hood and deck lid air shocks

[Monkey Wrench]

all mine are weak. for the hood and for the hatch. the PO took off the wiper motor and I thought of putting it back original but I'm aware of the glass separation issues so i'm pondering that.

I noticed some companies sell them overcharged and the end user can let some pressure out so they have adjustment. others seem to be rechargeable and maybe they can all be recharged.

thought of soldering in a tire valve and trying to pump them up with air. I'm not sure its worth the hassle or if that may work at all. maybe? .

some notes seem to refer to the interior lamp not working right... I think I might be able to just use a mercury switch from a volvo hood or trunk for that. the use of mercury was likely discontinued. I'ts almost the same part as an old thermostat uses.. one of those bulbs could also work.

any advice where I should obtain them. I can't buy through pelican as their policies evidently dont allow them to ship to Canada. I cant; control that but it would be nice to support the site owners and pelican does seem to offer some OEM stuff.


If people eliminate the wiper motor, do they then go with weaker versions of the air shocks? I dont want to exasperate issues with the glass separation. I have the motor but not the wiper arm.

a poor mans solution is simply to cut lengths of plastic pipe and put them over the shock so they can be wedged in to prevent them compressing or it can be readjusted so it falls down over the shock itself.

they are full of nitrogen and air might not be the same but maybe. the welders here use an inert gas, maybe that works. originally I think they use nitrogen but it leaks away over time and it may not take long for the cheap ones to just fail again. evidently there are places that can recharge them but I imagine the cost savings would be pretty negligible. for now I have my calibrated stick but that's not a great option. i even wondered if a gas like propane or butane would work or if that would be dangerous because it's flammable?

I dont really care if it can pop and lift by itself, Im ok opening it manually. I just dont like holding it up with my head.

some of the manufacturers list the extended and collapsed length and I can measure that but I waasnt; sure if they had used a stronger one on one side than the other, maybe the side with the wiper moor is supposed to be stronger? same for the hood, I can measure the lengths.. I do not know the weight I should expect them to have though. I thought maybe asking might help avoid buying inappropriate ones. I assume I can measure them on a bathroom scale.

[djnolan]

[Monkey Wrench]

I wonder how well a 12 V motorized linear actuator would work. they dont slip and they can be super powerful. but it might need an interlock so it can't be activated causing self destruction if the hatch was locked or latched.

Here is an example of a few for under $100.
https://www.princessauto.com/en/12v-dc-135-lb-linear-actuators/product/PA1000001114

I wonder if there are even lighter examples that might be more appropriate.

lifting machines in hospitals and such often use them to lift disabled people, but the hatch or hood isn't so heavy as to need that much force. There could be lighter duty versions that are similar in design. these ones might be a bit slow. theoretically you could have a button to unlatch , a switch to verify it was unlatched, and then it could open on it's own under the 12 V motor power until it reached a limit switch. it would need a different circuit to reverse the motor. I think it's possible, but maybe its a bit too complicated..

some of the newer cars have a thing where it can sense your foot and activate, I wonder if they use an air cylinder or a motor?

[HugoBlack]

I replaced my Hood lift supports for the rear glass on my '83 944 NA with struts that are for a Jeep. I can't remember the year and make of the Jeep model but Advance Auto had it last year. Part e4578, sku 19940286. Not as powerful as Porsche lifts but plenty adequate and less stress on the glass panel's hinges at the roof. Even has the stab fitting for the rear window defroggers!

[Monkey Wrench]

Thanks for that HugoBlack..

I changed the ones for the hatch on my volvo 740 wagon and thought maybe I should compare before ordering them. If I'm lucky enough I might find those old ones are still strong enough for the Porsche. They may be totally wrong too.
easy enough to do a side by side comparison. many of the suppliers state the two lengths and the tension weight.

[wildcat077]

Monroe P/N 901169 , those are the Jeep application , about 1/3 less tension than the Porsche units and they are a direct bolt on.
I have those on the lexan rear hatch of my SP2 car and they are perfect !
Picked them up on Amazon a few years back for something like $20.00 dollars a piece.

[Racerbvd]

As most know, putting fresh shocks on a old hatch can make the glass separate from the frame even more.

There is a guy who sells a carbon fiber prop for 911 lids, I installed one on my 87 944S.

[Mericet]

Or keep the old ones in and add this: https://hoodstay.com/

[wildcat077]

Byron, i got clobbered on the head too many times by the front hood of my 911 and the front hood and rear hatch on the 944 ...
New struts are cheap , the Jeep ones are perfect for my lexan hatch on my SP2 car, no more bumps on the head when i fill my fuel cell.
Amazon is your friend !

Just sayin ...

[Monkey Wrench]

thanks for the tips.
i have a friend with a jeep around that era so I asked if she had replaced them. Yes she did. She said she was driving and suddenly the end of one of them them came right off and sounded like an explosion. her replacement were only around $20 apiece. it made me think this could actually break the window..

I think I like the fix of just inserting a plastic tube over the shock can work. then you just slide it down near the rod section when it's open and then you lift up and re center the plastic tube and it fits over the shock and collapses. I think tha'ts as good as a solution as the clamp ring part..
Really I'd rather just make it work normal. I have not seen any glass separation issues but don't want to create one either. I thought I'd put the wiper motor back on to make it stock, but maybe I should reconsider that.
If It's original, I can get collector plates and drive for $300 per year but not to work. if I insure it in a normal manor it's $1200 a year.. For a sports car that I might use part time it might be a nice option to keep it original, since it's not really changed much from stock anyway. I do that with my 66 Volvo and it allows me to drive it at least enough so it doesn't seize up.
I'm thinking that for now what I should do is just fix the hatch so it can stay open and the hood won't be any different than normal but it wont stay up now. will the Jeep ones work for the hood too or just the hatch?

I might drive it on a daily basis.. I have a van I insure too but I dont like paying 5 bucks a day to have a bunch of cars all on the road at the same time.. so I try to sort of alternate, and do a bunch of service in the summer when its warm enough out to be comfortable. I've been in the situation many times where I'm fixing my only car to get to work and that's stressful, so rather than new cars I just have a few that I sort of rotate, fix in summer and then try to roll through the winter doing minimal repairs.

I have not gotten to the point where I can start the Porsche. I sure am looking forward to that. I'll do all the belts and fuel pump and fuel filter gas line hose , then when I can start it I can assess things more. I'd like to go over all the things that would make it unreliable and cause a breakdown and my plan is to do those basic maintenance things like trans oil , grease the CV joints, maybe check out the starter and alternator bearings and brushes, and clean them inside , wheel bearings, inspect and lube, stuff like that. brakes are all a bit frozen from it sitting but I don't think its anything serious.
my back bumper was pushed in about 2" but I got the end caps and new shocks I just need to do some touch up and paint the bumper ends guards red.

right now Im trying to learn as much as I can and I have to order some parts.
I need to source the funny wrench for the CV joints, then I should disassemble and lube all that while the back is jacked up. maybe I should change the rubber boots but they look ok. I'm not in a financial position to go all crazy with the parts orders so the plan is to order parts in lots, as I can get them installed, and not try to go all nuts. I'm really excited about the car.. I might love driving it and just use it as a daily driver, I'll see how I do moving forward. for the past few years Ive been daily driving a raised roof van , a 1988 ford with a 300 L 6, Its been reliable but it's like driving my own house everywhere..

[Racerbvd]

Originally Posted by wildcat077

Byron, i got clobbered on the head too many times by the front hood of my 911 and the front hood and rear hatch on the 944 ...
New struts are cheap , the Jeep ones are perfect for my lexan hatch on my SP2 car, no more bumps on the head when i fill my fuel cell.
Amazon is your friend !

Just sayin ...

I fully understand that, but also understand what generally happens to 944 rear hatches when you install new hatch struts. That is why I installed the titanium hardware, carbon fiber rod to hold my hatch.

[Monkey Wrench]

here is a short video where the guy solders in a schrader valve from an old tire.
he pumps it up to 400 PSI.

https://www.google.com/search?client=firefox-b-d&q=recharging+gas+shocks#kpvalbx=_Y_p8Y8X7B9CB0PEPi sCfuAQ_27

soldering in the valve looks easy. there doesn't appear to be any rubber down at the cap end of the gas cylinder that will burn up, but maybe some have parts inside that can't take the heat of soldering there..?

It sounds worth a try because then the shock would be adjustable but how do I get 400 PSI pressure? My compressor wont go that high.
maybe some sort of compressed gas could work.

I was surprised there is no piston , it's just using the diameter of the rod as the piston which is a critical part of the pressure formula.. pressure x area = force.

Here, we know the diameter of the rod so we calculate the surface area of that and with that and the pressure exerted by the rod, the third factor ( the pressure in the cylinder) is easily calculated.

If there was a piston in there then the proportional capacity wouldn't work because there would be no where for the captive gas to go to without changing the strength substantially as it moves.

one way to get high air pressure is to use hydraulics, an example might be to use a hydraulic jack to force a piston to, in turn, move the air.

oxygen is easy to get but if you combine oil and oxygen that can cause an explosion so I think that would be a bad idea but perhaps an inert gas like argon or CO2 could work?

He buys a gauge capable of 400 PSI for this but since he can measure the rod diameter, its actually very simple to use that and the force of the piston to determine the pressure inside so I think it could be pumped up and the force measured on a bathroom scale rather than using that 400 PSI gauge at all.

welding torches have regulators and the bottles contain high pressure but the regulator that feeds the torch that i have maxes out at 200 PSI for the 02, much less for acytelene. I can try to find out what the maximum pressure that a shielding gas regulator can deliver but I suspect it is also under 200 PSI.

one might need to be careful as if the end cap comes off with 400 PSI in it, that could go off like a bullet. the cap has a much larger surface area than the rod so the force of that would be pretty extreme. We dont want to apply 500 PSI for example as the cylinder isn't made for that.

there are companies that refill them, here is an example
https://lstechnologies.ca/services/custom-gas-spring-charging/

here is a video that shows how a gas strut is filled with the appropriate commercial equipment. It appears they don't need to install a valve but the rig basically seems to seal around the cylinder and the rod and force the pressure in through the end seals.

https://www.youtube.com/watch?v=_V6mJ-NatPI&ab_channel=UESInternational

at 20 bucks a pop it's likely not worth he cost to recharge them but it does demonstrate they can be recharged and how easily it can be done.

it may make sense to recharge them from an environmental perspective as the old ones aren't really bad, they just loose some charge and then are normally discarded.

as a bit of an afterthought , If the valve were installed on two cylinders but the valve stem itself were itself left out of one of them.. Then applying about 40 PSI to the rod end will produce a gas pressure of around 400 PSI in the cylinder.. Coupling one shock to another and applying the force to one cylinder would result in the other being pressurized to that same pressure. the valve could be permanently installed on the cylinder being filled so it acts as a check valve. you could disconnect the line if more than one "pump" is needed.


as a bit of a bonus, you'd be left with a cylinder with a valve which can be used to pump up your tires. It's essentially a bicycle pump but capable of 400 PSI that you have created here.. It would just need a second check valve for inlet air and you could pump continuously and fill a tire.


whether or not those schrader valves are capable of maintaining 400 PSI for a long period of time is another issue but maybe if a brass cap were installed on the end of the stem with loctite then it might prevent the valve failure issue.

I think it might be possible to recharge a gas shock then , using a second gas shock as the "pump" and all that would be needed would be a short hose with couplings and two schrader valves. the pressure can be measured with a bathroom scale. by using the diameter of the rod which is the piston size and the force in pounds the pressure can be calculated but it's really the force you are interested in. If the pressure is kept reasonable, the cylinders are made to withstand that force.

they use nitrogen at the factory, but that might not be important .

[Dano944]

I purchased new struts from Pelican Parts (yes, the website we are blogging on), and they seem to work just fine. The hood struts are perfect. The hatch struts are perfect too, but I keep looking at my glass to see if I have separation. No problems yet.

[Monkey Wrench]

Its probably easier just to replace them. I think I just found the concept of rebuilding them and being able to adjust the pressure interesting so I went off on a bit of a tangent with that in mind. good to Support Pelican! Ill encourage that as I like the forum and the info they help provide. unfortunately they won't ship to Canada at least right now but I can buy them from most other parts vendors.

I might try soldering in a tire valve just to experiment. I have some older cylinders so it's not a cost, just time. I kind of like the idea of connecting one to the other then just put pressure in by pressing on one to fill the other.. The "filling" cylinder might have a check valve so it can work like a bike pump but be able to produce 400 PSI with about 40 pounds applied to the rod. If I can make that work I might find it useful for other reasons. It would take forever to fill a tire but might be good for some things. a portable "air blaster" maybe? blow dirt out of tight spots?