Rear Air bags

[Redemptioner]

Hey Gents,

With the new springs in it's time to add the airbags to the rear coils for towing, taking measurements shows I have a 130mm wide and 300mm high space inside the coil sitting level if I remove the bump-stop and cup. Looking around it appears some people leave the bump-stop in and others don't, most manufactures install instructions show to remove the bump-stop but leave the cup which seems crazy as the cup would cut into the bag IMO. The bag pressure will be adjustable from in the cab with individual bag pressure and control.

From what I understand with airbags they basically need to be 1/2-3/4" longer than where the bump-stop would normally bottom out as the airbags act as the bump stop. Not sure how this goes once you deflate the bag to 5psi for offroad without the the towing load..... If it was a JK it would be easy with external bump-stops but I can't see anyway of running additional bump-stops outside of the springs with the TJ.

The 3 places I visited today all seemed to think you just fill the entire coil with airbag (so 250mm seems to be the largest bag then 2x30mm spacers) which doesn't seem right to me as then there won't be any bump-stop point.

Going to work out on the weekend what the bump-stop lengths are going to need to be with the new springs/shocks/shock mounts, then I assume I remove the entire bump-stop assembly (cup and foam pad) then get a bag that is 1/2-3/4" longer than the 300mm above minus the bump-stop length I work out (so 300mm + 1/2" - bump-stop).

Anyone got any further insight into this I would love to hear it.

[projoe]

redemptioner wrote
"most manufactures install instructions show to remove the bump-stop but leave the cup which seems crazy as the cup would cut into the bag IMO"

X2 but i dont think the cup can be removed? I"m guessing though there are a lot of TJ's out there fitted up like this?

I should fit mine soon, had for over a year, so I'm slack.

[Redemptioner]

Originally Posted by projoe

redemptioner wrote
"most manufactures install instructions show to remove the bump-stop but leave the cup which seems crazy as the cup would cut into the bag IMO"

X2 but i dont think the cup can be removed? I"m guessing though there are a lot of TJ's out there fitted up like this?

I should fit mine soon, had for over a year, so I'm slack.

Cups come off front and rear on mine with a bolt that goes up the centre of them leaving a nice round "bulge" which I would think is a much better thing to be against the bag.....

[Redemptioner]

So after doing a bunch more research and talking to some more people it appears the right way to setup the coil-rite bags on a TJ is to leave the bump stops in and make sure the bag height is shorter than the level spring gap but long enough to act as the lower bump-stop pad. To work this out you need to take the level spring gap to the bump-stop cup with all bump-stop spacers removed (about 11" in my case), then minus the up travel you need/want (4" in my case) plus up to 1 inch for bag depression when the bag is acting as the lower bump-stop pad (dependant on bag PSI). This means with my 4.5" synergy springs I need a bag that is approximately 8" long and a little over 5" in width. You definitely want to put the jounce back in after measurements as this protects the bag from the cup and adds further dampening when you hit the bump-stop which combined with the bag apparently gives a similar overall effect as a hydro bump stop (note I said "similar" not the same).

Reading a lot of reviews it seems like the firestones are the only way to go, they are a much thicker bag and are backed by a lifetime warranty on the bag itself, I will probably put the bags in kevlar sleeve to help protect them a little further or possible carry an extra bag when doing long trips in the middle of woop woop.

Taking everything into account above it appears the Firestone 4172 bags are the perfect size for my needs, no plastic spacers will be needed and should give me everything I want as far as travel and support goes. I could run the 4175 bags and run longer bump stops (add 2.5" on bump stop extension) but I would imagine the more spring that is filled with the airbag the better the control you will have over the spring rate and therefore a better overall ride quality.

[low ranger]

I assume that you will be bringing the air lines out through the lower spring mount after drilling a suitable sized hole (20mm)...?

[Redemptioner]

Originally Posted by low ranger

I assume that you will be bringing the air lines out through the lower spring mount after drilling a suitable sized hole (20mm)...?

That's the plan my man

Going put a crimp hose clamp on airline connection to the bag and then put a rubber grommet in the hole that is the the right size to allow the line through with a snug fit to ensure no rubbing or movement, then will be controlling the bag pressure from my custom switch panel that I have being made which will house a dual needle digital pressure gauge (well to be honest can't decide between dual needle or digits yet) so I can have the full "wank factor" in the cockpit for controlling the airbags pressure remotely. Will of course use some flow control valves to make it nice and easy to control the air pressure accurately.

I also spoke to the airbaman up at brendale that my comp mechanic suggested to go an see, seems like they have a cup that goes over the entire bag on the top rather than having the centre force a traditional bump-stop creates, they also have the bags I want so I will take the Jeep up there on Monday and see what they have and what they think. The airbags come in at only $30 more than shipping them over from the states so they will probably get my cash if they know what they are doing, will update on Monday after I have been to see them

[low ranger]

airbagman know their stuff. don't make the air line too snug a fit in the hole or you will end up pulling the fitting out of the bag. leave enough slack line to allow the bag to move up & down as the suspension cycles.