any idea on what this could be

[boonaroo]

on the highway today and wanted to do a bit of a top speed run.noticed that from 150km/h to 160km/h @ 3500rpm in 5th, the car trembles and shudders. however, from 170km/h onwards, it calms right down again and the shuddering stops. I tried this on various sections of the highway where the tarmac is in various states on disrepair and uphill/downhill. outcome was quit consistent. furthermore, 3500rpm in other gears is perfectly fine.it doesn't really bug me but I'm curious to see if anyone has had similar experiences or knows what the possible cause may be.thanks.

 

[mizhan]

had the same problem at similar speed. rectified by applying grease to the driveshaft bearings. apparently after all these years, all the grease dried up. hope that will solve your problem too..

 

[fabianyee]

sounds like it's the wheel balancing issues... I had similar vibration due to one of the rear tyres off balanced by 5gm... Mine was vibration between 140kph-160kph... After doing the wheel balancing, vibration was gone...

 

[chili e30]

if i not mistaken 4 wheel need to do on wheel balancing.

 

[boonaroo]

thanks guys. both are fairly inexpensive options to try. my gut feel was the balancing too. I'll try that first and see how the highway feels tomorrow.

 

[Strider]

i'm quite sure it is wheel balance. Do the balancing as precise as possible and the problem will solved

 

[boonaroo]

my mech advised at one point in time that one ought not perform on-wheel balancing on the rear wheels as the process will damage the LSD mechanism. mechanically speaking, I guess there's some truth to it.

 

[fabianyee]

my mech advised at one point in time that one ought not perform on-wheel balancing on the rear wheels as the process will damage the LSD mechanism. mechanically speaking, I guess there's some truth to it.

Your mechanic is right... Just need to do the normal balancing... I have never done on wheel balancing for my car..

 

[pussy]

Boon... what gearing is your car ? 160km/h at 3500rpm is quite a high gearing...

is yours a 325i ?

 

[boonaroo]

Yep, 325i. diff is a 3.45.

 

[boonaroo]

wheels were balanced but experienced much of the same today on the highway again. will chat with my mech about the drive shaft bearing.

one thing I did noticed when the wheels were out for balancing was that the right front tyre had significant wear on the inside. I got it rotated to the rear along with the side as well. I wonder if the shuddering has anything to do with it.

 

[mizhan]

good luck bro..

 

[boonaroo]

ok so to add closure to this. I had my drive train serviced. a new drive shaft and a couple of couplings later, the shuddering is gone. also gear changes are now less jerky and buttery smooth.