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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Wavetrac Installed (6MT) - thud/thump noise when upshift gears



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      03-28-2015, 01:47 AM   #155
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Yes, you are correct, and will depend on the condition of the axle stubs.

Most quality LSD's will be machined precisely to specification, based on a new set of "unworn" axle stubs i.e if new axle stubs are used, there should be very limited play between the meshing of the splines (there will be a little due to the fact that they are not press fit and just freely slide in and out). If old axle stubs are used, then there will be slightly more play due to wear/compression, and this will contribute to the overall backlash, thus the "thump".

Thank you for mentioning this, and I will make sure to include this in the Differential FAQ that I am putting together for the forum
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      03-28-2015, 04:54 AM   #156
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From what I've gathered from reading this thread if you only get it putting it into gear from a stop its normal. Wavetrac, quaife and mfactory guys are all getting it. ...if however is happening all the time between gears, not so good.
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      03-28-2015, 05:20 AM   #157
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When moving, the gears in the LSD and Ring & Pinion are in a constant state of mesh, turning all the time regardless of whether the clutch is engaged or not, so there will always be this free play when changing gear.

The only time that they are not turning is when the car is stationary. However, when stationary and in neutral, your transmission gears are still turning, so when you put it into gear, this locks the gears together causing the propshaft to turn very slightly which causes the "thump" due to the free play between the propshaft turning and the axles turning. As the axles are basically locked into position and can't move due to not enough power being applied (i.e clutch is still disengaged), this is why the thump (i.e vibration) is more noticeable when putting it into gear from stationary, compared to changing gear when moving.

Remember, the thump is not "noise" per se, it is vibration through the chassis.
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      03-28-2015, 03:28 PM   #158
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Quote:
Originally Posted by MFactory View Post
When moving, the gears in the LSD and Ring & Pinion are in a constant state of mesh, turning all the time regardless of whether the clutch is engaged or not, so there will always be this free play when changing gear.

The only time that they are not turning is when the car is stationary. However, when stationary and in neutral, your transmission gears are still turning, so when you put it into gear, this locks the gears together causing the propshaft to turn very slightly which causes the "thump" due to the free play between the propshaft turning and the axles turning. As the axles are basically locked into position and can't move due to not enough power being applied (i.e clutch is still disengaged), this is why the thump (i.e vibration) is more noticeable when putting it into gear from stationary, compared to changing gear when moving.

Remember, the thump is not "noise" per se, it is vibration through the chassis.
I am not that familiar with all the stuffs in the drivetrain... Some nice discussion here.

So you are saying that this thump is fixable? Or at least making it less obvious?

Do you mind making a list of stuffs that the owner of "thumpy diff" wants to check for? I bought my unit through DiffsOnline, and take it to 3D Autowork (a BMW race car shop..) and wasted another $700 for them to check for the thump and reinstalling and sxxt. At the end they tell me it's from INSIDE the unit, nothing they can do but tell me to contact Wavetrac.

When I had it on my car is less than 30,000 miles, few months back. Now I still suffer with this clunky thumping pounding throbbing fxxking diff every morning, really shakes my heart.

Already wasted too much money on it... sigh

btw, does it happen on a clutch type too?
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      03-28-2015, 03:30 PM   #159
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and the original poster had it fixed by putting a new half shaft. Can half shaft be rebuilt?f
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      03-28-2015, 03:36 PM   #160
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Quote:
Originally Posted by MFactory View Post
The two main causes of "thump", and both have to do with free play:

1) Worn or misaligned (during reinstallation) centre bearing of the propshaft. The only solution for this is to check the centre bearing, and replace if necessary.

2) Backlash. All LSD internals have free play in them (i.e backlash). This free play is a necessity because steel expands when heated. If there was no free play in the gears, they would end up welding themselves together due to the friction, and because of this, there is a compound effect i.e the backlash between all of the internal gears of the LSD (at least 12 of them for most Helical LSD's) plus the backlash of the Ring & Pinion. What this means is that there is a small "lag" between turning the propshaft, and the axles locking (i.e turning), which results in the "thump" noise you are hearing. It is not noise from the diff that you are hearing, but noise due to the vibration through the chassis and the propshaft/axles locking into place. This is also why it is normally louder during hard acceleration, especially so if you've upgraded any chassis components (mounts, diff bushings, subframe bushings, braces, suspension etc) or upgraded your clutch. There is no full solution for this, however, warming the diff up (thus reducing the overall backlash) will quieten it down slightly, as will using thicker gear oil. Baby'ing the clutch will also reduce it a lot, however, this will also increase the wear on your clutch. If you drive an MT, try dumping the clutch. Feel/sound familiar?

Regarding some of the comments about the AT (including the DCT), the reason why this is not so much of an issue is because of the ECU and Clutch, which smooths out the engagement of the diff (like slipping the clutch). However, a worn/misaligned propshaft centre bearing will cause the noise regardless of AT or MT.
These two points make so much sense to me. But they check my driveshaft and said it has no problem lol.
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      03-28-2015, 03:38 PM   #161
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Quote:
Originally Posted by MFactory View Post
Yes, you are correct, and will depend on the condition of the axle stubs.

Most quality LSD's will be machined precisely to specification, based on a new set of "unworn" axle stubs i.e if new axle stubs are used, there should be very limited play between the meshing of the splines (there will be a little due to the fact that they are not press fit and just freely slide in and out). If old axle stubs are used, then there will be slightly more play due to wear/compression, and this will contribute to the overall backlash, thus the "thump".

Thank you for mentioning this, and I will make sure to include this in the Differential FAQ that I am putting together for the forum
Sounds like having new half shaft will fix part of the problems?
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      03-29-2015, 10:57 PM   #162
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It's not the shaft, but the centre bearing on the shaft that is the issue. It's a little bit finicky when bolting back up to the diff, so can be misaligned. Or it could simply be worn.

I will be adding some suggestions to help fix/limit the thump in my Differential FAQ, yes, but in the meantime, the first area to check is the propshaft centre bearing. If all is ok there, check your axle stubs for excess free play (although most that we've seen are within acceptable limits. This is because all the cores we get in are low mileage).

once these two are ruled out, only then should you be thinking about looking inside the pumpkin and checking to see if the preload and backlash is within tolerances.

also, you need to remember, as with "gear clatter" when installing a new Flywheel, this "thump" is always going to be there, even on a brand new oem pumpkin. How much though (and whether you will hear/feel it or not) will depend on what other modifications have been done. A new clutch will bite harder than a used clutch, so this will contribute to the "thump", even more so with an uprated clutch. Similarly, upgrading to stiffer bushings, stiffer suspension, swaybars, braces etc etc will affect how much "thump" there is.
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      03-30-2015, 12:38 PM   #163
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Quote:
Originally Posted by MFactory
It's not the shaft, but the centre bearing on the shaft that is the issue. It's a little bit finicky when bolting back up to the diff, so can be misaligned. Or it could simply be worn.

I will be adding some suggestions to help fix/limit the thump in my Differential FAQ, yes, but in the meantime, the first area to check is the propshaft centre bearing. If all is ok there, check your axle stubs for excess free play (although most that we've seen are within acceptable limits. This is because all the cores we get in are low mileage).

once these two are ruled out, only then should you be thinking about looking inside the pumpkin and checking to see if the preload and backlash is within tolerances.

also, you need to remember, as with "gear clatter" when installing a new Flywheel, this "thump" is always going to be there, even on a brand new oem pumpkin. How much though (and whether you will hear/feel it or not) will depend on what other modifications have been done. A new clutch will bite harder than a used clutch, so this will contribute to the "thump", even more so with an uprated clutch. Similarly, upgrading to stiffer bushings, stiffer suspension, swaybars, braces etc etc will affect how much "thump" there is.
Center bearing seems decent to change or realign?

But it the stub is bad, you need a new half shaft right?
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      03-30-2015, 12:59 PM   #164
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1st thing is to check your propshaft centre bearing, and replace if worn

2nd is to check your axle stubs. If these are worn, they will need to be replaced. Your axles can be re-used
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