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Poor mans Air bumps (Check my design)

9

93xjcowboy

NAXJA Forum User
Location
Savannah, GA
I was talking to my buddy about air bumps and he said he had seen someone do something similar to this. Its basically a poor mans air bump that I want to try and build as soon as I can handle a welding torch and grinder (just had hand surgery).

I will probably try and make the top so it can screw off but this is what I have so far. The Zerk fitting is so I can try and keep the springs quiet/happy. Should the "stopper be made of UHMW or steel? I dont see it taking much weight other than the springs and they will transfer the pressure to the washer on the end. The UHMW will act as a good seal/gasket and allow me run another gasket that wont fall apart right away.

springbump2labled.png
 
1.25'' OD is pretty small. And are you using valve springs, as in engine parts, as the compression part?

Do you really need air bumps, or do you really just need some bump stops? There is a reason air bumps cost as much as they do.
 
Freakin server maintenance causing lag and double posts. To add further....


I see a lot of failure in the size of those parts. That bottom washer is the only thing keeping that piston located will cause a bent piston. How much compression are we talking about here?


Might I suggest you look into some air bump alternatives?
http://www.pirate4x4.com/forum/showthread.php?t=347598&highlight=timbren
 
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Compression should be a little less that 4" at ~300lb/in accounting for the size of the springs. And yes they are the valve springs your thinking of.

As for failure I wasnt sure if it would work or not. I can always make them bigger. I was making the ID slightly bigger than the springs themselves to keep everything inline.

Would the rod still bend with the "stopper" in the tube to help keep it all inline?


I dont necessarily need Air bumps (yet) but with the setup I want to run (3-4" on 35's) It would be nice to have them. Untill then I will have 33's on 3" of lift and I still run enough high speed stuff to bust out regular bumpstops.


I dont think that this is a great substitute for true air bumps but I am curious to see if I can make it work considering how cheap it would be to make. I have access to a lathe and drill press as well as anything else I could need for this.



edit Im liking those bumpstops that you posted to and looking into those.
 
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I have been bumping something like that around in my head for a few months, but have not had the time to do anything with it. I dont see why it wouldnt work. Probobly not good for High speed abuse, but for crawling\ trail riding I see some potential.
 
I dont see whats going to stop the piston and whole assembly from dropping out the bottom...:dunno: If those parts arent sealed, like the washer against the cylinder, the only compression rebound you will have is the springs which defeats the purpose of an air bump right? As for guiding the piston in the cylinder you could do something similar to what I did for my brothers mini sand rail nitrogen shocks. Notice the UHMW guides on the top cap, or in your case it would be on your bottom cap. I recessed them into a groove I machined in the cap. Stuff like this is all designed with high tolerances within .005
shock.jpg
 
I'm all for building your own stuff, but I think in this case there are much better alternatives out there already. From the looks of your drawing you're just adding an uncontrolled pogo stick in your suspension. You don't have a way to control compression or rebound and if the only limit on compression is your "bumpstop" at the end, I think its going to be very harsh. Also, in order limit slop it's going to have to be built to very tight tolerances.
 
I applaud your ingenuity but I'm afraid this current design will prove neither durable or effective enough to be worthwhile. With some changes it will work but then you will be basically making the same thing that is available in the market now. Once you figure in the costs of developing it you may have been money ahead to simply some air bumps. Not trying to discourage you but just save you a great deal of frustration. Good luck.
 
redrider2911 said:
I dont see whats going to stop the piston and whole assembly from dropping out the bottom...:dunno: If those parts arent sealed, like the washer against the cylinder, the only compression rebound you will have is the springs which defeats the purpose of an air bump right? As for guiding the piston in the cylinder you could do something similar to what I did for my brothers mini sand rail nitrogen shocks. Notice the UHMW guides on the top cap, or in your case it would be on your bottom cap. I recessed them into a groove I machined in the cap. Stuff like this is all designed with high tolerances within .005
shock.jpg
Click to expand...
The aluminum tube will have to be pretty thick to take the pressure. The seals are your other big issue. They have to seal a ton of pressure and the wear on the inside of the tube pretty much means you should probably go steel.
 
old_man said:
The aluminum tube will have to be pretty thick to take the pressure. The seals are your other big issue. They have to seal a ton of pressure and the wear on the inside of the tube pretty much means you should probably go steel.
Click to expand...

Already made them... This was 3 years ago, ran them for a year and sold the whole sandrail. .25" wall aluminum and I had it anodized. Nice slick surface and minimum material wear. This was a mini 1 seater sand rail powered by a 440 snowmobile engine. Shocks took the weight just fine. The proper valving was the hard part.
Do they use fluid in air bumps too? I honestly dont know much about them. What is the usual air pressure?
 
The hard anodizing answers the wear problem question I had. How did you get the seals to hold?
 
9T3XJ said:
I'm all for building your own stuff, but I think in this case there are much better alternatives out there already. From the looks of your drawing you're just adding an uncontrolled pogo stick in your suspension. You don't have a way to control compression or rebound and if the only limit on compression is your "bumpstop" at the end, I think its going to be very harsh. Also, in order limit slop it's going to have to be built to very tight tolerances.
Click to expand...

I can pick and choose between many different spring rate springs if I go this route so that controls the compression and the weight of the vehicle controls the rebound. Its not going to be riding on these like it does coil springs.
 
redrider2911 said:
I dont see whats going to stop the piston and whole assembly from dropping out the bottom...:dunno: If those parts arent sealed, like the washer against the cylinder, the only compression rebound you will have is the springs which defeats the purpose of an air bump right? As for guiding the piston in the cylinder you could do something similar to what I did for my brothers mini sand rail nitrogen shocks. Notice the UHMW guides on the top cap, or in your case it would be on your bottom cap. I recessed them into a groove I machined in the cap. Stuff like this is all designed with high tolerances within .005
Click to expand...

I have the same exact design drawn out already when it comes to the UHMW guide. In the picture look at the "stopper" I can make it as thick as is needed.

Its not supposed to be an airbump. Its supposed to be a poor mans alternative to an airbump.
 
jeeperjohn said:
I applaud your ingenuity but I'm afraid this current design will prove neither durable or effective enough to be worthwhile. With some changes it will work but then you will be basically making the same thing that is available in the market now. Once you figure in the costs of developing it you may have been money ahead to simply some air bumps. Not trying to discourage you but just save you a great deal of frustration. Good luck.
Click to expand...

I am just throwing some ideas around in my head and I figured I would post it up to see what problems I would run into. Now that I see those bumpstops that were posted by StarboardM I will probably just go with them for simplicity.

Thanks for the critique everyone.
 
That link to Stengel Brothers, in the Pirate thread, has Jeep (and other vehicle) specific kits. Those are pretty nifty, although they aren't exactly cheap.
 
old_man said:
The hard anodizing answers the wear problem question I had. How did you get the seals to hold?
Click to expand...

lol I dunno. never leaked oil. i was told the o-rings would be the best way to go so I did. lol the sand rail probably weighed max 800 LBS with driver. I cant rememer how much pressure we ran in those things either. What do they normally use to seal em? a brass crush washer?
 
redrider2911 said:
lol I dunno. never leaked oil. i was told the o-rings would be the best way to go so I did. lol the sand rail probably weighed max 800 LBS with driver. I cant rememer how much pressure we ran in those things either. What do they normally use to seal em? a brass crush washer?
Click to expand...

No there is a lipped seal that uses the pressure to cause the seal to contact the wall with more pressure. In most cases the seal actually is really composed of multiple seals in series.
 
old_man said:
No there is a lipped seal that uses the pressure to cause the seal to contact the wall with more pressure. In most cases the seal actually is really composed of multiple seals in series.
Click to expand...

Ok, yea that makes sense. Like a double lip crank shaft main seal. Well If I ever feel like makin up another set for like my jeep then Ill go that route. lol and then of course I would have to go to stainless or something for the cylinder and such to put up with the abuse.
 
Just to comment on the OP's design, one of the big qualities of air bumps, or any good bumpstop, is that the effective spring rate ramp up is not linear it's exponential. If you use any type of additional spring, like the valve springs that were proposed, you have a linear spring rate that just won't do the job that a bumpstop needs to do.

Air, or some type of big soft bushing, provides progressively more spring rate/resistance as it is compressed, so the last bit of travel of the stop is really firm. For example, a 300 lb spring has 300/600/900 lbs of spring force as it is compressed 3". An air bump can have 300/1000/5000 lbs of spring force as it compresses 3" (random numbers only for explanation purposes).
 
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