Aligning the 69 body to the frame.

[Greg L.]

I could use some hits or tips on aligning the body with the frame. I have the 1/2" rods that go through the door sill and frame rail in place but there is still a lot of movement allowed.

The drivers side muffler touches on the lower fender lip even though it's the correct distance from the spare tire tub.

How can you determine how high to set the front frame support that the rad support sits on? If it''s too high or too low won't it put undue stress on the fiberglass and cause cracks around the hood surround?

Thanks.

[Greg L.]

Re: Aligning the 69 body to the frame.

How can you determine how high to set the front frame support that the rad support sits on? If it''s too high or too low won't it put undue stress on the fiberglass and cause cracks around the hood surround?

I pretty much have the rest of the body install figured out but does anyone have any advice on this part?

Thanks

[Harmon C.]

Re: Aligning the 69 body to the frame.

Greg
I have used the 1/2" rods and when I got all the bolts in and started I don't think their was much movement at that point.
The muffler could be off location if the pipe bends are not perfect. It takes some time and adjusting to get the tips to come out centered in the beizels after the car is complete so I would fix the muffler issue later. I
think people notice the exhaust tips more than the tub clearance.
I usally lift on the front end by hand and adjust the front frame so it is holding up some weight maybe 50# or so. Check the gaps at the front of the doors as some have said their is some movment but I have not seen this condition.
Lyle

[Chuck S.]

Re: Aligning the 69 body to the frame.

...How can you determine how high to set the front frame support that the rad support sits on? If it''s too high or too low won't it put undue stress on the fiberglass and cause cracks around the hood surround?...

Gregster, I have wondered how they did this as well. As far as cracking the hood surround, that part is unlikely...if you don't get the nose height correctly, the area reacting the loads is back where the fenders are attached at the cowl.

This what I would (will) do: Examine the frame horns closely. Around a couple of the holes (four total) on each frame horn, you will see "circles" where the teeth on those "special washers" bit down. Set the frame horns that support the front cross member at the exact height that puts the special washers right back over those "circles". This assumes the frame horns have not been tightened by Bubba multiple times, and there are so many "circles" that nothing makes sense.

[Greg L.]

Re: Aligning the 69 body to the frame.

Well this muffler thing I think will be an issue because I can't see how to adjust it without BENDING the pipe! It's one piece from the x-member on back so the only adjustments are at the rear hangar. I had to mod both pipes where they join at the x-member just to get them to mate so now the right side fits perfect. The left side fits perfect too until just aft of the bends under the diff where it is off. There isn't near enough body adjustment to make up for this so I'll worry about it later. For what it's worth they are Corvette Central carbon steel pipes...

I can't see any of those old washer marks for the front height adjustment so I'll just push up on the support to what I think is about 50 lbs and leave it at that. I was thinking that this might cause cracking if not set up right but you guys are right in that the load will be where the fenders attach to the A pillars so I should be okay.

[Chuck S.]

Re: Aligning the 69 body to the frame.

...I can't see any of those old washer marks for the front height adjustment so I'll just push up on the support to what I think is about 50 lbs and leave it at that. I was thinking that this might cause cracking if not set up right but you guys are right in that the load will be where the fenders attach to the A pillars so I should be okay.

Yeah, my mistake...I'm looking at my AIM now (UPC 14, Sheet A2), and the grip tooth washer marks would actually be on the outer brace assembly which supports the bumper ends; these supports siamese against the frame horns (extension assemblies). Since there is a lot of slop in the mounting holes on both the "extension assembly" and the "outer brace assembly", the marks would appear to be of little value for answering this question. There is also the chance that 69 and 70 bumper supports are totally different.

I thought you were talking about the fiberglass in front of the hood when you say "hood surround"...If you mean the the sides of the fenders along the hood, I would say there is some chance of cracking along the fender peaks if the front end is left completely unsupported for years. Since a restorer would have to be pretty dumb to do that, I would prefer not to discuss how I suspect this will happen.

My previous explanation of the loading was also oversimplified. Unsupported, the C3 front end is essentially two cantilevered fiberglass beams (the fenders) with a load (the nose forward of the radiator support) across the cantilevered ends.

As I said before, the moment of the entire weight of the front end is being reacted at the cowl, but the moment distribution or increasing weight loading along the fender length is creating tension in the fender peaks...this can result in cracking along the peaks IMO.

That loading is also attempting to alter the "beam" cross section by spreading or flattening the fender, and ultimately to buckle the fender. That tendency is being resisted by the inner fenders and bulkheads at the front and rear which maintain the "box section". Fortunately, this is not from my personal observation, but just a visual analysis of the components.

The 50 pound figure seems to be completely arbitrary WAG as far as I know, but from playing with my front end, it may be in the ball park. The total weight of the front end has to be considerably more than 100 pounds. If the intent is to support the front end equally at the cowl and the radiator support, then 50 pounds wouldn't seem like enough.

A slightly more scientific method may be to measure the height of the nose totally unsupported, then measure the height when upward force is applied to remove all the EASY movement, then take an average height and see if it makes any sense. It would probably be better to lift the radiator support manually since you will have a better idea when the resistance begins to increase significantly or non-linearly. (How much can you bench press? ).

Have a friend measure the height while you lift, calculate the average, then measure the load needed to lift the front end to that height. The load measurement will serve no purpose except for comparison with the 50 pound figure. The theory is that the you are measuring the loaded height, then removing all the weight load (by lifting), and then loading by lifting in the opposite direction by about the same amount...i.e. until the front end structure begins to resist your lifting just as it resisted the structure weight.

If you try this approach, let me know how it works out. I'm faced with the same question; can't have a shark with a hook nose or up-turned nose.

Edit: If you could determine the exact weight of a complete front clip for a 68-72 Corvette (The Corvette Image?!), it would seem to make sense to apply half that weight as an upward force at the radiator support using a hydraulic jack and a scale. It seems to make sense from elementary statics, but I would stop lifting if you begin lifting the body at the cowl (assumes body bolts loose) or you begin to hear creaking, snapping, etc.

[Harmon C.]

Re: Aligning the 69 body to the frame.

All I did was see how much I had to lift when the body was hanging on slings to make the rear start to drop. About 50#s is just a guess from someone who has done a few shark frame offs. The front end is a package deal so if other parts won't fit you could need to make an adjustment.
It's all part of a restoration.

[Wayne W.]

Re: Aligning the 69 body to the frame.

WoW, Yall sure doing a lot of annalizing here. It aint rocket science. Just set the body down, find the center line and try to adjust it on the frame to be straight with that as near as possible. Adjust the shims as near level as you can. Lift up on the front nose a little just to relieve the sag. Thats it fellas. You might have to tweak the shims at mounts near the door to get them to hang right, especially if its a convertible.

[Greg L.]

Re: Aligning the 69 body to the frame.

That's an awesome explanation Chuck but call me a coward because I think I'm going to go with Wayne's advice and just lift the front up a bit. I've been sort of playing with it(lifting it up and down) so I think I have a bit of a feel for it's happy spot now.

Wayne do you have any advice to make sure that I hit the center line or do you just use a calibrated eyeball?

[Wayne W.]

Re: Aligning the 69 body to the frame.

That's an awesome explanation Chuck but call me a coward because I think I'm going to go with Wayne's advice and just lift the front up a bit. I've been sort of playing with it(lifting it up and down) so I think I have a bit of a feel for it's happy spot now.

Wayne do you have any advice to make sure that I hit the center line or do you just use a calibrated eyeball?

Just make sure that bumper bkts etc. are within their adjustable range and will bolt up.

[Chuck S.]

Re: Aligning the 69 body to the frame.

That's an awesome explanation Chuck but call me a coward because I think I'm going to go with Wayne's advice and just lift the front up a bit...

Quite all right...Wayne is a pro who's done a ton of these restos and I'm just an overly analytical amateur who has yet to finish one.

Wayne do you have any advice to make sure that I hit the center line or do you just use a calibrated eyeball?

Yeah, get Wayne to tell you which centerline (there's three of them; one for each "axis").

I think he's telling you to get the body mounted straight on the frame; i.e. parallel to the frame rails, so it doesn't appear to be side-tracking down the road like an old hound dog. (City boys that have never followed an old hound trotting down a country road won't know what this means. It means the rear end of the dog is not on his, er...centerline...It's like the dog's rear is trying to catch up to his front. HaHaHa...).

Gregster, aren't you in the aircraft business?...I started to suggest you must have friends that know how to mount strain gages, and maybe that could help you with this question. However, strain gages would only tell you the change in stress from the rest position, not the point of zero stress.

[Greg L.]

Re: Aligning the 69 body to the frame.

Well I got her all bolted down. Wayne that was excellent advice about making sure that the bumper brackets line up! I had the body bolted down to where I thought it was right and then tried the rear bumper brackets and found that they were about a half hole off. I could have pushed them over to align but instead I loosened the body and repositioned it. Then I found out that the two bolts in the bottom of the rad support didn't line up so I moved the body until the rad support AND the rear bumper brackets align nicely and then bolted the body down.

One thing that I found interesting is that the 1/2" rods would slide in and out when the body was "off center" AND when it was properly aligned. So I'm thinking that they were just for an initial guide with the actual positioning being done with the bumper brackets & rad support.

Chuck, ya we have all that fancy stuff at work but like you say, to make good use of it one would have to know what the front end of the clip actually weighs.

Now I get to install the rad and all the "fun" stuff that goes with it. Whom ever designed that set-up should have been made to R&R a rad 20 times and then fired! Considering that it's only a radiator, this is definitely one of the, if not THE most difficult tasks to do on this car!

[Chuck S.]

Re: Aligning the 69 body to the frame.

...Now I get to install the rad and all the "fun" stuff that goes with it. Whom ever designed that set-up should have been made to R&R a rad 20 times and then fired! Considering that it's only a radiator, this is definitely one of the, if not THE most difficult tasks to do on this car!

If your car has that big rubbery fiberglass fan shroud, it appears to me one should place the fan shroud loosely over the front of the engine BEFORE you do the body drop; maybe even before the engine stab...at least that's what I thought when I finally wrenched the *&%#@ from the chassis.

[Greg L.]

Re: Aligning the 69 body to the frame.

If your car has that big rubbery fiberglass fan shroud, it appears to me one should place the fan shroud loosely over the front of the engine BEFORE you do the body drop; maybe even before the engine stab...at least that's what I thought when I finally wrenched the *&%#@ from the chassis.

My car has a hard plastic shroud. I tried doing as you said when I first had to pull the rad years ago and there was no way it was going to come out like a typical car. You can only move the shroud about an inch or two and then it hits on the pass side upper control arm. The only way I was able to remove the rad was to remove the hood and eight bolts that attach the rad support to the body and frame. Then I could tilt the rad, shroud and support assy forward and then I was able to remove the rad and shroud as an assembly.

The funny thing was that my buddy had a 77 at the time and we removed his rad in about a 1/2 hour the usual way by moving the shroud towards the engine and then just lifting the rad out.

I don't know if mine is a pain in the butt because it's a 69 and his was a 77 or because mine is a 427 and his was a 350 or what but there is a day and night difference between them when it come to pulling the rad.

[Chuck S.]

Re: Aligning the 69 body to the frame.

The short answer is check the archives...someone, I think it was Jim Trekell, devised a short-cut that involves loosening the right? control arm. Otherwise, I think it makes some sense to install the shroud with the engine.

If you have an AC car, there is really no way to remove the top right hand bolt of the radiator support to rotate it out of the way because the AC hoses and shield covers that bolt...it is literally inaccessible.