Lowering the rear of your hood or front of your trunk: alignment

[MARTINSR]

How to lower the back of your hood or trunk.

I have seen this come up on forums for so long and lately there seems to be a run on it so I felt the need to explain this a little different.

There are a number of different hood hinge designs, but they all follow in basically the same general geometry.

Be it this 1965 GM A body.



This 1959 Rambler.



Or this 2003 Dodge Caravan which has only one part and one pivot.



They all follow the same basic geometry in that the pivot point is moved back behind and below the hoods top surface line.

[MARTINSR]

As you can see by my crude drawings I too am in the dark about the exact geometry that is at play in these old hinges but I have the basic idea. Where the exact intersection (pivot point) I don’t know but it is something like this.

On my wife’s family truckster (the Caravan) it is very simple, here is the hinge with the hood lowered.




If you were to add a shim between the hinge and the hood on the front bolt like this. It effectively forces the hinge to go down lower right?



When you add a shim between the hood and front of the hinge the hinge is then forced to go down further because the front of the hood will only go so far right?
You can see by this drawing with my paper hinge how when it lowers further like if it is pushed by a shim, it lowers the rear too. You can clearly see that in this model, it IS lower at the rear.

[MARTINSR]

Which results in the hood going down at the rear!



In both of these photos the hood is fully latched at the front and no other adjustments were made.

Now, I understand this is a last resort, you don’t want shims showing under your hood. I don’t think it is that big of a deal being there are a whole stack of them at your fender bolts not ten inches away, but they didn’t have them there from the factory so many of us don’t want one there now.
The solution is to rotate your hinge back. Lifting the front higher and lowering the rear. If you wanted to go as far as you could as an example you would loosen all the bolts on the hinge and with the hood open simply push it up in the front opening it as far as it will go while someone tightens the bolts to the fender. At that point the rear of the hood is going to be as low as you can get it without hogging holes in the hinge or shims. Notice how this will make the hinge go further down just as it did on the wife’s truckster hinge.



If you want to go further without a shim you would need to enlarge the lower portion of the front hole and the upper portion of the rear holes in your hinge where it bolts to the fender. Then you can repeat the pushing up on the front of the hood to lower the back.

When the hinge is rotated UP in the front, it lowers the pivot point LOWERING the rear of the hood.




Just part of the dance you often need to do to fit body panels. This information is more about understanding the geometry than anything else. Sure you could open up holes you can add shims but if you understand the geometry you can also understand that bending the hood or trunk structure or hinge if it’s designed like the wife’s truckster or the trunk hinge on your Mustang or Chevelle you can also lower it that way. But I’ll tell you what, if you understand the geometry and stick a shim in there to see and it fits, you are way ahead of the game, now you may choose to bend something or open a hole for more movement.

[fixdent]

Great tip you have shown there MartinSr. You took alot of time to show this.

Thanks,
Gordon

[MARTINSR]

Ok here are a few photos of how you would tweak the hinges. (that sounds so much better than "bend".) I can't stress enough I just walked out to my car and grabbed a couple of pieces of wood I use around the garage and held them for photos. They are not the perfect length and are leaning a bit. But still would probably do the job. The piece across the trunk floor would be needed though as you need to spread out the pressure. Just the 2x4 going into the floor would likely damage the floor as you are providing quite a bit of leverage with this. With that wood where it's at you have about a 10-1 ratio there, YES you can bend that hinge in half doing this. Which is why it works so great, the more leverage you have the less you have to pull to tweak the hinge.

I will be referring to the "front" of the trunk lid as the point nearest the front of the car at the hinges. The "rear" of the lid is at the rear of the car over the rear bumper. Things can get a little weird in my head when I talk about the trunk so I just wanted to make this clear.

Lowering the front of the lid at the hinge:

To lower the front of trunk lid you need to do just as rotating the hinge of the hood back did (bringing the pivot point down). In this case of course we are going to "rotate" that pivot point down the same way by changing the shape of the hinge. You can do the exact same thing on the hood of my wifes family truckster.

I took a small block of wood and put it above the hinge.




By putting this block there and then pushing the rear of the lid open "too far" just as we did with the hood rotating the hinge back, in this case the block is stopping the hinge from moving so something, be it the hinge or the structure of the hinge or lid "gives" a little or "tweaks" (that sounds so much better than "bends" don't it? ) Lowering the front edge of the lids pivot point thus lowering the front of the lid. You need to be careful because you do have a LOT of leverage and you can bend things you don't want to. Be sure that the wood is stopping the hinge from moving and is on something that is strong enough that it won't collapse.


Raising the front of the trunk lid at the hinges:

In this case pulling down on the rear of the trunk lid as if to shut it will raise the front of the lid. So when you removed the wood and shut the lid the front would be higher in relation to the body than before (near the rear window). You are simply stopping the hinge from moving to close the lid, with a little force it moves things to let the lid "close" a little, tweaking the hinge and structure.

It's like trying to move anything, when you have a lot of power you are much less likely to damage something. When ever you do something like this you are putting ALL the forces on that spot the wood is on the hinge.(realistically, if you are an engineer you see things different, but that is a whole different story) So with the wood where it is placed in this photo the force will be right there at the bottom of the hinge. It would likely bend right at that spot. However, the hinge is very strong there so the weakest point will still be the place where it bends, which is likely in the structure of the trunk right where it mounts to the hinge. How much do you go? Well, that is something you need to simply do to find out. Let me tell you this though, you do NOT need to bend a bunch to get big results. This is the beauty of having a lot of power. Just a tad, pull down just a tad and check it. You have a LOT of power and over the hinge and structure of the gate and hinge mount only has to move a hair to raise that back up a bit. So you have all the power in the world to make it move.



This method would localize the force right on the hinge where it mounts to the lid, this would more than likely tweak the lid's inner structure more than anything. But again, it only takes a tiny bit! You won't be buckling the structure and ruining it, we are talking a TINY amount here.



Not only is this done every day in bodyshops around the world it was done at the factory!

By they way, on this 65 Buick that I am working on, there was a dent in the center of the trunk lid inner structure. I have owned a number of these cars and they ALL had this dent in the middle of the inner structure. One day it hit me, these trunks were hit with a large hammer or bend up using something like this wood method to raise the center of the lid to fit the body! Yep, if it was good enough for the GM factory I guess it's good enough for us!

Brian

ps I have re-read this a number of times but I am sure I still missed where I mixed up the front and the back of the lid, if I did I'm sorry.

[RottenRodney]

Just noticed this thread. Good tech! Good job all the way around...

[Henry]

It takes a long time to put together all the stuff you write on this forum. I'll say thank you and I'm sure many members are grateful with your whole series in BASICS. Good job Brian.

I enjoyed the Caravan one because those hindges can be a real pain.

Henry