Chassis/cabin vibration at highway speeds only

[Mozza1219]

Replaced the rear half of the tailshaft with a 2nd hand one. Unis are in moderate condition so no idea how long they'll last.

Vibration is gone now (went on a 30 min test drive).

I suspect the unis were not properly aligned on the rear of the tailshaft so it was always off centre. The shop tried to fix this by welding a big weight on back of the shaft but that didn't work.

it's hard to explain but out of the 4 directions the uni can bend in, one of them always felt like it couldn't reach as far as could. This wad because the yoke was hitting the other side of the yoke too early which was caused by the uni not being centred properly.

I'm disappointed in the tailshaft shop but at the same time I'm relieved that it's finally gone.

[Mozza1219]

Good job in being through!

Thanks mate. It's either more money down the drain or it'll actually lead somewhere but I've got a rear half section of a tailshaft on order so we'll try that out and go from there.

[jbontke]

Good job in being through!

[Mozza1219]

Another update.

Disconnected the cv shafts today and ran the car up to speed whilst on jack stands. Unsurprisingly, vibration happening between 45mph to 60mph and then sort of smoothing out after that (but not really, the frequency just seems to change).

I've pretty well convinced myself that something has gone wrong with the tailshaft rebuild (replacing unis). I suspect that the rear uni is not perfectly centered. I've been through everything else, apart from the diff bushing, but I doubt that this would be causing such a vibration. and its still in one piece. Going to try and get my hands on another tailshaft, which is tricky in Australia but we'll see. Worst case scenario the yokes get cut off and a new serviceable uni gets installed.

Will report back once I get a new tailshaft, balanced and installed.

[Mozza1219]

Thanks Twright. I'm arranging to borrow a set of wheels in 2 weeks and will report back after testing.

[twright]

[QUOTE=Mozza1219;n10046635]

I took a closer look at the wheels and yes, one wheel is definitely in worse shape than the rest. The other 3 are ok, with the exception of 1 which also has a slight warp in it. So that makes 1 bad wheel and 1 sort of bad wheel right?

So I got my spare wheel from the boot and went through each wheel, swapping it out one by one. The spare is in perfect condition and the tyre seems ok.





THIS is the cause of your vibration. Swap a set of wheels/tires and try it again. Or, get the wheels straightened.

The vibration on this car will not stop until the wheels/tires are sorted out.

[Mozza1219]

Got the driveshaft back. The guy said there was a bit of a vibration in the diff end of it, so they put another small weight on. Bolted it all back together as above. Problem still there.

Spent today rebuilding the front brakes, changing the seals on the pistons because I think they were catching a bit. There was a bit of dirt in there, but nothing crazy, brakes definitely don't catch anymore. Drove the car. Problem still there.

Replaced the front strut top mounts because it's one of the last things I never changed on the front suspension. Problem still there.

Replaced the engine mounts. Problem still there.

Starting to lose hope in this car, no matter what I replace it doesn't seem to make a difference. Vibration now between 80-95km/h. Smooths out at higher speeds, but quite 'vibraty' at 80-90km/h.

Trying to get my hands on a set of wheels and tires that I can just borrow for the day, but this is proving to be tricky.

Exhaust seems to have good clearance from front to back, it's been re-done too.

Any help/advice is appreciated.

[twright]

It's hard to say. The good part is this should be easy to find: Drive until it vibrates and then climb under the car. If the exhaust is touching ANYTHING, that can be the source of your vibration.

[Mozza1219]

It's a good thought, but it doesn't line up with the vibration being speed specific?
Driveshaft is still with the shop.

[twright]

I have a crazy idea: Exhaust systems grow significantly as they heat up. Is it possible that your exhaust (after being driven a while) has grown and is now touching something on the body?

[Mozza1219]

I've figured that if I leave the car for an hour or so and then drive it, it is initially smooth and then after a few minutes it starts vibration, which then gets worse within about 10 minutes of driving. My theory is that either the CSB is faulty from the factory, or it was damaged by the mechanic when it was installed on the shaft.
Because of the above, I doubt that the issue is alignment or a bushing because that would make itself evident straight away. It seems to me that the vibration occurs when a bearing or something heats up after being rotated multiple times.
I'm going to take it back to the driveshaft shop today and ask them to run it on their balancing machine. I had a long chat with them about bmw shafts and phasing and they do seem very knowledgeable on the subject, but they agree that bmw shafts are a pain to work on.

I havnt replaced the engine mounts or diff bushing yet. I've got the engine mounts ready to go but I haven't had the time to install them yet.

This is a strange vibration, it defies all logic and I can't get my head around why it's initially smooth and then starts vibrating after a few minutes of driving. Thoughts?

[82eye]

I have had this problem with an 325i and a 318 M42 car. the solution each time was new OEM bushing/mounts at the engine, trans and differential. The 325 was smooth with rubber on the driveline and poly on the subframes. The M42 car I am still chasing last bit of it and I am removing the delrin trailing arm bushings and frame bushings in favor of poly.

every poly bushing i've seen transmitted more nvh from the driveline to cabin. oem rubber is the best way to get rid of it.

[OSAH racing]

I have had this problem with an 325i and a 318 M42 car. the solution each time was new OEM bushing/mounts at the engine, trans and differential. The 325 was smooth with rubber on the driveline and poly on the subframes. The M42 car I am still chasing last bit of it and I am removing the delrin trailing arm bushings and frame bushings in favor of poly.

[ADEN]

Let someone set in front seat then move to rear seat trying to locate where it feels more or all the same?

[Mozza1219]

Sorry to revive a dead thread...but guess what. It's back! or it was never actually gone?

The car has sat in storage for months and low and behold when I took it out for a drive, vibration is back. It's not as serious as it used to be, but its still just as annoying.

Starts at 90km/h on the dot and it changes a little as the speed increases, almost like its getting smoother but you can notice the rear view mirror shake more and more as the speed increases.

Doesn't matter if I'm coasting, accelerating or braking.

I've put the car on a lift and run it up to speed with the rear wheels and brakes removed - still vibrating. So this tells me its something with the driveshaft or alignment with the driveline.

I replaced the transmission mounts ages ago, but I never touched the engine mounts as they 'looked' ok.

The refurbished driveshaft honestly looks good, can't see any missing weights, points where its contacted the chassis etc. And the Uni's look to be set up correctly.


Could this issue be due to me replacing the transmission mounts and not changing the engine mounts and this has somehow caused the entire driveline to be at a strange angle which causes a speed sensitive vibration?

Engine mounts are in the mail and will be replaced hopefully this week.