I hope I don't have another major design flaw...

[Zandoz]

This time in the rear suspension. For multiple reasons I want to use air bags for my rear suspension...specifically Slam Specialties SS-6s. The relevant spec on these bags is that they have a constant 6" diameter, regardless of inflation level.

The upper bag brackets are CTS units. They are very heavily made...1/4" material or better. The flat platform that rides on top of the bags is roughly 8-1/2" square, with the bag located centered. The brackets have full length, 4" tall angled gussets on either side.

So far, so good. Actually the bag brackets are way heavier and oversized for a typical T-Bucket sized vehicle. They are recommended for 3500 series trucks.

Where the potential flaw comes in is with the shocks. On the lower end they will mount to the factory locations on my T-Bird/Mustang 8.8" rear end. The factory hardware fix the shocks near vertical, and roughly 8" out from the side of the frame. There was the initial problem. Nothing there to mount them to.

After a lot of playing around, the solution I came up with...and am now questioning...is to replace the hardware between the shock and the axle bracket. The change would allow the shock to be angled slightly towards the frame, and moved slightly rearward. This change gets the upper end of the shocks positioned so that they can be mounted through the outside rear corner of the air bag bracket. Even with the modification, the upper ends of the shocks are 7-1/4" out from the sides of the frame

The purple dashed lines indicate 6"x4"x1/4" gussets added under the bag brackets for added reinforcement.

That brings me to the dreaded flaw. Is the additional load out on the ends of those bag brackets going to be too much, even with the additional gussets?

 

[choppedtop]

I wouldn't think it would be a problem. The bags are a cushion, not as if it was a rigid mount. That will not cause a sledge hammer effect on bumps. More like a rubber hammer blow. If you look at coilover shock mounts, they really don't have near that much support.

 

[golddredger]

You are good to go! Mount them and get to cruising. Your setup is good. On this light duty application on the back end of a t bucket it will work great. I have the same brackets you do on another truck project i have and they are more then strong enough for what you are doing mounting the shocks there. Just make sure you have a good 1/2" clearance between the airbag and anything around it. Ie, shocks, brackets ect....basically you can slide your finger in between the bag and anything around it.

 

[fletcherson]

The only complaint I have with air bags besides losing air over time is I have had to replace one that rubbed a hole in its side due to bulging of the bag and inside dually tire even with prescribed clearance, but you won't have any where near the weight to contend with in your bucket, so it shouldn't be an issue.

 

[Zandoz]

You are good to go! Mount them and get to cruising. Your setup is good. On this light duty application on the back end of a t bucket it will work great. I have the same brackets you do on another truck project i have and they are more then strong enough for what you are doing mounting the shocks there. Just make sure you have a good 1/2" clearance between the airbag and anything around it. Ie, shocks, brackets ect....basically you can slide your finger in between the bag and anything around it.

Between the SS-6s having a constant diameter, and the shock having a slight angle away from the bag, I'm hoping there will be no clearance problem. The only potential issue would be at full compression

The only complaint I have with air bags besides losing air over time is I have had to replace one that rubbed a hole in its side due to bulging of the bag and inside dually tire even with prescribed clearance, but you won't have any where near the weight to contend with in your bucket, so it shouldn't be an issue.

Some say air loss is inevitable...others say if there is no leaks in the plumbing there should be no loss. Initially the only plumbing should be the schrader valves on top the bags, so not a lot to leak. If they do leak I have a portable compressor, and by then I should have a 50ft air line at the end of the drive.

 

[fletcherson]

Between the SS-6s having a constant diameter, and the shock having a slight angle away from the bag, I'm hoping there will be no clearance problem. The only potential issue would be at full compression



Some say air loss is inevitable...others say if there is no leaks in the plumbing there should be no loss. Initially the only plumbing should be the schrader valves on top the bags, so not a lot to leak. If they do leak I have a portable compressor, and by then I should have a 50ft air line at the end of the drive.

I have used them on several trucks. I like them, but they have all lost air. It's sort of like tires that need air when the seasons change, etc. I know there were no leaks. It's just the nature of them from my experience. As long as you pay attention to them, no problem. The issue I had with rubbing was due to both the bag and tire bulge, I think. It was mounted exactly in the prescribed position, with the correct clearance. I doubt it would be an issue in a passenger car. This was in one of my small dump trucks and it happened while loaded on a bumpy road that kept rocking the truck, I think that was the killer. It may have been that the air had leaked down again and it allowed the truck to sway more than it should have. I was frustrated by them losing air. I had to check them routinely. If I did t check, I wouldn't know till the truck was loaded, then it was too late. If I ever use them again, I will install a air supply system to maintain constant pressure. I don't use them on my dump trucks anymore because it happened twice. I now use old fashioned overload springs with no problems at all. Just be aware and be sure you have ample clearance and remember that the tire will bulge in certain instances, etc...

 

[Zandoz]

I have used them on several trucks. I like them, but they have all lost air. It's sort of like tires that need air when the seasons change, etc. I know there were no leaks. It's just the nature of them from my experience. As long as you pay attention to them, no problem. The issue I had with rubbing was due to both the bag and tire bulge, I think. It was mounted exactly in the prescribed position, with the correct clearance. I doubt it would be an issue in a passenger car. This was in one of my small dump trucks and it happened while loaded on a bumpy road that kept rocking the truck, I think that was the killer. It may have been that the air had leaked down again and it allowed the truck to sway more than it should have. I was frustrated by them losing air. I had to check them routinely. If I did t check, I wouldn't know till the truck was loaded, then it was too late. If I ever use them again, I will install a air supply system to maintain constant pressure. I don't use them on my dump trucks anymore because it happened twice. I now use old fashioned overload springs with no problems at all. Just be aware and be sure you have ample clearance and remember that the tire will bulge in certain instances, etc...

I'll definitely keep an eye on them. Being in clear sight should make it a bit easier. The only spot I have any worry about potential rubbing is with the shock body when near fully compressed. Since the SS-6s are fixed diameter bags I think I should be OK. If there is an issue, a shield between them should take care of it.

An automated air supply is on the "after I get it running" wish list. I've already allocated space for an air tank and compressor.

 

[golddredger]

Hey zandoz,
With a simple 2 bag system all you will need is a compressor. no need for a tank unless you are looking for a faster fill from fully deflated. You can run a single compressor with one line that splits with a t then a one way check valve on each line to the bags. One manual bleeder valve per side. So a t and the bleeder from each bag plumbed to the dash or floor for easy access. This way you can hit the power switch which turns the pump on and fills the bags, the one way check valves keep the air from transfering sides when turning or when loaded to one side more. Then a bleeder on each bag allows you to drop pressure on one side. Maybe your battery side of the car is a bit heavier so it needs 52 psi and the other only 50psi for the car to sit level. Maybe you are a hefty guy and your gal is skinny chick and your T leans to your side when cruising. Simply air the system up to ride height then bleed the lighter side to level the car up. Stick a small RV bubble level down on the firewall or back of the floor shifter base or even the dash so you can adjust side to side level from the drivers seat. This setup uses less room and having a tank costs about 3 times more in hardware over a simple compressor only setup.

 

[RPM]

We will be building a Model A rat rod frame here soon and the entire frame will be the air tank. Lots of pressure testing checking for leaks.

 

[old round fart]

Slick idea Ron. And thanks for the phone number.

 

[Zandoz]

Hey zandoz,
With a simple 2 bag system all you will need is a compressor. no need for a tank unless you are looking for a faster fill from fully deflated. You can run a single compressor with one line that splits with a t then a one way check valve on each line to the bags. One manual bleeder valve per side. So a t and the bleeder from each bag plumbed to the dash or floor for easy access. This way you can hit the power switch which turns the pump on and fills the bags, the one way check valves keep the air from transfering sides when turning or when loaded to one side more. Then a bleeder on each bag allows you to drop pressure on one side. Maybe your battery side of the car is a bit heavier so it needs 52 psi and the other only 50psi for the car to sit level. Maybe you are a hefty guy and your gal is skinny chick and your T leans to your side when cruising. Simply air the system up to ride height then bleed the lighter side to level the car up. Stick a small RV bubble level down on the firewall or back of the floor shifter base or even the dash so you can adjust side to side level from the drivers seat. This setup uses less room and having a tank costs about 3 times more in hardware over a simple compressor only setup.

Hiya Gold,

A bit of background on the reason for going with the bags in the rear, and a tank. My mobility issues make climbing in the car impossible. I need to have the seat low enough to just sit down. Right now, based on a lot of evolution my CAD model, I've gotten the layout of the frame and suspension to the point of being borderline height. If ride height is too high, I'll have to use the bags to lower then raise the car every time I get in...a process that would become annoying if slow. Thus the need for the tank.

The only other reason for the bags is that the car may be pulling a small trailer for my power chair, and/or having a rack on the back for my manual wheelchair.

If I can get by with a static height for getting in...and until I can justify/afford the tank, pump, plumbing and controls to automate the system...I'll not be worrying about other bag adjustments. After all, if I had a conventional spring suspension I'd not be making any ride height adjustments.

 

[Zandoz]

We will be building a Model A rat rod frame here soon and the entire frame will be the air tank. Lots of pressure testing checking for leaks.

I'd thought about trying a series of crossmember tubes between the kicked up frame members. It would work if the kick up is high enough that the axle pumpkin did not hit the tubes.

Another sort of related idea I played with but could not afford to experiment with would be to make the frame rails out of extruded aluminum beams. One feature of the beams is that they have internal cavities that can be pressurized to 150 psi, and can be used for most gases and fluids. Also they make sealing caps that are threaded for fittings. I doubt the cavities would be large enough for air storage, but I could see them as an alternative for long runs of lines.

 

[butch27]

Ron: One heck of an idea!!!

 

[old round fart]

Ron, think about a drain for condensation. The more I think about it the more I like that idea.

 

[fluidfloyd]

Built an alcohol dragster back in the '80s that had the roll cage and several seat support tubes pressurized. Had a pressure gauge in the driver's bay and told NHRA tech that if the pressure dropped we knew the frame had a crack in it. They never realized there was no nitrogen bottle to shift the Lenco. Following year there was a no pressurized frame rule. Guess somebody talked!

 

[RPM]

Ron, think about a drain for condensation. The more I think about it the more I like that idea.

It will have several drains in it.