HELP!! rear clunking under acceleration,clutching & shif

[sharkyM5]

hey all need help....first new poly subframe bushings,diff mount,guibo,U joint 40000miles ago,dog bones and new shox and mounts...so if your a little sloppy at shifting it clunks mainly clutching from1st to 2nd to 3rd, but on acceleration it clunks on quick throttle and letting off the gas quickly(in all gears) it clunks as well....my mechanic says i need a new drive shaft which im all for but its expensive and if it doesnt solve the issue....well you know!? i was under the car today and it seems like when in neutral there is play from the diff(normal?) in gear no play...thats good right...ass swell just rolling in 1st (idle speed) if you press the clutch in and out it clunks every time...WTF???
has anyone ever had the same issue?

regards
jon

[m535is]

This clunking you describe is called driveline backlash. All cars have it, even my brand new BMWs have it. The point is 2 fold. The amount of backlash in the driveshaft and in the half shafts can be measured and you can sit in the car and see if the noise can be replicated by a friend. To test the driveshaft, have the car in neutral hold the input shaft to the diff still and try to rotate the guibo. To test the half shafts you can hold the output of the diff and try to rotate the wheels.
Secondly the amount of clunk can be minimized by how you drive the car...if you hear/feel the clunking then you are being too rough with the driveline and will cause it to fail eventually.
Just like you said if you sloppy shift then it clunks. If you load and then then quickly unload the driveline it will clunk and lastly, if you are in first and dip the clutch you will also cause this because in such a low gear you can go from one to the other direction of load quickly.
My car has a new diff, new bushings, new driveshaft and known good half shafts and I can get it to clunk in all of the situations you describe.

[MicahO]

Did this clunking appear when or immediately after the new poly subframe bushings and diff mount were installed? If so, have you revisited them to ensure that they were all properly and fully tightened? A badly torn subframe bushing can create that sort of on/off throttle clunk. I bet a loose one could too.

[sharkyM5]

thanks for the reply guys! ok so some backlash is normal, it just so seems excessive now from a year ago...and for the the poly mounts it seemed great for awhile but now i cant tell what would be causing what diff mount seems good!?....i just want my tight rear end back haha (no pun intended) myabe the U joint is worse then i thought and my mechanic is right, they are awesome guys and know what there doing!?!....but just dont want a huge bill for no reason....we all hate chassing problems! ok so even if im gingerly on the clutch i get the jiggly clunking maybe my clunking is different(so confused now) ya when i clutch and all the things i described, i get a( ge ge ge clunk) is this different then just the clunk? any more ideas or info is greatly appreciated before i drop the car at the shop...

kindest regards
jon

[m535is]

Video will help on this one.

[sharkyM5]

thanks again for the info guys! gonna get the new driveshaft then will see if that tightens things up...and then i will post a video if it continues at the same severity...cheers!

kindest regards
jon

[sharkyM5]

ok so new driveshatft(u joint) the car is as tight as new....i truly didnt think i had play in my u joint but i guess i did..bought the oem m5 driveshatft and glad i did, came with new guibo and center support bearing and of course a 2 year bmw warranty....Anyway thanks for all the help and suggestions!

regards
jon

[Mab1957]

That old black car is just going to keep giving you fits, Jon. Be done with the headaches and give it to me.

Pleased to hear you got it sorted. Next year you can join us at The Vintage and test it at the Farmington Dragstrip

[S38Mike]

That old black car is just going to keep giving you fits, Jon. Be done with the headaches and give it to me.

Pleased to hear you got it sorted. Next year you can join us at The Vintage and test it at the Farmington Dragstrip

That's an awesome picture

[ilikemybike]

GOOD GAWD!!!! Don't you know how to use a period?!?!?! I have a headache.