Does frame need to be straightened? - Team Camaro Tech
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post #1 of 15 (permalink) Old Oct 27th, 11, 03:52 AM Thread Starter
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Does frame need to be straightened?

I'm about to have subframe connectors welded to my 68 Camaro with an LSX. I don't know whether the frame has been in an accident, whether the front and rear frames are square with themselves and/or each other. Car seemed to drive straight and now I put in solid body mounts (one side at a time - haven't tested it at speed).

If the car runs straight at speed and aligns fine, how big of a deal is it to make sure the frame is perfectly square? I tried measuring it but I am not quite sure that my measurements are accurate. I went to a collision shop and they told me 8-12 hours of labor just to measure the frame. I promptly left. I assume welding SFCs will make the front frame impossible to move relative to the rear. Do you guys think it will be ok to just weld up the SFCs and go, or should I make sure the frame is 100% straight first?

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post #2 of 15 (permalink) Old Oct 27th, 11, 04:15 AM
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Re: Does frame need to be straightened?

Subframe dimensions are posted on this site numerous times, and easily measured by yourself. I was in collision for over 20 years. The shop that quoted you that time also needs an alignment.
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post #3 of 15 (permalink) Old Oct 27th, 11, 04:49 AM
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Re: Does frame need to be straightened?

To check frame alignment in the horizontal plane using the reference points in the Fisher Body Manual, hang a plumb bob from each of the points, to just above the ground level, then measure between them. IMO, if the car tracks straight and true on the highway, your frame is probably fine, but it's straightforward to check the alignment and worth the peace of mind before you fire up the welder. As Scott said, the collision repair shop that quoted you 8 - 12 hours to do this has issues, they either don't know how to do it or they must have thought they had an easy mark..... avoid at all costs.

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post #4 of 15 (permalink) Old Oct 27th, 11, 06:03 AM
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Re: Does frame need to be straightened?

I recently rechecked my frame alignment with the help of a buddy. I just wanted to know if it was ballpark close. I hung strings from the rear diff and the front ball joints. He suggested we not use the rear diff as it might not be installed square, so I hung more string from the rear frame . The diagonals are off a little and one side of the car is longer then the other by 1/2 inch. Considering what I started with I'm calling it good. It took us a about 2 hours including the "whys and Hows" discussions.

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post #5 of 15 (permalink) Old Oct 27th, 11, 06:28 AM
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Re: Does frame need to be straightened?

Excellent idea of hanging a plumb bob to the floor.
Lay down masking tape on the floor for X'ing the point.
Make a chart, label the points, mark the points from the same lt-hand & rt hand spots.Move the frame/car, and measure lengthwise, widthwise, and diagonally and compare.

I would give =/- 1/4 inch tolerance because of human assembly, no CAD back then.

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post #6 of 15 (permalink) Old Oct 27th, 11, 07:26 AM
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Re: Does frame need to be straightened?

Quote:
Originally Posted by Everett#2390 View Post
Excellent idea of hanging a plumb bob to the floor.
Lay down masking tape on the floor for X'ing the point.
Make a chart, label the points, mark the points from the same lt-hand & rt hand spots.Move the frame/car, and measure lengthwise, widthwise, and diagonally and compare.
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post #7 of 15 (permalink) Old Oct 27th, 11, 10:34 AM
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Wink Re: Does frame need to be straightened?

Quote:
Originally Posted by Sauron67MM View Post
... The shop that quoted you that time also needs an alignment.

Boy, you can say that again
In a shop with the correct equipemnt and training this should never take more than 2 hours to check and complete unless it's a rebuilt 'total' ...

There is normally a good amount of 'Play' in the sub-frame mounting hardware (even solids) to allow for moving things around to get good adjustment prior to installing the connectors.

After completing the procedures recommended in the above replies, and installing the Sub-frame connectors, take the vehicle to a good local Alignment shop and have them perform a "Thrust" alignment on your vehicle.
This will insure the front a rear wheels are tracking 'in-line' and square to each-other and the vehicle is truely tracking straight down the road.
Not that much more expensive than a standard front alignment in many shops that specialize in this type of work.

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post #8 of 15 (permalink) Old Oct 27th, 11, 11:10 PM
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Re: Does frame need to be straightened?

Next to the center subframe mounts are the factory alignment holes. On the assembly line the subframe with engine & trans was assembled to the unibody with .610" diameter alignment pins on the subframe cradle. Check that the sub holes line up with the unibody holes.
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post #9 of 15 (permalink) Old Oct 28th, 11, 02:50 AM Thread Starter
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Re: Does frame need to be straightened?

Does the car need to be perfectly level to make the frame measurements? I imagine that the way to do this is to jack the car up off of the suspension, but I'm sure jackstands would be uneven with each other to some degree. Wouldn't this effect measurements?

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post #10 of 15 (permalink) Old Oct 28th, 11, 03:11 AM
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Re: Does frame need to be straightened?

Recommended, but not required. Get the rocker panel close to level.
Drive the car up onto 2X10's or 2X12's so you may get underneath to lay tape and mark the spots from the plumb bob, if this route is taken.

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post #11 of 15 (permalink) Old Oct 28th, 11, 08:24 AM
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Re: Does frame need to be straightened?

I leveled mine before the measurements, I couldn't believe how far out it was just sitting on the stands. When I finished it was only sitting on three stands, the rear diff didn't touch on one side.

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post #12 of 15 (permalink) Old Oct 30th, 11, 03:08 AM Thread Starter
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Re: Does frame need to be straightened?

The bottom of the rear frame at the front master gauge hole on the passenger side is 5 5/8" off the ground on the driver's side, and 5 3/4" to 5 7/8" to passenger side (the difference could be human error).

The front of the front subframe is 10 5/8 off the ground on the passenger side, and about that on the driver's side.

The alignment holes seem to be dead on just by eyeballing it and sticking my pinky in there.
It looks like the frame is bent or warped in the front driver's side thus making front gauge hole not a reliable (is it datum?) point. So I went by one of the other holes in the side of the frame, and just hung a string from the edge of that hole. Those were the front of the subframe data points, or point "F".
The rear subframe, or the middle of the car was measured with a bent metal hanger to try to get the middle of the hole as close as possible. That is the middle data point, or point "M"
The rear frame rail was measured in the center of the master gauge hole in the front bottom of frame rail. They is my rear data point, or point "R".

In these measurements, "P" will connote passenger, "D" driver sides.


Measurements are as follows:
RP to MD = 79 5/8
RD to MP = 79 13/16
MP to FD = 50 1/2
MD to FP = 50 5/8
RD to MD = 69 5/8
RP to MP = 69 7/16
MP to MD = 44 3/4
FP to FD = 38 5/16
MP to FD = 28 7/8
MD to FP = 29 1/16

So basically, the lines from the master gauge hole of the rear frame to the opposite center of the master gauge hole outboard of the firewall body mount are 3/16" different. Is that too much?

It appears that the front subframe isn't 100% square - the lines from the master gauge hole to the front of the frame are 1/8" different. Is that OK?

Strangely, the lines from the rear frame master gauge hole to the sub frame master gauge hole out board of the body mount on the same side are about 3/8" different, and the same for the subframe master gauge to the front. Is that a problem?


What about the differences in ride heights?


I tried my best to measure, but it is extremely difficult to get it 100% perfect. These numbers are best estimates, but they look decent.
This was done with the suspension fully loaded, and the car on the ground. Is my frame OK?

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post #13 of 15 (permalink) Old Oct 30th, 11, 04:21 AM
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Re: Does frame need to be straightened?

Looks pretty good to me, including height.
Generally, height is taken from wheel center, the hub, to the fender edge, eliminates the tire factor.

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post #14 of 15 (permalink) Old Oct 30th, 11, 07:07 AM Thread Starter
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Re: Does frame need to be straightened?

Quote:
Originally Posted by davidpozzi View Post
Next to the center subframe mounts are the factory alignment holes. On the assembly line the subframe with engine & trans was assembled to the unibody with .610" diameter alignment pins on the subframe cradle. Check that the sub holes line up with the unibody holes.
David
Eyeballing this David, they look dead on. What do you think?

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post #15 of 15 (permalink) Old Oct 30th, 11, 07:10 AM Thread Starter
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Re: Does frame need to be straightened?

If you guys note, all of these measurements seem to be within 1/4" of one another. Am I good to weld?

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