Vibration under hard acceleratiion

Hello all
New to forum and new to BMW ownership. I have a 2002 745i 74K miles, generally perfect other than a severe vibration under hard acceleration. Seems to come from under the front seats. I'm thinking universal joint? No codes or warnings. Transmission shifts smooth and seamles under normal acceleration conditions and the L/D and shift buttons work as advertised. Any ideas on this, I have searched the forum under this topic with no joy.Also buying the program and fault reader from Bavarian Tech" since I am relatively handy in DIY repairs, is this a good choice. Thanks for your consideration

Seems like you're heading in the right direction there by trying to do stuff on your own. Go for it. Lots of us here at least trying to do almost anything we can think of on our own. Thanks to this site and everyone here, especially that guy Kief... Thanks Bro...lol I am also sure he must have been offered the Super Moderator job here but he must have refused cuz he's too busy...lol

Anyway... You didn't mention if it happens while you're driving and/or in park and/or at stop or what not. But sounds like either like you said the u-joint or motor mounts or something.

Vibration occurs under 3/4 to full throttle aplication and onset is immediate , sio I have to lift. So occurs probably as torque is rapidly increasing. No vibration in any other mode

Change the guibo. This is located on the drive shaft.

Yes, check the guibo, it's only good for 50k miles or so.

Thanks for the replies, I will replace the Guibo and report back.

Looking forward to the update.

Originally Posted by jim.mcnelis

Hello all
New to forum and new to BMW ownership. I have a 2002 745i 74K miles, generally perfect other than a severe vibration under hard acceleration. Seems to come from under the front seats.

Has your wife been driving it more recently

I'll get me coat

Seriously, hope it works out for ya. Mine's annoying me with a little rough engine issue so I can't imagine what that's like

good point, never thought about the adaptive systems. Unfortunately she has not been driving it much at all, so I'll stick with driveline for the time being. Thanks for the input though.

I was actually making a 'woman on a spin dryer' gag (hence the 2nd line) to prove something positive could come of it

Epic fail at forum humour there

+1... Guibo joint (a.k.a. flex disc) if only upon hard acceleration. Once you have the car up in the air, taking down the exhaust is very quick (especially if you get someone else to help hold one end of the system), after which you can freely take down some plastic and the heat shields, and be able to check the guibo joint for cracks. If you want to get an idea for what to expect, run through some of my pictures/descriptions --> here.

Assumptions: you've wiggled all wheels in various directions and no joints seem sloppy, you've checked air pressure in all tires (yes, I've really had under-inflated tires cause some shake in mine and felt like a dummy once I figured it out), you have no engine malfunction messages upon hard acceleration, and the shake truly feels like it's coming from the middle of the car (roughly at your feet).

If you are looking to do diagnostics, and you're decent with computer stuff, skip the Bavarian Technic cable and read up on the VAG-COM KKL 409.1 cable instead. With that you can use BMW's own software for diagnostics, troubleshooting, and various resets/changes. I bought my cable on eBay for around $12 (get the one with the FT232RL chip instead of the FT232BL chip, if possible). Once you have that, you can download and install INPA to help you diagnose. There are a bunch of good threads in bimmerforums' "Diagnostic Software" forum about setting up and using the VAG-COM cable and EDIABAS/INPA, and there are a number of knowledgeable members on here as well that are always willing to help -- but reading the existing information will go a long way.

T, thank you for the kind words, you're a good man!

Thanks for the detailed response. To confirm your assupmtions, tires and pressures good, have not checked all suspension joints, but no adverse handling noted, and no clunks over rough terrain. Also no codes or warnings after the event.This severe vibration only occurs when I get on it, and literally shakes the whole cowl area from pedals to dash. Smooth as silk under normal driving conditions. I will get the flex disc checked/replaced, seems to fit your description well. Thanks for the input on the fault reader and software, I will head down that path.