Not sure if this should be here or in Suspension. I'm putting it here for now.
I've been thinking about putting the cab on my crew cab SD on air ride for years.
These cabs are suspended by 4 rubber isolators on each side. One is under the driver/passenger footwell. The second one is between the front and rear seats and the back one is behind the rear seat. You access them by removing a rubber cover in the floor board.
The 4th isolator attaches the front fender to the front of the frame.
Frames such as those under a pickup truck are subject to something called "beaming". That is when the middle of the frame vibrates like a diving board when the truck hits bumps. This causes the cab to shake.
GM in particular has had trouble with this. So much so that they issued a revised rear cab isolator that incorporated a visco elestic component that smoothed things out. The 2010+ Dodge trucks also use a hydrodynamic rear cab isolator.
Here is what the isolators look like from my '99 SD. One part mounts between the cab and the frame mount and the other mounts under the frame mount to stop the cab from rebounding too high.
There is how they mount.
In the search for a better ride, last fall I replaced the upper part of the rear 3 of my isolators with some Timbren rubber isolators.
This change definitely made an improvement in how my truck rode. When I drive down the freeway and look out one of my towing mirrors, I can see the box moving up and down quickly relative to the cab, which seems to float much better.
However, its not a total solution. For one thing, if you go over the right type of bump the cab actually moves more because for the most part its totally undamped.
I would like to put my cab on an air ride system using air bags, in a similar manner to how its done on MD and HD trucks.
The cabs on MD and HD trucks typically pivot on a bushing up at the front and ride of bags in the rear. They have one or more shock absorbers to dampen the cab movement. They typically have a control arm or two to control the side to side movement of the cab.
The problem with doing this on a SD is that there is no room under the cab for the control arms that are present on MD and HD trucks. SD cabs sit an inch or two above the frame in the rear. And the underside of the SD cab isn't flat like it is on a MDT.
Recently I came to find out that the new International Prostar sleeper cabs ride on an integrated strut/air bag instead of using the traditional control arm system.
The struts themselves are available directly from Monroe at a price of about $150 each. (part number 66128 for a short sleeper strut) That may sound like a lot of money, but the Dodge hydrodynamic damper is over $100 by itself and it still needs an isolator element.
The struts are very innovative. They handle the whole issue of controlling the cab movement. They have rubber mounted plates at the top that allow the cab corner to move up and down but not move side to side or front and back.
I'd like to remove the back 3 isolators on each side of my cab, leave the isolator up by the radiator in place and replace the back isolators with a pair of these struts.
The problem with this idea is that the cab struts are very long. They measure 21 inches fully extended. They have about 5" of travel.
At ride height , they measure 7.5" from the underside of the mounting plate to the bottom of the air bag piston. The rest of the strut measures about 11 inches for an overall length of 18.5 inches.
With the air let out of them, they measure 6" from the underside of the mounting plate to the bottom of the air bag piston. This allows 1.5" of downward travel, which might allow the cab to touch the frame, but maybe not.
The issue I am having is that of having a strut sticking down 18.5" from the underside of my cab. The underside of the cab to the bottom of the frame measures about 13" on my truck. That means the strut is going to stick down another 5 inches or so. That puts it about 12" off the ground on my truck, running 20 inch rubber. Its about 2" lower than the fuel tank.
Should I be worried about the ground clearance ? (I don't off road with it, but I do drive on back roads.)
The channel across the back of the cab that the stock isolator mounts to is 2" high. I could cut it where the strut mounts and reinforce things around it ????
I could also take the shock apart and shorten the body and such, making it into a strut only and then mount the air bag beside the strut instead of over it.
I also thought about mounting the strut upside down with the damper body sticking up in the cab behind the rear seat. The problem with that is the strut body is mean to mounted securely to something beefy like a frame and the pads are meant to mount to something loose like the cab. One would have to build some heavy infrastructure behind the seat to properly secure the bodies to the cab. I ruled out mounting them this way for that reason.
Ideas ? Comments ?
Thanks
Disclosure: I cross posted this over at pirate4x4.com to get their input too.
I've been thinking about putting the cab on my crew cab SD on air ride for years.
These cabs are suspended by 4 rubber isolators on each side. One is under the driver/passenger footwell. The second one is between the front and rear seats and the back one is behind the rear seat. You access them by removing a rubber cover in the floor board.
The 4th isolator attaches the front fender to the front of the frame.
Frames such as those under a pickup truck are subject to something called "beaming". That is when the middle of the frame vibrates like a diving board when the truck hits bumps. This causes the cab to shake.
GM in particular has had trouble with this. So much so that they issued a revised rear cab isolator that incorporated a visco elestic component that smoothed things out. The 2010+ Dodge trucks also use a hydrodynamic rear cab isolator.
Here is what the isolators look like from my '99 SD. One part mounts between the cab and the frame mount and the other mounts under the frame mount to stop the cab from rebounding too high.
There is how they mount.
In the search for a better ride, last fall I replaced the upper part of the rear 3 of my isolators with some Timbren rubber isolators.
This change definitely made an improvement in how my truck rode. When I drive down the freeway and look out one of my towing mirrors, I can see the box moving up and down quickly relative to the cab, which seems to float much better.
However, its not a total solution. For one thing, if you go over the right type of bump the cab actually moves more because for the most part its totally undamped.
I would like to put my cab on an air ride system using air bags, in a similar manner to how its done on MD and HD trucks.
The cabs on MD and HD trucks typically pivot on a bushing up at the front and ride of bags in the rear. They have one or more shock absorbers to dampen the cab movement. They typically have a control arm or two to control the side to side movement of the cab.
The problem with doing this on a SD is that there is no room under the cab for the control arms that are present on MD and HD trucks. SD cabs sit an inch or two above the frame in the rear. And the underside of the SD cab isn't flat like it is on a MDT.
Recently I came to find out that the new International Prostar sleeper cabs ride on an integrated strut/air bag instead of using the traditional control arm system.
The struts themselves are available directly from Monroe at a price of about $150 each. (part number 66128 for a short sleeper strut) That may sound like a lot of money, but the Dodge hydrodynamic damper is over $100 by itself and it still needs an isolator element.
The struts are very innovative. They handle the whole issue of controlling the cab movement. They have rubber mounted plates at the top that allow the cab corner to move up and down but not move side to side or front and back.
I'd like to remove the back 3 isolators on each side of my cab, leave the isolator up by the radiator in place and replace the back isolators with a pair of these struts.
The problem with this idea is that the cab struts are very long. They measure 21 inches fully extended. They have about 5" of travel.
At ride height , they measure 7.5" from the underside of the mounting plate to the bottom of the air bag piston. The rest of the strut measures about 11 inches for an overall length of 18.5 inches.
With the air let out of them, they measure 6" from the underside of the mounting plate to the bottom of the air bag piston. This allows 1.5" of downward travel, which might allow the cab to touch the frame, but maybe not.
The issue I am having is that of having a strut sticking down 18.5" from the underside of my cab. The underside of the cab to the bottom of the frame measures about 13" on my truck. That means the strut is going to stick down another 5 inches or so. That puts it about 12" off the ground on my truck, running 20 inch rubber. Its about 2" lower than the fuel tank.
Should I be worried about the ground clearance ? (I don't off road with it, but I do drive on back roads.)
The channel across the back of the cab that the stock isolator mounts to is 2" high. I could cut it where the strut mounts and reinforce things around it ????
I could also take the shock apart and shorten the body and such, making it into a strut only and then mount the air bag beside the strut instead of over it.
I also thought about mounting the strut upside down with the damper body sticking up in the cab behind the rear seat. The problem with that is the strut body is mean to mounted securely to something beefy like a frame and the pads are meant to mount to something loose like the cab. One would have to build some heavy infrastructure behind the seat to properly secure the bodies to the cab. I ruled out mounting them this way for that reason.
Ideas ? Comments ?
Thanks
Disclosure: I cross posted this over at pirate4x4.com to get their input too.