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Go Back   E46Fanatics > Tuning & Tech > Driveline, Engine & DME Tuning

Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 11-26-2011, 02:23 PM   #1
mildon77
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Rear subframe reinforcement as preventative main??

My car has no sign of subframe damage. Its an 02 330i with 150k miles, I havent dropped the rear crossmember to really check it out properly.

My question is would you do the subframe reinforcement to prevent future damage or just wait and see how it goes? Thanks
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Old 12-01-2011, 02:19 PM   #2
Jim Murphy
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Originally Posted by mildon77 View Post
My car has no sign of subframe damage. Its an 02 330i with 150k miles, I havent dropped the rear crossmember to really check it out properly.

My question is would you do the subframe reinforcement to prevent future damage or just wait and see how it goes? Thanks

I have been told that bumpy roads and salt are contributing factors to the failure. With 150K miles, at the very least a visual inspection will put your mind at rest.

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Old 12-02-2011, 07:25 PM   #3
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Apparently, rear subframe failures are caused by bad rear subfame bushings...my guess is that yours are close to the end or dead already. No way to know without dropping your whole rear.
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Old 12-02-2011, 07:54 PM   #4
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Apparently, rear subframe failures are caused by bad rear subfame bushings...my guess is that yours are close to the end or dead already. No way to know without dropping your whole rear.
That's the first I heard this. When they fixed my subframe at around 200K miles, they said my bushings were fine...so you've got me curious. I thought these were junks hunks of rubber, not fluid filled like the motor mounts or CABs.

I thought the defect was that the floor was too thin to support the loads and that over time metal fatigue sets in and starts them tearing around the subframe bushing.

In any case, OP, there are aftermarket reinforcement pieces that guys have had welded in. There's also the foam epoxy mitigation approach. Foams are injected to reinforce the area between the two floors in the trunk above the rear bushings. That would be the cheapest and worth a try...but I don't know what then welding around that might do...probably not good for the foam.
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Old 12-02-2011, 08:11 PM   #5
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Many experts have come up with this theory. Basically the subframe bushing goes bad which causes excessive movement in the rear suspenion carrier/subframe. This then loads up the mounting points, especially on one side, forget which one. The loading and unloading fatigues the metal and causes the failure.

I've gone with PF subframe bushings to eliminate the failure prone rubber. Other have gone with solid bushings and reported good results. I noticed no increase in NHV with the poly bushings.

FYI, at 88k miles, I noticed my diff bushings were shot but the subframe bushings were still good.
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Old 12-03-2011, 02:08 AM   #6
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I think the front left subframe mounting area is the most likely to fail.
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Old 12-03-2011, 03:12 AM   #7
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Apparently, rear subframe failures are caused by bad rear subfame bushings....
This is absolutely correct.

First the diff bush goes and puts more stress on the subframe bushes , then they go and then your subfloor goes.

BUT E46s had subfloor failures as early as 20kmiles back in 2000, all true and documented by BMW. So you are never safe, but I would recommend new bushes simply as maintenance. Reinforcement plates would be overkill for a car with such low value already.

BMW realized that the desing of the rear subfloor is ch1t and tried fixing it in 2002 , thats when they introduced a new design of the whole rear subfloor (thicker and it even looks different) but the problem still shows up on cars build in '04 and even some very very late '05 build M3 with super low miles.

Point is, they tried but failed.

Rumor has it that the failures were due to the bad quality sheet metal used by BMW at some point and not teh design but this rumor is just a rumor.
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Old 12-03-2011, 03:20 AM   #8
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My car has no sign of subframe damage. Its an 02 330i with 150k miles, I havent dropped the rear crossmember to really check it out properly.

My question is would you do the subframe reinforcement to prevent future damage or just wait and see how it goes? Thanks
Sadly the only real way to tell is to take it all apart then check it all out. Most likely when it's easily visible the condition of the subframe is dire...

Just do it when you have the cash or if you plan on keeping the car. And make sure you also replace corresponding bushings etc...
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Old 12-28-2011, 04:00 AM   #9
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I did this on mine when installing the 3.91 diff and new bushings. It's a headache I wanted to eliminate.
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Old 01-13-2012, 04:23 AM   #10
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Basically once you get a reinforcement kit installed (Turner Motorsport's for example), the whole subframe problem should be gone correct?
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Old 01-13-2012, 08:39 AM   #11
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Basically once you get a reinforcement kit installed (Turner Motorsport's for example), the whole subframe problem should be gone correct?
With proper welds and rust prevention along with some fresh bushings, then in theory, yes. Didn't work out that way for me but my car is also heavily modded and experienced a diff failure which lead to an unusual shock load on the subframe which may have been largely responsible for my second round of problems.
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Old 01-14-2012, 07:00 PM   #12
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With proper welds and rust prevention along with some fresh bushings, then in theory, yes. Didn't work out that way for me but my car is also heavily modded and experienced a diff failure which lead to an unusual shock load on the subframe which may have been largely responsible for my second round of problems.
I'm terrified of Subframe Mounting Failure. Any good shops around Houston TX that KNOW how to install the Reinforcement kit for a good price?
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