Thunking after subframe reinforcement and new subframe bushings?

[sammyf]

Hi guys, I tried to searching and may have looked in the wrong places but I've got an interesting situation. Had my subframe reinforced (Turner kit) and had the them install PowerFlex Yellows. Also replaced the nose diff, flex disc, tranny mounts and engine mounts. Now, when I am in the car (especially in sport mode) when I punch the throttle in a higher gear (6spd manual), I get a pretty noticeable "thunk" coming from the back. We actually had the car on the lift in the air and are able to hear it inside the car, but when we are looking around outside underneath, we can NOT hear/see anything. Has anyone else had this experience with PowerFlex bushings or urethane bushings? Is it normal?

[Sid_E46]

What Differential bushings do you have?

I had Powerflex bushings on my diff and it was atrocious, switched to OE diff bushings and solid subframe bushings and it is a million times better.

[maw1124]

+1 on non-OE diff bushings... seems like almost 100% when people use nonOE diff bushings, yes?

maw

[sapote]

when I punch the throttle in a higher gear (6spd manual),

Higher gear as 5th or 6th? Or 1st?

I asked because the rear end is under higher load with 1st or 2nd than 5th or 6th.

[lvm3sm46]

Drive shaft support and bearing. Replace that. It solved my clunk

[sammyf]

Its a brand new front BMW diff bushing but the rears are original as they didn't look bad on inspection. Car is 2002 with 112k miles.

[sammyf]

lvm3sm46 We took a camera and it looks like there might be a crack around flex disc. Will replace and report back:

[Arith2]

Solid suffrage bushings plus ploy diff bushings aren't for the faint of heart. It stresses me out to hear my diff chatter sometimes. I also have a lightweight flywheel so that really changes things. You'd be amazed at how much a stock flywheel actually dampens.

[Tbonem3]

Pre-load the CSB

[old///MFanatic]

lvm3sm46 We took a camera and it looks like there might be a crack around flex disc. Will replace and report back:

You sure that’s the flex disc? Almost looks more like top side of a motor mount.

[SteelGreyM]

Oh no I just installed powerflex poly diff bushings. Not liking what I’m reading.

[jet_dogg]

Will never understand why people exchange US currency for polyurethane bushings.

[sammyf]

So we replaced the center bearing with factory part...UNFORTUNATELY, the thunk is still there. Any other ideas? Again it only happens during initial acceleration.

[Tbonem3]

It's really bad? It's not just the natural clunkiness of the driveline?

Poly bushes will exacerbate noises.

[sammyf]

Here's the bushing setup in the rear. Diff bushings are all BMW (BRAND NEW NOSE and ORIGINAL REARS). We have video evidence that the DIFF is NOT moving under load.