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Thread: Rear subframe reinforcement. Weld vs. Epoxy

  1. #1
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    Rear subframe reinforcement. Weld vs. Epoxy

    Ok, so the time for me to overhaul most of my rear end is coming soon, reinforcement plates, subframe and diff bushings, etc.

    I have found a ton of info on e46 subframe reinforcements but havent had much luck with our chassis. Now the question is, does anyone here have their subframe reinforcement plates in using a structural epoxy such as jbweld, 3m 08115, or anything similar? Before I get flamed for considering it, I know of a few people who have used these compounds instead of a weld and it seems to be a popular alternative amongst e46 owners. There seems to be pros and cons of each.

    I just dont know if there are any different factors to consider with our chassis compared to the e46.

    Any input is appreciated, Thanks.

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    JB weld is not structural. Anything you buy at a hardware store or Home Depot is not structural. There are indeed industrial adhesives that are capable of replacing welding. Check with a local body shop and see what they use for patch panels.

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    Elmers.

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    Harbor Freight has several specials this upcoming month on welders. They are cheap (quality and price) but for about $300 you can set yourself up (welder, wire, helmet).

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    Quote Originally Posted by flyfishvt View Post
    JB weld is not structural. Anything you buy at a hardware store or Home Depot is not structural. There are indeed industrial adhesives that are capable of replacing welding. Check with a local body shop and see what they use for patch panels.
    I didnt plan on using jbweld, but just threw it out there to give an idea. Thanks for your input

    Quote Originally Posted by rajicase View Post
    Elmers.
    hah

    Quote Originally Posted by 1215 View Post
    Harbor Freight has several specials this upcoming month on welders. They are cheap (quality and price) but for about $300 you can set yourself up (welder, wire, helmet).
    Well, in research ive done i have read that if the weld isnt precise enough/done well enough, the heat can possible create other weak points in the chassis? I can get a hold of a welder if thats the route I decide to go, and I know some experienced welders that id have do it before I do it myself.

    That said, id like more input on the actual question in the OP. Who has used epoxies on our chassis, which epoxies have been used and worked, and why choose a weld over some of todays strong epoxies.

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    Quote Originally Posted by pmerg View Post
    Well, in research ive done i have read that if the weld isnt precise enough/done well enough, the heat can possible create other weak points in the chassis? I can get a hold of a welder if thats the route I decide to go, and I know some experienced welders that id have do it before I do it myself.

    That said, id like more input on the actual question in the OP. Who has used epoxies on our chassis, which epoxies have been used and worked, and why choose a weld over some of todays strong epoxies.
    Guess: No one.

    Why: Because it is a BAD IDEA.

    Reasons: Two of them (and they are good): First, the composite won't expand/contract at the same rate as the steel/chassis therefore causing the composite material to separate. Second, the composite material will not flex at the same rate as the steel/chassis and will therefore crack and/or separate. **there are body epoxies that are being used but for non-structural body panels only.

    EDIT: If you can't weld or if you are out of practice, don't use this as a starter project. Do you need to do this job or are you looking to add value/strength to the car "just because"?
    Last edited by 1215; 01-27-2016 at 08:00 PM.

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    Quote Originally Posted by 1215 View Post
    Guess: No one.

    I dont know that to be true, which is why I started this thread. Apparently a ton of the e46 guys are doing it and prefer it so i wanted some opinion here.

    Why: Because it is a BAD IDEA.

    Reasons: Two of them (and they are good): First, the composite won't expand/contract at the same rate as the steel/chassis therefore causing the composite material to separate. Second, the composite material will not flex at the same rate as the steel/chassis and will therefore crack and/or separate. **there are body epoxies that are being used but for non-structural body panels only.

    Good info to know, it seemed that many who vouched for welding were doing so with no science behind it.

    EDIT: If you can't weld or if you are out of practice, don't use this as a starter project. Do you need to do this job or are you looking to add value/strength to the car "just because"?
    Like I said, I dont plan on doing this or anything like it myself until I learn to weld. I can turn a wrench but i'm not afraid to admit im still learning. Im doing this because I plan to install a welded diff and overhaul my bushings anyways as they are completely shot, and I will be driving the car hard. So in the process of dropping my rear end anyways I figured id check for any cracks and do this as preventative maintenance.

    - - - Updated - - -

    Quote Originally Posted by MisterM52 View Post
    This has to be the most disturbing thread I could read in a BMW community, are these cars become so cheap that they are now owned by ...... let me now even get there.

    Are you seriously asking if SUBFRAME Re enforcement Plates that Reenforce a METAL Subframe that Twists and Tears will hold up and actually work using Eproxy as JBWELD basically magnet & alloy dust IIRC?? JBWeld is Great Stuff, I use it all the time, for small repairds where you wont see this kind of power/pressure/force as in repairing some oil pan, some plastic part/metal part, whatever...but mind you, this is not what its meant for, will you join a DRIVE AXLE with Jb Weld? Or Steel Real Weld? See Calling this stupid is an understatement of the decade. This is not STRUCTURAL. If you seriously think Eproxy can replace actual welding..then you should not be working on these cars. No offense but this is just bloody stupid..

    Grab the Re enforcement Plates, Tow it to a nearby Welding Shop, Have them do it for a bit of cash...
    Yes because after viewing a 28 page thread (http://www.m3forum.net/m3forum/showt...287849&page=23) of BMW owners that own cars that typically exceed 2x the value of ours doing it, I didnt think it was a very out of line question to ask...

    And im just a beginner and clearly new to the forums, this is why im asking questions. No need for the shitty attitude, these forums exist so people like me can get help

    EDIT: By the way, if you read the thread youd see that another forum member has already instructed me not to use JB weld in a constructive manner. There are other epoxies that exceed the strength of jb by a long shot according to members of other forums (3m 08115, Scotch dp420, etc.)
    http://www.m3forum.net/m3forum/showt...433006&page=13 another example
    Last edited by pmerg; 01-27-2016 at 08:22 PM.

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    I know nothing about it and I'm a bean counter who sits behind a keyboard by trade so this is just my opinion: If the e46 guys are doing it then why not. Do you have any more info as to what they are doing?

    My biggest issues are chemical vs. mechanical bond with the chassis (glue vs. weld) and (as can be the case with poor welds) differences in flexibility creating cracks or separation.

    If the e46 guys are doing it, and it is well documented, and it is sound/safe, please provide more info and share with us. I'm interested.

    EDIT: I have no professional background to state any valid opinion on this and as it just so happens, I am welding rear subframe reinforcements into a car this evening (metal is cooling between welds as I type this) so I do not even have a vested interest in this thread going one way or another because by the time this thread sorts itself out mine will be done and I will have no further need. I'm only interested from an educational standpoint.
    Last edited by 1215; 01-27-2016 at 08:24 PM.

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    ^^Im with ya OP.

    I am not and I doubt anyone in here is an expert on this topic;

    I would personally recommend welding them for several reasons 1215 listed. Also, its 100% tried and tested.

    If you really want to go the epoxy route, I would look for long term, successful examples on other platforms and do what they did. Dont reinvent the wheel on something like this.

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    Quote Originally Posted by 1215 View Post
    I know nothing about it and I'm a bean counter who sits behind a keyboard by trade so this is just my opinion: If the e46 guys are doing it then why not. Do you have any more info as to what they are doing?

    My biggest issues are chemical vs. mechanical bond with the chassis (glue vs. weld) and (as can be the case with poor welds) differences in flexibility creating cracks or separation.

    If the e46 guys are doing it, and it is well documented, and it is sound/safe, please provide more info and share with us. I'm interested.
    The two links I included above gave me a ton of information.

    Quote Originally Posted by rajicase View Post
    ^^Im with ya OP.

    I am not and I doubt anyone in here is an expert on this topic;

    I would personally recommend welding them for several reasons 1215 listed. Also, its 100% tried and tested.

    If you really want to go the epoxy route, I would look for long term, successful examples on other platforms and do what they did. Dont reinvent the wheel on something like this.
    Thats the plan


    Also, Im not just looking for any excuse I can to get out of paying someone to weld for me/buying a welder and learning myself
    Yes im on a budget, but no I wouldnt take a leap of faith on something that I had no grounds to believe would work other than I wanted to save a few bucks. The links I have posted give me legitimate reason to believe that this is an option in my opinion

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    Quote Originally Posted by pmerg View Post
    Also, Im not just looking for any excuse I can to get out of paying someone to weld for me/buying a welder and learning myself
    Yes im on a budget, but no I wouldnt take a leap of faith on something that I had no grounds to believe would work other than I wanted to save a few bucks. The links I have posted give me legitimate reason to believe that this is an option in my opinion
    As I said earlier, the use of epoxy at body shops to bond body panels together is now commonplace. Additionally, integrating body panels into the chassis as structural components is now also more commonplace.

    That said, you never answered my question: Do you NEED to do this or do you WANT to do this? If this job is a want I'd hold off until you are certain on what you want to do. If this is a need, I would weld. If you already have cracks the only way to properly fix them is with chemical bonds, not mechanical. Weld it and do it properly.

    back to welding...

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    Quote Originally Posted by 1215 View Post
    As I said earlier, the use of epoxy at body shops to bond body panels together is now commonplace. Additionally, integrating body panels into the chassis as structural components is now also more commonplace.

    That said, you never answered my question: Do you NEED to do this or do you WANT to do this? If this job is a want I'd hold off until you are certain on what you want to do. If this is a need, I would weld. If you already have cracks the only way to properly fix them is with chemical bonds, not mechanical. Weld it and do it properly.

    back to welding...
    Im hearing a slight clunk from the rear upon accel/decel but its not too bad. Im aware it could be shock mounts or something of that sort as opposed to a subframe issue, but I will find out.

    Now I dont feel this needs to be done immediately, but I do want to. For now im just trying to weigh options.

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    A lot of these cars clunk for various reasons.

    Hold off on your rear-end rebuild, save some money and do it properly when you are ready. "Do it properly" means have the cash reserves or alternate transportation lined up to handle the unknowns that come with owning an old BMW.

    Sounds like you won't know for sure until you get in there --either plan for worst case (already cracked, needs to be welded for proper repair)... save up and have at it, or take a chance that you get in there and end up over your head on the job. Best case everything is fine and no welding/epoxy is needed. Worst case you underestimated the job, didn't save enough and end up without a car for a bit. Don't just plan on glue/epoxy. If it is already cracked you are going to need to weld; no way around that.

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    Yeah I know if its already cracked Im going to need someone there to weld regardless, so now its starting to make more sense to me to just go ahead and have them welded. Would the cracks be visible with everything in tact? Would i be able to tell by just sliding under the car on jackstands?

    Im not sure why youre assuming I dont have the funds for any of this, I already have a subframe a diff and all new bushings that ill put together outside of the car, I can do it whichever way I have to. The point of this thread is just to get opinions and input on epoxy vs welding. I do appreciate your insight though.
    Last edited by pmerg; 01-27-2016 at 10:11 PM.

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    This got me thinking just because it's an interesting idea. Windshield adhesive is both flexible and also capable of holding 500+ lbs per square inch. It is technically a structural adhesive as these days windshields are part of the roll over protection on cars. If you cleaned both side thoroughly and then primered them with the windshield adhesives primer and then used one of those putty scraper things with the V's cut into it to spread it on the plate and put V peaks across the whole thing it would allow you to get a strong and thorough bond between both pieces. I actually think that would be a logical solution.
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    Quote Originally Posted by pmerg View Post
    Yeah I know if its already cracked Im going to need someone there to weld regardless, so now its starting to make more sense to me to just go ahead and have them welded. Would the cracks be visible with everything in tact? Would i be able to tell by just sliding under the car on jackstands?
    I'm finishing up this job right now. I wish I had taken photos or I wish you had posted 3 days ago. Its easier to see once its apart but Google "bmw e36 rear subframe crack" and look at the photos. If yours is bad you'll see it.

    Quote Originally Posted by pmerg View Post
    Im not sure why youre assuming I dont have the funds for any of this, I already have a subframe a diff and all new bushings that ill put together outside of the car, I can do it whichever way I have to. The point of this thread is just to get opinions and input on epoxy vs welding. I do appreciate your insight though.
    Habit. I feel like I am a rare e36 poster as I'm old, money isn't a concern and I maintain several (five) of these things for my kids (and myself) to drive because we like them, nothing more. Most people here seem to be in a different situation. Your comment "Yes im on a budget" in post #11 led me to assume that somehow you were tight on cash for this project. I apologize for my drawing conclusions.

    Quote Originally Posted by somebody5788 View Post
    This got me thinking just because it's an interesting idea. Windshield adhesive is both flexible and also capable of holding 500+ lbs per square inch. It is technically a structural adhesive as these days windshields are part of the roll over protection on cars. If you cleaned both side thoroughly and then primered them with the windshield adhesives primer and then used one of those putty scraper things with the V's cut into it to spread it on the plate and put V peaks across the whole thing it would allow you to get a strong and thorough bond between both pieces. I actually think that would be a logical solution.
    I know enough about composites and adhesives (VERY little) to re-state my initial concerns: mechanical vs. chemical bond and dissimilar materials/bonding mediums. If the adhesive is flexible enough; and regardless of mechanical vs. chemical, the bond is strong enough --go for it.

    Notwithstanding the aforementioned, as of this post, cracked metal needs to be drilled and welded regardless of adhesive.

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    @1215
    No worries. Ill take a look and see if i can figure it out.

    If you havent already, and have the time to check out the links I posted in post #11. I see where your coming from but it makes me wonder why so many people are opting for other methods if that is most always the case

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    Hot glue is all you need.
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    Quote Originally Posted by MisterM52 View Post
    Two Surfaces Welded/Bolted Togather would always be stronger then eproxy that sits on the outter edge of the steel, welding is melting and changing it at a molecular level if I am able to put my point right, JB Weld is great for what it does, and this is not what it does.
    His question is not a dumb one, there is some engineering merit behind it. Your reaction kinda is dumb though. Ever watch "How It's Made Dream Cars" Even the top supercars are glued together these days.
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    ^ pretty much this. @Misterm52 im not sure why youre so hung up on this jbweld thing or why its making you so upset, but if you read the thread youd realize that youre beating a dead horse. Youre not adding any value to this thread and youre obviously refusing to consider that epoxy(you know the other ones i suggested that arent jbweld) might actually be a feasible option for this job.

    Also consider that its not only the edge being epoxied around the plate, the surface its being applied to and the plate itself would have coating, giving it a much larger bonded surface area than and outer edge weld.

    oh and im not your pal, bud
    Last edited by pmerg; 01-28-2016 at 10:42 AM.

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    Quote Originally Posted by MisterM52 View Post
    This has to be the most disturbing thread I could read in a BMW community, are these cars become so cheap that they are now owned by ...... let me now even get there.
    ^^This disturbs me more.

    Cars have to survive long enough to be classic. any repair no matter how good or bad that keeps them from being crushed long enough to be worth enough to be restored is a good repair.
    No warranty of any kind implied or given and no liability for any loss, damage or injury, no matter how incurred accepted.

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    http://multimedia.3m.com/mws/media/6...hite-paper.pdf


    Some info I dug up about epoxy vs bolt, rivets and welds.

    I think 3M probably knows more than the resident troll.

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    I think the very few mechanically inclined people that are watching and posting in this thread would agree that...

    Yup, that about sums it up.
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    Anyway, here is my install.
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    Also, is anyone needs , I stock these and you can have these for $95 shipped.
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