Rear clunking!!

[jlevie]

Get the car up in the air, set the parking brake, and rotate the drive shaft back and forth. If you do it vigorously you may be able to reproduce the thunk. If you can you'll be able to find where it is coming from. Also while the car is up in the air take a look at the motor/trans/diff mounts for wear and or damage. While less likely, loose diff mount bolts, bad subframe or rtabs or damage to the car/subframe is a possibility.

[iamsam]

Get the car up in the air, set the parking brake, and rotate the drive shaft back and forth. If you do it vigorously you may be able to reproduce the thunk. If you can you'll be able to find where it is coming from. Also while the car is up in the air take a look at the motor/trans/diff mounts for wear and or damage. While less likely, loose diff mount bolts, bad subframe or rtabs or damage to the car/subframe is a possibility.

I will try this. I did something similar, where I lifted one rear wheel in the air, and with the car in 1st gear, I rotated the wheel back and forth vigorously. I noticed significant play in the diff, but I also noticed a clunk coming from the transmission. Now that's waaay up front, but I COULD be hearing it from the rear simply because there is nothing but thin sheet metal and poly bushings separating the diff from the cabin of the car, and the noise could be transmitting down the driveshaft, and through the diff mount into the trunk, which of course is devoid of all material other than sheet metal, and no rear seat, open ski hole, etc.

The diff mount bolts should be fine, I tightened them pretty well when I re-assembled the rear end, and also the rear has all new poly bushings.

[iamsam]

OK I messed with my car a little today, jacked up the entire rear end of the car, and put in in neutral. Then with my hand i grabbed the drive shaft near the diff and twisted it back and forth as hard as I could. Sure enough, I could replicate the clunking almost perfectly, but one thing still has me baffled.

I couldn't see much play between the driveshaft movement and the diff out-drive flanges. I could see alot of visual play between the diff out-drive flanges and the wheels of the car, i.e. in the CV axles. Now the CV axles are brand new, could this clunking sound still be coming from the diff? I couldn't pinpoint the sound no matter how hard i tried.

halp!

[bryant.cw]

Yank on the driveshaft like you did and have a friend listen closely to wheels, cv, diff, driveshaft and transmission. Forget what you are seeing, its probably misleading you.

[Ceeker]

using hand power can't possibly duplicate the inertia/torque created by the drive line. I would get your drive shaft checked since the u-joint is the weakest link. get the car on a hoist with someone inside. have them simulate the action by going through the gears. keep in mind you won't have the same load as you would on the ground but at least you'll be able to listen from outside and below the car as opposed to inside. there is always some play\lash in the diff for heat expansion; but in any case you could narrow it down more easily. Get a long screw driver and or stethoscope(some techs have one) place it on the area where you think the noise is coming from. Move it around to see if the noise gets louder or quieter depending on where you place it. To many moving parts sometimes makes it tricky to pinpoint exactly what is wrong. You save money doing it this way or you play the game of "process of elimination" as you already experienced. (Grin) while you're under there might as well use the same procedure for your output shaft on the trans. use your ears and eyes. Better still get the tech to do it he'll have more experience with this stuff.

[iamsam]

Ceeker, You have some valid points. My next step at the moment is to change the diff fluid. Doubtful that this will fix anything, but I know it needs to be changed and its super easy to do. Also, I am looking to buy a lsd because i want one anyway, and when i get that, it will further narrow down the problem, and then I can really start looking into the driveshaft.

[Faviolosky]

same thing is happening to mine, all new poly bushes in the back, new guibo, new diff mount, new poly tranny mounts. and i did too move the wheel back and forth and it did replicate the sound, is like coming from the CSB but its not it. i strongly think is the u-joints, so soon i will have it rebuilt and balanced i think you should do it too.

[iwantspeed]

my previous e30 did this
my new e30 does this, it pisses me off immensly.
and I want to address it to.
I want to get the driveshaft rebalanced and put on a new guibo, new bolts, and a new csb.

then if it doesnt fix it.
replace my 3.73 open diff with a lsd 3.73

[!kid]

my 87 325i and my 88 325is did/do this i get a clunking sound from the back of the car when i unload the drivetrain.

you think the back lash in the diff is so bad that it causes this sound?

[iamsam]

hey guys! someone resurrected my thread, but it is probably a good thing, because my car is still clunking, and so far the only things that I haven't replaces is my diff and my driveshaft. However, I am picking up an E30 M3 diff this week from a friend, and this weekend we will see if that fixes anything.

[TimKninja]

My car did this as well, I'm interested in the result, always thought it was the differential

[llll1l1ll]

I still think it's just slack in the differential. Mine does it if I am too rough with a shift. Sometimes it will clunk putting it in gear, though, and that makes me think driveshaft.

Really, though, I'll get some clunking if I messily disengage the clutch in first gear while crawling along.

[iamsam]

update. Replaced diff w/ E30 M3 diff, no change in clunking whatsoever. I can get it to clunk by holding the brakes slightly and releasing and depressing the clutch quickly while in gear.

[dreamchasin]

if it only happens when you're moving. or when your drivetrain is under torque check your driveshaft right in front of the subframe, i bet it's hitting your gas tank.

[unrlmth]

I still think it's just slack in the differential. Mine does it if I am too rough with a shift. Sometimes it will clunk putting it in gear, though, and that makes me think driveshaft.

Really, though, I'll get some clunking if I messily disengage the clutch in first gear while crawling along.

Mine is pretty much identical. Rough shifts cause it to clunk and putting the clutch in. Also occasionally clunks over big bumps.