Rear end vibration in upper reaches of 2nd gear

Carbon01 · 25th February 2007, 20:20

I have an issue I need some input on and have done as much searching as I can to no avail.

Anytime I lay into the throttle in 2nd gear, as I get into the upper half of the rpm range I start getting a vibration from the rear end best described as being like axle hop. Problem is it does it with traction control on or off, regardless of road condition (rough or smooth). It seems to me it used to be only at the very top of 2nd, but it is now showing itself lower in the rpm range, and only during aggressive throttle input. It does not trigger the traction control light if DSC is on. The one time I didn't get out of the throttle fast enough it made a terrible racket and thumping.

I don't speed away from stops, smoke tires, etc. and don't feel I have mistreated the car in the 1500 miles I've owned it. The problem showed itself again this morning with the family in the car just merging with traffic. Its annoying because after all this time looking for a nice low mile (25k) M5 I'm afraid to actually use it beyond driving it like a Honda.

I had BMW replace both rear sway bar brackets this week (one was broken and one was cracked - have to assume from prev owner), and the tech indicated the rear trailing arm bushings were a little worn, but am not certain they would contribute to this issue (I'll be honest - I don't know what rear trailing arms do at all. I have to schedule the car in for that repair). He said the diff mounts were fine.

Doesn't appear to be an issue in other gears, but not really hammering on the throttle for fear of breaking something. What else should I look for?

The clutch pedal has a little vibration feedback on dowshifts, the tires are recent Dunlops, and there are no unnusual vibrations in the trans or shifter (those were some of the things mentioned in search results). The car is completely tight and solid otherwise.

Thanks in advance and sorry for the long post length.

jclyman · 25th February 2007, 23:26

I would focus on the tires ... could be out of balance, or out of round ... even new tires sometimes are out of round ... If the shocks are almost worn out (possible, as it sounds like the previous owner thrashed the car ... which by the way is not necessarily bad, if it is properly warmed up first and he didn't really do anything "stupid") ... that could contribute to the problem. And, have them check the rear half shafts for abnormal wear.

Carbon01 · 26th February 2007, 00:59

That's a really good idea. I didn't even think about rear shocks, and yet I now recall a friend of mine that took his '00 to a track day a couple of years ago and had a terrible time with rear axle hop - all attributable to worn out rear shocks. I hadn't thought of them on this car because it has so few miles but it is 6 years old. I'll look into that as well.

I like to think the previous owner didn't beat on this car - it is exceedingly clean and proper, with all of its service documentation. It checked out with flying colors and was a CPO, had no stored codes, runs perfectly, and every perepheral system seems to function as it should. But you never know I guess. I don't imagine sway bar brackets and trailing arm bushings show wear by simply driving to church on Sunday. Unless church is at the end of a long straight away without a law enforcement presence. And the neighbor who also attends has an AMG. And the first guy there gets the better seat. heh heh

Thanks for the tip.

jclyman · 26th February 2007, 01:10

AND, don't assume the tires are round (one may be out of round or both) ...

I want to state, AGAIN, that driving the car "like it was stolen" is probably the best course of action with an M5 ... you DON'T want to baby it ... DRIVE IT ... just make sure it is at operating temperature first ...

If you baby it, it would begin to have all sorts of problems (IMHO) and you will never get full enjoyment from it ...

It is "The Ultimate Driving Machine."

By the way, my car looks new (4 years old), has 62,000 miles on it, and has been perfect ... and I drive it hard ... it has seen 153 MPH and has been over 135 MPH many, many times.

Habu · 26th February 2007, 01:25

Carbon01,

I wonder if it is your guibo.

Bob

emccallum · 26th February 2007, 01:36

If you have ever looked at the rear sway bar mounts, you would be amazed they held up during transport from germany. They are a bit thicker than a beer can. I wouldnt even bother replacing them with oe. As for the noise you may want to get an independent shop to check it out...they are usually better diagnostitians than dealers. Could be a number of different things.

suprfknman · 26th February 2007, 04:58

I had the same problem I avoided 2nd gear like the plague. Until my trans went bad. When the trans was swapped (approx 46K miles) I had them install a new dual-mass flywheel and a new clutch and no more 2nd gear vibrations. I dont think the clutch had much to do with it although the older throwout bearings can start to bind up, which is probably your clutch vibrations during downshifts. I believe the dual-mass flywheels wear out and dont absorb as much vibration as they do when new. I would install a new clutch/flywheel and change the fluid in the trans and rear diff.
Will

Carbon01 · 26th February 2007, 05:17

Thanks everyone.

I crawled under there today and snooped around some more and did see some stress lines in the Guibo, but no fracturing or rips. The rear trailing arm bushing seals were dried up and cracked a little.

And I did see the frail factory sway bar links. But the OEMs were cheap and it got the problem fixed in 30 minutes. The dealer wasn't looking specifically for any issue except to replace the failed sway bar brackets (as I figured that was the problem to start with) so they didn't have the instruction or time to go any further.

I'll swing it by an excellent independent this week and get his opinion.

Thanks again...

emccallum · 26th February 2007, 14:25

Post what you find. Hope it isnt the tranny like suprfknman!

graffix000 · 26th February 2007, 14:35

Does your beast have aftermarket Tranny Mounts? I know I had a vibration issue on my M3 that was related to having my aftermarket tranny mounts torqued too tightly. Once they were torqued properly, the vibration was gone. I know it is a stretch since we are talking different cars, but it is an easy fix if your have aftermarket mounts.