active bumpstop used as a shock absorber substitute

[working on it]

Since I just completed the frame repair and axle/spring upgrade on my trailer,http://www.tnttt.com/viewtopic.php?f=21&t=58985 I was seeking a way to prevent a recurrence of breakage and also a way to absorb/spread the impact of large shocks to the suspension components. After much research and measurements as to which way to mount a set (requiring modifying the tie-plates for the lower mounts, and drilling more holes in the frame for the upper mounts), I wondered if all the added hardware would accomplish that task any better than a method I had used before. It seems to me that the shock and resulting jounce could be ameliorated to a satisfactory degree by inserting a progressive-rate EVS foam bump stop in between the frame and axle. Pretty much the same as Timbren uses hollow rubber "springs" in their axle-less systems, and in their Aeon line of suspension aids. I had used a similar bump stop, also mounted to be in close contact with the frame (except it was a solid polyurethane block- and was much stiffer than the EVS foam) in the rear suspension of my '86 S10 (modified for flat cornering and excessive weight loads). At first, it was very stiff and unforgiving over all surfaces, but I drilled varying sizes of holes in the poly, to create progressive stiffening, and it served me well for many years. The newer material, EVS urethane foam, acts in a progressive rate manner, without mods, so it should be what I want straight from the get-go. There was also a recent thread concerning bump stops, that served to jog my memories of my S-10 mods. So why not try what I've already done before, with success. I ordered a set of these

from Amazon. I haven't decided yet, but I will probably attach them with the mounting tabs under the axle u-bolts, so they will follow the axle movement as it travels rearward under compression. If they are too flexible for that, then I will attach the tabs thru the 1/4" thick repair piece (1/4" TEK screws?).

I will shave off about .25" (depending on actual density of the foam - TBD) from the top of the stop, and when the spring closes the gap under compression once on the ground, the bump stop will stay in constant contact with the frame, hopefully absorbing sharp impacts and reducing the major fluctuations in suspension travel. I don't expect too much spring compression anyway; the now 1600-1700 lb trailer is on a new 3500lb Dexter axle with 3000 lb/pair springs, and the 14" tires should absorb most road shock.

 

[working on it]

USPS just delivered the bump stops...they are very well constructed and heavy-duty. However, they are as inflexible (to the small pressures I can exert on them by hand) as the old solid polyurethane blocks I had used before, except for the molded slots in their construction. I mistook them for the more modern "micro-cellular foam jounce bumpstops", used on many late model cars as an active component of their suspensions. I can, and will be able to soften them up (slightly), to accomplish my stated objectives, but maybe not as I had envisioned. No way to "squeeze" them into the gap between axle and frame, as I had planned, without cutting a u shape to match the curve of the axle (if I mount them cone-side down). The slotted base is too thick and solid to bend to wrap around the 2" wide repair piece I made (hoped to mount it sideways, to the 3/8" bolt thru the frame). And too thick to fit under the axle u-bolts, either. I looked around for other possible ways to fit it in place, but the only viable alternative would be to use just one, mounted under the central spine of the trailer (1.5"x3" rectangular tube,

but easily reinforced with 1/4" angle), and cut them into the aforementioned u-shape. Then it would be an easy install. But, I don't know how the Dexter axle tube would handle the stress of the compression in it's un-supported center (will it bend or not?) and whether or not the center of the axle being in constant contact with the frame would make it act as a fulcrum, accentuating/transferring the force exerted on one spring to the other, possibly inducing sway. I, as a rule, like to try new methods differing from the normally accepted practices, just to see if they would work, but this may not be one to try out now, given the 500 mile trip coming later this week, on an untested new suspension. If the engineering cadre on this forum has any opinions on this matter, I'd like to read them. I have read so much data on bending moments and point loading that have become more confusing than clarifying in their sheer volume... making a sound decision becomes rather doubtful now. If the center mount is OK, LET ME KNOW, please. Otherwise, I'll forego the center mount (used on Camaros, Dodges, Chevelles, and some drag cars, over the differential as a pinion snubber, but not as an active shock-absorbing simulacrum), and wait until I have a little more time to install them conventionally, directly above the accepted springs/axle nexus.

 

[working on it]

After a 500 mile road-trip, and after consulting with experienced trailer builders at the BB2014 gathering, I am scrapping the bumpstop/shock absorber/active suspension idea because it simply is not needed! The frame repair I reluctantly (but successfully-luckily-welded up), new axle and springs, and maybe even the new heavier tonguebox all contributed to making the trailer ride and handle perfectly. I appreciate the advice of old hands, especially when they take the time to actually look at the pieces with me. Thanks again; now on to the next repair (I pulled the generator off its' mounting!)

 

[working on it]

After a 500 mile road-trip, and after consulting with experienced trailer builders at the BB2014 gathering, I am scrapping the bumpstop/shock absorber/active suspension idea because it simply is not needed! The frame repair I reluctantly (but successfully-luckily-welded up), new axle and springs, and maybe even the new heavier tonguebox all contributed to making the trailer ride and handle perfectly. I appreciate the advice of old hands, especially when they take the time to actually look at the pieces with me. Thanks again; now on to the next repair (I pulled the generator off its' mounting!)

After reading citylights' build thread, concerning his broken spring trouble, I am again planning to use the bumpstops, after all. I don't want to chance spring breakage. I'll cut away about 1.5" from the top of the bumpstop, creating a pocket for the axle to nest in (when in compression; no contact unless road skock occurs), when the spring closes the 3.125" gap at full compression, on the ground, and loaded (at full droop , there is a 4.25" gap).Cutting away the hard top of the bumpstop will make the bumpstop more compliant, thus softer, and can act as I originally planned to use it.

It will be mounted on the new frame reinforcement piece, upside down, with #14 TEK screws, directly over the spring/axle nexus. I'm also considering a Monroe 555002 shock absorber (4.125" travel), but with 3k lb springs and an active bumpstop, and noting the mere 1.125" difference between full droop and compression, I'd have to mount it at an acute angle of 46-48 degrees, which would pretty much render it pointless. Better to rely on the polyurethane bumpstop to dampen shocks.

 

[citylights]

Those bump stops you got are huge! I can see why you have to cut them down. I am considering some too. Easy fix to stop over compression on the springs. I will wait and see how stiff my springs are though.

 

[working on it]

Those bump stops you got are huge! I can see why you have to cut them down. I am considering some too. Easy fix to stop over compression on the springs. I will wait and see how stiff my springs are though.

After adjusting my rear brakes on my HHR today (a necessary, regular chore on HHRs), I started the construction of my "active bumpstop" suspension addition. Yes, I had to cut away some material from the 4.5" tall stops in order to fit them in the spot I want, and to keep them in constant contact with the axle (making them always "active"). And even more critical, the bumpstops needed softening (decreasing their normal smooth-road stiffness, yet leaving them progressively stiffer when under heavy compression). To do so, I used a 2.25" holesaw to cut away material down to the first level of poly (below the first void).

I also cut some 3/16" 2'x2' angle to weld them to, and then the assembly can be bolted to the frame rail, using one existing bolt and two additional #14 TEK screws as further anchoring. I plug and perimeter welded one together, but ran out of wire. Stay tuned to this channel....

• 
  bumpstop insertion point
• 
  inverted installation
• 
  will nest under frame rail,between u-bolts
• 
  axle will fit into bumpstop
• 
  holesaw used to cut away material
• 
  bumpstop with material removed
• 
  welded to angle, mount hole drilled

As I was composing this post, my wife returned home from her errands...and told me where she put the wire (I left it on the kitchen counter, a no-no). I finished welding the first, and did the second one, ending just now (twilight). I have to re-build our '02 Dixon mower tomorrow (parts finally arrived), so I don't know when I'll get to the trailer.

 

[working on it]

Yes, I had to cut away some material from the 4.5" tall stops in order to fit them in the spot I want, and to keep them in constant contact with the axle (making them always "active"). And even more critical, the bumpstops needed softening (decreasing their normal smooth-road stiffness, yet leaving them progressively stiffer when under heavy compression).

Didn't work on anything all day; went shopping with the wife and had a steak for lunch! Upon returning home, I whipped up a MSPaint photo

to try to explain how the active bumpstop will work as a shock, to show a guy at work who routinely overloads his trailer (cargo-only hauler) why bump stops are good to have, and how I think my "active" bumpstop will work as a cross between shock absorbers and solid bumpstops. It's intended to act like a hollow rubber spring and stop combination. Since I had modified a polyurethane bumpstop to be used much the same way on my S-10 years before, this method came to mind. If it is too stiff (my S-10 rode like a logging truck when loaded, on a much more solid polyurethane piece), I can sever (in half, but not removing it) the # 3 ligament to soften it (the surrounding poly will act even more-so as a hollow spring), while the solid poly base will act as a final "stop" to prevent frame contact. If further mods are needed, the whole thing is a bolt-on, easily removed. P.S. I just weighed the pair of stop assemblies...I'll be adding 15 more lbs to my trailer (approaching 1750 again!). At least they're at axle centerline.

 

[48Rob]

I don't understand why bump stops are needed?

If your axle is hitting the frame, the springs are not rated for the weight they carry, or the shackles are too short.

Shocks are for soft spring setups to keep the vehicle from excessive bouncing.
If the trailer bounces so much as to need shocks, it may need springs designed to carry more weight.
Once the proper springs are fitted, shocks are not needed.

Am I missing something in your explanations, or are you just trying to plan for every circumstance thinking that some day you might bottom out?


Rob

 

[citylights]

I don't understand why bump stops are needed?

If your axle is hitting the frame, the springs are not rated for the weight they carry, or the shackles are too short.

Shocks are for soft spring setups to keep the vehicle from excessive bouncing.
If the trailer bounces so much as to need shocks, it may need springs designed to carry more weight.
Once the proper springs are fitted, shocks are not needed.

Am I missing something in your explanations, or are you just trying to plan for every circumstance thinking that some day you might bottom out?


Rob

I don't know about working-on-it, but I am installing bump stops for offroad use. I broke a 1000# spring (2@2000# total) on a 1750# teardrop off-roading. I will be installing 1400# springs (2@2800# total) with bump stops. The springs are rated right, but the may not take shock loading from an offroad rock or pot hole, so I will install the bump stops.

I should add that my bump stops will be placed so that the spring will only contact them at about maximum spring deflection. The bump stops will only be in use to protect the spring from deformation or breakage. If the bump stop is used the remaining force of the compression will be transferred as a jolt into the trailer frame and teardrop body... Better than breaking a spring on the trail.

 

[working on it]

I don't understand why bump stops are needed?

If your axle is hitting the frame, the springs are not rated for the weight they carry, or the shackles are too short.

Shocks are for soft spring setups to keep the vehicle from excessive bouncing.
If the trailer bounces so much as to need shocks, it may need springs designed to carry more weight.
Once the proper springs are fitted, shocks are not needed.

Am I missing something in your explanations, or are you just trying to plan for every circumstance thinking that some day you might bottom out?


Rob

Remember, I had a spring hanger break and I reworked everything, spring-wise, and since I wish to keep my work intact, l wanted to use energy absorbing devices to prolong the life of the components. First thought was a airbag, but I've had them fail me twice before, or a hollow air spring, which I haven't used before and are rather expensive. Then I considered shocks and of course a bumpstop (in any case, a necessity). But, I reverted back to what I've experience with, polyurethane bumpstops. So that is why I'm trying to make an all-purpose piece. Plus, I like to try new approaches, and just "working on it".

 

[KCStudly]

I have automotive springs with shocks and bump stops. The bump stops are positioned to keep the shocks from bottoming out and being damaged. On my trailer this is the bump stops' primary function.

The long soft Jeep YJ rear springs on my trailer are rated at 765 pounds each (1530 total) which is my upper design goal fully loaded. (I'd rather see it down around 1200 when loaded... they may end up being too soft... we will see.) The idea is to let the spring work rather than just be stiff. So a wider longer spring can carry the load while still allowing articulation over whoops and whatnot. The shock is there to dampen unwanted oscillation but does not support any load; it is not a spring. The stop is there to provide a rapid deceleration rather than a hard stop when the suspension bottoms out, but none the less, it is still a stop. Unless a wheel takes a hard hit the springs and shocks will do their thing as designed with a nice range of motion.

Frankly, I think WOI is headed in the wrong direction with this mod and will end up with an extremely stiff riding trailer with zero , or near zero, range of motion. Bump stops are not shock absorbers, they are stops. By pre-loading the axle into the stop I believe that you will create a much firmer spring rate, if not eliminate all spring action entirely. Think about it, taken to the nth degree, you are just one step away from adding a solid block between your axle and frame. What good would that do? Maybe start bending or breaking spindles?

 

[working on it]

KCStudly[/b]":tizs0qxy]...
Frankly, I think WOI is headed in the wrong direction with this mod and will end up with an extremely stiff riding trailer with zero , or near zero, range of motion. Bump stops are not shock absorbers, they are stops. By pre-loading the axle into the stop I believe that you will create a much firmer spring rate, if not eliminate all spring action entirely. Think about it, taken to the nth degree, you are just one step away from adding a solid block between your axle and frame. What good would that do? Maybe start bending or breaking spindles?

working on it[/b]":tizs0qxy]...considering a Monroe 555002 shock absorber (4.125" travel), but with 3k lb springs and an active bumpstop, and noting the mere 1.125" difference between full droop and compression, I'd have to mount it at an acute angle of 46-48 degrees, which would pretty much render it pointless. Better to rely on the polyurethane bumpstop to dampen shocks.

I considered shocks, which probably wouldn't dampen a thing on my trailer springs, which are short and stiff compared to automotive types, which can utilize shock absorbers better ("The long soft Jeep YJ rear springs on my trailer are rated at 765 pounds each (1530 total)"). I intentionally picked 3k springs over the 3.5k springs to gain some flexibility, but at the same time, strong enough to take the load , with a 2:1 factor. I fear that the 1750 lbs-at least 1200lbs of which is "sprung weight"- will be oscillating on those springs countless times, and sooner later, metal fatigue will have its way (=breakage), so I wanted to try dampening those oscillations, and polyurethane is widely used for such applications. My bumpstops, upon arrival, surprised me with their size and stiffness- had I ordered the wrong compound? I decided to save those parts for another use, down the road. But, I examined them closely, and decided that they could be modified to suit my needs. By eliminating the rigid top structure, and using the flexible inner "ligaments" like hollow balls, the flexibility would be magnified, progressively stiffening, and still perform ultimately as a "stop" upon full compression. The "ligaments" are easily deflected by finger pressure, yet upon complete collapse of the triangle shape, firm up greatly (equaling a 2" bumpstop to protect against frame contact, more than enough to prevent spring ). And, if even the current configuration proves as stiff as you warn, then by severing or even removing the penultimate ligament, I can tune the firmness to practically nil.

If proven an untenable design, I can remove the piece(s) in a minute.

 

[48Rob]

WOI.

Nothing wrong with experimenting.

I was just curious why you were taking the long road around a short problem.

If the setup works as you hope, won't the blocks limit travel in an extreme situation, such as a pothole on one side, and a speed bump or the like on the other?
If it did limit travel, it would place a lot of pressure on the axle, and frame at the point of contact.
Probably not a big thing given the relative light weight and short length of the frame, but something to consider.

Rob

 

[working on it]

Rob- that's exactly what I'm doing- experimenting. At first look at the bumpstop, un-cut, it has the potential of creating a very hard secondary impact on the axle tube (I'm not worried about frame impact, thru the two pieces of angle stock- that load will be spread out over a large area). But the poly, after modification, is really quite pliable (now), and will only stiffen up progressively, after the springs flex upward a lot. What is most important to me is to limit the extreme push/pull on the rear hangers (the hangers are pushed rearward on a compression cycle, and pulled forward on rebound) as the springs flex. If there is a weak link in my new axle's suspension, it would be found at the rear hanger to frame attachment point. This "soft bumpstop" should limit travel just about enough to prevent it from ripping loose (as my first set-up did). (edited for clarification)

 

[working on it]

Rob- that's exactly what I'm doing- experimenting. At first look at the bumpstop, un-cut, it has the potential of creating a very hard secondary impact on the axle tube (I'm not worried about frame impact, thru the two pieces of angle stock- that load will be spread out over a large area). But the poly, after modification, is really quite pliable (now), and will only stiffen up progressively, after the springs flex upward a lot. What is most important to me is to limit the extreme push/pull on the rear hangers...

I just returned from a short trip to Cleburne State Park, where I experimented with various sidetents, sidetables, food storage and usage, water consumption, trailer loading, truck-bed loading, bathroom use!, ice requirements...everything I could think of, for deciding what I need and what I do not need. I also used the occasion to test my trailer hitch phobia (I actually towed home without using my Weight Distributing spring-bar attached!- first time in years) And I intentionally ran my trailer wheels over (minor) potholes and whoop-de-doos (as I neared home), as the penultimate test of the active bumpstop concept. Perhaps a better name for the piece would be "a progressive, multi-stage, shock dissipator". I set some items in strategic locations inside the trailer, to measure how much displacement occurred going over bumps. And I watched the effect on the trailer for each bump as it occurred, in my mirrors. Not scientific, but it gave me an idea of how my design was faring. I normally tow with the WD hooked up; it limits the movement of the trailer, since the much heavier tow vehicle exerts a stabilizing influence on the trailer over rough roads. When I removed the WD hitch, I could see more reaction from the trailer, but the difference was not as much as I had expected. The test objects inside the trailer were all moved, but not far; since I left the ligament between bumpstop sides attached, I see now that if I sever it (#3 in the photo), the remaining harshness in compression will be reduced to a negligible amount.

As I intend to eventually convert to an off-road multi-axis coupler (kudos to Woodyperk6), I'll need the added "give" in the suspension. Testing will continue, as I am an inveterate, unabashed, incessant tinkerer.