Diff Noise - Not fixed with new Diff!
Discussion
Hi Guys,
Hoping someone might be able to shed some light on this.
I've got a rumbling/frictional sound coming from the Diff. From about 30mph it's audible. Gets louder at higher speeds, does not change under acceleration, coasting etc. Garage jacked the car up, spun the wheels etc, and the sound is *really* the diff.
So swapped it for another one.
Sound remains! Hmmm. At a bit of a loss to be honest.
In tandem with this i started getting severe vibration from the driveshaft under heavy acceleration - garage changed the centre mount, which has *fixed* it, but they said it shouldn't have been worn, they don't know why it was, and it will probably wear again.
I'm inclined to agree as I can still feel the beginnings of vibration at the same point when accelerating, it's just heavily damped by the new rubber mounting in the center mount.
Any opinions welcome - if anyone correctly diagnoses I will courier you a crate of the beer of your choice!
Hoping someone might be able to shed some light on this.
I've got a rumbling/frictional sound coming from the Diff. From about 30mph it's audible. Gets louder at higher speeds, does not change under acceleration, coasting etc. Garage jacked the car up, spun the wheels etc, and the sound is *really* the diff.
So swapped it for another one.
Sound remains! Hmmm. At a bit of a loss to be honest.
In tandem with this i started getting severe vibration from the driveshaft under heavy acceleration - garage changed the centre mount, which has *fixed* it, but they said it shouldn't have been worn, they don't know why it was, and it will probably wear again.
I'm inclined to agree as I can still feel the beginnings of vibration at the same point when accelerating, it's just heavily damped by the new rubber mounting in the center mount.
Any opinions welcome - if anyone correctly diagnoses I will courier you a crate of the beer of your choice!
Edited by BMWBen on Monday 23 July 07:53
tr7v8 said:
My Alfa 75 had this problem, sounded like a wheel bearing. Eventually after 2 bearings under warranty turned out to be rear tyres! If the Prop has a centre bearing it can also be that.
This noise is def coming from the diff unfortunately - when you spin the wheels by hand with the car jacked up there's no doubt.tr7v8 said:
My Alfa 75 had this problem, sounded like a wheel bearing. Eventually after 2 bearings under warranty turned out to be rear tyres! If the Prop has a centre bearing it can also be that.
My wife's 3 series (96) had exactly the same problem and we had both rear wheel bearings changed, sound was still there. Took it back to the dealer and he advised changing rear tyres. I would have laughed but it needed two tyres anyway so i popped round to nearest tyre fitters and guess what, it was cured. Common problem apparently with BMWs and Goodyear eagles, they don't mix.Andy
I am going to keep this as simple as I can - having fixed a number of diff noise issues in production.
Generally speaking, diff noises are heard in the car by two methods - airborne noise and structure borne noise.
The airborne noise will be more obvious when you wind a window down, but most noise is structure borne
What you have to realise is that each panel and component has a frequency at which it is set off at, and if there is sufficient transmissibility between the noise source and that panel, it will make noise.
If the gear ratios chosen are 'integer' or near integer e.g. 4.1:1 or 3.07:1 or 2.88:1 then you get much more chance of hearing noise because the panels will be set off at the same frequency, double it, three times, four etc. That won't happen if the ratio is non integer e.g. 3.6:1.
Similarly the same goes for gearbox ratios. That is why it is rare to find any cog the same. But if the overall gearing is 'integer' then you get noise in that gear.
If the gearset is by geometry noisy either by design or wear it won't ever be cured, just mitigated, by limiting transmissibility. That means tuning the mounting system to absorb peak noise at the point where it is most annoying in the vehicle. Bottom line to the enthusiast: change the mounting rubbers for hard ones and the diff may seem noisy, when it really isn't.
In addition, you can also change the freqency by changing the noise path. The prop alignment can be tuned to be straight at the annoying frequency, allowing the engine / gearbox to become a dynamic absorber.
In this situation I would check gearbox & diff mounts, if they look to be on their way out then change them. I would endeavour to maintain the diff by topping oil up regularly. Good luck.
Generally speaking, diff noises are heard in the car by two methods - airborne noise and structure borne noise.
The airborne noise will be more obvious when you wind a window down, but most noise is structure borne
What you have to realise is that each panel and component has a frequency at which it is set off at, and if there is sufficient transmissibility between the noise source and that panel, it will make noise.
If the gear ratios chosen are 'integer' or near integer e.g. 4.1:1 or 3.07:1 or 2.88:1 then you get much more chance of hearing noise because the panels will be set off at the same frequency, double it, three times, four etc. That won't happen if the ratio is non integer e.g. 3.6:1.
Similarly the same goes for gearbox ratios. That is why it is rare to find any cog the same. But if the overall gearing is 'integer' then you get noise in that gear.
If the gearset is by geometry noisy either by design or wear it won't ever be cured, just mitigated, by limiting transmissibility. That means tuning the mounting system to absorb peak noise at the point where it is most annoying in the vehicle. Bottom line to the enthusiast: change the mounting rubbers for hard ones and the diff may seem noisy, when it really isn't.
In addition, you can also change the freqency by changing the noise path. The prop alignment can be tuned to be straight at the annoying frequency, allowing the engine / gearbox to become a dynamic absorber.
In this situation I would check gearbox & diff mounts, if they look to be on their way out then change them. I would endeavour to maintain the diff by topping oil up regularly. Good luck.
Try disconnecting the propshaft and spinning the diff over by hand, or with an electric motor somehow.
as the previous chap said check engine and gearbox mounts also check propshaft UJ's and get it balanced, I'd reccommend Dave mac propshafts in Coventry if its fine, he won't charge for checking it.
Matt
as the previous chap said check engine and gearbox mounts also check propshaft UJ's and get it balanced, I'd reccommend Dave mac propshafts in Coventry if its fine, he won't charge for checking it.
Matt
350Matt said:
Try disconnecting the propshaft and spinning the diff over by hand, or with an electric motor somehow.
as the previous chap said check engine and gearbox mounts also check propshaft UJ's and get it balanced, I'd reccommend Dave mac propshafts in Coventry if its fine, he won't charge for checking it.
Matt
Handy hint - I'll give him a call today. Coventry is a good 100 miles away tho :Oas the previous chap said check engine and gearbox mounts also check propshaft UJ's and get it balanced, I'd reccommend Dave mac propshafts in Coventry if its fine, he won't charge for checking it.
Matt
bobt said:
Hello Ben
Sounds like your Z is suffering from diff mounting cracks. i.e. cracks in the boot floor/cross member in the area where the diff mount attaches. A more common problem in the the 2.8/3.0/3.2 engined cars.
Lots of info on Bimmerforums.com
beer please ?
I've checked the boot floor - all the welds still good, no sign of distortion. Garage said they didn't see anything wrong when they swapped the diff.Sounds like your Z is suffering from diff mounting cracks. i.e. cracks in the boot floor/cross member in the area where the diff mount attaches. A more common problem in the the 2.8/3.0/3.2 engined cars.
Lots of info on Bimmerforums.com
beer please ?
Keep trying though please!
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff