Bagged LCA arm modification question

[vortech71chevy]

I tried numerous searches about this and came up with nothing, so figured a new thread was in order- forgive me if its been discussed and I didnt find it.

Im a newb to bagged suspensions- this is my first ever actually. Complete frame off on a 67 SWB and finishing out the frame, and i have the rear all buttoned up. The rear bags are bolted to the trailing arms and bolted to the frame with no cups. I have moved to the front and have the upper bag mounts installed and am mocking it up, intending to mark the LCA’s for cupping. I was looking at things and got to thinking, why do i need to cup the lowers 2.5 inches for a cup bolted to the bag? It seems i could drop it less, saving the scrub line issue, and bolt the bag straight to the LCA? Has this been done? Is there any reason why it couldnt be done? Im thinking of doing a large square recession maybe an inch down and bolting the bag right to it.

Thanks in advance guys!

[Backpayne]

Won't the bag rub on the LCA if those are not cupped?

[EVRLET]

Maybe this will help you:

http://67-72chevytrucks.com/vboard/s...d.php?t=393323

There’s discussion on cups and plates.

[Overdriven]

Originally Posted by Backpayne

Won't the bag rub on the LCA if those are not cupped?

It’s my understanding that “cupping” refers to making a recess in the LCA. From what I’ve seen an airbag will make contact with the surface it’s mounted to in certain situations, the airbag simply folds over the top and bottom plate of the airbag and contacts the mounting surface. Unless you space the airbag top and/or bottom plate away from the mounting surface this can occur whether you cup the LCA or use a flat plate.

But let’s look at this as a whole and make up some numbers to justify cupping. At ride height let’s say that you need an air bag 5 inches tall if you used plates. The bag you picked rides really soft at the required pressure for your desired ride height, could really use more pressure and rubs. If you ditch the plates and cup you can gain 2 inches, you can put more pressure in the bags to maintain the desired ride height, get a firmer ride and have the bags be less likely to rub. Let’s say 5 inches is fine and your cupped, now you can build spacers to get the bag plates off the mounting surface so the bag won’t rub.

I bought my truck equipped with a cheap airbag kit that uses plates, the bags rub the mounting surfaces at ride height but it rides great and gets worse with more air pressure. I’ve inspected the bags and see no ill signs after a year of my ownership. In no way am I saying this is a worry free situation and I’d like to cup and use spacers to eliminate the rubbing so it will be worry free.

[SCOTI]

Originally Posted by Overdriven

It’s my understanding that “cupping” refers to making a recess in the LCA. From what I’ve seen an airbag will make contact with the surface it’s mounted to in certain situations, the airbag simply folds over the top and bottom plate of the airbag and contacts the mounting surface. Unless you space the airbag top and/or bottom plate away from the mounting surface this can occur whether you cup the LCA or use a flat plate.

But let’s look at this as a whole and make up some numbers to justify cupping. At ride height let’s say that you need an air bag 5 inches tall if you used plates. The bag you picked rides really soft at the required pressure for your desired ride height, could really use more pressure and rubs. If you ditch the plates and cup you can gain 2 inches, you can put more pressure in the bags to maintain the desired ride height, get a firmer ride and have the bags be less likely to rub. Let’s say 5 inches is fine and your cupped, now you can build spacers to get the bag plates off the mounting surface so the bag won’t rub.

I bought my truck equipped with a cheap airbag kit that uses plates, the bags rub the mounting surfaces at ride height but it rides great and gets worse with more air pressure. I’ve inspected the bags and see no ill signs after a year of my ownership. In no way am I saying this is a worry free situation and I’d like to cup and use spacers to eliminate the rubbing so it will be worry free.

If any rubber from the bags construction rubs while driving, it will fail eventually. Even if it rubs only when air'd out, it can cause enough damage each time it happens to eventually fail. Start figuring out the cure now.

From the quote above.... The bags will work best @ the proper specs from the manufacturer & that should be the starting point for fine tuning. From there, you can get the right height & pressure that you want/like.
If the bag is spec'd @ 5-6" @ x-psi for ride height, it's usually easy enough to mock things up & see if plates will work for an application or if arms that are properly clearanced are required (modded OE arms or aftermarket).