CGLockRacer
CGLockRacer GRM+ Memberand Reader
8/26/10 10:00 a.m.

Oh wise GRM folks, I need some help diagnosing a problem for my dad.

Car: 2001 BMW 325Ci Recently replaced: Driveshaft (due to a bad rear u-joint), Guibo, front control arm bushings.

Problem: Under moderate to hard acceleration, there is a VERY big vibration from the rear of the car. My dad described it as running over alligator teeth on a racetrack. Nothing obvious from looking under the car. He said the half shafts move a bit at the diff, one side more than the other though (I think it is normal plunge distance, but not sure). The car drives fine at highway speeds and made it from MI to DE after the problem surfaced. It happened at a trackday at Waterford rather suddenly and he pulled in immediately after noticing it. The driveshaft is still tight and the guibo and center bearing are OK according to him.

Diff. bushings looked OK when we were replacing the driveshaft. We are thinking something in the diff may be going, or a halfshaft. I cannot inspect the car, but if you guys can help me, I can have him check things.

Thank you!!!

ansonivan
ansonivan HalfDork
8/26/10 10:38 a.m.

If it's something inside the diff you should have metal flakes in the fluid.

My guess is the new drive shaft is bad or assembled out of time.

WilberM3
WilberM3 Reader
8/26/10 11:08 a.m.

first thing to double check is the center support bearing, they'll make a lot of noise if bad/torn. also theyre supposed to be preloaded a little to the front of the car iirc.

the other thing to look and and hope not to find is a torn out rear subframe. ive repaired 3 standard e46s with that problem. the left-rear subframe mount tears itself out of the unibody and ultimately migrates the problem to the other 3 mounts, but it makes AWFUL noises and requires the entire rear subframe removed, subframe mount relocated into the unibody, welded back solid, both underneath and on top inside the trunk after cutting through the trunk floor. i'd also recommend the reinforcement plates that turner motorsport sells to prevent the problem from recurring. under the car look for cracks in the unibody around the LR subframe mount.

http://www.turnermotorsport.com/html/photo_gallery_e46sf.shtml

Giant Purple Snorklewacker
Giant Purple Snorklewacker SuperDork
8/26/10 11:28 a.m.
ansonivan wrote: My guess is the new drive shaft is bad or assembled out of time.

That would vibrate your teeth loose at highway speeds.

"Under hard acceleration" is something flexing or moving.

  • Does it upset the handling? - bushings, control arms, CVs, subframe mounts... etc
  • Does it shake the shifter? - driveline
  • Does it shake the whole car or is it just a noise he hears? Stuff like a broken swaybar hitting the exhaust or spinning axle when the back compresses under load... or wheel hop + LSD kick because of a bad damper or broken mount can make a racket but otherwise not rattle your teeth.
pigeon
pigeon Dork
8/26/10 12:12 p.m.
WilberM3 wrote: first thing to double check is the center support bearing, they'll make a lot of noise if bad/torn. also theyre supposed to be preloaded a little to the front of the car iirc. the other thing to look and and hope not to find is a torn out rear subframe. ive repaired 3 standard e46s with that problem. the left-rear subframe mount tears itself out of the unibody and ultimately migrates the problem to the other 3 mounts, but it makes AWFUL noises and requires the entire rear subframe removed, subframe mount relocated into the unibody, welded back solid, both underneath and on top inside the trunk after cutting through the trunk floor. i'd also recommend the reinforcement plates that turner motorsport sells to prevent the problem from recurring. under the car look for cracks in the unibody around the LR subframe mount. http://www.turnermotorsport.com/html/photo_gallery_e46sf.shtml

BMW finally agreed to pay for previously done repairs and future repairs on the subframe issue a while ago. I got a letter from the class action lawyers about it long after I had sold my E46.

SupraWes
SupraWes Dork
8/26/10 5:32 p.m.

I agree the unibody/subframe area needs a good checkin over!

CGLockRacer
CGLockRacer GRM+ Memberand Reader
9/1/10 1:31 p.m.

UPDATE: Well, turns out the center bearing and Guibo are shot. We had installed the center bearing incorrectly. New parts are on order and the correct instructions have been found for installation. Ugh...expensive lessons...

I have a .pdf file if anyone else needs it.

benzbaron
benzbaron HalfDork
9/1/10 4:28 p.m.

On my car and other r107s even small cracks in the flex disc(guibo) will cause driveline vibration so it sounds like that also happens to BMWs, good to know.

pco
pco
4/4/19 1:46 p.m.

In reply to CGLockRacer :

Do you still have have that .pdf?

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