I have been working on my 51 GMC 1/2 ton. I got the notch done, 4 link installed, bolted on the bags, temped a air line to them and this is what I got... I wanted the bags to be straight up and down at ride height but you can see in the pic what that does when it's aired out. It's 1" off of center. Not good. Here's what I'm thinking... I need to move the bottom bracket back 1" so the bags are in line when aired out. My question is will it be bad to run the bags 1" off of center at ride height? This is where it will get the most abuse. The bags are Slam Specialties RE7's. They say "Linear and Off-Axis Actuation" on the spec sheet. Will this work? I'm afraid the bags will eventually get cut or worn when aired out if I leave it as is. Anybody got any suggestions?
Running them off axis is not a problem. What is a problem is having any portion of the rubber come in contact with metal, like in the aired-out picture above. If you can move the bracket or axle back a bit so the rubber does not touch metal, you should be ok. It looks like you have a bit of room to move the axle back. I would set it up so the upper and lower bag brackets are aligned at the 1/2 way mark of the bag stroke, or just move it back enough to where the bag no longer touches metal. SS bags have integral bump stops, so adding one is just limiting potential travel.
I set them up so they are parrallel at full compresion. Any bag other than a slam specialties should be used in conjunction with a bump stop. You might also want to think about swapping those out for a F9000 style bag it will ride 1,000 times beter in a truck.
Are your lower 4 link bars set to be parallel at ride height? Is the one picture of the bag at full inflation?
It looks like you desire a lot of lift. You aren't going to get that with your bags over axle. The long bar 4-link was a wise choice but you may have to run trailing arms with the bags mid mounted to get the lift desired.
Thanks for the replies... From aired out to ride height it will come up 5" at about 40 to 50 psi. I may have had a little more air in it in the picture. I'll make new lower bag brackets to move the bags in line when aired out. I don't want to move the rear end because I've got the wheels lined up in the fenders where I think they should be. This is the first air bag rear end that I've done but I'm please with it so far. I am open to any suggestions. Thanks again for the replies.
Just make different lower brackets, with some offset in them, or get a circle of metal that matches the bag end cap, and weld it on to the existing bracket, offset to the rear.
More pics might be helpful...some pics looks like a parallel 4 bar, another looks triangulated. With drop, you're going to get some "twist" to the axle...but the pictures look drastic....I wouldn't expect that kind of twist in 5" IF the lower bar is moving in a shorter radius than the upper, you'll get the "pull" in the pics. Sidedump made a good suggestion with mounting mid trailing arm.
In case I didn't make it clear...the axle shouldn't twist in either set up...move forward or back in the opening, yes...but not twist.
Kind of hard to see what your bars are doing in the pics. It almost looks to me like you need to undo your front 4-link bracket off the frame and then get the bag straight by moving the axle back a little. then retack the front mount about an inch or two higher then it was before and run it through it's motion and see what it does.
if you have that much change in wheelbase with only that small drop, you are going to have the back end of the truck steering you around, its going to feel unsettled when one side is higher than the other (cornering, big bumps, any time one side is lifted and the other side is lower) Getting that much change in wheelbase will also be bad for your driveshaft and carrier bearing (if you have one) Looks to me like you should reinstall the link bars, this time tack them in with the frame on stands and the axle on a jack so you can watch what it does as you go through the range of travel. If they do weird stuff like what you have there, break the tacks and do it again. You dont want the wheelbase changing too much, and you dont want the pinion angle changing too much either.
Its hard to tell in the pics but it looks like your panhard bar is heading at about a 45 degree angle from the axle. you want to get that panhard bar parallel with the rear end otherwise its going to pull and push your rear end foward and back.
If it were mine, I would put in longer lower links to get the axle running on the arc that you installed the bag mounts along. If you didn't factor in the arc that the axle travels in locating those and setting the seat angle, you know where your problem started. If you did factor it in, you missed. You can get away with it as is, but it won't be right.
It is a parallel 4 link. There isn't any twist to the axle. The pinion angle stays the same as in moves in its arc. Everything seems to work fine - I guess the problem is that I didn't take into consideration the arc when I set up the rear end and now I'm having to compensate for it. Although, with the notch it travels a lot lower. But the ride height should be the same. It will just be lower when aired out. I wondered about the panhard bar being at a 45 degree angle. This is the kit that I bought. It's similar to the TCI 4 link kit which has the same style panhard bar. I have thought about making a different panhard bar. Again, thanks for the help and input.
A couple things: It "appeared" in the photos the rear was twisting. On closer inspection, it's only an optical illusion - the bag is hanging over the lower mount, making the mount to visually appear turned. Is the the photo showing full extension (full limit to travel) on the airbag? If so, when you encounter a "dip", will the rear be able to drop away from the frame? It looks like "ride height" is set up with the bag full, which relates to 0 suspension travel. I think I'd set it up with the bag in a "mid" position with the 4-link parallel at that point. From there, neither up nor down would be drastic.
I have been thinking about that too. The bags have 8" of travel. Aired up with 5" of lift that gives me 3" of upward travel left. Is that enough? Does anyone run limiting straps?
Outlaw, At ride height, there would be only 3" of extension travel. Mike, My thoughts are that would potentially put a lot of strain on the bag causing premature failure. If the bags fail, is the truck still going to be drivable? Or is the body going to be grounded? Since it is doubtful the rear end will ever be airborne causing the whole axle to hang, the bigger concern would be do you have enough travel - thinking of the rear as a "teeter totter" with the 3rd member being the fulcrum: With the bags inflated to ride height, can you jack one side of the axle all the way up (to the compression limits of the bag, the bump stop, or frame) without the other side trying to extend past the full 8"? If you can, I'd say the 3" is probably "safe". There has to be others with a similar setup that can weigh in.....
set the shocks so they limit the travel of the bag. A shock is not supposed to be the limiting device but chances are the only time it will see past the full drop is when it goes on a lift.
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