BMW M5 Forum and M6 Forums banner

Thumping noise from transmission tunnel under wot high revs

5K views 20 replies 6 participants last post by  Joe_stack 
#1 ·
So after putting on the "micky thompson street et" tires and did one run on the track I heard a thumping noise from the tranny tunnel in the rear of the car.... with some advice from other bmw members in my local club the Said to look at the driveshaft center support bearing and diff bushings....also said to look for any wear above diff or driveshaft where they may be hitting the floor ....which I seen the flange on the diff where the driveshaft connects was hitting the floor and grinding from the way the metal on the under floor looked.

So I brought it to the shop and had the csb and all 3 diff bushings replaced with powerflex poly bushings....

I went to track yesterday and used my regular street tires (michelin pss) and I heard the same thumping....yet it only happens under certain conditions....

I can burn rubber no problems....when I take off the line and break traction and burn rubber or take off with more grip I don't hear anything ...but when I take off and the tires spin and I shift to 2nd and start to get grip I hear a thumping noise coming from the rear floor near the tranny tunnel ..

It seems to only happen as the spinning g tires are getting their grip....if I wot and already have grip it's fine....if I wot and spin the tires it's fine....seems to only happen when the tires are spinning and start to get grip...

Going to my buddy's shop who has a lift buy I don't think I would let him work on my car lol...but I can at least put it on the lift and look under...where should I be looking...and what could this noise be? I keep thinking driveshaft hitting tunnel but I'm not sure...GuiBo is good and I just changed the csb and 3 diff bushings...tranny bushings were changed last month....
 
See less See more
#4 ·
Yes kw v3 lowered about an inch

If the input flange on the diff was hitting the bottom of the car, the input bearing could be compromised. Maybe the CV but it usually makes a clicking noise, not a thump. Do you have a pic of the damaged area?
I can take pics tomorow when it's on the lift...my jack broke a piston so I need to buy a new jack...tomorow I'll have it on lift and take pics and video if I need
 
#3 ·
If the input flange on the diff was hitting the bottom of the car, the input bearing could be compromised. Maybe the CV but it usually makes a clicking noise, not a thump. Do you have a pic of the damaged area?
 
#5 ·
On another note .though I don't think it's related...when I go from n to 1st ...an then from n to reverse I hear a slight clung/cling ...this is only since I had the diff bushings and center driveshaft support bearing changed out....it sounds like it may be coming from driveshaft or gear lash in diff...sounds like if I lightly hit some metal with a hammer or something...just one ding when I release clutch into first...then if I got to reverse and release clutch I hear the same ding...but like I said don't know if it's related...just thought I'd mention it
 
#14 ·
  • Like
Reactions: Joe_stack
#16 ·
I'd take it easy on it. If the CV is in that bad of shape, it isn't doing the input bearing on the diff any favors. If it fails catastrophically the driveshaft is going to beat the living hell out of everything it can reach and probably set off the airbags like someone else had happen recently. In either case you are looking a several thousand in repair parts vs. $180 and a little patience to replace the CV.
 
  • Like
Reactions: Joe_stack
#17 · (Edited)
I am going to suggest you get a whole rebuilt shaft. There has to be more wrong here. I don't know how you missed this when you did the diff bushings, so I have to guess you are missing other things too. Your diff does not look like it is spewing oil so it is fair to say you are not get any movement there. Maybe there is 3/4" of play in the CV but I would think it would fall a part. You must have some play in the center bearing and maybe no weight on the shaft to make it wobble. Your subframe bushings are also suspect. With your new diff mounts something else has a lot of movement. Are you sure you are not getting some wheel hop? These cars wheel hop easy and if you are getting then maybe something in your suspension is shot and the other things are fine.

I have no idea what is going on but following your two threads on this I know the whole picture is not there yet. Have you considered taking it to a pro?
 
#19 ·
I didn't change the bushings and csb...the shop did...so ya been taking it to the pros...so to say...but I know when there is still an issue....I plan to change the entire shaft next week and not **** around....I also plan to make sure I'm in the shop while they do it this time so I can inspect their work...they have offered me a discount on time to keep me as a client....figure I'll give them a chance

I guess I'll also change out all sub frame bushings at same time ... considering diff is poly should I go poly for sub frame or stock?
 
#21 ·
Taking the car in today...staying at the shop for 3 weeks...getting a custom shaft rated for 1000+hp put in...will be getting more info later today when I talk to the shop in person when I drop the car off....next will be a custom diff from Bavarian diffs
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top