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Old 07-05-2004, 04:39 PM
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How to design hood holder-open-er

I have a 39 Pontiac Coupe from which I removed the hood springs. The stock springs are mounted where the distributer will be when I put in a 350 V8. I am trying to figure out which gas strut thingies, (like hatchbacks have to push the hatchback up), I need. I know where they should go, and I can figure out the collapsed size and open size, is a no brainer. What is an easy way to arrive at the push power of these hatchback propper things?

R

PS Thanks for thinking about it.

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Old 07-05-2004, 04:48 PM
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Find something in the boneyard of equal size and weight of your hood , remove all the hardware from the donor car and test fit it on your car. See if it works? Then buy new ones, the strength will be slightly greater than the donor car, because of use.
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Old 07-05-2004, 06:29 PM
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Here is a person that has tried to make the method somewhat scientific.

Gas spring design technique.

For a simple design with a pivot near one end of the hood I would just use the hood weight multiplied by the leverage ratio created by the gas spring mount distance from the pivot.
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Old 07-06-2004, 12:55 AM
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R: I have purchased cad drawing plans for 4 link bars and suicide door hinge plans from a guy that sells them on ebay. His email is chicks1@sympatico.ca

You build these from parts available at parts/hardware stores in your own town. The drawings are professionally done with parts lists. He is not selling any plans on ebay at this time so reach him thru his email. Very professional plans and parts are easy to find.
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Old 07-06-2004, 05:52 PM
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I think this text will end up at the current end of this "thread", but if it does not, please excuse the error, I am new to this BBS stuff.

To alittle1: Thanks for the info re finding a hood like mine and copying the structure. It's a good idea, thanks.

To 4 Jaw Chuck: I went to the web site and WOW, there was a spitfire! I used to own one myself even! I read the stuff there, but never found a formula or such. It looks like the guy just punched out a couple gas strut things and tried them. That was neat though, it helps me to see the pictures.

To pronash: I don't want to buy plans made to order. I want to know "how to go about figuring out how to do it", not "how to do it". But thanks for the answer to my post.

Thanks to all who read this post too... this place is a real fine place to find out car stuff a?!

R
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Old 07-07-2004, 08:14 AM
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Do you still have the original springs?
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Old 07-07-2004, 12:06 PM
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Quote:
Originally posted by barbabart
Do you still have the original springs?
Yes, however... they are 1)VERY STRONG and 2) mounted in a "spring thing" which mounts in the center of the firewall and connects to the hood brace at the center.... this hood brace is the thing that connects to the car by use of several parallel steel braces similar to mid fifties cars which are mounted at the extreme rear of the hood and on each side... So, yah, got the springs, but they are super on this spring thing and I don't think I'm man enough to get them suckers off! Then, once I have them off, what the heck do I do with them? They pull, not push.
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Old 07-08-2004, 08:53 AM
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so if i understand it right you want to change the system from pull to push?.
Getting "pulling springs" out is not that bad. I guess if you change the linkage because of the change from pull to push you could just grind the brackets off??
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Old 07-08-2004, 01:03 PM
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Quote:
Originally posted by barbabart
so if i understand it right you want to change the system from pull to push?.
Getting "pulling springs" out is not that bad. I guess if you change the linkage because of the change from pull to push you could just grind the brackets off??
Yes, change from pull to push! However, the original springs were 1) part of a device which I had to remove to allow an engine component, the distributer, to take up the space where the springs once were, and 2) they are part of and consist in a two hinged lever contraption which will not lend itself to use at some other position... ie I need something which pushes up on the hood and holds it open.
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Old 07-09-2004, 04:46 AM
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how about this one....
If i understand it right you allready know where you want to fit the strut??
go to the salvage yard, check out an old hatchback, measure the positions of the strut. Then get it out, and install in the same way under your hood?? The strut is probably too strong but that's not so bad is it?

Maybe hang a bit of lead under your hood so it's heavy enough
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Old 07-09-2004, 11:49 AM
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Go to a store that seels these things and take a look at what they have in your size. You may find that this limits your options a great deal, and may even make the choice for you. If you do have a choice, simply find a vehicle listed that has a hood of near the same weight as yours. If your hood is really heavy, go with struts for a LIncoln towncar, or nearly any for a large hatchback. A rear hatch with a big sheet of glass in it ways a ton, although those often use very long struts.

Chances are that if you use math to figure out the right pressure, you won't be able to find that pressure in your size. Be aware that too much pressure can be a huge pain in the butt, because it is difficult to get any leverage on a hood that is all the way open (since it is usually a foot or so back from the front of the car when up) so it can be very difficult to close.

Chris
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Old 07-09-2004, 01:29 PM
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Quote:
Originally posted by barbabart
how about this one....
If i understand it right you allready know where you want to fit the strut??
go to the salvage yard, check out an old hatchback, measure the positions of the strut. Then get it out, and install in the same way under your hood?? The strut is probably too strong but that's not so bad is it?

Maybe hang a bit of lead under your hood so it's heavy enough
Excelent idea... except for the lead under the hood part ;-)

Quote:
Originally posted by chrisflock
Go to a store that seels these things and take a look at what they have in your size. You may find that this limits your options a great deal, and may even make the choice for you. If you do have a choice, simply find a vehicle listed that has a hood of near the same weight as yours. If your hood is really heavy, go with struts for a LIncoln towncar, or nearly any for a large hatchback. A rear hatch with a big sheet of glass in it ways a ton, although those often use very long struts.

Chances are that if you use math to figure out the right pressure, you won't be able to find that pressure in your size. Be aware that too much pressure can be a huge pain in the butt, because it is difficult to get any leverage on a hood that is all the way open (since it is usually a foot or so back from the front of the car when up) so it can be very difficult to close.

Chris
Got out my mechanical engineering book, began doing cross products of vectors and figuring first moments and what not last night. I think math-ing my way out of this problem is more work than just trying it out for real... This moring I was thinking about using a bathroom scale and some pieces of 2X4 to weigh the hood when it is as open as I want it... place the scale on my engine, (a flat head six), use the 2X4 as a prop to hold the hood open by proping at the same point as the strut would go... use the scale to hold the prop up... This would "weigh" the hood when it was as open as I want it. That number would be a good place to start in terms of strut "power"?? foot pounds? What ever!

R

Quote:
Originally posted by chrisflock
Go to a store that seels these things and take a look at what they have in your size. You may find that this limits your options a great deal, and may even make the choice for you. If you do have a choice, simply find a vehicle listed that has a hood of near the same weight as yours. If your hood is really heavy, go with struts for a LIncoln towncar, or nearly any for a large hatchback. A rear hatch with a big sheet of glass in it ways a ton, although those often use very long struts.

Chances are that if you use math to figure out the right pressure, you won't be able to find that pressure in your size. Be aware that too much pressure can be a huge pain in the butt, because it is difficult to get any leverage on a hood that is all the way open (since it is usually a foot or so back from the front of the car when up) so it can be very difficult to close.

Chris
Got out my mechanical engineering book, began doing cross products of vectors and figuring first moments and what not last night. I think math-ing my way out of this problem is more work than just trying it out for real... This moring I was thinking about using a bathroom scale and some pieces of 2X4 to weigh the hood when it is as open as I want it... place the scale on my engine, (a flat head six), use the 2X4 as a prop to hold the hood open by proping at the same point as the strut would go... use the scale to hold the prop up... This would "weigh" the hood when it was as open as I want it. That number would be a good place to start in terms of strut "power"?? foot pounds? What ever!

R

Last edited by rwruther; 07-09-2004 at 01:28 PM.
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Old 07-10-2004, 02:03 AM
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I think you have a nice startingpoint, i do mechanical engineering education right now but i cant remember the calculations for such thing....If you have the book in your hand you are probably gonna make it ...
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