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Air ride cab ideas.

64K views 70 replies 21 participants last post by  SammyBoyce 
#1 ·
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.
 
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#2 ·
Will the cab be strong enough to only be supported only on each end?

Would you be able to mount the airbags off the side of the frame?
 
#3 ·
Will the cab be strong enough to only be supported only on each end?
That is the question of the day over on Pirate. I say yes. Someone else is saying that Ford cabs fail all the time.

Would you be able to mount the airbags off the side of the frame?
Yes.

I think this may be one of those things that one just needs to try to see if it works. Anyone have a donor truck ?
 
#4 ·
Why could you take some small box and link the three mounts together and cut the factory brackets off the frame. Then mount the air bag in between the last two cab mounts. It would support the cab and should still help ride.
 
#5 ·
You would lose a few more inches of ground clearance doing that, but yes, that is a very possible way to do it.
 
#6 ·
in the pictures you posted it appears the rear mount is higher. Maybe you could move it back so you wouldnt lose any ground clearance.
 
#7 ·
you could do a body lift so you are working with more room between the frame and the cab.
 
#8 ·
What about putting more than just one bag on the back on each side. Put the damping equipment on the very back and then a couple smaller ones in the middle to help support it. May be to compliated. Could figure out some way to link the bags together so they would all support the same weight. Wouldn't have to worry to much about flex either.

Could put some bump stops on there to like what is used in offloading to prevent the cab from banging on the frame.
 
#9 ·
Honestly I think the cab is going to give out in the center. That's ALONG way from the front mounts to the rear. The other problem your going to run into is brake lines, as the cab moves those metal brake lines are going to give out after awhile.
On MD and HD trucks the cab pivots on the front cab bushings, the hood and fenders are separate.

I'm not at all trying to discourage you from giving it a shot, it's a very good idea. You just have to think of a the little crap, that's when it becomes a real PITA
 
#10 ·
I think that just putting some flexible brake line I would solve that problem. Even if the back of the cab was to move 4" that would only equate to about 1" or less movement at the lines.

You might could even get away with leaving the rubber bushing on the front mount to keep from having a hard mount on the front.
 
#23 ·
I think that just putting some flexible brake line I would solve that problem. Even if the back of the cab was to move 4" that would only equate to about 1" or less movement at the lines.
Lots of vehicles use flexible lines from the body to a wheel on independent suspension. If I need to go to those length to make it work, I will.
 
#11 ·
You could but that's only the beginning. You would have to solid mount your Intercooler and radiator. Headlights are going to bounce with the cab movement, turbo will probably hit the firewall just to name a few.

It would be some job to get done but would be one hell of a nice ride if it could get done:D
 
#12 ·
I did a bunch of measurements and testing yesterday. And I disassembled the cab struts. The project is a go. I bought the steel for the mounts this morning. Pictures and such to follow shortly.

My truck measures 11 feet (132 inches) from the front (fender) mount to the back cab mount.

I'm looking for 2 inches of movement (1 inch down and 1 inch up) at the back of the cab. That equates to 3/8" of movement at the front cab mount (under the front floorboard). And just about no movement up by the radiator.

I am going to leave the front cab mount in.

I am going to remove the middle cab mount. If I find any evidence of cab flexing, I will install a small air bag under that mount to even out the loads on the cab structure.

The air bag (spring) on the strut is going to be fairly stiff compared to the factory International spring rate because I'm installing it near the end of its travel and my cab is lighter than a short Prostar sleeper cab. And it will be somewhat overdamped too.

But both of these are fine because I'm not looking for something really floaty. I'm looking for something that has more travel and is softer than the stock isolators. Basically, I want to isolate the cab from any beaming that might be occurring near the middle of the frame. The Prostar cab strut should be exactly what I am looking for.

I'm setting the strut up so that I have 1 inch downward travel before it hits the end of stroke cushion. And I will be shortening the end of stroke cushion so that its shorter, so that the overall length of my strut assembly is about 18".

If I ever need to, I could disassemble the shock and shorten it.
 
#13 ·
I don't know where you are but I would sure like to ride in your truck if I was ever in the area. Be like riding in a Lincoln town car.
 
#14 ·
If this is for ride quailty have you though instead of just doing air ride seats. That is far less involved and has been done by a few people already. Same end effect I woudl think from your bodies perspective.
 
#15 ·
I'm looking for something that rides good for everyone in the cab, including those in the back seat.

Its not going to be that hard setting up the cab air ride system now that I have things figured out. Its always the researching part that takes the time.

I don't think it would be that much easier installing air seats. There are issues with seat belts and seat tracks with the air seats. I have power seats in both front seats in my truck. I'd hate to lose that adjustability.

Yeah, I'm hoping it rides like a high end car. I rent an Impala from time to time for long trips and my truck isn't too far off from it already. Its a huge difference compared to stock. The air ride cab (and soundproofing) should be the icing on the cake.

As usual, I'll post everything I learn.
 
#17 ·
I run a fleet of Prostars, ride like no other truck Ive ever driven.
Tell us more !

Do you have long sleeper trucks or short sleeper trucks ? I'd love to know the air pressure in the bag at ride height. That would help me compare the Prostar cab load with a pickup truck cab load.

You'd have to install a gauge downstream of the cab height control valve to get it. Luckily the air system on these bags are the simple push/pull fitting system.

I love your posts.
Thanks.
 
#18 ·
I started building a strut mount for the driver's side today.

The main structure is 2x6x1/4" mild steel with a piece cut out of it. Its 13" long right now, but I'll probably trim it once I cut (!) the isolator mount off the truck. It will bolt to the frame via bolts placed in the open area of the 2x6.



I welded on a 7" piece of 2.5" 1/4" wall DOM tubing. Its a bit more complicated than just welding it on. I put a piece of 1/4" flat behind it and welded it to the 2x6 first and then welded the DOM on to that. I did it for the right spacing away from the frame and so that I could get a good weld between the DOM and the 2x6.



I slit the 2x6 with my angle grinder. Then I inserted the strut. The strut is shown here without the air bag. I'll be turning the DOM tubing into a pinch clamp with the addition of bolts to close the seam tomorrow.



This is how it looks with the bag on, fully extended. When mounted on the truck, the mounting plate is going to be about 2" above the top of the notched 2x6. I'll drill the open area of 2x6 and bolt it to the frame where the isolator mount is now.





I hope to continue working on it tomorrow.
 
#19 ·
Just a thought but 2" is a lot of movement, I think 3/8” to ½” would be enough. Right now it doesn’t move at all. But all you want is just stop the bang, bang. Think about the softer mounts you installed they didn’t move. So any movement would be a big help.
I would also leave in the center isolators and bolt, just cut down the isolators and maybe a longer bolt, this is just for safety.

I do love the idea.
 
#20 ·
Just a thought but 2" is a lot of movement.
I think 3/8” to ½” would be enough.
I hope you are right.

Right now it doesn’t move at all. But all you want is just stop the bang, bang. Think about the softer mounts you installed they didn’t move. So any movement would be a big help.
Actually, the Timbren mounts do allow the cab to move. When I'm driving down the freeway I can see the cab moving relative to the box. It isn't much, but its something.

I would also leave in the center isolators and bolt, just cut down the isolators and maybe a longer bolt, this is just for safety.
I'll probably leave the bolt in without the isolator or put a strap to the frame to replace it.

I do love the idea.
Thanks. Hopefully it works out.
 
#21 ·
Having gotten the strut frame mount figured out, I tackled the body mount.

First thing I did was remove the isolators so that I could get some body movement.

Here is where the rear isolator bolt is located. The material you see there is the soundproofing I have installed in my cab.


After some wrenching, out comes the bolt that ties into the isolator. They are different sizes on each side. 22mm head on the passenger side and 24mm on the driver's side.


Here is where the middle isolator bolts are hidden. Did I mention that you have to strip everything in the cab to get the carpet loose enough to get at it ?


That allowed me to do this. Even at this travel (+2 inches), everything was fine under the hood. NB I don't have a fan shroud, but it would still probably be OK.


The isolator mount was then in the way.


So I removed it. Like everything that Ford attaches to a frame, it takes a bit to get it off. Nasty job !




The isolators bolted through a 2 x 4.5" beam under the cab. The upper strut mount is flexible so that the cab can tilt and such and it won't bend the strut shaft. Thus the strut plate must be mounted below the cab so it can flex properly. You can see the beam in some of the above pictures.

I then set about building the body mount.




As a previous poster pointed out, mounting directly to thin cab sheet metal is prone to tear out after a period of time. I also didn't want to drill the beam as its thin metal to begin with and I didn't want to weaken it. So I made a plate that sits inside the cab, on top of the beam, centered on the hole the isolator bolt went through.


This allows the strut to clamp to the beam itself, preserving its integrity. The beam and the back of the cab and the rear door pillar (C pillar ?) are all tied together. Its probably the strongest part of the structure. I'm using a 2x4 here to demonstrate how it will work. The truck beam is wider than the 2x4. I spaced the holes so that it would miss the area where the beam is welded to the rest of the cab. The bolts are 3/8" grade 8. The beam has an insert in it so the isolator bolt wouldn't crush it.









To be continued.
 
#22 ·
I'd like to see how this comes out. I'm also interested to find out where you got the Timbren isolators from. That may be my route to go. what was the part numbers on the ones you used? and did it raise the cab at all over the stock isolators?

To be quite honest, I thought of this after looking at my cab mounts the other day after stretching my chassis. I wasn't sure I would be happy with all the movement up at the front though. After seeing how far a semi's cab moves, I wouldn't be happy with it.
 
#24 ·
I'd like to see how this comes out. I'm also interested to find out where you got the Timbren isolators from. That may be my route to go.
Special order at a local HD truck shop. They were Timbren dealers.

what was the part numbers on the ones you used?
170-55

and did it raise the cab at all over the stock isolators?
About 3/4" at the back. Just that you could tell that the trim on the cab didn't line up with the trim on the box. You had to look closely though. I've since removed the trim on my truck. You probably wouldn't notice it with the modern trims.

To be quite honest, I thought of this after looking at my cab mounts the other day after stretching my chassis. I wasn't sure I would be happy with all the movement up at the front though.
It doesn't move up front. The front rocks a bit when the back moves up and down. 1" in 11 feet is nothing.

After seeing how far a semi's cab moves, I wouldn't be happy with it.
Most semi cabs aren't 11 feet long from front to back. And most, like the Prostar have 4 inches of travel downward.

The cab on my truck is lighter. The air spring is going to be stiffer than on the Prostar because I'm running the bag at the last 1.5 - 2" of its travel, where the bag gains area. It will be very progressive too.

The strut damper is set up for a heavier cab. On my truck it will be over damped.

I'm not looking for big movement, just basic vibration reduction when the frame beams.

I haven't shown this yet, but there is a rubber bumper inside the strut assembly. One could play with them too, even put the Timbren I took out inside the strut ! (Though the OD might make it a bit difficult...)

There are all sorts of ways to make this work.

The Timbrens have a big hysterisis in their force curve AND they are not damped. I expect the Prostar strut system to work much better, though the Timbrens were much better than stock.

Dodge and GM now have visco elastic dampers on the back mounts on their trucks. I think this is going to be one step better than that.

I'll shoot a video of the cab relative to the box sometime and you'll see what I mean.
 
#26 ·
On my truck they were all the same. Cab front, mid and back were all the same. I have not removed the isolator up by the rad, so I can't comment on that.

The only thing I did different between the three was put some washers between the bolt and the bottom isolator part on the mid and back so that it has more room to travel upward. You'll see what I mean when you take yours apart.

The Timbrens are borderline for needing a damper and panhard bar on the cab. My cab was moved to the left about 3/4" when I took off the Timbrens. They don't hold it side to side as well as the stockers. I won't have either of these problems with the struts.
 
#27 ·
What are you going to do with the body lines where the cab and bed meet? Are you just gonna leave them unmatched?
 
#28 ·
I dunno yet.

Stock, with body lines matched, there is about an inch of travel until the cab touches the frame.

With the Timbrens, I was running about + 3/4" and I don't think it was really noticeable.

**IF** I run the back of the cab higher than that, I could always dump the air from the cab bags to lower it so it looks nice when parked ??? I'm not worried about what it will look like when I am driving it.

I guess I could always put a lift under the box.

I'll wait to see how it works and where I run it before I worry about how it looks.
 
#29 ·
the only thing with lifting the box is youd have to comeup with something to space the fifth wheels as well...
 
#30 ·
With my 5th wheel hitch that would not be a problem.

We are not talking about 4 inches here. Maybe an inch, maybe 2 at most.

I'm looking for 2 inches of travel. 1 inch down, 1 up. There is an inch between the cab and frame on a stock truck.
 
#31 ·
I think its going to work.

Having measured everything 8x, there was nothing left to do but try it.

So I drilled the holes in the cab. Here is what they look like from the bottom.


Then I bolted the strut into place on the cab and held it in place on the frame with a jack. This is about how low its going to hang beneath the frame. The strut mount is the same height as the bottom of the fuel tank. If the strut ever got damaged, I'd take it apart and shorten it. No big deal. It has 5.5 inches of travel right now and I only need 2.5 to 3" so its totally possible to have everything be at or higher than the fuel tank.


Here is what it looks like supporting the cab.


I spent some time jumping on the running board and I think it has a really good spring rate and damping. I'm 200 pounds and a good knee flex up and down moves the cab about 1/2". With the Timbren isolators it moved about half that or less. Jumping faster and harder doesn't move it more. I think the damping takes over and keeps the travel about the same.

I checked the doors and such for flex and I can't seem to see any.

I don't see any reason not to finish the project. There is nothing left to do but bolt everything to the frame and do the other side and take it for a road test.
 
#32 ·
Love Your work, keep up on posting the pics.
 
#33 ·
you would probably be able to come up with a lever system for that to set the bag on its side so it doesn't hang down quite so much. similar to the way some suspension systems run them.

i'm tryin to find a picture of it, but cant right now.
 
#34 ·
you would probably be able to come up with a lever system for that to set the bag on its side so it doesn't hang down quite so much. similar to the way some suspension systems run them.
The reason I chose that strut is because it handles all the cab movement. Its a strut with a flexible plate on the top that secures the cab in all three axes and yet flexes so that one doesn't have to worry about fancy linkages.

As soon as you introduce a linkage between the strut and the cab you need control arms, etc. And there isn't room for any, at least going side to side. I've literally thought about putting my Superduty cab on air ride for years and this is the first practical way of doing it. Everything else gets very messy and complicated very quickly.

You can't lay the strut over because a) the strut rod is designed to support a mainly vertical load and b) the flex plate doesn't flex to a big enough angle.

The cab strut has 5.5 inches of travel. Our application needs ~ 2.5 inches. The difference, 3 inches, is how much the strut hangs below the frame. If I ever have ground clearance issues, I will take apart the strut and shorten it 3 inches. It would actually be pretty simple to do.

I was thinking about things tonight and I'm going to look into putting a small sub frame on each side tying together the front, mid and back cab mount. I'll probably use 2x2 or 2x4 tubing. Should be pretty simple. Would be a shame to bend the cab when its so easy to tie those three mounts together.
 
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