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  1. #1
    Member wrc3's Avatar
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    Mar 2002
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    Arlington, VA
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    226
    Corvette(s)
    1976 L-48

    Default Body Mount Install - Lessons Learned...

    Ok so I am about half way done with the body mount install on my 76 and I figured I would write up something real quick just to let folks know how it goes so far.

    First I would say unless you are willing to pull the entire body off the frame you probably shouldn't start this project. The reason why is this. On a 76 you have 8 mounts 4 on each side numbered 1-4 from the front of the vehicle to the back. Numbers 1 and 4 on each side are bolts that can be snapped off or cut out and you can still do the work, but if for some reason you snap off the bolts for 2 and 3 on either side you are utterly screwed. Both 2 and 3 on each side screw into brackets welded on to the frame that hold square nuts in them. If for some reason those bolts snap in there, and they very easily could, then you will need someone to cut the old brackets off the frame and replace with new ones and I am just not sure how that would be done with the body still on the frame.

    So if you are still willing to take the chance and do this, it goes something like this.

    First finding all the bolts...

    Number 1 is located behind the front wheel and the top of the bolt can be seen and reached from inside the engine compartment. The bottom obviously can be seen from laying under the vehicle and looking just inside where the intake vent is. To remove this bolt you will probably need two guys, one holding the bolt from the top the other working the nut from underneath. For this bolt you need an 11/16 deep socket and an extension to get on the nut and the excess bolt. In my case one of them snapped off and the other had to be cut out.

    Number 2 is located behind the kick planel on the inside of the vehicle and only the top portion of this can be seen as the bottom is screwed directly into a bracket on the frame.

    Number 3 is found by removing an access panel with 4 screws that is in the front of the rear wheel well and same as #2 only the top can be seen.

    Number 4 finally can be seen by removing the rear compartment carpeting and going to the far rear corner inside of the vehicle. From underneath the vehicle you can see the bottom of this bolt which is behind the rear tire sitting on a bracket welded to the frame.

    Next Preparation....

    Douse all the bolts in PB or some other type of penetrant and let them sit. Do this a couple of times. Then go to each bolt and loosen them (see if you can at least). I personally was lucky and got all number 2 and 3 bolts loose, but snapped off #1 and had to cut the other #1 out and both number 4's snapped right off.

    Take off the rocker panel (or whatever it is called that runs along the bottom of the car between the wheels. If you have sidepipes (which I do) you have to take those off too.

    Actually doing the work...

    Now jack up oneside of the car on jack stands just enough to get the rear tire on that side off. Take the rear tire off to have access to the #3 and #4 bolts. You can go ahead and remove these bolts entirely now. The #4 bolt bracket is probaby shot so you will need to fab a new one or buy one. I bought mine from Paragon at 37.00. I thought it was a bit steep for what you get, but I am not sure how much a fab job would cost. You can now also completely unbolt #1 and 2 bolts as well.

    Now that all bolts on one side of the vehicle are off and the bolts on the other side are loose you can jack up the body enough to get the old bushings out and the new ones in. To do this I ran a peice of 2x4 across where the rocker panel was on the metal strip that is there and put a jack in the middle of the 2x4 (you may even want to use 2 jacks to spread the stress out on the body if you have 2 available, but one will work). Now jack the body up. When doing this you should be sure that only the body is moving and not the entire vehicle. Those old bushings wedge in there pretty tight sometimes and may actually start to move the frame with the body. Particularly at #4 i had to wedge a crow bar between the bracket on the frame and the bracket on the body to get the rusted and squished bushing to come out.

    The body should move fairly easy up about 2-3 inches off the frame you now have enough room to pull the old bushings and put the new ones in. In doing this I fit one new bushing at a time each time lowering the body to basically press the new bushing into place.

    Once I got the old bolts off and the old bushings out, putting the new ones in wasn't that big a deal. Everthing went pretty fast from there. Run the new bolts and keep them loose.

    Now you are basically done and just need to repeat the process on the other side. Finally once you are done you should tighten all bolts (i have yet to get to this so I am not sure what the torque spec is, if there is one) and you should be done.

    My Personal Hangups...

    The things that took me the longest to do were the following:

    #1 on the drivers side stripped so I had to cut it out. There is little room to get a dremel on it so it took forever to get through the bolt

    #4 brackets on both sides were shot. To get these out you need to go to the inside of the car and cut off the tops of the rivets that hold them in place...ya that was a pain. You then need to remove the old bracket or the chunks of rust that were the brackets and then replace with a new one and either re-rivet or bolt. I am probably just going to get some rivets, but I have seen other posts where people use bolts instead.

    Well that is about it. So if you are willing and feel that you need to, you can probably do body mounts over a weekend or so. Just realize that when starting this project you may end up having to take the body all the way off if the wrong bolts snap...

  2. #2
    New Member
    Join Date
    Jul 2004
    Location
    Minnesota
    Posts
    13
    Corvette(s)
    1977 Coupe

    Default

    Thanks for the detailed report on your install.


    Jeff

  3. #3
    Member TWINRAY's Avatar
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    Jul 2003
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    Long Island, NY
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    462
    Corvette(s)
    '67 Goodwood Green Coupe, '69 Lemans Blue Roadster

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    Sounds like just your typical Corvette project (lol). Now the only question is, when are you coming over to do mine?

  4. #4
    Member Thumper's Avatar
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    Jan 2003
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    McKinney, TX
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    318
    Corvette(s)
    Just a bunch of parts....

    Default

    I feel your pain. Actually I only snapped one bolt off, (#1, passenger side), the rest came out fine after soaking all of them with PB for a few days and using a long breakover bar. I was lucky that my 76 has been a Texas car its entire life. With the hassle that I went thru, I really began to feel sorry for those of you in northern states. It was fun to lift the body off the frame while my neighbors looked on thinking that I had completely lost my marbles. But then again, they have to hire someone to install a ceiling fan. Good luck with the rest of your project.

  5. #5
    Member
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    Nov 2003
    Location
    Sunshine State
    Posts
    108
    Corvette(s)
    1969 coupe

    Default

    I sense your frustration in what can be a difficult and questionable part of body removal. There are many on this board who have been there and can offer suggestions. It all comes down to availability of tools. The frame to body mounting boss is available aftermarket and can be easily removed by grinding the welds. I removed all mine to insert an undercoating wand and rewelded them afterward. I fabricated the inside #4 parts and replaced the outside with salvage parts. There is always someone on this board who can make suggestions on getting us through the areas of uncertantity.



  6. #6
    rbryce
    Guest

    Default Cause of #4 mount failure

    Since you (and I) are going through all of the trouble of replacing body mounts, especially the #4 mounts, I would like to inject some information here about the most common cause of #4 mount failing. The C3 Corvette has Astro-Ventillation, which uses two slotted panels in the rear deck of the car to exhaust air from the interior. You can see these from the interior if you look at the far rear wall of the rear storage compartment (may be behind carpet on your car). When it rains, water flows into these vents and out of the bottom of the cavity via 2 drains on the bottom. These look like clamshells on the underside of the body, just between the rear wall and the gas tank. Convertibles also have slotted drains that flow into this same cavity for drainage of the hinged deck. If yours is like mine, I found it to be full of leaves, dirt, etc, and not passing much water. When these clamshell drains plug up, the water overflows into the interior of the car via the Astro Ventillation rubber flap, and once inside the car, it goes unnoticed because the water then drains directly into the #4 mount cavity. This causes the bolt, nut and the nut cage to rust away rapidly. Once the nut cage rusts away, there is nothing to stop the nut from turning when you try to remove the bolt. No matter, the nut and bolt are by this time rusted together beyond recognition as well. You can buy the nut and cage at most all of the Corvette supply houses. My advice is for you to use as much "Rust Bullet", "POR-15" or what ever rust encapsulation paint you chose to protect these items from future deterioration before you reassemble the mount. Also, take action to keep these two drains clear. Myself, as I have a custom Corvette, and the Astro Ventillation system fights the car's air conditioning system, I have removed the exhaust air flow vents from the car. I still need to watch the drains on the convertible top deck though.

    Hope this helps.

  7. #7
    Member 6880 Mike's Avatar
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    Jun 2006
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    The Bluegrass State
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    2,623
    Corvette(s)
    1968 convertible; 1980 L-82

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    Quote Originally Posted by rbryce View Post
    ...The C3 Corvette has Astro-Ventillation...
    Only through '75. Astro-Ventilation was gone beginning with the '76 models.

    Good advice about keeping the drains open.


  8. #8
    Member
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    Apr 2010
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    California
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    Corvette(s)
    1973 Stingray

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    Can anyone tell me how to test the Astro system to see if it works on a non a/c car? Mine is installed but I don't know how to "trip it" to verify operation.

  9. #9
    Member Vette79's Avatar
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    Jan 2007
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    Millersville, MD
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    1,391
    Corvette(s)
    1979 L-48 Black Coupe

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    Awesome post. Someday I will get around to doing this.

    JEFF

  10. #10

    Join Date
    Jan 2002
    Location
    Washington, Michigan
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    7,267
    Corvette(s)
    '67 Marina Blue Convertible

    Default

    Quote Originally Posted by herminator View Post
    Can anyone tell me how to test the Astro system to see if it works on a non a/c car? Mine is installed but I don't know how to "trip it" to verify operation.
    The system description is in your owner's manual.


  11. #11
    Member
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    Apr 2010
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    California
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    Corvette(s)
    1973 Stingray

    Default

    Quote Originally Posted by JohnZ View Post
    The system description is in your owner's manual.

    Thanks. Is there a way to trip it manually so I can verify operation while I am watching/listening for the shutter to open/close? It's vacume operated but there must be a switch somewhere.

  12. #12
    rbryce
    Guest

    Default How Astro Ventilation Works

    Astro ventilation is a natural (non-powered) air flow through the interior of the car. In front of each door, behind the fenders, are two air scoops. They catch air as the car moves forward and the air passes through plastic ducts to the round vents in the dash. Some cars have a small manual (no power or vacuum)pull lever right beside the ball vent which can shut off this air flow and others do not. If your car does not have the pull lever, the only way to shut off the AV airflow is to rotate the ball until it blocks off the air duct. The air flows to the rear of the interior where it exits the car via a rectangular duct with a rubber flap. Once flowing past the rubber flap, the air moves upward and exits the car through the two slotted panels on the rear deck behind the rear window. The photos are from the interior of my car, which is in the middle of a body off restoration. One shows the outlet vents from a distance, the next is a close-up, and the third shows the rubber hose drain line which usually plugs up. It also shows the level of deterioration of the rubber flap, which will need to be replaced.

  13. #13
    Member
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    Apr 2010
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    Corvette(s)
    1973 Stingray

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    Thanks for the pic's, looks like a lot of work. One item, that is a convertble, my t top has a solenoid with vacume tube connected as if it would open and close?

  14. #14
    rbryce
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    Don't know for sure on the later years. It was discontinued totally in 1976. I do know that starting in 1969, they went totally wild with vacuum lines. It seemed like they would have tried to start the engine with a vacuum line if they could have. Does your car have a rear window defroster? If so, is this part of that?

  15. #15
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    Corvette(s)
    1973 Stingray

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    Quote Originally Posted by rbryce View Post
    Don't know for sure on the later years. It was discontinued totally in 1976. I do know that starting in 1969, they went totally wild with vacuum lines. It seemed like they would have tried to start the engine with a vacuum line if they could have. Does your car have a rear window defroster? If so, is this part of that?
    No A/C. I have been told that it is part of the Astro but haven't been able to find the mechanical details of it's operation?!

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