# Proper way to jack car up with bag?



## mkim (Jun 17, 2008)

Hi is there a special way I need to do something before I jack my car up or go on a jack stand to change my wheels? Like air it all up or can I just stay at my ride height? 

I'm just scared if the rear bag might fall out if it's lifted... Or am I talking non sense? :screwy:


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## cb8xfactor (May 31, 2007)

mkim said:


> Hi is there a special way I need to do something before I jack my car up or go on a jack stand to change my wheels? Like air it all up or can I just stay at my ride height?
> 
> I'm just scared if the rear bag might fall out if it's lifted... Or am I talking non sense? :screwy:


i asked the person that did my install about oil changes and he said air it up to get the lifts underneath, then airout. could be less, but no more than 10psi all around on the lift... Im assuming same should go for when changing tires?


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## ummkay3 (Feb 18, 2009)

you should always be aired out when jacking up the car.


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## dano17 (Aug 24, 2008)

Why should you always be aired out? I haven't been doing this... I air up enough to get jack under car then leave the same psi in as I work on the car when it's lifted. BUT I'm a noob at air ride so I hope I'm not damaging anything..


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## bboy_jon (Jan 19, 2010)

hmmm, I am almost done getting all the parts for my air setup so this intrigues me. I always figured I would be able to ditch my ramps (to get high enough to fit a jack under the car) and just air up to the max, and jack the car up as if it was normally that height.


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## najob08 (Apr 28, 2008)

Air up > place the jack under your car > air out any corner that is going to lifted off the ground.


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## Tucked (Jun 12, 2007)

bboy_jon said:


> hmmm, I am almost done getting all the parts for my air setup so this intrigues me. I always figured I would be able to ditch my ramps (to get high enough to fit a jack under the car) and just air up to the max, and jack the car up as if it was normally that height.




You should be able to. Heck, I drive on two 2x4's and crawl under the car.


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## KyleRI (Nov 11, 2008)

Why would you air it out after you jack it up? Your damaging the bag by having too little of air in it, at least for the fronts. Structurally if the bag don't have enough air in it your going to stretch it out and stretch out the clamps that hold the bag to the strut. If you jack up your car, and air out one of the front bags i guarantee you'll see fresh black rubber above the clamp that holds the bag to the strut assembly. I always leave my bags at 60psi when I work with the car up in the air so it can support the weight of the axle, arms, hub etc etc. If not i would highly suggest jacking up the hub so it puts less stress on the bag. :thumbup:


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## mkim (Jun 17, 2008)

KyleRI said:


> Why would you air it out after you jack it up? Your damaging the bag by having too little of air in it, at least for the fronts. Structurally if the bag don't have enough air in it your going to stretch it out and stretch out the clamps that hold the bag to the strut. If you jack up your car, and air out one of the front bags i guarantee you'll see fresh black rubber above the clamp that holds the bag to the strut assembly. I always leave my bags at 60psi when I work with the car up in the air so it can support the weight of the axle, arms, hub etc etc. If not i would highly suggest jacking up the hub so it puts less stress on the bag. :thumbup:


Sounds good thx


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## najob08 (Apr 28, 2008)

http://forums.vwvortex.com/showthre...g-the-car-on-a-lift.-Ya-or-Nay&highlight=lift


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## MechEngg (Jan 13, 2009)

KyleRI said:


> Why would you air it out after you jack it up? Your damaging the bag by having too little of air in it, at least for the fronts. Structurally if the bag don't have enough air in it your going to stretch it out and stretch out the clamps that hold the bag to the strut. If you jack up your car, and air out one of the front bags i guarantee you'll see fresh black rubber above the clamp that holds the bag to the strut assembly. I always leave my bags at 60psi when I work with the car up in the air so it can support the weight of the axle, arms, hub etc etc. If not i would highly suggest jacking up the hub so it puts less stress on the bag. :thumbup:


You have a good theory but can i discuss one issue i see with it?

So you are saying you are worried because of the gravity forces acting on the bag. Let me correct you and say that whether the bag has air in it or not, there will be gravity forces acting on stretching the bag out. 

What you forgot to include was the fact that if you have zero air in the bag the only forces acting on the bag are gravity. If you have air in the bag you also have the pressure forces of the bag acting downwards trying to stretch the bag out.

Lets assume that the hub/strut assembly weighs 40lbs, that is the total weight if you have the wheel off and then you try to lift the hub up. The forces pulling down on the bag will be equal to the mass x acceleration due to gravity and therefore equals 178N.

The air pressure acting downwards on the bag is categorized as a pressure force. The pressure over a certain area (psi) multiplied by the square area will give you your force. So assume you have 50psi in your bags (344738 N/m2) and the airlift strut is 5" wide with a 2" center. This gives you an area of 0.0106m2. Multiplying you find that the force of the bags due to the pressure inside them is equal to 3666N. This is ~20 times greater than just the forces of gravity.

Therefore by keeping 50 psi in your bags you are technically putting much more stress on your bags when you jack it up.

Discussions?? :thumbup:


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## reynolds9000 (Oct 16, 2003)

I always air out onto the jack. 

And i usually drop the rear pressure to around 50psi. It seems like when i jack up the front, the rear bags will become more compressed and i don't want to pop a bag if i jack the front up too high.


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## KyleRI (Nov 11, 2008)

MechEngg said:


> You have a good theory but can i discuss one issue i see with it?
> 
> So you are saying you are worried because of the gravity forces acting on the bag. Let me correct you and say that whether the bag has air in it or not, there will be gravity forces acting on stretching the bag out.
> 
> ...


Mathematically your right. And I understand everything you explained. However by letting the bag sag, the weakest part of the entire assembly is going to be the bag no? I'm not going on any sort of background knowledge on this, I'm just stating what makes sense to me. From personal experience though, when i let my bags hang empty when i first got them, the crimped rings on the bottom started to move lower and lower. A friend of mine said to keep air in it when i jack it up, so i marked the spot where the crimp ended and from that point on i left air in the bag anytime i jacked it up and it hasn't moved since. I'm not at ALL saying im right, maybe the crimped rings had to set? Idk. Just my 2 pennies.


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## bboy_jon (Jan 19, 2010)

both of you guys make sense but heres the thing...if keeping air in the bags is putting more downward force onto the hub and what not, how would that be any different than the stock suspension? Wouldnt the spring be pushing down as well? Or would the stock suspension be similar to coils and hang down from the strut tops? (I dont remember the stock suspension) 

If you dont have air in the bag (hell, even if you do have air), the bag would end up being stretched by the weight of the hub assembly right?


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## mkim (Jun 17, 2008)

My tech says ride height is fine :thumbup:


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## MechEngg (Jan 13, 2009)

I will reply properly to all three posts tomorrow night, got a busy day tomorrow :thumbdown:


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## cb8xfactor (May 31, 2007)

This thread just got real interesting. How about we let Airlift, or Bagriders, or Airassisted chime in on all of this...


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## SMG8vT (Oct 8, 2004)

I've been airing out onto the jack / lift for over a year with no issues if anyone cares, and my car breaks / gets worked on a lot.

I leave a few PSI in the bags (5-10) just so they keep their shape. The suspension only falls so far when the car gets jacked up. I don't think stretching a bag because there's no air in it makes any sense. I can see how it would be bad to have the bags at 0psi and have them stretch almost with a vacuum inside and deform. I saw it happen with my Firestone rears but luckily they just fall off the body when that happens rather than stretch.


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## mkim (Jun 17, 2008)

if i tell my tire shop that i'm on bags he should know what to do i assume?


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## lowerthanzimmy (May 7, 2010)

mkim said:


> if i tell my tire shop that i'm on bags he should know what to do i assume?


never assume though. thats when problems happen.


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## reynolds9000 (Oct 16, 2003)

Yeah, i would definitely NOT assume that they'll know what to do. The majority, if not all the cars a typical tire shop work on, are not on bags. I wouldn't assume that the average tire tech has any experience with air suspension whatsoever.


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## lowerthanzimmy (May 7, 2010)

reynolds9000 said:


> I wouldn't assume that the average tire tech has any experience with air suspension whatsoever.


this.


a friend of mine took his car to get a notch.....the shop said they have messed with a few cars/truck on air. When they went to pull the car in they tried to drive the car out of the parking spot air'd out.....then didnt know how to work his controller.....


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## SMG8vT (Oct 8, 2004)

mkim said:


> if i tell my tire shop that i'm on bags he should know what to do i assume?


Haha..


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## Clean PG (May 9, 2005)

LowerThanZimmy said:


> this.
> 
> 
> a friend of mine took his car to get a notch.....the shop said they have messed with a few cars/truck on air. When they went to pull the car in they tried to drive the car out of the parking spot air'd out.....then didnt know how to work his controller.....


:facepalm:


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## lowerthanzimmy (May 7, 2010)

Clean PG said:


> :facepalm:


yea, i dont understand how you walk up to a car...practically laying on the ground.....but think youll be able to drive it into your shop


its so hard to find people you trust with your car:facepalm:


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## steeLh (Sep 1, 2010)

Wish I had a more concrete answer yesterday when I jacked up my car to put a new exhaust on. There was only a few reponses with conflicting opinions - ended up keep the bags about half inflated.

Glad this question was asked though, was wondering the same thing.


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## [email protected] (Dec 15, 2010)

Guys-

All our kits are designed so that the strut or shock is the limiting component in droop. So you can jack them up at any pressure (as long as you stay away from the maximum listed in the manual) without harming anything. :thumbup::thumbup:


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## bboy_jon (Jan 19, 2010)

still would really like to see what airlift, or bagriders has to say 

Edit: spoke too soon! Good to hear


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## mkim (Jun 17, 2008)

[email protected] said:


> Guys-
> 
> All our kits are designed so that the strut or shock is the limiting component in droop. So you can jack them up at any pressure (as long as you stay away from the maximum listed in the manual) without harming anything. :thumbup::thumbup:


Tyvm


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## Retromini (Nov 7, 2004)

[email protected] said:


> Guys-
> 
> All our kits are designed so that the strut or shock is the limiting component in droop. So you can jack them up at any pressure (as long as you stay away from the maximum listed in the manual) without harming anything. :thumbup::thumbup:


Great feature and good to know :thumbup:

Bagyards can potentially blow/tear the internal o-rings if you lift the weight of the car off the strut while they are filled. I always deflate mine before jacking them up.


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## joelzy (Aug 20, 2007)

i had an RE-5 blow straight out of the bellow by having air in it and then jacking it up.
No one warned me about that possibility so after that i always dumped once the jack was under.

also witnessed a chassis-tech strut blow out from being jacked up with air in it.


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## KyleRI (Nov 11, 2008)

So final say is that either empty or max (listed in manual) is acceptable for being on jacks? Just so this is clear. Beating a dead horse i know sorry.


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## [email protected] (Jan 26, 2006)

I always let the pressure out. I don't take chances with customer cars, when I could end up paying for a new one. Even the factory cars have a proper procedure. It takes only a second to empty the air. It really depends on what is limiting the travel of the suspension. Different answers for different applications.

Every year, some one calls me in a panic. So I understand when you say, you have done it many times with out a problem. My answer to you is keep doing it, one day you will be that guy. It happens.


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## mkim (Jun 17, 2008)

[email protected] said:


> I always let the pressure out. I don't take chances with customer cars, when I could end up paying for a new one. Even the factory cars have a proper procedure. It takes only a second to empty the air. It really depends on what is limiting the travel of the suspension. Different answers for different applications.
> 
> Every year, some one calls me in a panic. So I understand when you say, you have done it many times with out a problem. My answer to you is keep doing it, one day you will be that guy. It happens.


So air it out after you roll on a stand?


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## kaos1260 (Jun 29, 2006)

*FV-QR*

its the same as any oem air suspension you need to shut off the pump and air out, but most oem setups dump everytime they are turned off


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## KyleRI (Nov 11, 2008)

[email protected] said:


> I always let the pressure out. I don't take chances with customer cars, when I could end up paying for a new one. Even the factory cars have a proper procedure. It takes only a second to empty the air. It really depends on what is limiting the travel of the suspension. Different answers for different applications.
> 
> Every year, some one calls me in a panic. So I understand when you say, you have done it many times with out a problem. My answer to you is keep doing it, one day you will be that guy. It happens.


I was just trying to get a straight answer, not "be that guy" I wouldnt bother calling you anyways :thumbup:n


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## MechEngg (Jan 13, 2009)

KyleRI said:


> I was just trying to get a straight answer, not "be that guy" I wouldnt bother calling you anyways :thumbup:n


Is it just me or was that just plain rude? :sly:


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## cb8xfactor (May 31, 2007)

If I'm changing wheels which I'll be doing one wheel at a time, do I air out all 4 or just the side I'm changing the wheel? If so, how much psi should be left in bags of which wheels are not being changed?


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