[335i54n]

ok, so halfway through my spirited drives when braking the whole rear will shudder which is felt through my seat. the car has a whole new oe suspension with m3 front arm set, rear poly diff mount, diff brace, and subframe inserts.

the shudder has always been there before and after all the new parts and it only occurs after the car been drive hard for a while and seems less when under load like when cornering, I already plan on rear m3 guide arm but curious if any other have experience with something similar?

[Brian86]

This might be leading you in completely the wrong direction... but intermittent shuddering from the rear made me think of it.

How tight is your parking brake?

I have an e91 mt 325xi. I've always installed new parking brake shoes just a smidgen too tight, and just let them drag for the first hundred miles to seat to the drum and maintain very short engagement with the handle.

When I did this on the wagon I would periodically get massive vibration/shudder from the rear end. Sometimes one side, sometimes the other, sometimes both. Sometimes after braking, sometimes when accelerating to a certain speed, perhaps potholes did it? I don't really know.

I backed off the parking brake shoes a few notches and it hasn't happened again for several months and several thousand miles.

Never had drum parking brakes do something like before. Unique to the e9x or to my wagon? Perhaps there is some interplay with the spring preloading the cable under the handle, or some geometry in the drum assembly that wedges the shoes against the drum like a trailer brake that was bouncing in and out of position.

[autoart]

If it only happed when braking then it's possible you have a warped rear disc, or maybe a abs issue.
Check rear brakes in general, sticking or loose pads, sticking piston.
Have you bleed the brakes?

[Three_thirty_I]

I'm more inclined to think you have warped brake disks than a suspension issue.

Originally Posted by Brian86

This might be leading you in completely the wrong direction... but intermittent shuddering from the rear made me think of it.

How tight is your parking brake?

I have an e91 mt 325xi. I've always installed new parking brake shoes just a smidgen too tight, and just let them drag for the first hundred miles to seat to the drum and maintain very short engagement with the handle.

When I did this on the wagon I would periodically get massive vibration/shudder from the rear end. Sometimes one side, sometimes the other, sometimes both. Sometimes after braking, sometimes when accelerating to a certain speed, perhaps potholes did it? I don't really know.

I backed off the parking brake shoes a few notches and it hasn't happened again for several months and several thousand miles.

Never had drum parking brakes do something like before. Unique to the e9x or to my wagon? Perhaps there is some interplay with the spring preloading the cable under the handle, or some geometry in the drum assembly that wedges the shoes against the drum like a trailer brake that was bouncing in and out of position.

This reminds me of something that happened to my E90 many years back, the BMW dealership that serviced my car and replaced brake pads had adjusted the handbrake too tight, and a few days later when driving back home on a freeway I suddenly started to hear a distant rumble, at first thought it was my music, then thought it was a truck I was passing, but then I began to feel a vibration. This is all in the space of less than a minute, so I quickly pressed the clutch pedal in to see if that changes anything which it did not, so ruled out engine, but being in the fast lane, and the vibration continuing to worsen by the second, had to make an emergency stop on that side of the road which isn't ideal. I carefully got out and did a walk around checking that all wheels were secure at least. All I could do then was limp the car to the nearest BMW dealer (not the one that worked on the car) and see what they find. So I carefully rejoined the traffic and immediately moved to the slow lane where I drove at no more than 80 km/h, and for a min or so it was fine, but the rumble and then vibration quickly returned and I decided to stop again, this time in a safer spot on the side of the road. This time I was able to pay closer attention to each wheel and I could smell and feel some excessive heat from the rear brake disks, so continued to make my way to the dealership. The moment the mech got in my car after I explained what I was experiencing, he checked the position of the handbrake by the number of clicks and said it had indeed been adjusted too tight. The vibration and rumble was due to the shoes binding against the drum, they adjusted it on the spot, but I took the car back to the dealer that had done the work and insisted on them replacing the rear disks and shoes, which they did.

It's not really necessary to bed these in though, this is just the handbrake (or parking brake), it never has to slow the car down, just has to keep it stationary when parked, but if you want to bed it in, all you do is drive as normal and every now and again, just lift the handbrake a bit to allow it to drag (you will get a warning beep), then release again so that it can cool off (it will overheat quickly I would imagine).

[Phil325i]

Could your shudder be a form of axle tramp? If so have you thought about fitting a diff brace..?

[335i54n]

only happen if you push the car hard for a while, not sure if it a combination of things being overworked. normally car feels great with great brakes and already has diff brace, subframe inserts, and poly diff mounts, and if anything ebrake a little loose for my taste but have it set up to hold on a slight incline at 6 clicks.

m3 rear guide arm and upgrade a few of the rubber bushing to mono balls in the works