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Rod End Selection for link suspension..... Sizing / Safety Factors

Discussion in 'Center Of Gravity' started by Greg72, Nov 4, 2003.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I'd like to solicit information on how other people select rod ends (or equivalent products) for link suspensions.


    Some of the offline discussions with Triaged taught me that it's possible to calculate the actual loads on the link ends....so it's not a total "W.A.G." (Dan suggests a 10X safety factor on front end stuff, since it involves steering and can KILL you!)

    The key specification is the Radial Load, which is spec'd in psi? It's pretty easy to find rod ends that go up in the neighborhood of 55,000 psi. That's pretty good, and if you play around with the link seperation distances of your suspension design, you can keep the loads within this range. (More separation means lower loads).... (By the way Jason, if you create brackets with multiple mounting holes, these loads are going to change, so you/we/I will need to be sure to calculate all the different positions to determine the "worst case" load scenario! /forums/images/graemlins/thinking.gif)


    The catch:

    1. A rod end that actually supports 55,000 psi is around $100 ea. If you design a link suspension that needs 7 or 8 of these....you're spending LARGE cash!

    2. They don't last forever by their very nature....so that $700-$800 investment, is going to become an ongoing expense if you put a lot of miles on your rig.



    Some Ideas:

    1. Revise the suspension design, making some concessions to link separation (further apart) which will reduce the loads (and therefore allows you to use a lower rated, and CHEAPER rod end)

    2. Find an alternative to a rod-end....like a Johnny-Joint, or Spherical Ball Socket-type end. The only problem is that I have never seen a Radial Load spec (psi) to compare them strengthwise to rod ends....

    3. Durability and Street-Friendliness - Boy it would sure be nice to find a product that would last longer than a rod-end, and maybe contained a urethane or hard plastic insert so it wouldn't be so punishing on the street. Even an expensive end that was at least rebuildable would be a better alternative....but again, I've never seen strength specs???



    I'd like it if this post could contain a few pieces of info....


    1. Links to websites that sell appropriate products, or show specs that will help with correct rod end sizing

    2. More detailed discussion of how people are addressing these issues currently, and any BTDT experiences on particular products.





    Ready, Set.....Go! /forums/images/graemlins/thumb.gif


    http://www.aurorabearing.com/
    http://www.fkrodends.com/
    http://www.qa1.net/
     
  2. marv_springer

    marv_springer 1/2 ton status

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    [ QUOTE ]
    The key specification is the Radial Load, which is spec'd in psi? It's pretty easy to find rod ends that go up in the neighborhood of 55,000 psi.

    [/ QUOTE ]

    Greg,
    I believe the "ultimate radial load" is expressed in lbf...

    Marv
     
  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Any truth to the comment that a rod end with a zerk fitting is inherently weaker than a non-greaseable one?

    I'd believe it was true, but the spec sheets I've seen don't indicate a different spec for load.....???
     
  4. marv_springer

    marv_springer 1/2 ton status

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    I just looked at an Aurora catalog and could tell no difference in rating. Looks like they installed the zerk in an area that I'd guess would be lower stress, but still... /forums/images/graemlins/thinking.gif I don't really know.

    Marv
     
  5. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    Going with overkill helps with the zirked ends, we've started using the zirks since the teflon linings tend to beat out of the ends too easy.
    One problem with calculating link loads is the assumption you have to make for traction, there's a LOT of room in that assumption to make or break a rod end selection. This is where some experience comes in.
    Also remember that your ends may work under pure torque loads but when you drop the weight of the truck on your lower link arms, that hiem shank better be big enough to take it. That's why I'm not too fond of 3/4" shanks on lower arms, even if the forces are low enough to make it work. I've seen more than a couple of them broken from external forces, like bouncing on rocks.
     
  6. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    this is kind of a funny post. Greg, and some of the others have done a great deal of research on the link subject. what to use, what not to use, good ways, better ways, and ways that just will not work. yall are like me in one major case like this. you start thinking about the big deal no sh!t things that can, have, and will kill people if not done right, or kept in check. KUDOS on this.

    but you are missing small soloutions for small problems. this is something i SHOULD keep my mouth shut on and should just start making them and selling them.

    them is this. DUST BOOTS. if made with velcro on one end(where the link would come out to inspect the joint from time to time) and clamps on the other end they would keep the joints clean of large and most small particles. if made out of vinal(or an oild canvas like outback dusters with duckback(also read as old levis saturated with furniture wax)) they could also keep the lube in and on the joints without attracting the dust and dirt.

    this will prolong the life of the joints by far and only add around 16 ounces per joint if that.

    maybe i need to make a few. but i think to do that i would have to have a linked suspension.
    Grant
     
  7. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    [ QUOTE ]
    Any truth to the comment that a rod end with a zerk fitting is inherently weaker than a non-greaseable one?

    I'd believe it was true, but the spec sheets I've seen don't indicate a different spec for load.....???

    [/ QUOTE ]

    dealing with a slightly different type of rod end on helicopters (belive me, they CANT fail, but you knew that already) i can tell you that most, if not all, rod ends are made with "extra" material. now, from what i have seen is that the rod ends have repair limits for corrosion removal. for the most part you can remove a 16th of an inch of material before it is deemed bad. take into consideration that if this item in any one of the locations it is used fails, 2 or more people are dead. and that the loads supported are far greater than 99.9% or the folks on this board will ever put on a rod end. so, i think it wold be safe to say you COULD remove more. now, how big is the hole for a zerk fitting? the ones i use are 1/8th inch tap with 3/32nds for the grease to travel through recomended. one could put a smaller hole in and use better grease. there are also locations in a rod end that are not very structural at all, or should i say nowhere enar as structural as the rest of it. and thats where the zerk is. normaly dead top fenter, or in the back by the threads.
    again, i have done little research on them, but this is all from what i have seen on helicopters and the few rod ends i have looked at.
    Grant
     
  8. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Grant,

    Are you actually referring to an "idea" for a dust boot.....or something you have seen "in real life" (helicopter application perhaps?)...

    I know that companies sell dust caps for rod ends....really just a small version of what is on TREs or DLEs....presumably if you use greasable rod ends, the pressure of the grease being squeezed-in would help push OUT any dirt or grit that was trying to get in the joints???

    I dunno, they seem to be widely available, but nobody seems to mention them....leading me to wonder if they don't work OR maybe most people just accept the fact that rod ends wear out anyway, so they don't take even simple measures to protect them???? /forums/images/graemlins/thinking.gif

    My question did attempt to also cover the aspect of "streetability"....not just longevity. There still may be options that aren't quite as harsh as a metal-on-metal rod end....but to be fair, if I can make rod ends LAST....I might be willing to put up with the harshness.....



    /forums/images/graemlins/deal.gif
     
  9. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    Greg,
    im thinking of a new dust boot idea.
    imagine a sock in a way. but it would cover some of the tube, the threads, the rod end and the mounts at the rod end. keeping everything nice and cleanl this will prolong life of the joints no matter what kind you use.

    the problem witht he rubber boots used on TRE and DLE are that rod ends move in a bit of a different fashion. as you have seen, tey get cut easily due to the fact that they are in the path of movement. and once a small cut is made the grease they contain destroys the TRE or DLE if not tended to in a nice quick manner.

    i have never seen boots for the rod ends on the helicopters. the HH-1N i work on now does not have any large load bearing rod ends like the AH-1W i used to work on. they are HUGE. but have litle movement in them. we had boots for them, but only for when washing the AC and we never used them.

    i think im going to get some small rod ends from work and moc up a boot idea i have. then ill post up pics. it will be after Dec. 5th or so though.

    i feel is being able to prolong the use of the rod ends then one could use teflon or non-all steel rod ends and soften up the ride a bit. and still keep the cost in check a bit.
    Grant
     
  10. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    The boots already exist, not along the lines of the "sock" but more like a tre boot. I think the company is called Sealz-it or something like that. Circle track places would probably carry them. The problem I see is that they have a somewhat limited sized selection, but if they went up to 3/4 x 3/4, we'd be mostly set.

    Oh, looking at the first post:
    We can get the 3/4 x 5/8 heims or the 3/4 x 7/8 heims that are both around a 55K ultimate load for about $35-45 each. It's not really too bad. Until you buy 16 of them.
     
  11. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]

    We can get the 3/4 x 5/8 heims or the 3/4 x 7/8 heims that are both around a 55K ultimate load for about $35-45 each.



    [/ QUOTE ]


    Stephen....so by "we" do you mean customer's of ORD can get that price, or is that just you showing off?? /forums/images/graemlins/grin.gif

    /forums/images/graemlins/thumb.gif
     
  12. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    All I know is I can't wait for my 1-1/4's to be here in a few days /forums/images/graemlins/grin.gif
     
  13. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    3/4 x 7/8 with 55K ultimate radial load should retail for about $47-$50 with a jam nut. This is what I use for all my front links and my uppers in the rear.
    A 5/8 x 3/4 with 40.5K ultimate should run about $32-35 with a jam nut. I haven't set the final pricing but that's a good ball park. We keep a few ends in stock now and will be keeping more as we go.

    We're looking at carrying the Teraflex modular ends and they'll run around $100 with the urethane spherical bushing in them and I think they'll be a pretty attractive end. They use a long threaded shank so all your adjustability will be on one end which lets you use a cheaper part on the other end of the link.
    This compares somewhat favorably with the big heims I use for my rear lowers that are around $80 each and have to be bushed down for the smaller mounting bolt and don't have as much anglularity.

    I think that if you want to have links you can bash and good strong ends on them, you need to plan on spending some good money, probably $200 per link or maybe a bit more depending on the application. Going with lighter, cheaper tubing, smaller cheaper ends, and maybe even using weld in inserts will get the job done for less money, but it's not the same job as a length of 1 3/4 x 3/8" wall threaded directly for a pair of 1 x 1 1/4" zirked hiems.

    You wonder why good link suspensions cost a lot? This is a big part of it. We've been putting a lot of thought into how to build a good cheap suspension link and it's just not going to happen if you want to really bash it.
     
  14. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Stephen,

    Any specs (ulitmate load rating) on the TeraFlex item?

    I did a quick Google search and think I found a pic.... looks cool and rebuildable, with different bushing material options (street, offroad, whatever) Could be a nice option for a guy like me who refuses to give up on the plan to still drive on the street!!! /forums/images/graemlins/grin.gif

    I'd also be interested to know if you have pricing estimates on the "rebuild" kits for the TeraFlex stuff.....

    I wouldn't mind paying the $100 per link ONCE, if I could rebuild them for maybe $20??? I understand that quality costs money....and I want to build it right. I'd just like an option that gives me maximum longevity also.

    /forums/images/graemlins/deal.gif
     
  15. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    I just got a rough idea of the pricing at the SEMA show, I have to do the final stuff in the next few days so I won't know all the component prices for a little while yet. I'm a bit skeptical about replacing some of the parts after they sit in there and rust for a while, but a good press and some penetrating oil should be able to get them out. I think the real winner is going to be the TF end with spherical urethane insert on one end of the link with either a barrel bushing or a welded-on urethane spherical on the other end. Good adjustment, good angularity, minimum cost. It will probably eat bushings periodically if you don't use a pivot on one end but that's just a periodic maintenance point you have to deal with to get the cheaper arm.
     
  16. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    It seems I get to the posts late but as far as the zerked rod ends go you have to contact the company and they can give you specs on them I have used rod ends before in stuff and since there are so many vairables its nice to have someone who has used them on a simalar aplication. Note that on advantage of using a somewhat larger rod end is increased degree of misalignment up to a point. One point I run mud a little and spraying the heim out good and then putting a heavy grease on the outside does make them last longer /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif
     
  17. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Just as a followup.... Stephen had suggested seaching for those rod end caps for dirt protection, and I was able to find them:


    Seals-it:

    5/8" Hole = p/n WS6250
    3/4" Hole = p/n WS7500
    1.0" Hole = p/n WS1000 /forums/images/graemlins/thumb.gif

    Remember that's the "bore" hole size, so it looks like they have everything covered up to the 1-1/4 -12 thread BIG ends (TeraFlex, Aurora, FK) that people might want.

    http://www.sealsit.com/rodend.asp




    On to the subject of tube sizing for links.....Stephen suggested a 1.75" x .375 wall tube for a 1-1/4 - 12 rod end. This has an I.D. of 1" (duh!), so what's the correct drill size needed before running the 1.25" tap?

    I did a quick analysis of the weight penalties of running tube that THICK....and it does add up:

    36" link @ 1.75" x .375" = 16.53 Lbs
    42" link @ 1.75" x .375" = 19.29 Lbs
    48" link @ 1.75" x .375" = 22.04 Lbs /forums/images/graemlins/blush.gif

    I understand that "bashing strength" is important, but I had an idea that I haven't full worked out yet. What about using a thinner-wall tube for the link, and then grafting on a thicker section of tubing on the bottom half of the tube (where it would hit the rocks?). The effect would be like having a 1/4" wall tube on top, and a 1/2" wall tube on the bottom.....

    Potential Weight savings:

    36" = 3.0 Lbs per link
    42" = 3.5 Lbs per link
    48" = 4.0 Lbs per link


    I know, I know.....most of you don't care about saving 3 pounds on a 5500 Lbs truck, but it IS unsprung weight and could represent between 25 to 32 Lbs saved in suspension weight.....?????

    I haven't spent any time yet considering the bending loads, torque loads, etc.....the thinner wall tubing may not be properly sized anymore for other types of dynamic loads, but for rock bashing it did seem like an interesting idea.

    Any comments?
     
  18. blk87K5

    blk87K5 1/2 ton status

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    [ QUOTE ]
    Potential Weight savings:

    36" = 3.0 Lbs per link
    42" = 3.5 Lbs per link
    48" = 4.0 Lbs per link


    I know, I know.....most of you don't care about saving 3 pounds on a 5500 Lbs truck, but it IS unsprung weight and could represent between 25 to 32 Lbs saved in suspension weight.....?????

    Any comments?


    [/ QUOTE ]

    Take a crap before you go wheeling. You'll probably save more than 4 lbs per "link" of SPRUNG weight. I think you are beginning to split hairs here. Just use a piece of thick heavy tubing that will never bend, then you don't have to ever worry about it.
     
  19. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    [ QUOTE ]
    Potential Weight savings:

    36" = 3.0 Lbs per link
    42" = 3.5 Lbs per link
    48" = 4.0 Lbs per link


    I know, I know.....most of you don't care about saving 3 pounds on a 5500 Lbs truck, but it IS unsprung weight and could represent between 25 to 32 Lbs saved in suspension weight.....?????

    Any comments?


    [/ QUOTE ]

    Take a crap before you go wheeling. You'll probably save more than 4 lbs per "link" of SPRUNG weight. I think you are beginning to split hairs here. Just use a piece of thick heavy tubing that will never bend, then you don't have to ever worry about it.

    [/ QUOTE ]




    How much do you imagine that I eat?????? /forums/images/graemlins/rotfl.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/rotfl.gif
     
  20. Triaged

    Triaged 1/2 ton status

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    [ QUOTE ]
    so what's the correct drill size needed before running the 1.25" tap?

    [/ QUOTE ] You don't have a tap drill size chart on the tack board next to your computer /forums/images/graemlins/confused.gif /forums/images/graemlins/rolleyes.gif /forums/images/graemlins/rolleyes.gif

    1 1/4-12
    1 5/32 1.1563 87% thread REAMING RECOMMENDED
    1 11/64 1.1719 72% thread REAMING RECOMMENDED

    I got that from http://www.widell.com/drillsiz.html so I wouldn't have to type all of it in. Bottom line you won't be able to drill or tapp the links at home anyway so just let the shop you take it to worry about stuff like that.


    [ QUOTE ]
    What about using a thinner-wall tube for the link, and then grafting on a thicker section of tubing on the bottom half of the tube (where it would hit the rocks?). The effect would be like having a 1/4" wall tube on top, and a 1/2" wall tube on the bottom.....


    [/ QUOTE ]

    This gets into some more math /forums/images/graemlins/ignore.gif
    The equation for bending stress is M*c/I. "M" is the bending moment (or bending torque). "c" is the distance from the nuteral axis to the edge (with round tubing this is O.D./2). "I" is the moment of inertia...this is the # that makes tubing stronger than a solid rod of the same weight. When you weld some more material onto the bottom of the tube you will change the "I" of the tube. That equation isn't too bad...but you also have to find a new "c" if you were to bend the tube with extra material welded onto the bottom of the tube it wouldn't bend on the centerline any more. All of these equations are out there...have fun pluging them into the excel spreadsheet /forums/images/graemlins/thumb.gif


    BTW: links are generally considdered to be half sprung and half un-sprung.
     

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