A new suspension noise
 

ok the sound is like when you run off the road and hit the "wake me up" strips. Its coming from the rear end now, but only when i make a left hand turn at cruising speeds, and when the rear end dips down. It doesnt make it when i turn to the right and it doesnt happen at all at slower than 40. Almost as if something is happening on the passenger rear side, so when i turn left, the passenger rear sits down more and gives me that loud noise/vibration. could i have moved any drivetrain noise back there from putting in new engine mounts? sounds likely

Now a little background. The engine was idling rough as h3ll. so much that the glove box door would shake enough to turn on the light inside, and you could see the hood bouncing. There was also an rpm based vibration that could be felt through the floorboards. I replaced the engine mounts and transmission mounts and holy *****, its so effing smooth now, and the vibrations are gone. BUT now im getting some weird stuff happpening in the rear end that was not happening before. What would i be looking for to diagnose this, and what to repair?

Check the exhuast hangers, make sure the exhaust system is not rubbing.

Also check all the rear suspension bushings.

Don't forget to check the rear bushing stops. When the bushings collapse, there's more of a gap. If the bushings are weak, it can allow the subframe arm to slam up or down. Won't sound like a rumble, but more like a thunk. Turns and rear weight load will cause different vertical forces on the subframe arms.

patbob, Do you mean the subframe bushings? If so, i highly doubt that is where this sound is coming from. It is identical to running off the road onto the tirestrips. very loud and very fast thuds.
Im at a loss. i just looked under there and could see no real damaged parts.

could be the axle joints too...
not to mention the stinking anti-swaybar links.
John

ok. so i just spent over an hour looking at everything from transmission back. i can see nothing that would make this noise.
1. all bushings look good, for their age. dont seem to be compressed.
2. plenty of oil in diff
3. sway bar links look good. (rubbing backing plate at times it seems)
4. all muffler bushing/hangers etc look good
5. no cracked or leaking axle boots
6. wheels on tight.
7. brakes and parking brake working correctly

so other than shocks being completely shot (cant tell really) i am lost.

How do the rear tires look? Any odd wear?

rear tires look good. no odd wear. its just boggling to me, that this weird noise started immediately after i changed engine and tranny mounts.

Hmm, is the noise coming from the back at all? my tranny tunnel will shudder something fierce on left turns unless I am under power.it's been this way since the tranny was replaced... I figure the tranny mount is soft and it's allowing the transmission to contact the tunnel.
John

Could something have worked loose? Like the mount bolts or engine shocks?

What is the condition of the air cleaner bracket?

Left hand turn shifts weight to the right.

Do you have any items moving around in the trunk?

Just grasping at straws now...

haha. i know rrgrassi. im grasping at straws too. im laughing because i didnt want to admit it, but i did take the jacks and tools out of the trunk. no difference. would have been embarrased if it were that, but its not. i hate to say, you need to hear it, but i guess i cant explain it any better.

vstech - i dont know how to tell if my trans tunnel is loose. i didnt know it could. the mount is brand new, just put it in yesterday. nothing weird there. i checked all the bolts again today. nothing came loose.
yes the noise is definitely from the rear. passenger side to be exact.

thanx everyone. ill keep an eye/ear on it. if you can think of anything im open to try it.

Hmmm, now I guess we have to look at the not so obvious aka more straws...

RLEO was searching for the last straw...I wonder...

How does the right side axle feel, and what about the rear bearings? How are the CV Joints? Can you hear anythng when you turn the wheels by hand? Could the diff be making noises, like a bad spider gear?

Could the rt rear spring have any cracks? How are the rear shock bushings, the ones behind the back seat?

Any odd wear on the flex disks? How about the drive shaft center support bearing?

Does the sound change with road speed?

My 300E made a similar noise from time to time. Mine was mostly at low speeds. It was in the rear on the passenger side. Came and went. Then it came back big time as the CV joint tried to seize up.

Steve