Fender alignment to aprons

I have a quick question on fender alignment in relation to the left and right aprons on my 71 Mach 1.

The car was stripped and repainted in 2013. Not until I had to remove the hood to get the engine out (which is finally about to go back in!!) and while I was re-detailing the engine bay, I noticed that at the front by the rad support, the fender overhang was greater on the left side than the right by about 3/8th". I thought that when my body guy put the front end back together, he somehow got it all miss aligned, biased to the right side. Then I was looking at a buddies almost identical 71 and I noticed his left fender had the same amount of overhang to the apron.

Were they built like this, or is it just a coincidence? Should I re-align to have equal overhang both sides? Has anyone else seen this?

I don't need to get into a long drawn out thread here, but just some opinions

Thanks,

Geoff.

You never know on how the tolerances stacked up. If your door gap at the rear of the door is good and gap at the door to fender you would screw something up moving it. There is actually one model of a Chevy I think in the 70's the one rear door is wider than the one on the other side by by over 1/2".

The first very early 1964 1/2 mustang cars that have been found can be as much as 1" wider than full production models. They were made from prototype tooling that got refined for production.

It could be worse like the Chevy Nova with the door hinges welded on with no way to adjust except to weld to the edge or grind off. These were cheap cars in the 70's that a bag boy at the grocery could buy. Not like today when a car can cost three times what a house cost back then and no bag boy can afford one.

If it looks good as is leave it. My thoughts.

You never know on how the tolerances stacked up. If your door gap at the rear of the door is good and gap at the door to fender you would screw something up moving it. There is actually one model of a Chevy I think in the 70's the one rear door is wider than the one on the other side by by over 1/2".

The first very early 1964 1/2 mustang cars that have been found can be as much as 1" wider than full production models. They were made from prototype tooling that got refined for production.

It could be worse like the Chevy Nova with the door hinges welded on with no way to adjust except to weld to the edge or grind off. These were cheap cars in the 70's that a bag boy at the grocery could buy. Not like today when a car can cost three times what a house cost back then and no bag boy can afford one.

If it looks good as is leave it. My thoughts.

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Thanks. I'm just curious why. Was it my body guy or Ford?? I'll be checking everything before I move anything. It's just not the way I build anything......... to finicky I guess.

If your looking for exact symmetry it can be done

Did some cars come deviate from factory tolerance I'm sure they did, the factory tolerance at that time was + or -3/8".

In order to get perfect symmetry you have to start at the chassis (unibody)

If your looking to have the sheetmetal line up perfect side to side you need to "tram" the aprons-towers-and radiator support to make sure every thing is equal and square from a center line drawn down the middle and then x measured from known good points for square. Once thats confirmed your on your way ::thumb::

Btw your spec of 3/8" is within factory tolerance

If your looking for exact symmetry it can be done

Did some cars come deviate from factory tolerance I'm sure they did, the factory tolerance at that time was + or -3/8".

In order to get perfect symmetry you have to start at the chassis (unibody)

If your looking to have the sheetmetal line up perfect side to side you need to "tram" the aprons-towers-and radiator support to make sure every thing is equal and square from a center line drawn down the middle and then x measured from known good points for square. Once thats confirmed your on your way ::thumb::

Btw your spec of 3/8" is within factory tolerance

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Thanks Qcode, 3/8th" eh!! I'm used to working to 3/10000"!! No wonder I don't like the fit. I will be checking as you suggest, but perhaps that is just the way it was built. If so it stays as is. I talked to a buddy of mine who works in the restoration business and also worked in the manufacturing of vehicle parts and he thought that " if that's all I'm out, that's good"! He told me that on one car he worked on, they had to move the firewall back 3/4" just to get it all to line up square. Now, that's a lot of "tolerance".

As I first said, I'm just curious whether it was built this way or my 'guy' did a sloppy job. I'm putting the engine back in today and when that is done, I'll be putting the hood back on so I will find out for sure what's what. I'll post the results later.......stay tuned!

Geoff.

If you can get your hands on a body dimension sheet for your car, you will see that measurements are compiled at specific points. The surrounding material is no factor as long as the reference points are within specifications from the datum line specified.. (Usually holes of a specific diameter). I.E. if there are two holes punched out at the same area, the one with the correct size is the reference hole.

We use those same data points on the frame machine when pulling..

If you can get your hands on a body dimension sheet for your car, you will see that measurements are compiled at specific points. The surrounding material is no factor as long as the reference points are within specifications from the datum line specified.. (Usually holes of a specific diameter). I.E. if there are two holes punched out at the same area, the one with the correct size is the reference hole.

We use those same data points on the frame machine when pulling..

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Good info, but I doubt I can find a dimension sheet in time. I will have to check the outer body lines and set it up from there. The problem is likely right from the factory. If it looks good and I never noticed before, no one else will either, it's not being judged.

I have uploaded the chassis dimensions out of the Ford manual before do a search here. There are other manuals that have more dimensions that the shops use also. I checked and this computer does not have the scan or I would attach again.

I did a quick search and found one of the threads on this subject it has dimensions. http://www.7173mustangs.com/thread-chassis-dimension-questions

Q is correct in stating the the first place to start with any car is head to a good frame shop have them hang the gauges and check the chassis before doing anything.

Don't want everyone thinking that the tolerances on the stamped parts were 3/8". On mating surface usually .5 mm or less. Trim lines or the cut edges on the part can be 1 1/2 mm back then. Every part that goes into the weld fixtures has a two way and four way locator that positions it for weld.

When you are just getting parts ready for production Ford and most other car manufacturers have you make parts hold them in your check fixture which also uses the same locators and clamp surfaces as the welder. You apply bluing to the parts and scribe the body position coordinates on the panel in X - Y -Z. The entire car has been designed around the center line left to right and usually the firewall and a line under the body as zero for the XYZ.

You carefully ship those parts to the Ford assembly plant and send a representative to be there for a Screw Build. They have huge master plates with 100 mm grids that position the Buck. The Buck holds each part in it's correct position in the body and they can check with CMM. The key to quickly seeing if the parts are mating correct is the scribe lines. If they line up with mating parts you are usually pretty good. If not then they start to dig deeper. They screw those parts together then add the next until the entire welded body is assembled on the Buck. You look for corner radius that interferes that can hold the parts apart.

I have seen Ford employees pick up a part and throw it into the weld fixture after our plant just pulled our hair out meeting their tolerances. I am talking front floor pan at Ohio truck plant. It has gotten a lot better with the robots doing most everything in the body shop now. No hang over, not pissed at the wife, no breaks or vacations.

David, a good read and explanation. I for one am quite familiar with tolerance limits, but back in the early 70's, I don't think we had quite the control we have today. I know I saw huge improvements in my side of the industry.

All my original question was about, was did my body guy get sloppy when he reassembled the front end, or was there a possibility that some could have been from the factory that far out as a friend's Mach1 is the same as mine, 3/8th inch out on the left fender (3/16th" a side if it were to be corrected)

To date, no-one has posted with the same finding on a factory car. I'm sure restored cars have the fenders mounted as they should be.

Thanks to all for the input,

Geoff.

I related an earlier thread along these lines where the hood blackout on my car was 3/8" off true centre when originally painted at the factory. My shop wanted to properly re-centre the hood treatment during the re-paint and I decided against it, put it back to original. Most people will never notice, but an eagle eye will catch the discrepancy if you compare at the hood scoop openings. You can see a slight difference in the width of the blackout at that point.

I have seen many different fender install applications, so 3/8" is not bad at all.

I related an earlier thread along these lines where the hood blackout on my car was 3/8" off true centre when originally painted at the factory. My shop wanted to properly re-centre the hood treatment during the re-paint and I decided against it, put it back to original. Most people will never notice, but an eagle eye will catch the discrepancy if you compare at the hood scoop openings. You can see a slight difference in the width of the blackout at that point.

I have seen many different fender install applications, so 3/8" is not bad at all.

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I will soon be re-fitting the hood, so I figure I will make any adjustments if possible at that time. As you say, most will not notice. It was that way for some time and even I didn't notice and I do have an eagle eye......... if I have the right glasses on!!

Nothing was/is ever perfect, but some of us have a tough time dealing with imperfections, sad to say.

Thanks for your input.

Geoff.

Ok, I finally got the engine in again and all the bits and pieces bolted on. Looks good other than I'm a little disappointed with the paint I chose, but that's another story!

As for the fender alignment, it is now within 1/16th" side to side. It WAS my body guy who did some sloppy work. I had to adjust the entire left fender and minor adjustments to the right side. From the posts here, I was reminded that there are datum holes at various location throughout the body. There is one such datum hole centered in the rad support. Using this, I now have a car that looks straight.... finally!! Got a couple of other issues, but nothing that can't be fussed with later.

Anyway guys, thank you for your comments and help here. I'll post a picture later once I get some mechanical stuff finished up.

Geoff.