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Old 09-20-2010, 09:43 PM   #1
lsejlowe
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C3 Body Mount Replacement

A lot of guys dread this project because there are a few things that can go wrong and really ruin your day. If you discover significant rust at any of the mount locations it can mean welding on new frame mounts and cage nuts.

However, if your frame is generally in fair to good condition I don't think there's much reason to worry. I've tried to be as explicit in this how-to as possible so that those who are on the fence might take the plunge and give it a shot.

I'm working on a '69, so anyone with later C3's with soft bumpers have some slight differences for loosening the bumper supports. Alright, lets get started.

First you have to choose which material you want to use for your mounts. From '68 to '72 GM used solid aluminum bushings. Starting in '73 they switched to rubber to soften the ride a bit. Since then, manufacturers have made polyurethane mounts so that's a third option.

I opted to replace my aluminum mounts with poly from Energy Suspension. They should last longer than the rubber mounts with a little more forgiveness than the aluminum mounts and they're also a bit less expensive than rubber. Because there is very little movement between the body and frame and the mounts are graphite impregnated there should be no issues with squeaking.

You can buy kits at most of the major 'vette part houses that include all the bushings, bolts, washers, and shims you will need to do the project. Here are the kits offered by Zip.

Aluminum ($99.95):

Rubber ($149.95):

Poly ($109.95):


However, I'm a cheapskate so I looked up the Energy Suspension part number (3.4216) for the poly bushings included in the Zip kit and found them on Amazon.com for $40.40 with free shipping.

It says the application is for '73 to '82 'vettes, but they fit the chrome bumpers just fine. The poly cushions are .625" thick plus a flat washer that's about .125" thick where the aluminum bushings I pulled out were about .440" thick, but I don't expect the 1/4" ride height change will be very noticeable. Here are the instructions for the kit that shows what it includes:

http://www.energysuspension.com/asse.../pdf/17050.pdf

So now I've got the bushings figured out, I just need hardware. The original bolts are 7/16-14 about 3.5" long with a tapered tip. The original style bolts in the Zip kits are grade 5 and plated to prevent corrosion. I decided to go grade 8 because they're less than $1 per bolt at the hardware store and I trust the yellow zinc plating on the grade 8's more than typical platings I've seen on grade 5.

I bought eight 7/16-14 by 3" bolts, two 7/16-14 nuts, eight 7/16 lock washers for a total of about $8 after tax. The 3" bolts are just about right for the poly bushings. They're long enough to start threading without any trouble, but won't protrude past the nut very far when torqued. If you're using aluminum bushings kit the stock length of 2.5" will be better.

Finally, you'll need a few shims if your originals are shot. Some guys just use fender washers instead of the original style shims, but for $1.00 each through Paragon I figured I'd just get the original style so someone doing this to my car in another 40 years would recognize them rather than thinking they were just extra washers.

Now that we've got parts figured out, let see what to do and how to do it. There are 8 mount locations. One at the front of the birdcage, one below the A-pillar, one at the rear frame kick-up, and one just aft of the rear wheel:



For the purpose of this thread I'll refer to them by number according the above illustration for the driver's side and as #5 through #8 on the passenger side.

The first step will be to soak the bolts with your favorite penetrating oil. I use either WD-40 or PB Blaster. WD-40 isn't quite as affective, but PB Blaster has a fairly strong odor. You want to squirt them down once or twice a day for a least a couple days to hedge your bets against breaking off bolts or cage nuts. In order to get to the mounts you have to remove a few parts.

To get to the #1 mount you need to remove the splash shield just behind the front tire. This is looking up just aft of the front tire. Front of the car is to the left:



There's the #1 mount:



Mount #2 is accessed from inside the car, so you have to remove the door sill plate, kick panel, and speaker:



Here's a look inside that pocket:



Hopefully yours looks less rusty than mine. All that rust (and the pile of rusty metal chips I vacuumed out before this shot) is a sign of rotting birdcage . I'm not looking forward to that project.

Mount #3 is hidden behind a small access panel in front of the rear tire. Well, for most people it will be behind an access panel. Said panel was missing on both sides of mine which undoubtedly contributed to the fact that my #3 cushion had completely corroded and was missing on both sides.



The fiberglass damage is from a previous owner who installed the trailing arm bolt from the outside pointing inboard rather than the way you see it there. Thank you bubba



This shows the missing #3 cushion. You can see the body sitting directly on the frame mount.



Mount #4 is the most accessible in the aft part of the wheel well.



This was the only mount that had any shims on my driver's side. Don't mind all the bits of burnt rubber spackleing the inside of the wheel well



So now you know where each mount is and how to get to it and you've squirted them down. Now you can start removing and loosening the rest of the components to be able to raise each side of the body about 4 inches. You'll need to:

1. disconnect steering column from box
2. loosen master cylinder and proportioning valve bracket
3. disconnect clutch linkage
4. remove rocker panels
5. remove antenna ground (may not be necessary)
6. remove ground strap on #1 mount bracket
7. remove battery ground (may not be necessary)
8. loosen or remove rear bumper support
9. loosen front bumper support and radiator support

Some of these are more self explanatory than others, so I'll describe each of them.

1. Disconnect steering column from steering box
On stock applications this can be done one of two ways. Either loosen the steering column and pull it upward and inward inside the car to disengage it from the rag joint, or remove the 3 bolts holding the box to the frame and disengage the box from the rag joint. I have a U-joint in place of the rag, but I still ended up removing the bolts holding the box to the frame.



2. Loosen master cylinder and proportioning valve bracket
I didn't want to mess with disconnecting brake lines, so I just loosened the two nuts holding the MC to the firewall and removed the one bolt holding the proportioning valve to the frame. Here's the valve between the control arm and steering box:



3. Disconnect clutch linkage
I don't have a good pick for this one because my whole clutch linkage was out for sidepipe installation. Here's the clutch pushrod coming through the firewall where you'll want to disconnect it:



4. Remove rocker panels
Sorry, no good pics of this either, but it's fairly self explanatory. Just look for the philips head screws along the rocker panel below the doors.

5. Remove antenna ground
This may or may not be necessary depending upon how high you're lifting the body. Here's a pick from another person's project looking at the inner rear driver's fender with the tank removed. Just look for the strap terminating at the frame in that area and remove the small bolt (3/8" wrench).



6. Remove ground strap on #1 mount bracket
Remove the small bolt (3/8" wrench) going through the #1 frame bracket



7. Remove battery ground
This may or may not be necessary depending upon how high you're lifting the body. It's a 1/2" bolt (5/8" wrench).



8. loosen or remove rear bumper support
I decided to completely remove the rear bumperettes because I didn't want them hanging off the body and then have something snag them and damage the body or the bumpers. There are 4 mount locations for each bumperette. You'll need 5/8, 11/16, and 3/4 wrenches and sockets.



I don't carry a spare tire, so I'm not sure how difficult all of this would be to access with the carrier installed. I also completely removed the outer brace seen going to the very corner of the body in the above pic. Don't forget about the bolt just above the marker light! As I said before, I have no idea what this is like for a soft bumper car.

9. loosen front bumper support and radiator support
This was a bit of a challenge. There are 4 bolts that hold the front end to the frame that are accessed from the front wheel well.



The first three are obvious. The fourth is hiding behind the bubble in the front bumper brace.



The middle two bolts thread into weld nuts on the back of the frame horns. The other two require you to get a wrench on the nut behind the frame horns. This isn't too bad on the driver's side (I used a 3/4 deep socket on the nut and held the head of the bolt with the wrench) but on the passenger side the lower radiator hose gave me trouble. It might be a bit easier to access with a stock radiator. As I recall, the lower hose neck isn't as close to the bottom of the radiator on a stock unit. You will also need to loosen the front bumper from the bumper support so you can move the support outboard enough to get the bolt out of the hole. There's one bolt holding the support to the bumper which you can see through the front grill:



I found a 5/8 socket on the end of a 6" extension reaches perfectly.



Completely remove the 4 bolts on the side that you plan to raise first. Just loosen the bolts on the opposite side. I also supported the front end with a section of 2x4 to keep the whole front clip from sagging.

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Old 09-20-2010, 09:44 PM   #2
lsejlowe
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We're almost the point of lifting the body, so take a break and go from front to back making sure there is nothing else attaching the body to the frame. I had two seat bolts that went through the frame from my C5 seat install, so I had to remove those as well.

Now that the body bolts have been soaking for a few days you're ready for the moment of truth: trying to break each bolt loose. Hopefully you don't have any trouble and everything loosens up nicely. Remove all the bolts on the side you plan to raise first and just loosed the bolts on the opposite side.

That will keep the body from shifting too much, making it difficult to align to get the new bolts in. With all 4 bolts on one side removed it's time to lift. I used a 36" section of 2x6 and cut a few notches in it to clear the tabs on the body of the rocker channels. Make sure it doesn't extend too far forward or it will block access to the #2 mount.



The 2x6 gives you enough room to get the body raised a few inches before the jack pad reaches the frame. The body should lift fairly easily. If you hear a lot of popping and cracking STOP and figure out what you forgot to disconnect. The front end support might take a few whacks with a deadblow to make sure it's not rusted to the frame.



I was doing this before the poly cushions had arrived, so I put some jack stands under the 2x6 and left it jacked up while I cleaned and painted the mounts. Here are a couple lifted pics:
front support:



#2 mount:



Looking fwd down frame rail:



Once the Energy Suspension bushings arrived I discovered that their instructions are a little misleading. The pictures indicate the thicker bushing should be sandwiched between the frame and body, but according to the part numbers the thinner one should be sandwiched. Fortunately the bushings have their part number stamped into them, otherwise I wouldn't have noticed until I had finished up both sides and realized how high the body was. Here are the two bushings next to each other. The thicker #7019 is on the left with the thinner #4072 on the right.



The #4072 is about 5/8" thick while the #7019 is about 1" thick. Put the thinner one between the frame and body unless you want the body jacked up an extra 3/8" Unfortunately for me, I didn't realize my error until I had all 4 bolts started and the body set down. Here's the #3 with the bushings in the wrong spots!



In spite of the duplication of effort to jack up the body again and swap the bushings it didn't take very long and I had no trouble getting the bolts to line up and start threading in the cage nuts.

The #2 mount is a little tricky, but the sleeve for the poly bushings fit tightly enough to keep the upper and lower bushings in place so I only had to worry about keeping the flat washer from moving while the body was lowered. Just take your time and check the alignment as you set it down. Here are a few pics of #1 and #4 with the new bushings (in the correct positions).





You'll notice that I didn't replace the metal reinforcement that's supposed to be on the body for #4. I would have had to remove the rear inner fender and deal with getting it bonded back in place, so I just made a thin metal plate to help distribute the load a little more than the washer. Not ideal, but it's more than bubba did the first time.

However, with the body sitting loosely on the mounts I've noticed that the #1 and #4 bushings are not supporting any weight. The driver's door also doesn't line up with the striker as well as it used to. I attribute this to the body sagging and settling while the #3 and #7 mounts slowly disintegrated. Hopefully it will conform to the new mounts, but I may add a few additional shims to #4 to compensate a bit.

I'm also hoping that I will have enough adjustment at the door hinges to get it to line up with the striker better.
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