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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Fri, Dec-15-2017, 03:24:04 AM   #21
rpearl555
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Default Re: Adjusting Diff backlash (eliminate M clunk)

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Originally Posted by Braymond141 View Post
It's not the lash (which is no different than any other BMW diff), it's the shortened passenger side output shaft flange. The shortened length doesn't provide enough support allowing it to flop around slightly. This is noted ALL over this forum and anything BMW printed about the "M clunk". It's a design characteristic and you will never notice it if a) your car is maintained properly b) you drive manual properly.
I never knew the actual reason for the clunking. What can be done maintenance wise to reduce it? New passenger side output flange?
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Old Fri, Dec-15-2017, 03:57:44 AM   #22
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Default Re: Adjusting Diff backlash (eliminate M clunk)

Do those of you who think our drivelines should be quiet actually think that most E46 M3s are broken?

I can hide driveline noises if I drive carefully like Braymond said earlier. All parts have been replaced along the driveline, so nothing's broken, In fact, I just R&R'd the diff last weekend and would have noticed anything wrong then.
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Old Fri, Dec-15-2017, 04:41:03 AM   #23
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Default Re: Adjusting Diff backlash (eliminate M clunk)

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Originally Posted by rpearl555 View Post
I never knew the actual reason for the clunking. What can be done maintenance wise to reduce it? New passenger side output flange?
Quote:
Originally Posted by TboneM3 View Post
Do those of you who think our drivelines should be quiet actually think that most E46 M3s are broken?

I can hide driveline noises if I drive carefully like Braymond said earlier. All parts have been replaced along the driveline, so nothing's broken, In fact, I just R&R'd the diff last weekend and would have noticed anything wrong then.
Agree here.

Read the last few posts in this thread about the pumpkin design...http://www.m3forum.net/m3forum/showt...=593444&page=5

Similar to Tbone, I have everything replaced in the driveline and a freshly rebuilt 4.1 diff (which is still a bit tight) and have the noise. Moving the output flanges with a screwdriver for leverage does not get around the design problem and you can see/hear the noise from the extra movement.
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Old Fri, Dec-15-2017, 05:18:47 AM   #24
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Default Re: Adjusting Diff backlash

Having driven several E46 M3's, it's definitely a case of some do it, some don't. I don't think it will be purely backlash related, as many diffs are setup with the same kind of tolerances and don't exhibit the same noise. More likely to be the diff output flange movement, driveshaft play or mounting bolts not torqued correctly.
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Old Fri, Dec-15-2017, 04:01:21 PM   #25
nowanker
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Default Re: Adjusting Diff backlash

The term 'backlash' when applied to a differential is typically defining the relative movement between the pinion gear and the ring gear, and is a critical dimension when building a diff.
But in my experience... the pinion/ring gear backlash is not the cause of the clunk. It's been excess clearance between the spider gears inside the diff carrier.
Replacing the ring and pinion, and resetting backlash properly won't cure that play, so a fresh built 4.11 on a clunky carrier will still clunk.
And no, BMW diffs with the M clunk aren't 'broken'. They were just poorly manufactured.
BMW has done a snow job here.
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Old Fri, Dec-15-2017, 05:07:52 PM   #26
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Default Re: Adjusting Diff backlash

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Originally Posted by nowanker View Post
It's been excess clearance between the spider gears inside the diff carrier.
Q F T.
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Old Fri, Dec-15-2017, 07:35:02 PM   #27
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Default Re: Adjusting Diff backlash

I just drove another M3 today, and it didnt have that clunk. So the plan is to chase this issue until it's fixed. I have to take nowaker's side here, this clunk is not normal.

I just noticed my flex disc needs to be replaced, so ill do that along with tranny bushings and centering sleeve. I dont suspect it will fix the clunk, but might mitigate it. If it doesnt, then it will be time to open the diff and figure out if its my ring and pinion or the spider gears. If its the spider gears, then Ill just get a new lsd unit.

Back to the original question, and assuming i do find excessive backlash (pinion and ring) , does anyone have any additional advice regarding the specific process of setting yhe backlash back to spec ?

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Old Fri, Dec-15-2017, 08:30:28 PM   #28
nowanker
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Default Re: Adjusting Diff backlash

I wouldn't recommend DIY diff work. If you search here, there are some good writeups about it. I did mine out of pride, and it sucked from start to finish.
Find a diff shop that's familiar with these, worth the $$. BMW makes some of the parts difficult to get and painful to buy!
Internal parts for the carrier (where the play is likely to be found!) are NOT available from BMW.
Blanton Performance Gearing
Diffs Online
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Bimmer World
Sure there are others that are worthwhile!
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Old Fri, Dec-15-2017, 11:05:54 PM   #29
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Default Re: Adjusting Diff backlash

I think alot of the noise comes from two things provided the bushes, guibo and CSB are new.

1. Worn CV joints - CV on prop can be replaced , CV on driveshafts not so much. And I think drive shafts have alot to do with it. ( This is nothing related to the up and down flange movement people love to video as that is flange related and not drive shaft)

2. Internal spider and planet gear lash combined with the sort stubby right side flange. Which is actually in connection with a spider gear as it's splines mate with the spider gear. This is contributing but cannot be fixed and is characteristic to them all. Some people think that movement is bearings. it's not!

Then there is a 3rd possiblity and will only come into play after a diff seal job. When doing the input pinion seal. There is a technique to doing it and making sure the pinion nut is replaced with exactly the same amount of torque to achieve exactly the same amount of preload. Well I did an experiment . I did the seal on my 3.62 which was previously quiet as a mouse. I marked the nut 2 different places and counted the turns yada yada . But before I did this I measured the break away torque using an inch pound torque wrench and measured my overall rotational torque ( no side shafts attached) at 25in/lbs. I then put it back together and put the nut on exactly as it came off but I did not check the rotational torque. Put it together and drive it. I had a mild increase in clunk. Back on the lift and disconnected the shafts and measured the rotational torque. It was only 12in/lbs. So I tightened the preload back to 25 in/lbs and it was back to normal.

What was happening here was the pinion depth was getting sloppy and in turn affecting backlash. This caused the increase in audible noise. This extra lash wasn't enough to cause problems.

My point is that without a proper torque measurement when doing diff work you cannot gauge it by marking. The tiniest hair width of a turn on that pinion nut will make the difference and what looks like it's back to the original position, it probably isn't. The gears don't wear a whole lot and they won't wear so significantly that they will put them selves out of tolerance. Something needs to cause it. Lack of oil or poor work in the past like my previous experiment or contamination .

4th point is that poly or solid diff bushes will definitely make you hear the diff working and cause you to hear a clunk and this is normal . Your diff is mechanical. It makes noise. OEM diff bushes do a great job at masking it usually and why anyone would change them I don't know. The OEM front bush for example weighs like 6-700 grams and is more less solid and well engineed.

That's my two cents from my own experience.

I then built my 4.1 and set the backlash to the tighter end of the tolerance. ( Shorter gears the tighter the lash) I set it to .09mm vs .12mm that my 3.62 had. The diff is silent and I have the typical amount of up and down movement In the right flange which they all have.

Also worth mentioning here is that there is a thing called flywheel slap. And you can make the car do this by labouring the engine. Stabbing the throttle I'm 1st or second and making the car jerk. This will cause a clunk which is actually coming form the flywheel even though it can sound like it's the back end. Provided everything in the back end is in order of course , otherwise it could be your back end. Haha. This is proven when you drive the car without the sound / heat rubber boot which encloses your gear lever and what protects the cabin from the underside fumes and keeps noise out. Take it out and go for a drive. You can hear everything going on and I traced that noise to be coming from the flywheel. Another one of my whacky experiments. Before I did this I was convinced it was the back end. But I have to make the car do it. Very rarely will I get that noise accidentally.

Last edited by schoonerm3; Fri, Dec-15-2017 at 11:26:44 PM.
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Old Fri, Dec-15-2017, 11:46:30 PM   #30
rpearl555
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Default Re: Adjusting Diff backlash

Great post. Really informative!
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Discussing Adjusting Diff backlash in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)