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Discussion Starter #1
OK, sorry because I know there was a post on this before (in fact I commented on it). I have a 69 and I am interested in being reasonably accurate where this goes. I have looked all over and found a few references.i know the tach should mount where there is a void under the hood skin (no brace). I think I am reasonably sure where it should go, but it looks far away.

Can someone with a 68 or 69 that was originally equipped with a hood tach, please validate the distance from the rear-left point of the tach to the hood's left edge, and the same point of the tach to the rear edge of the hood. Like the diagram that I drew that is attached.

Based on what I have found, the rear left point of the tach should be 6.5 inches from the driver's side edge of the hood and 12.25 forward of the rear most edge.

Thanks so much!
Mike
 

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If you do a search using the red "SEARCH" option found in the upper right corner (I assume everyone has this on their screen, but maybe not as I often can find an answer using this feature trying to help answer questions. Not being a smart butt either, but does this show up on all screens or do some computers/phones not show this feature?)

This may help:

http://www.gtoforum.com/f12/1970-gto-hood-tach-installation-help-38892/

AND if that is not enough, check out this YouTube video with instructions and dimensions:
 

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The hood tach on my 68 was dealer installed. Here is a photo of the template I made when I transferred the holes to the new hood.


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Discussion Starter #6
Hi Shake and Bake, I made a template as well and I think I am close, but I don't have a hood to reference. The good thing is that these were dealer installed so no 2 are perfectly matched. I am having trouble reading some of your numbers.

The rear most 'rivet' hole: I think I read 9 3/4 to the side edge of the hood, but not sure about the rear edge. Is that 15 5/8?

The left most stud: I can't be sure about either of those numbers

The right most stud: Looks like 12 inches to left edge of hood, but I am not sure of the distance to the rear edge of the hood.

I think I know where I am going to place the tach, but I would like to do a sanity test with your numbers. One final question, the left and right stud - if I were to place a framing square on the left edge of the hood, they would be in line, right?

Thanks,
Mike
 

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Hi Shake and Bake, I made a template as well and I think I am close, but I don't have a hood to reference. The good thing is that these were dealer installed so no 2 are perfectly matched. I am having trouble reading some of your numbers.

The rear most 'rivet' hole: I think I read 9 3/4 to the side edge of the hood, but not sure about the rear edge. Is that 15 5/8?

The left most stud: I can't be sure about either of those numbers

The right most stud: Looks like 12 inches to left edge of hood, but I am not sure of the distance to the rear edge of the hood.

I think I know where I am going to place the tach, but I would like to do a sanity test with your numbers. One final question, the left and right stud - if I were to place a framing square on the left edge of the hood, they would be in line, right?

Thanks,
Mike
Mike, sorry about the sloppy writing....I originally made the template and then took the photo for my own reference because I like to be able to double check my work. I should have taken time to improve my penmanship so I could share the photo with others later. :)

I believe the dealers had a template to follow whenever they were installing a hood tach. I have seen the instruction sheet for Firebirds but haven't seen one for a GTO but I presume they existed. Even so, it's reasonable to think that each install was slightly different. I have compared the location of my dealer installed tach to a factory hood tach car and the two were very close. If memory serves....the side to side dimension was dead on and the front/ back was 1/4" difference. I decided to match the dealer installed location exactly.

The rivet hole dimensions are 9 3/4" from left edge of hood and 15 5/8" from back edge of hood without the stainless molding in place.

Left stud dims are 7 5/8" and 13".
Right stud is 12" from left edge of hood and 12 3/8" from back edge of hood.
I don't think the two studs are perfectly square....I will check when I get home. If memory serves....I think the tach is just slightly rotated counter clockwise when viewed from above, but I will double check that and report back.

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Discussion Starter #9
Thanks for both your replies and of course no worries on the clarity of the writing. Your post will help others so any information is good information. Just to be clear, when you say "square to the centerline of the hood", that is the same as my comment that if one were to lay a framing square along the left edge of the hood the two stud holes for the tach would be in a straight line, correct?
 

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I am not sure exactly because my original hood is kinked on the left edge near the hinge location so i can't lay my framing square flat to check. I was able to check against the centerline ridge on the hood but even that was a bit challenging. My car is in the spray booth now so I can't check the replacement hood yet.

If both sides of the hood are parallel, then I would expect the stud holes to be square to the sides. If true, then this should also mean the rivet hole should be the same distance from the side edge as the center of the large hole. But my dimensions taken from the original dealer installed holes show a 1/8" difference (rotated 1/16") when measured from the sides.

When I get to check my car at the shop....I will measure the width of the hood at the front and back and see if those dimensions are the same....if so, then the side edges must be parallel and my template might be slightly off. If the hood is slightly wider at the rear compared to the front then perhaps the tach is "clocked" correctly.

Either way, there is likely enough play in the holes to install the tach so it is located correctly.



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Discussion Starter #11
Thanks again, I appreciate this so much!

I just went out and measured mine. I got 53 7/8 at the rear (by the windshield) and 54 at the front. But, it is hard to measure the front because the raised center. Therefore, I bet if I were to set up a frame that extended the edges above the ridge and measured, I bet it would be pretty close to 53 7/8.

IF it really is skinnier at the back, that would explain the stud holes not being aligned, but that small of a difference in width front to back is negligible. I would be interested in your confirmation of the rivet related to the centerline of the larger hole, but I think I am fairly safe to assume those stud holes would be square to the edge of the hood.

Thanks again - good info!

Mike
 

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Wanted to circle back to this item....
My hood measures 53 3/4" front and rear so the sides are parallel to each other.

However, the two studs on my hood tach are not the same distance from the tach face.....one is a bit further back than the other...and the rivet hole isn't in the centerline of the tach. The hood tach is asymetrical so you really need to test your template on something before drilling your hood.

In my case I just verified that my replacement hood tach fit on my old hood....which it did so I then just made a template to transfer the holes on to my new hood.

So, I am going to say the two studs holes aren't square to the edge of the hood and the rivet hole is not aligned with the center of the large hole. They all are close....but not aligned with each other so a template is really the only way to be sure the holes are in the correct spot.

My replacement hood tach didn't come with a template so I was lucky that I had my old hood as a reference. Here is a photo of a square laid on top of my new hood.


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So, I guess I should have checked the 68/69 assembly manual. It shows the mount holes rotated counter clockwise 2 degrees. I guess the measurements I have are fairly correct. Actual dimensions are in the manual.


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Discussion Starter #15
Thanks! Interesting drawing and very informative. I cut the holes last weekend. Mine wont be rotated 2 degrees unless I make the rivet hole and one of the stud holes bigger to let it rotate a bit. I have the 69 chassis manual and there is nothing like this in there.....

Thanks again!

Mike
 
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