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Thread: The "bomb proof" diff mount

  1. #1
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    The "bomb proof" diff mount.

    Hello all,I wanted to present a new creation of mine that I came up with out of frustration over a slightly less than stellar item on our cars.I have 2 e24's in my life that I care for including my own and both have needed new diff mounts.This seems reasonable on an 80's vehicle however in looking at the part it is clear to me that this must be a common issue and from what I have read online it is.So to the point, I have designed a beefy replacement diff mount that is not only far stronger but has replaceable urethane bushings so the unit itself is essentially rebuild-able.

    I am not a stranger to fabricating and marketing parts but I have not done so in some time,however I decided to get something going again and I think this is where I will start.The pics and specs are listed below.

    This unit pictured is a prototype and is the unit that will stay on my car.With enough interest I will be Building jigs and getting prepped to make a run of these.I have learned in the past not to jump into offering an item to market without first testing and getting some feedback.My problem here is that I don't currently have access to a running car to do so myself so I want to present an offer to fellow forum goers to help me out.

    This is what I would LIKE to do.If anyone one is interested I would be willing to ship 5 of these units out to willing guineas at 75% cost compared to what I feel I need to get when producing these.The only requirement is that the person to request must have a running e24/e28 that they can install the mount into ASAP and and put some miles on it.I am fully confident in the unit but I wont go ahead until I have some legitimate opinion based on road testing.

    Upon approval from buyers and after any needed changes are made, I will go ahead and offer a group buy to the forum and possibly other forums as well.From what I have figured I think I am going to shoot for something in the $175-$195 per unit range.It wont be worth my time at any less than that and I think considering you wont have to buy another it int bad compared to $80ish for an OEM piece.Also the bushings are readily available at local parts stores and are inexpensive,not to mention you probably wont need to replace them anyways.

    Anyone interested should understand that there is obviously going to be less deflection in the diff due to the added rigidity,this is not a "solid" mount by any means but this item may be more suited to those concerned about putting down additional torque and not so much those obsessed with the smoothest possible ride.However until testing I don't know just how it will feel and it very well may be that there is nothing but a positive difference...we will see.


    Rough specs:

    Back plate reinforcement - 1/8 "

    Brackets and bushing bores - 3/16's "

    Diff mounting tab - 1/2"

    Bushing through-pin - 7/8' solid bar

    Weight - not sure yet, roughly only about double the stocker surprisingly...weight weenies beware

    All parts are TIG welded,plasma cut and will be acid dipped and painted one of possibly a half dozen colors or so.I also will include hardware which is needed to clear the bushing.If anyone wants un-coated I can do that as well,at this point I most likely will not get into powder-coating them.

















    This is essentially what would arrive at your door



























    So,as I stated if anyone is interested and follows the criteria I would like to treat this as a first come first serve in terms of those to receive test units.If I get 5 people to agree I will collect needed materials,get them fabbed up and will not request payment until I am ready to ship (give or take 1 week).Also keep in mind that I stand behind everything i make 100%."If I make it and you break it,then back I will take it" .Please contact VIA PM if you would like in on the deal,and anyone who would like to comment on future interest please do so.I really need to get an idea of how many would be interested in this,thanks.
    Last edited by GI Jonas; 05-12-2015 at 02:04 PM.

  2. #2
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    Looks nice. Does it transmit any vibrations?

    Also, the next weakest link is the structure it's bolted to. They have been know to crack in that area.

    I'm pretty sure I would be in for one.
    Last edited by ShapeShifter; 02-13-2012 at 10:42 PM.

  3. #3
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    Very nicely done. I'd like to see one in a finished paint.
    Tom
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    ...

  4. #4
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    Looks nice! You might want to post on the E23 and 28 boards for additional interest
    00 740iS
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  5. #5
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    Quote Originally Posted by ShapeShifter View Post

    Also, the next weakest link is the structure it's bolted to. They have been know to crack in that area.
    .
    IMO it would probably be ok because the diff can rotate on the bush rather than transmit force to the place it's mounted on.
    I don't think the diff would transmit a lateral rotational force, or much anyway.
    1986 Euro RHD 635 auto Zinnerberot / Natural Buffalo
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  6. #6
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    Quote Originally Posted by Flash635 View Post
    IMO it would probably be ok because the diff can rotate on the bush rather than transmit force to the place it's mounted on.
    I don't think the diff would transmit a lateral rotational force, or much anyway.

    Agreed.
    Last edited by GI Jonas; 02-14-2012 at 12:10 AM. Reason: incorrect info

  7. #7
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    I was getting car wood looking at the pics.

    I am a little dismayed with how much strengthening these cars need in particular places when you consider how much they cost when new.
    A lot of the parts are only just strong enough to hold on with very little safety margin.
    1986 Euro RHD 635 auto Zinnerberot / Natural Buffalo
    1997 Ford Explorer
    1996 Ford Mondeo dead
    1986 525e gone
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  8. #8
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    What kinda price are we estimating here? I may be interested in on for my e28.

    Looks like a very nice piece, I would take one raw and paint it myself I think.
    1988 BMW 535is - 5spd - H&R - Magnaflow Exhaust
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    Certified tire technician, 7+ years experience. Send me a PM if you have any questions.

  9. #9
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    I would be interested. Let me know your price. Pink might be nice.
    demet
    88'535is, 88'M5, 89'535i, 01'525it

  10. #10
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    Price is in the post folks .I posted a link at e28 forums and have about enough people on board for a test run of these.Anyone serious should send me a PM.I am only counting those who are sure they want to be a tester and those who can get on it soon.Im going with $135 shipped on test units.

    thanks

  11. #11
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    nice looking assembly, and it looks very well thought out. I do have one question, potentially it looks like the diff could move side to side under heavy corning. I could be missing something, but I am assuming the output shafts will have some flex in them and won't keep the diff fixed.

    Again, not complaining, I like the concept. Just making sure all possibilities are covered.

    Thanks,

    Eric

  12. #12
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    What's your fab time/ shipping schedule looking like?

  13. #13
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    I will comitt to one of these for my race car, even if I dont use it immediately. I fabbed up this over a year ago but it hasnt been track tested yet...



    http://bigcoupe.com/phpBB2/viewtopic...858&highlight=

    Erik Brannfors
    RedShark Racing http://www.brannfors.com/
    1988 M6 #71, SPM
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  14. #14
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    I'm going to post what I posted over on MyE28:

    That looks rock solid for sure. I have a question or two, though. What is the plate for? Do you weld it to the body for structural reinforcement? Do you think maybe you have made it overly bomb proof? Not saying it should be made weaker, just that it may be possible to reduce welding time, material costs, and cost to the customer if you made it less massive.

    Good luck. I love to see stuff like this out there.
    _________________

    It is a good design and would definitely be bombproof. Looking at it more closely, I would add something to prevent the back of the diff moving side to side. If you make the center a tube rather than a bar and run a long bolt through it, you can put fender washers on either end to prevent lateral movement. It would add very little cost and no additional fabrication time.

    If you want additional pointers, send me an email through the board and we can talk about optimizing the design for effectiveness, cost, and ease of production. I'd also be interested in carrying them on my website.

  15. #15
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    I want to post a link over to the e28 board.However I will try to stay in the conversation in both threads. http://www.mye28.com/viewtopic.php?t=101969.

    Here is just a copy paste of my response over there.

    Thanks for the attention guys,I'll try to respond in some order here.First off is the confusion about the backing plate.In all honesty I am not entirely sold on that particular parts necessity myself,however I though it was a good additional measure as far as spreading the load.The mounting area on the car is a bit thin,but it is possible that it can be omitted without issue,but I have yet to regret piece of mind from overbuilding something.And to answer the mounting question,moosehead is right as far as it being basically a spacer that the mounting bolts pass through...no welding.

    Quote: On bf someone asked about lateral movement, should that be a concern?

    If you look at the mount you will be able to picture that no movement of the diff is eliminated in any plane or direction, but rather DECREASED in all directions.Is this an issue? well this is why I need some folks to test the unit.I am not offering a handful of miracles here just hoping to make an improvement on a weakness that i see.I do not have a lab laden with calibrated test equipment and wouldn't use it if I did.I know that at the end of the day real world testing and street miles are the ONLY thing that really counts.Many questions will be answered after it gets some time on a few cars.

    Quote: I would add something to prevent the back of the diff moving side to side. If you make the center a tube rather than a bar and run a long bolt through it, you can put fender washers on either end to prevent lateral movement. It would add very little cost and no additional fabrication time.

    I considered this as well.However with the diff being solidly mounted to the sub frame I think any side to side "walking" of the rear of the diff would signify that you have bigger issues.I also didn't want to compromise any of the integrity of the pin,though Im sure a good chromoly tube would do the trick.I think though if i did go that route I would just drill and thread the ends of the rod on the lathe.

    It looks at this point like I have a half dozen folks or so who have contacted me with the interest in taking a test unit.I am going to be sending a PM to all interested here and at BF to solidify their intentions.Once done I hope to have these units ready to go by late next week,then we can see whats really going to happen.Either it will not be worth the time and energy or Im going to get some good input that will inspire me to get the ball rolling.Once the test units are out there it will be up to the testers to answer all your questions, without any bias.

    Thanks,Jonas

  16. #16
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    Remember that the rear diff mount also resists the forces trying to twist the subframe about the Z axis of the car as well lateral lateral loading due to cornering. Allowing it to float laterally takes away some of this resistance, which is generally a bad thing. The forces on this would not cause issues with a tube vs. a solid bar. If you plan to make these as a production piece, you have to think about totaling up your time and tooling requirements. Why bother boring holes, and doing a bottoming tap, two operations that require time and tooling wear, when you can just cut a tube to length?

    http://www.onlinemetals.com/merchant.cfm.....p;id=250&top_cat=0

    In addition, I would use a U channel for the mount tab instead of flat bar with those formed straps. Cut a 7/8" channel across it with a ball mill and mate the tube to the U channel with 2 or 3 welds. I'd also be tempted to use a weld nut rather than tapping that hole. Remember, the tab it is bolted to is cast aluminum. It doesn't need to be super thick, and neither does the tube (though I know it is 7/8" to gain bushing size.)

    You also spend a lot of time welding those bushing tubes all the way around on both sides. Considering the direction and magnitude of the forces on those parts, this is unnecessary time, filler, and welding gas spent and potential extra heat to warp the part.

    Anyway, those are my $0.02. Take them or leave them.

  17. #17
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    All good points.And you are certainly right about cornering loads.Consider a pin retainer done on the test units!As far as the production is concerned I already have many ideas on improving the design for building multiple units.What is pictured is just a prototype,it works but yes the end product will be of better quality and more efficiently put together.The one you see was made from my box of scrap

    Good stuff guys,keep it coming.

  18. #18
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    You definitely don't have any quality issues there, just time sink issues that might reduce the financial viability of the project. Nothing like having to give up because it costs too much to make.

    BTW, here is the U channel I'd use- McMaster Carr P/N 7779T12, assuming it is wide enough for the task, though you can probably find a wider one with the same 1/2" flanges at a metal supplier.

    I was thinking that you wouldn't need that base plate if you changed the design a little, but I like the idea that you could weld it in place to reduce the chance of cracking that Porsche Dude was talking about.

    I had been thinking about making something like this using BMW mount bushings from an E34, but this thing looks like it'll work just fine (and saves me the trouble of developing it.) Those poly inserts are probably cheaper and just as effective at noise isolation. Now if the initial units prove to be too noisy, I can see ways to make that change with your basic design.

  19. #19
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    I am also interested - 1 or 2 units...

  20. #20
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    Does the diff need lateral control seeing as it's bolted to the subframe?

    If so, the bar could be a bit longer and circlips fitted to retain the bush and prevent lateral movement.
    Squeaking might be a problem, I know it's common to fit PU bushes with moly grease but I find that it can dry and gall the bushes. Teflon grease would be better or dry graphite.
    You can also get PU bushes impregnated with moly or you could use phosphor bronze.
    Another alternative is to drill the bar and fit zerk grease nipples.

    I think I'd use teflon grease.
    1986 Euro RHD 635 auto Zinnerberot / Natural Buffalo
    1997 Ford Explorer
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  21. #21
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    Quote Originally Posted by Flash635 View Post
    Does the diff need lateral control seeing as it's bolted to the subframe?

    If so, the bar could be a bit longer and circlips fitted to retain the bush and prevent lateral movement.
    Squeaking might be a problem, I know it's common to fit PU bushes with moly grease but I find that it can dry and gall the bushes. Teflon grease would be better or dry graphite.
    You can also get PU bushes impregnated with moly or you could use phosphor bronze.
    Another alternative is to drill the bar and fit zerk grease nipples.

    I think I'd use teflon grease.
    I think the lateral movement is enough of a potential issue to justify an easy bit of insurance on it,It shouldn't move MUCH,but a little is enough to cause undue fatigue and likely performance problems.

    As far as the squeak,I doubt it. the pin isn't going to be pivoting on those bushings like a control arm.Any pivoting will be slight enough I do not see them making noise,of course lube is good anyways and the fit is tight enough it needs it anyway for installation.I am really hoping these bushings work well as they are readily available and are a good durometer.What exactly I don't know but they are notably more supple than typical aftermarket poly bushings,sometimes more akin to black stones.

  22. #22
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    That looks great. If I hadnt just replace mine I would totally try one of those nice job looks like you could run doughnuts all day and not worry about losing your rear end

  23. #23
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    Great design and rework!
    What I'd be worried about is not so much the re-design of the mount but BMW's use of one hold down attach bolt. That's pretty lame if you ask me. You could design all the strength into the mount itself but the one bolt that attaches the case to the the mount will find some way of coming loose. In fact even more so now with your strengthened design as it will be less forgiving to the attach bolts and hardware. It was mentioned by another poster that a welded nut to the plate would be better than a tapped thread on a thin plate as you have it now. In any case the more rigid the mount, the more stress on the attach hardware. The original rubber mount "gave" a lot which put less stress on the attaching hardware.
    '88 635, '92 325IC

  24. #24
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    Guys I did a quick rework and made up sketch.Im thinking of using the idea of channel in 3" width mounted to the pin and also flipping the bushings as suggested.The channel would act as the lateral stop against the bushing flange as well as being the diff mount.This also allows for using the stock hardware which was impossible before.Also considering flipping the channel opposite of whats shown so that it actually saddles the "horn" of the diff cover preventing it from deflecting and making contact with the brackets.Let me know what you think.









    Great design and rework!
    What I'd be worried about is not so much the re-design of the mount but BMW's use of one hold down attach bolt. That's pretty lame if you ask me. You could design all the strength into the mount itself but the one bolt that attaches the case to the the mount will find some way of coming loose. In fact even more so now with your strengthened design as it will be less forgiving to the attach bolts and hardware. It was mentioned by another poster that a welded nut to the plate would be better than a tapped thread on a thin plate as you have it now. In any case the more rigid the mount, the more stress on the attach hardware. The original rubber mount "gave" a lot which put less stress on the attaching hardware.
    Unfortunately you are right.However there is only so much I can do here!

    Every time you strengthen one thing you open a can of worms for breakage elsewhere,just look what happens when you boost a motor

  25. #25
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    Quote Originally Posted by GI Jonas View Post
    Guys I did a quick rework and made up sketch.Im thinking of using the idea of channel in 3" width mounted to the pin and also flipping the bushings as suggested.The channel would act as the lateral stop against the bushing flange as well as being the diff mount.This also allows for using the stock hardware which was impossible before.Also considering flipping the channel opposite of whats shown so that it actually saddles the "horn" of the diff cover preventing it from deflecting and making contact with the brackets.Let me know what you think.








    Unfortunately you are right.However there is only so much I can do here!

    Every time you strengthen one thing you open a can of worms for breakage elsewhere,just look what happens when you boost a motor
    Great design and manufacturing but I'm not sure that this is not overkill. My OEM diff mounts seem to l last many hundreds of thousand miles and are relatively cheap and easy to replace.

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