factory suspension bags?

[screwballl]

ok i had a few free minutes looking over my new 91 burb R2500 and i noticed that it had what looked like a schrader (sp?) valve on the wheel side of the rear splashguard/cab step. I followed the line to see that it has bags between the axle and frame. This is in addition to the regular shocks and leaf springs.
I was wondering if this was a factory option or if it is aftermarket setup? I've never seen this before or setup like this. I tried to take a picture of the schrader valve but it came out too blurry and its too dark now but i did get a good picture of the bag on the passenger side...



Factory or aftermarket?
also does the bag look in good shape? i am curious to add some air to see if theyre still in working/good condition. Also if possible what is the psi rating of this type of setup?

Edit: hmmm found another pic and tried to get a better description as to the schrader valve location:

i appreciate any help possible.

[edman87]

I have never seen this factory, definately looks aftermarket to me. Pops had a 91 burb diesel set up for towing and this was not available that I I know of. Try putting some air in them and it should raise up the rear, not too much air- a little goes a long way. Don't know what these would be rated for but 20-30 psi makes a lot of difference in ride, handling and towing. I think they are usually rated for 100-150 psi, but I am not sure. Those appear to be fairly heavy duty and in pretty good condition. PO must have towed a travel trailer or such.

[screwballl]

actually it was used for towing 30-40ft. yachts for about a year, then the brother took it for his cabinet shop (light duty) and didnt need it anymore... no problems with power or other "abuse" symptoms so far.
It does seem stiffer in the back so i will try to let some out if it has any or will add some to see how it does.... ran a load of 40 bags of (wet) mulch the other day and didnt seem to hardly lower it at all when 30 bags lowered my 76 by at least 3-4"

[matthufham]

it's a suspension helper bag, it keeps the rear from bottoming out when it has a heavy load, keeping the truck more level.

[screwballl]

yeah i knew that much i just didnt know at the time if they were a factory option or not... i did do some looking and saw the same set on JC Whitney

[KShortell]

That's definitely aftermarket. GM didn't offer those on its light trucks.

[Bob Gervais]

I'm looking into those myself, it seems that Firestone is the most popular brand. From the research I've done, those bags are rated at 5k lbs. of extra load capacity ( along with the warning to not overload your truck, lol ) and have a 100 psi maximum pressure. The lowest price I've found so far is around $200. I'm really more interested in keeping the truck level when I tow the car trailer. I know the truck can handle it, but the lift springs I put in the rear are softer than stock. It'd be nice to hook up the trailer and not have the nose high.