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Old 11-18-2019, 11:22 PM   #1
SB325i
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Join Date: May 2018
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Year: 03
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Subframe "epoxy" Reinforcement DIY

Hello Fanatics,

I had this idea researching subframe reinforcement, while my 325i auto is lower risk of cracks, I wanted to do something about it. Plates are off the table as 1: I don't have the money to pay a shop to do it and 2. I would be terrified of dropping the subframe in my garage, and I've done quite a bit of work on BMW's. I found the structural epoxy method and came up with this lower cost alternative! I had confidence too since this method was created by BMW to treat cars with mild cracking in a TSB.

I used Loctite PL Premium Polyurethane Construction Adhesive (the 8x variant). Squeezed 1.5 of those suckers via a caulk gun in the lower cavity of the left rear subframe mount (like what BMW recommends in the TSB). I took a little risk using the polyurethane, but once it cured, it is rock solid like epoxy. Also the real OEM epoxy is NLA or very pricey if you can find it (2 tubes of Loctite was $16 at the hardware store, versus $160+ for epoxy online). I find this form of reinforcement to be very practical and effective if you don't have any cracks or very mild hairline cracks because it addresses a root cause of the design flaw: too much movement of the subframe floor, particularly in the Left Rear area. Welding plates is good and all, but this is an easy first step in keeping your subframe floor in one piece. And honestly for a cheap e46 is dropping half the car's value on a subframe-out subframe reinforcement worth it? Especially for one that isn't cracked. I'm happy with the peace of mind I get from doing this since I plan on driving this thing for years.





Totally subjective here but now that the polyurethane is fully cured, my butt tells me the rear feels more planted on harder acceleration. It feels almost like there's less "slop" in a way but it's subtle. Your mileage may vary but I think regardless of any noticeable effect, this is a worthwhile way to address the dreadful subframe issue cheaply and effectively!
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Old 11-19-2019, 12:09 AM   #2
se93
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Sounds interesting.

Does anyone have the actual BMW TSB in relation to their subframe repair procedure? Iíd like to see what is actually done and get familiar with the rear subframe components to possibly have this done as well

Regards,
Mark


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Old 11-19-2019, 12:14 AM   #3
SB325i
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Quote:
Originally Posted by se93 View Post
Sounds interesting.

Does anyone have the actual BMW TSB in relation to their subframe repair procedure? Iíd like to see what is actually done and get familiar with the rear subframe components to possibly have this done as well

Regards,
Mark


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Hey Mark, I've seen the TSB linked around the internet on various forums. I found this Google Doc in PDF form with the TSB: https://docs.google.com/file/d/0B818...VlE/edit?pli=1

Hope this helps you visualize it.
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Old 11-19-2019, 12:28 AM   #4
se93
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Quote:
Originally Posted by SB325i View Post
Hey Mark, I've seen the TSB linked around the internet on various forums. I found this Google Doc in PDF form with the TSB: https://docs.google.com/file/d/0B818...VlE/edit?pli=1



Hope this helps you visualize it.


Thank you

So you made the 3 holes as shown in the instructions and filled up each opening?




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Old 11-19-2019, 12:59 AM   #5
SB325i
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I inserted it only in the existing hole. The polyurethane is thick and so I wasn't worried about it spreading far. The other two holes are to keep it in that area sealed off with seam sealer. Using the polyurethane is cheap so It's okay if it spreads out in my opinion. So I solely used hole 1 for this process and filled it up.
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Old 11-19-2019, 01:19 AM   #6
se93
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Subframe "epoxy" Reinforcement DIY

Quote:
Originally Posted by SB325i View Post
I inserted it only in the existing hole. The polyurethane is thick and so I wasn't worried about it spreading far. The other two holes are to keep it in that area sealed off with seam sealer. Using the polyurethane is cheap so It's okay if it spreads out in my opinion. So I solely used hole 1 for this process and filled it up.


Got it. Hole #1 is covered with a plug so this can be handled easily. I thought that hole needed to be made. Is there a corresponding hole on the passengerís side?

So the most vulnerable side is the driverís side? In your picture of the trunk it looks like there is a plug on the right side as well. Why didnít you fill up the passengerís side as well? Does filling up hole #1 reach the area marked in the TSB as hole # 3? and towards the right of hole #1 thus treating the entire area?

Thank you


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Last edited by se93; 11-19-2019 at 01:32 AM.
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