Banging noise from rear end 328i

[SolTNutz]

I will try to explain best I can.
I have a 1998 328i manual it has about 300 RWHP and a stage 2 clutch.
On the odd occasion ( starting in first gear ) the car will jerk back and forth with a banging noise in the rear. The u-joints are now good but I noticed the left motor mount is broken and the right motor mount assembly is cracked. I just ordered these parts and they will arrive in 2 days. Could this be the issue or is something possibly wrong with the diff ( LSD ).
Thanks

[3x Beemer]

Sounds like a fart to me lol

Seriously, after changing engine mounts see what happens

[sb_600]

banging noise in the rear could be the subframe tearing out (or bad bushings), but yeah, if your motor mounts are done, see if it continues after you replace them.

[SolTNutz]

New good aftermarket bushings and subframe is good.

[Ceeker]

if it's a clunking sound that could be normal lash from the diff. But if it's REALLY bad as mentioned most likely the subframe tearing out. You'll need to play process of elimination.
once the new motor mounts are in; test the car.

[TMW]

The car needs to be in the air, and then you need to look at the floor where the subframe mounts to. If you hit the area with a degreaser like brake cleaner, many times it will run through the crack...or because you got rid of the road grime will have a better time seeing the crack.

I've welded plates to many e46 floors for cracks, the mount will look fine. but the flex actually comes from the floor. e36's and e46's have similar design flaws on the rear floor.

There's another test you can do where you load up the wheels and using a helper you can actually see where the floor gives.

Check youtube. there are many videos on how to check for cracked floors.

I'd check there first. Sounds like it happens when your putting load through the drivetrain. (first gear launch) Also your motor mounts being busted won't help the situation. But with busted motor mounts you'll hear more of a rattle under load or around a corner. If your mounts have been busted for a while it will also put extra stress on the rear floor.


Also when you say jerking back and forth....does the car buck like your riding a mechanical bull? or is it less obvious

[SolTNutz]

The subframe is NOT coming apart, it was modified last year and will never seperate. The car itself is rock solid, I am having it built for 600 hp when I am done and there is no issue with the car or frame of any kind. The motor mounts and supports are arriving tomorrow and will see how it works. Thanks.

[TMW]

word.

Report back after you swap out the mounts.

Are you doing the transmission mounts as well?

[Blackedout95]

So...how else is the car modified, full cage, sub frames, what?

[BMXWill]

RTAB popping in and out? That makes a banging sound lol

[richie_s999]

Well if its built for that much power why is it clunking and banging, sorry but you asked for help and a couple people offered advice and your sounding like a dick now.

Check your trunk, a loose spare tire or battery could be making the noise

And it's not the actual subframe that cracks, it's the mounts in the floor they bolt into that rip out, even if you had the m3 style reinforcement plates welded in, if they were loose and not properly repaired they can still make noise.

Also curious to what your putting in the car that you think you will have 600 whp?

[SolTNutz]

Sounding like a dick? Post #4 says subframe is OK and post #5& 6 mentioned the subframe again and I replied again post #7. I have listened to the advice but some I filtered out because I know it is not the issue. The additional power will be coming from an Active Autowerke supercharger system. They claim 510 but there are some other tweeks being done. The car is subframed but no cage. And the transmission mounts I just ordered. And if you read the post properly I said " I am having it built " first step was the structure which is done, next is the suspension which I am working on but this banging came up and I noticed the motor mounts broken, while waiting for parts I thought I would ask a question in case the problem is not fixed.
Kind of rude calling someone a dick.

[SickFinga]

Originally Posted by SolTNutz

The additional power will be coming from an Active Autowerke supercharger system. They claim 510 but there are some other tweeks being done.

510hp? out of an AA supercharger? on a 328?

Does it have an S54 swap or something?

[SiR]

he does that

[SolTNutz]

Just like the pot calling the kettle black