k member isolator bushings

Chassis, Suspension and wheels

  1. NoCar340

    NoCar340 Well-Known Member

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    The K-member isolator bushings have nothing whatseover to do with supporting the weight of the engine. The front suspension does that, and it's completely anchored to the K-member. The bushings simply insulate that assembly from the body. Any bushing material that flexes allows the frame rails to flex independently from one another, which negatively affects the already iffy (at best) handling of the FMJ front suspension. That's why both the Mopar service kit and the MP mounts (same kits, different part numbers) were made of cast iron. It's still the best option if you can find it, and even with those in place the ride is still more cushioned than in any A, pre-'73 B, or E body. There's almost enough rubber in the stock FMJ front suspension to start a tire company. :eusa_doh:

    Personally, I won't consider anything but solid metal isolators for my own car. If I have to make them, so be it.
     
  2. tallboy

    tallboy Member

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    Of course I know the bushings don't support the weight of the engine, I expressed myself unclear, sorry for that. But a too flexible, not very well designed k-member, softly mounted in 4 corners, will be subject to greater sideways forces and flexing and twisting forces from a heavy engine. A bigger engine is usually is more powerful as well, which means even more strain on the bushings at the anchor points.

    tallboy
     
  3. BigWhip

    BigWhip Member

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    Does the solid metal isolators squeak any?

    Michael
     
  4. Mr.Lopar

    Mr.Lopar Well-Known Member

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    nope, got the aluminum ones in my 5th ave
    make sure to use locktite on the bolts. somehow my left rear bolt fell out and I lost that biscuit
     
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  5. krytellan

    krytellan Active Member

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    In prepping for the rear spring job I'll be doing in the next couple weeks, I decided to get under the car to check out the k-frame bushings to see the status. They look really good, in that there is no cracking or other wear that I can see. Which led me to wonder if there is any inherent benefit to replacing these bushings with the parts mentioned above? If the stock bushings seem in relative good shape, is there a noticeable gain to be found by replacing them with aftermarkets?

    Which then led me to wonder further. Are there any other suspension related parts or bushings that would yield noticeable gains as an upgrade to the stock setup? That is, if I were to do a "midlife cleaning" of my wagon, are there relatively low cost upgrades I can make to make the driving more solid (other than rear springs)?

    Thanks guys.
     
  6. jasperjacko

    jasperjacko Well-Known Member

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    For what it's worth, My Modoba has all stock style rubber bushings everywhere. It's not an autocrosser, but it handles fine for a cruiser and the occational drag strip trip. From 100mph, hard braking causes no squirmy wandering feeling at all. All the components are new however. I just loved the feeling of a brand new stock type suspension with no play. Even new stock parts , it will be way better than the old ones.
     
  7. Poly

    Poly Well-Known Member

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    We finished installing these on our 83 Cordoba a couple of days ago. The old ones were the consistency of marshmellows. Got red ones just to show off at the next inspection. Fit fine. The most difficult part was unbolting and blocking up the steering gear, but all went well. 006.JPG
     
  8. BudW

    BudW Moderator Staff Member

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    The B and R-body mounts are the same as FMJ-body mounts – but the front and rears are reversed.
    I “Think” FMJ has “R” or “Rear” in the front holes and “F” or “Front” in the rear holes – but could be wrong. The larger mount will only fit one way.
    When looking for mounts – any mention of B-body – then you found what you are looking for (B, R, F, M or J-body).

    I do recommend Cast Iron (if a person can find a set) or Aluminum. Poly is far better than stock – but in my opinion, not quite as good as the metal versions are.
    On scale of 1-10, Metal would be a 10 and stock rubber would be a 1 (or maybe 0), the poly would be a 7 (my guess).
    If I had a K-frame removed from any FMJ car, I would not reuse the rubber mounts (new or used).


    What FFI wants is way too much (and I already have a set of FFI mounts), so I’m looking for a cheaper alternative for my second car.
    http://www.firmfeel.com/fmj_body_mopar_sub_frame_isolators.html

    Pictures and measurements of the cast iron version are located at https://www.forfmjbodiesonly.com/classicmopar/threads/solid-pucks.5656/page-3#post-63890 post # 49.

    I have a set of FFI aluminum mounts and placed the measurements somewhere in our forums, but after a quick search, I could not locate my forum post.
    I would think it wouldn’t be hard to make a set – says someone who has no metal working experience.

    A friend of mine installed a camera under front suspension on his B-body and took it out for a spin. The engine and suspension does its job – but the body does not respond well to the suspension (if that makes any sense). He posted his videos on YouTube – but that has been a long time ago.

    On either one of my cars, I can take a sudden very sharp turn. At first, I can feel the car turning, but you can also see the body of car, not turning – for a second or two – because the rubber mounts are giving.

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    BudW
     
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  9. M_Body_Coupe

    M_Body_Coupe Well-Known Member

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    POLY mounts here, all rest is new rubber with the exception of rear sway bar bushings and end-links. The car does have welded-in frame rail ties though, which means the chassis is very stiff. The stock T-bars are supported with afternarket adjustable KONI shocks, which help tremendously.

    The end result: no perceptible flex. Car is tight, especially given the suspension limitations.

    While I understand the "iron/aluminum all the way" argument, I honestly have to say that for about 99% of the intended use cases a poly vs solid install will never net a difference in the final road feel.

    The challenge remains finding the iron/aluminum pieces, so given the pricing of the available part why not go poly and put the $$$ difference into other usable parts?
     
  10. Dr Lebaron

    Dr Lebaron Well-Known Member

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    There's a NOS set of cast iron in a factory box next to my couch-when I'm worm food.
     
  11. Oldiron440

    Oldiron440 Well-Known Member

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    How thick it the actual space between k member and the frame rail, I've heard just over 5/8".

    I'd settle for the knowing the side thickness of the cast iron spacers, it would be a big help.
    I will be making stock thickness spacers and I'm going to try dropping the k frame, I'd like to use a flat hood or at least a shorter one.
    Thanks
     
    Last edited: Jul 18, 2018
  12. M_Body_Coupe

    M_Body_Coupe Well-Known Member

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    Well, if all you're going to do with them is to sit on them and admire their look, c'mon man...put them on the market, clearly folks here would want to use them!!! LOL

    Look, I've got a set of the iron bricks, the aftermarket aluminum stuff and the poly stuff, which is currently installed in my coupe. I will use one of these when restoring my next coupe, that being the '81 languishing in the garage, but that'll still be a few years.
     
  13. BudW

    BudW Moderator Staff Member

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