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2G Rear Diff Bushing Options - Split Motorsports Poly Failed

Posted by 95REGF150, Mar 5, 2018

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  1. ViciousLord

    ViciousLord Proven Member

    394
    58
    Joined Jul 27, 2005
    Orlando, Florida
    Hurry! Im at a standstill
     

    Street Build 585  1

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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  2. 95REGF150

    95REGF150 Proven Member

    164
    84
    Joined Mar 7, 2012
    Elk Grove, California
    Ok well I was going to wait until I had all the parts to show what the finished product looks like but I will post these now so you can see the design. This is just a mock up, the bolts are too short and the bushing's finish is not as nice as the ones I put on the car so keep that in mind.

    The biggest problem I saw with the Split Motorsports design (on top of the fact that the liquid poly fell apart) was how they dealt with the axial forces. The diff needs to be retained front to back. Originally the OEM bonded rubber bushings handled this with ease. But anyone that has ever tried to remove one knows how tough that bond is to the outer pressed in sleeve. Aftermarket poly bushings cannot achieve this. So what you see from companies like Prothane is 2 piece bushings that go on from either side with flanges that take the axial load.

    That is what I decided to implement here. I got the idea from TSIAWD666's bushings that he posted earlier in this thread as they were also flanged. So the rear 2 bushings each have flanges and are pressed in from either side wile the differential is out.
    20180709_101359.jpg
    20180709_102441.jpg
    Inner side has to be recessed as the original non-flanged bushings were designed to have the diff cover flush with the sub frame.
    20180709_102514.jpg

    Ideally I would have liked to do all three of the bushings with flanges on both sides. However, the front bushing housing is too close to the subframe. So the front bushing is a single piece with flange on the front side only. The rear bushings take all the axial load of the diff to the rear of the car. 20180709_102532.jpg

    As you can see in that picture the bolt is now too short. This is because the addition of flanges adds length to the bushings. This meant longer aluminum crush sleeves in the center. and the OEM bolts are now slightly too short. The washers in the pictures are also smaller in diameter and thicker than the ones I used on the car.

    On to the material. These are 3D printed out of Nylon filament with a 12,000 psi tensile strength. Nylon has an excellent resistance to oils making it great for this application. It is similar in hardness to the Delrin that TSIAWD666 used in his car. Which as solid bushings make these very stiff. Really too stiff for my liking. And since my car is not a race car I decided to try something else out.

    I ran some very rough calculations. If I put 500ft-lbs of torque through the rear axles that should create a reactionary force in the bushings of about 1000lbs upward on the front bushing and 1300lbs shared amoung the rear 2. This is an oversimplification as for some stupid reason there is only 1 front bushing. They are set up in a triangle so there are some out of plane forces I am not accounting for. Still from this I figured about 1000 lbs of load was a good place to start my testing.

    I have a 5" bore hydraulic press at work so for 1000lbs that was about 50psi. I put a solid nylon bushing in the bracket from the front of the diff and laid it flat on the table. Put a bolt through it and pressed down on the bolt in double shear. It didn't budge at all. Ran it up to 200psi which is about 4000 lbs and started to see ever so slight compliance.

    Since these are 3D printed they offer me the option to play with some design changes that normal manufacturing methods do not. Namely that I can make an internal structure so that they do not have to be solid. I did some more testing on various density per volume and found what I believe to be a sweet spot. At 75% solid with a triangular inner structure the bushing starts to show compliance at around 1500lbs.

    20180709_171856.jpg
    This is what I elected to go with as my car sees the street a lot and not a lot of launching. It has been holding up well so far. The only downside would be that if you hit the 4000 lbs mark repeatedly it does start to permanently deform the bushing.

    Unfortunately I have no way to measure the true forces the bushings are receiving on the car so it is hard to put these force numbers in perspective. If you were racing or being really hard on the car I would go with solid just for piece of mind which we all already knew. Even the solid nylon would still offer some more damping than solid aluminum bushings if you were looking for an in between point. From my testing I feel the solid nylon ones would perform just as well as solid aluminum ones. There is so much surface area and volume that the force would cause the subframe itself to show compliance before the bushing.

    The non-solid nylon bushings are still very stiff and not that comparable to a polyurethane bushing. Currently I am doing some testing with Polyurethane filaments to see if I can make a set that offer more vibration damping. I just will have to test it as if it is too soft or brittle they will end up with the same fate as the Split Motorsports ones.

    I am making up another set of the nylon ones currently. I will post the pictures of the final product later this week.
     
    Last edited: Jul 9, 2018

    Street Build 1K  0

    1995 Mitsubishi Eclipse GSX
    manual · 2G DSM
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  3. 95REGF150

    95REGF150 Proven Member

    164
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    Joined Mar 7, 2012
    Elk Grove, California
    Got some pictures of my testing I thought everyone might like to see.

    First here is the hollow structure bushing in the press at 4000 lbs load. It reaches this level of deformation after about 6 cycles at this load level. At the 1000-2000 lbs load there is some compliance but no permanent deformation like this. So as I said these are working great on my car but for a race car with a lot of shock loading I would go solid.
    20180710_170250.jpg
    20180710_170303.jpg
    20180710_170424.jpg

    Now for the solid bushing test. There was not noticeable compliance at any time during these tests at 4000 lbs load. In an attempt to get the bushing to fail I increased the press to over 500 psi in this shot which is about 10000 lbs of load. You can actually see the steel bolt bending but the bushing does not give at all. I didn't feel comfortable going any higher on the press for fear of breaking the thin cast metal diff bracket. After removal from the press the crush sleeve was still tight in the bushing.
    20180710_171434.jpg
    20180710_171449.jpg
    20180710_173112.jpg

    Well that's it for now. I am waiting on the hardware to come in for this second set of bushings I'm making. Will post some pictures of everything on the spare subframe when I get it together.
     

    Street Build 1K  0

    1995 Mitsubishi Eclipse GSX
    manual · 2G DSM
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  4. wasabi37

    wasabi37 Proven Member

    63
    2
    Joined Nov 7, 2005
    Raleigh, North Carolina
    Hey Mike, this is great. Keep it coming!!
     

    Road Race Build 693  2

    1995 Mitsubishi Eclipse GSX
    423.8 whp · 378.0 lb/ft · 2G DSM
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  5. ViciousLord

    ViciousLord Proven Member

    394
    58
    Joined Jul 27, 2005
    Orlando, Florida
    Bump
     

    Street Build 585  1

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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  6. rEclipserGST

    rEclipserGST Proven Member

    1,552
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    Joined Nov 17, 2007
    Columbus, Ohio
    Yes PLEASE!
     

    Street Build 569  25

    1995 Eagle Talon TSi AWD
    187 whp · 200 lb/ft · 2G DSM
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  7. 95REGF150

    95REGF150 Proven Member

    164
    84
    Joined Mar 7, 2012
    Elk Grove, California
    Ok well here is the conclusion to my long and drawn out solution to the rear diff bushings.

    Lets start with the 3D printed nylon ones. I ended up making a set for another member on here that needed to get his car going quickly. This is the full set of 3 bushings with the front and 2 rears with the longer bolts required for this design.

    20180711_171544.jpg
    20180711_171757.jpg
    20180711_171612.jpg

    At this point I wanted to make a set for my car that was polyurethane. The plan was to use TPU filament on the printer and test that out. I had trouble with the filament being too soft and getting bound up in the printer. I have a few ideas on how to fix the problem am kind of at a stand still on the 3D printed poly ones until I implement a solution.

    Since starting the project I have always hated how there are not 2 front mounts to properly support the diff even though there are mounting holes for it on both sides. I had often seen Boston Hatcher's thread where he sells custom aluminum mounts for both sides to solve this problem. I decided to bite the bullet and buy a set.

    20180726_073448.jpg

    I'll probably never be at a HP level where I actually need them but at least it was well worth it to fix my OCD which was giving me fits about the symmetry haha. In all seriousness its a tremendously well made kit he sells. I was super impressed with how well made the aluminum mounts are and the CNC plasma cut plate that comes with them for the second mount fits perfectly ready to weld without any additional fitting.

    20180726_182231.jpg
    20180726_182142.jpg

    So with the front taken care of I was now on my own for the rear. The Hatcher mounts have polyurethane bushings in them. So I knew I needed 2 for the rear that matched in material. I figured the easiest way to accomplish this would be to machine a set of rear bushings traditionally on a lathe. This was even easier now, since the bushing design for the OEM front mount was the only one that required any type of machining that couldn't be done easily on a lathe.

    I checked the shore hardness of the polyurethane on the Hatcher bushings and found them to be near 95A. This was perfect because that's pretty much as soft as you can go on Poly to be able to mill/lathe it with normal metal cutting tools. I picked up a 2.5" diameter black 95A poly bar online and borrowed my buddies lathe. Here is what I ended up with:
    20180725_215629.jpg
    20180726_160637.jpg
    20180726_162427.jpg
    20180726_162452.jpg

    A few of the surfaces got a little rough but I was pleased overall for my first go at machining polyurethane. And even better now I had matching front and rear polyurethane mounts. From this point all I had to do was assemble it. You can see here with this design why the longer bolts are needed to return the thread engagement to factory. (New bolt Right, OEM bolt Left)
    20180726_165943.jpg

    Here's the subframe all assembled:
    20180729_134705.jpg
    20180729_134709.jpg
    20180729_134735.jpg
    20180729_134719.jpg

    And Finally, In The Car:
    20180801_203011.jpg
    20180801_203033.jpg
    20180801_202928.jpg

    Taken a lot of work but it's come a long way from those dumb Split Motorsports bushings. Only wish I had done this from the beginning and I hadn't wasted my time with those guys. Hate doing things twice. But I don't think I'll ever have to worry about it again.
     

    Street Build 1K  0

    1995 Mitsubishi Eclipse GSX
    manual · 2G DSM
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  8. 99gst_racer

    99gst_racer Moderator

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    Joined Apr 5, 2003
    Coloma, Michigan

    Street Build 5K  67

    1999 Mitsubishi Eclipse GST
    609.8 whp · 541.2 lb/ft · 2G DSM
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  9. kenny2gdsmturbo

    kenny2gdsmturbo Probationary Member

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    Joined May 1, 2015
    PALM BAY, Florida
    So Talked to a buddy of mine and Ostar Motorsports sell billet diff bushings....so if cheap solution was not found its time to break the bank Lol
     

    Street Build 1K  20

    1997 Eagle Talon TSi
    awd · manual · 2G DSM
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  10. Druclipse

    Druclipse Probationary Member

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    Joined Apr 3, 2017
    Sacramento, California
    Hey Mike,
    will you manufacturing and selling your final product? i am starting on an AWD swap and I would like to swap out the old rear diff bushings on this subframe to your bushings. i see your in Elk Grove, im in Natomas so i could swing by and pick up a set if you have any for sale.
    thanks.
     

    292  0

    1995 Mitsubishi Eclipse GST
    automatic · 2G DSM
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  11. Detail

    Detail Supporting VIP

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    Joined May 28, 2003
    Marietta, Georgia
    The NVH ever since I broke my original mounts has been absolutely horrible. I've had gen one poly and now I have full aluminum which you can imagine is LOUD. I’m not trying to break any records here, I’d just like to have a conversation in the car while on decel. Any thoughts on the noise your setup makes?
     

    333  5

    1995 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM

    727  23

    1995 Eagle Talon TSi AWD
    14.000 @ 109.000 · 2G DSM
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