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Thread: Help Wanted - sizing shock absorbers

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    Default Help Wanted - sizing shock absorbers



    Hey Folks,

    I'm second guessing myself on ordering rear shocks for the jeep and I wish to have some input.

    The jeep's a 1990 Wrangler (YJ) with a BDS 3.5" leaf spring lift. The shocks are the style with an eye-ring mount at each end. The shock eye studs with an at-rest suspension give an 18" eye center to eye center measurement.

    What length shock should I order? I'm looking at basic / generic shocks.

    One of my assumptions is that I'd have equal travel up and down in the leaf spring suspension. Is this a correct assumption? If yes, would think of sizing the shock for six inches plus and six inches minus of travel with a roughly 12" shock body and then have 6" of shock rod extending out of the shock body.

    If that mentality is correct, might you have a shock you'd recommend?

    Thanks

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    Default Re: Help Wanted - sizing shock absorbers



    In short, yes you are on the right track. Lots of little details that aren't worth trying to type on my phone. Realistically you will probably end up with a longer shock body and a bit less in terms of extension....in other words, instead of a 12" shock going to 24 max (doubling the short length), it may be more like a 13 shock with 11" of travel. In your scenario you'd have about 5" up travel and 6 of extension/droop. With leaf springs on a standard shackle, it's ok to have just a bit more droop than compression travel.
    I've run relatively budget twin tube shocks for a long time on my jeeps. Most all the brands are pretty much the same (almost all use the same production shock body that is made in Mexico) - how they valve them is the proprietary part. But functionally they are pretty much the same. For budget conscious, I ran Gabriel ultra with good results on the CJ. I currently have some Monroe on my 58 - it's a different vehicle with more worn out suspension, but not as happy with them. They are made in the USA though. As you probably saw, I went monotube on the CJ recently and very much liking them. I went monotube for reasons unrelated to ride quality, but even on an old leaf spring jeep, ride quality is improved, and figure I'll add them to the 58 if/when I do the suspension lift. I went rancho 7000 for those, but it's a step up in price (I found a good deal on RA for them). Gabriel also makes a slightly more budget friendly monotube that I would certainly consider, but I couldn't find the length dimensions I needed.
    ___________
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    Default Re: Help Wanted - sizing shock absorbers



    Quadratec has some on sale https://www.quadratec.com/p/quadrate...ep-wrangler-yj

    Rear only https://www.quadratec.com/products/16116_0055_14.htm

    The measurements from above for 3-6" lift:

    Extended Length: 24.94"
    Collapsed Length: 14.91"

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    Jim (December 15th, 2022)

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    Default Re: Help Wanted - sizing shock absorbers



    The best way to determine what shock you need is to remove the shock, measure between the mounting points at ride height, then flex the suspension up and measure between the mounting points again, then let the suspension go to full droop and measure again. Find a shock that fits those measurements the best.

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    Jim (December 16th, 2022)

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    Default Re: Help Wanted - sizing shock absorbers



    I poked around on the BDS site. It looks like the 3.5" lift kit would come with the NX2 85955 shocks.

    Specs can be found here:
    BDS NX2 Shock Absorber BDS-85955 | RealTruck


    • Extended Length: 28.15"
    • Collapsed Length: 16.45"

      That's at least a decent starting point to verify against your own YJ.

      You may be able to call and chat with BS customer support too.

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    Default Re: Help Wanted - sizing shock absorbers



    Thanks to all for the input!

    I did spend a bit of time, with the comments, poking about different web sites for shocks. In the end, driving by Bullhide 4x4 today I pulled in and made a purchase. There still was reasonable question as to dimension and which shock to select. I told'm the 18" eye to eye at rest measurement and it was less than they calculated (about 20"). I can see, when warmer temps arrive, jacking the jeep to measure compressed and extended dimensions - comparing them also with the static dimension (is there more droop than compression (or just how much). Instead of jacking it - perhaps when I get to a trail that fully compresses one side and extends the other I'll park and measure.

    It's curious that the counter guy (Ray / Rick?) commented on the fronts - converting them from stud and eye shocks to eye to eye like the rear. He said I'd have a much easier time finding shocks. For now, it's not an issue I need to tend. Has anyone done that conversion? Is it "solid" and reliable or do the parts tend to get bent?

    The parts seem basic:
    https://www.summitracing.com/parts/exp-690001

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    Default Re: Help Wanted - sizing shock absorbers



    With shocks in hand - Rancho RS551216 - Paul hit the mark with a recommended size!

    https://www.gorancho.com/products/sh...r-rs55116.html

    14.86 - Compressed length
    24.05 - Extended length
    9.19 - Travel

    Thanks folks - I learned a few things from your posts.

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    Default Re: Help Wanted - sizing shock absorbers



    I installed the shocks tonight. I think they're too long (or call this incentive to install a taller bump-stop).

    The compressible distance for the shock looks smaller than the axle travel distance before contacting the bump-stop. As-is, the shock looks like it will be the travel limiting factor when a wheel gets stuffed into the wheel well. What are the odds such a stuff will kill the shock? Would it survive?

    Rancho RS551216

    14.86 - Compressed length
    24.05 - Extended length
    9.19 - Travel
         

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    Default Re: Help Wanted - sizing shock absorbers



    It will eventually damage the shock. You do not want the shock to limit travel, up or down.

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    Default Re: Help Wanted - sizing shock absorbers



    IDK why I thought down was ok. It makes sense that it wouldn't be.

    It's just the weight of the axle components the the full weight of the vehicle.

    I've seen people using limiting straps, but I really thought that was just to keep coil springs from falling out.


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    Default Re: Help Wanted - sizing shock absorbers



    JGRubicon previously posted:
    "IDK why I thought down was ok. It makes sense that it wouldn't be.

    It's just the weight of the axle components the the full weight of the vehicle.

    I've seen people using limiting straps, but I really thought that was just to keep coil springs from falling out.

    "

    On a solid axle set-up, when one side is pushed up, the opposite side is forced down as part of the solid lever arm - it's not just the weight of the axle. You can pretty easily pull the piston through the bottom of the shock trashing the piston plate and bottom of housing.
    As Jim is demonstrating, one big challenge of leaf spring lifts on old jeeps is that while the lift provides clearance for bigger tires, the wheel travel will often be limited by the shock. Extended shock mounts can really help - I'd like to put them on mine - but it's usually a cut off the old ones and weld in new. Adjusting the bump stop is usually the easiest way to protect the shock - it both limits up travel on one side, but with a solid axle, that will also limit droop on the opposite side so limit straps aren't needed. Due to the typical geometry of max tire stuff, the fulcrum point is usually closer to the stuffed tire, and the longer side is the droop side, and thus the droop is usually a bit more (along with typical jeep leaf spring shackle geometry allowing for more down travel in the shackle than up). Jim....in a perfect world, if you are maxed out at around 9" of travel, I'd shoot for closer to 4" up and 5" down as compared to the 3" up and 6" down that the current ones have.
    ___________
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    Default Re: Help Wanted - sizing shock absorbers



    that looks way wrong to me, are you sure those are 3.5" lift springs? Has the shock mount been moved, or maybe because it's not the OEM rear axle they're just different?

    edit- this video is about replacing rear OEM YJ shocks and it looks like your mounts are different


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    Default Re: Help Wanted - sizing shock absorbers



    Molasses and I are in a race these days and molasses will cross the finish line first...

    The jeep, as I purchased it with the overall mods, is in very reasonable condition, but it does have a few nit-pik items.

    The front tires, at full stuff, will push up on the fenders ever so slightly causing the fender flare and fender metal to bend upward/outward. Similarly, both front and rear tires contact the body very slightly - where the wheel well curves to the under-door line. Those metal contact areas have long ago been "moved by the tire" that nothing much happens - and the tires are not being gouged / damaged by the metal. Very low burn has been to change to extended bump stops. This event has me now purchasing these axle mounted bump stops:
    https://www.quadratec.com/products/16059_50.htm

    I considered replacing the factory rubber bump stops, and might consider doing that as well, with these:
    https://www.quadratec.com/products/16054_32X_PG.htm

    The metal stops might not fit the D44 axle tube as I'm guessing those listed are sized for a D30 axle tube. They are in shipping so we'll see. If only D30, I'm good with that and they'll get mounted on the front axle with something different (the extended rubber items perhaps) for the rear.

    I am removing the "just-installed" shocks and have purchased the RS55113 model which is two inches shorter at compressed length. The Rancho web site specifies, for both models of shocks, that an aftermarket shock mount is needed - the frame mount looks stock to me. Maybe (a very low list maybe) would be to look at modifying/replacing the upper shock mount to fit a shock with greater travel.

    https://www.gorancho.com/products/sh...r-rs55113.html

    RS55113

    COMPRESSED
    EXTENDED
    TRAVEL


    12.89"
    20.29"
    7.40"

    Paul's comment of "are you sure that's a 3.5" lift spring" - certainly understandable from that photo. The spring in the photo is a BDS 004351 (3.5" lift) that was installed on 09/25/2015. I do not know what the stock spring should look like for any comparison though I'd think it to be more "flat".

    For now, the brake caliper is in my hands and the shorter shocks and metal bump stops are in shipping. A bit of movement.

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