably the reason for the mounting scheme change. Perhaps one conclusion from this is that earlier sharks could benefit from the '73 mounts if you are running radials.

Duke

[Terry M.]

Re: '73body mount cushion change

Yes 1968-1972 body mounts were aluminum spacers. Solid as can be. It was common in 1974+ to change earlier solid mounts to rubber, but note 1973 frame had body mounting brackets about 1 inch lower than earlier to compensate for increased thickness of rubber mounts. Thus just installing rubber mounts on 1968-1972 results in a more visible frame at rockers, and if the car is side exhaust equipped, muffler will be more exposed. Not big deals, but best to know what to expect. This also makes change obvious to observant judge.

Terry

[Duke W.]

I had a suspision

Given the significant change between the '68 - '72 and '73 up body mounting scheme, I would consider it inadvisable for the amateur restorer to "re-engineer" this system and recommend they retain the production aluminum spacers.

Duke

[Jim T.]

Re: I had a suspision

What kind of point loss would result in the judging of a 68-72 Corvette that has the later model rubber mounts instead of the aluminum spacers? I have never "restored" a car before, but when I replaced the rusted top windshield piece, both upper corners and both lower corners, stripped and painted the body, I replaced the aluminum spacers with the later model rubber body mounts. This was no big deal to do in that my car was pretty much disassembled for painting. I am the original owner and in about 73 I read an article in HOT ROD about changing out the 68-72 Corvettes to the rubber mounts. I kept the article and a later up date knowing that one day I would do this. I even bought the rubber mounts years before doing the change out. I would not go back to the aluminum spacers for any reason. The ride is that much improved in my opinion. However the original parts are stored in a box and who ever ends up with this car can have them to change back to original if it means that much to them. I did not measure how much higher my car sits up, the above mentioned article mentioned about 1/4 inch. I did have the 69 side exhaust on the car, but had went to a 2 1/2 inch under the car system before the body mount change.

[Michael W.]

1 inch?

Terry,

You sure it's one inch? Maybe a metric inch?

I know of several '73 or later cars running around with '72 or earlier frames as well as pre '73 cars with 73 and up mounts and have never seen a difference in height or frame spacing.

To me an inch would stand out like a sore thumb. Even a metric thumb. No?

Mike


Quebec NCRS Chapter

[Terry M.]

Re: 1 inch? and body mount points

I never had occasion to actually measure it - We don't see this owner inspired option too often in NCRS Concours judging. Last incident I remember was in Oklahoma at that National - 1993. It is more obvious on a side exhaust equipped car, as that one was. I am guessing the distance from my recollection. If you have both the rubber mounts (I too have a set from 1973-75 range sitting on the shelf in the garage) and the old aluminum mounts, simply measure the difference in height.

The reason that incident sticks out in my mind was that we had judged that car 3 or 4 times at a Regional level before that event. Only at the National did an observant judge note the amount of exposed muffler as excessive. That led to further investigation and voila! Rubber mounts. I recall the story more for the level of observation necessary to be a good judge than for the mounts themselves. The owner, BTW, was as surprised as we were to find them. They had, apparently, been added by a previous owner (at least that was his story and he was sticking to it.)

I am sure there is no "set or dictated" point assignment for this item. There is, I however, a line item for body mounts in the 1968-1972 judging sheets - I think. Since I am out (well almost) of that end of the business - and don't have a current score sheet handy - I'll depend on others to address that item.

Free Tip: I would suggest to any owner bringing a car so equipped to an NCRS meet NOT to start their judging experience by asking the judges: "How many points will I loose for these rubber body mounts?"

Terry

[Patrick H.]

Re: 1 inch? and body mount points

Terry,

Does that rank close to "How many points am I going to lose for my restamped motor?"

(or restamped trim tag, replaced front clip, side exhaust add-on, etc.)

Patrick

[Terry M.]

Re: points for body mounts

Yes indeed Patrick. Add it to the list that Dennis Clark put in The Corvette Restorer several years ago.

Terry