New 2009 2010 BMW Z4 - ZPOST - View Single Post

proboner · 10-25-2021, 01:08 PM

And on to the next project, which is the reason the car has been on jack stands in the garage for weeks. As you may remember, I switched to an MFactory LSD diff a few months ago. Upon first drive, I immediately noticed a harsher engagement of the drivetrain upon engagement of the clutch in 1st gear and reverse. Initially it didn't bother me all that much, but after taking a couple long drives with the GF that landed us in a bit of stop and go traffic, it started to make me insane. The harsher engagement when getting into and out of the gas, a more audible whine at highway speed under light throttle, and a noticeable whine under WOT acceleration.

I racked my head over what it could be. I'd found other reviews of people saying their LSD's "clunked", but in my mind it never really felt like a clunk. Eventually I decided it must be related to the Meyle HD diff bushing I'd installed. I figured that perhaps all the other mounts in the drivetrain being stock, with this 1 stiffer mount, it was throwing the synchronicity of the entire system off and causing issues. I also remembered a YouTube video I'd seen before installing the diff, showing how you could replace the rear diff mount on an e46 without removing the diff itself:

Given what a PITA doing the entire diff would be, I thought this could be a great option to test my bushing theory while keeping the work load low.

Well, longer story short, I discovered the hard way that removing the rear diff bushing on an e89 isn't possible with the diff installed. The ring gearis physically in the way of where the bushing would need to be pushed for removal. I'd also found when pulling the diff cover, that the fluid inside had much more metal sheen than I thought was normal. Perhaps there's something actually wrong with this unit? So, with about 1/4 of a diff removal already performed, I bit the bullet and pulled the whole thing.

With the unit now fully removed and even more concern in my mind, I made a call to Synchrotech- the guys who had done the MFactory install originally. I spoke with the BMW tech there and received some insight that eased my mind a bit.

The LSD will whine more under WOT- especially low mileage units which are still breaking in
The LSD will whine more at freeway cruising speed- especially low mileage units that are still breaking in
All of the LSD units are installed "tight" which causes a bit more wear in the first several thousand miles- resulting in the gear oil sheen
Agreed that the stiffer diff mount was probably exacerbating the problems

The one piece of assurance they could not give me however, was related to the clunk. The tech suggested there would be a bit more slack introduced to the system due to the design of the LSD, but it shouldn't be so noticeable. Again I hemmed and hawed over what to do. If I just reinstalled with a new mount and all the issues persisted, I'd be pissed at doing all that work and not covering all my bases. So I continued my search to see if I could find feedback from others on what they were experiencing with similar MFactory LSDs.

I first began with posting on N54 groups to see if anyone else had an MFactory LSD installed and if so, were they all feeling the clunk. If the clunk is par for the course and just a part of owning an aftermarket LSD, perhaps it was just the wrong thing for me. Not many responded with actual experience but there were a couple who insisted they felt no difference at all from factory. My takeaway being, clunk is likely but not guaranteed.

Next I found a guy on a forum showing a bit more clearly what his clunking visibly looked like. When I was in the throws of removing the diff, I happened upon a situation that I only vaguely noticed but now realiz I should have paid more attention to and definitely should have recorded. When I was in the process of removing the driveshaft, I found that I could turn it almost a full 1/4 of a rotation before it would engage the output shafts. This seemed to explain exactly what I was feeling. The harsh engagement in R and 1st could easily be attributed to this slack for 1/4 of a turn and then immediate harsh engagement as the output shafts would catch and engage the wheels. If you take a look through the thread, you can clearly see a similar situation going on with this guy and his Fiesta. When he engages 1st and R you can see and hear that lagging engagement: https://www.fiestastforum.com/thread...y-folks.27667/

This very much seemed to mimic my issue, so certainly others are feeling it and are annoyed. But the final piece of evidence that put me other the top, was found in an N54 forum where MFactory had provided their own take on all of this: https://www.n54tech.com/forums/showthread.php?t=29755
For those of you who don't care to visit the link, the pertinent text is thus:
"- Common Problems -

Diff Thump:
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.

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.

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".

Remember, the thump is not "noise" per se, it is vibration through the chassis.

The above is applicable to ALL LSD's, regardless of type."

So there's the answer. At this point things became pretty clear to me. If what I was feeling was normal, I had no interest in reinstalling and continuing to use this LSD. I would go back to stock diff and just be eLSD and live with it. But this then brought another question into play... what if there's something wrong with this unit? It's very low mileage, but the PO was in a wreck which is why I was able to buy it. Maybe something weird went down internal to the LSD? Based on the above writeup and my experience, it seemed clear that I needed a way to check the backlash, which I was pleasantly surprised to find in this YouTube video:

So based on this I found a way to measure the backlash, and an understanding of what the suggested tolerance is.

Backlash should be between .002" and .009", and what I measured in mine was around .007". Within spec, but definitely on the higher end. Plus, this seemed like a pretty amateur way to measure, and I wanted to know FOR SURE if anything was wrong. So I bit the bullet yet again, and sent it off to Synchrotech (which I now realized was a partner of MFactory and does all of their LSD installs) to be torn down, measured, and inspected.

While it was gone I went ahead and replaced the diff mount for stock, and awaited the results... which were very frustratingly pretty much the exact same thing I already knew. "Within spec but at the high end of tolerance". They went ahead and fully disassembled, found nothing wrong, and reassembled with at the tighter end of spec. What are you gonna do?

So, given my own reasoning, this should have been enough to decide I didn't want to use the LSD and I should install my stock diff and just moved on, right!? OF COURSE NOT! I'm still nothing if not a glutton for punishment! I don't know what to tell you folks, I really want this to work!

The reassembled diff arrived this past Friday afternoon and I was set to reinstall on Saturday. To my dismay, however, when I got under the car on Saturday I realized the stock mount I'd installed didn't go in quite right, and was actually broken. I wanted to say fuck it, and just install the bastard anyways, but cooler heads prevailed and I drove down to O'Reilly to rent tools to remove it. Sure enough it's pretty messed up, and unfortunately it's going to take a week to get a new one!

In the meantime, I've got a couple other considerations to take into account. Once again going back to the MFactory writeup, it's suggested the driveshaft center bearing can be an issue, and as luck would have it I actually have a new one sitting in my garage. Perhaps that will need to go in this week. I also have done a direct comparison between stock and LSD to see if there really is a difference in clunking due to loose fitting axle stubs, and there is! I may try putting my low mileage stock stubs into the LSD diff to see if it can clean up the tiny bit of slop.

Anyways. We shall see if these things cure what ails me, or if it's all coming back out again and the diff going up for sale!

10-25-2021, 01:08 PM	#83
proboner Private First Class 67 Rep 198 Posts Drives: 2003 Z4 3.0 6-speed Join Date: Feb 2017 Location: Mountain View, CA iTrader: (0)	And on to the next project, which is the reason the car has been on jack stands in the garage for weeks. As you may remember, I switched to an MFactory LSD diff a few months ago. Upon first drive, I immediately noticed a harsher engagement of the drivetrain upon engagement of the clutch in 1st gear and reverse. Initially it didn't bother me all that much, but after taking a couple long drives with the GF that landed us in a bit of stop and go traffic, it started to make me insane. The harsher engagement when getting into and out of the gas, a more audible whine at highway speed under light throttle, and a noticeable whine under WOT acceleration. I racked my head over what it could be. I'd found other reviews of people saying their LSD's "clunked", but in my mind it never really felt like a clunk. Eventually I decided it must be related to the Meyle HD diff bushing I'd installed. I figured that perhaps all the other mounts in the drivetrain being stock, with this 1 stiffer mount, it was throwing the synchronicity of the entire system off and causing issues. I also remembered a YouTube video I'd seen before installing the diff, showing how you could replace the rear diff mount on an e46 without removing the diff itself: Given what a PITA doing the entire diff would be, I thought this could be a great option to test my bushing theory while keeping the work load low. Well, longer story short, I discovered the hard way that removing the rear diff bushing on an e89 isn't possible with the diff installed. The ring gearis physically in the way of where the bushing would need to be pushed for removal. I'd also found when pulling the diff cover, that the fluid inside had much more metal sheen than I thought was normal. Perhaps there's something actually wrong with this unit? So, with about 1/4 of a diff removal already performed, I bit the bullet and pulled the whole thing. With the unit now fully removed and even more concern in my mind, I made a call to Synchrotech- the guys who had done the MFactory install originally. I spoke with the BMW tech there and received some insight that eased my mind a bit. The LSD will whine more under WOT- especially low mileage units which are still breaking in The LSD will whine more at freeway cruising speed- especially low mileage units that are still breaking in All of the LSD units are installed "tight" which causes a bit more wear in the first several thousand miles- resulting in the gear oil sheen Agreed that the stiffer diff mount was probably exacerbating the problems The one piece of assurance they could not give me however, was related to the clunk. The tech suggested there would be a bit more slack introduced to the system due to the design of the LSD, but it shouldn't be so noticeable. Again I hemmed and hawed over what to do. If I just reinstalled with a new mount and all the issues persisted, I'd be pissed at doing all that work and not covering all my bases. So I continued my search to see if I could find feedback from others on what they were experiencing with similar MFactory LSDs. I first began with posting on N54 groups to see if anyone else had an MFactory LSD installed and if so, were they all feeling the clunk. If the clunk is par for the course and just a part of owning an aftermarket LSD, perhaps it was just the wrong thing for me. Not many responded with actual experience but there were a couple who insisted they felt no difference at all from factory. My takeaway being, clunk is likely but not guaranteed. Next I found a guy on a forum showing a bit more clearly what his clunking visibly looked like. When I was in the throws of removing the diff, I happened upon a situation that I only vaguely noticed but now realiz I should have paid more attention to and definitely should have recorded. When I was in the process of removing the driveshaft, I found that I could turn it almost a full 1/4 of a rotation before it would engage the output shafts. This seemed to explain exactly what I was feeling. The harsh engagement in R and 1st could easily be attributed to this slack for 1/4 of a turn and then immediate harsh engagement as the output shafts would catch and engage the wheels. If you take a look through the thread, you can clearly see a similar situation going on with this guy and his Fiesta. When he engages 1st and R you can see and hear that lagging engagement: https://www.fiestastforum.com/thread...y-folks.27667/ This very much seemed to mimic my issue, so certainly others are feeling it and are annoyed. But the final piece of evidence that put me other the top, was found in an N54 forum where MFactory had provided their own take on all of this: https://www.n54tech.com/forums/showthread.php?t=29755 For those of you who don't care to visit the link, the pertinent text is thus: "- Common Problems - Diff Thump: 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. 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. 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". Remember, the thump is not "noise" per se, it is vibration through the chassis. The above is applicable to ALL LSD's, regardless of type." So there's the answer. At this point things became pretty clear to me. If what I was feeling was normal, I had no interest in reinstalling and continuing to use this LSD. I would go back to stock diff and just be eLSD and live with it. But this then brought another question into play... what if there's something wrong with this unit? It's very low mileage, but the PO was in a wreck which is why I was able to buy it. Maybe something weird went down internal to the LSD? Based on the above writeup and my experience, it seemed clear that I needed a way to check the backlash, which I was pleasantly surprised to find in this YouTube video: So based on this I found a way to measure the backlash, and an understanding of what the suggested tolerance is. Backlash should be between .002" and .009", and what I measured in mine was around .007". Within spec, but definitely on the higher end. Plus, this seemed like a pretty amateur way to measure, and I wanted to know FOR SURE if anything was wrong. So I bit the bullet yet again, and sent it off to Synchrotech (which I now realized was a partner of MFactory and does all of their LSD installs) to be torn down, measured, and inspected. While it was gone I went ahead and replaced the diff mount for stock, and awaited the results... which were very frustratingly pretty much the exact same thing I already knew. "Within spec but at the high end of tolerance". They went ahead and fully disassembled, found nothing wrong, and reassembled with at the tighter end of spec. What are you gonna do? So, given my own reasoning, this should have been enough to decide I didn't want to use the LSD and I should install my stock diff and just moved on, right!? OF COURSE NOT! I'm still nothing if not a glutton for punishment! I don't know what to tell you folks, I really want this to work! The reassembled diff arrived this past Friday afternoon and I was set to reinstall on Saturday. To my dismay, however, when I got under the car on Saturday I realized the stock mount I'd installed didn't go in quite right, and was actually broken. I wanted to say fuck it, and just install the bastard anyways, but cooler heads prevailed and I drove down to O'Reilly to rent tools to remove it. Sure enough it's pretty messed up, and unfortunately it's going to take a week to get a new one! In the meantime, I've got a couple other considerations to take into account. Once again going back to the MFactory writeup, it's suggested the driveshaft center bearing can be an issue, and as luck would have it I actually have a new one sitting in my garage. Perhaps that will need to go in this week. I also have done a direct comparison between stock and LSD to see if there really is a difference in clunking due to loose fitting axle stubs, and there is! I may try putting my low mileage stock stubs into the LSD diff to see if it can clean up the tiny bit of slop. Anyways. We shall see if these things cure what ails me, or if it's all coming back out again and the diff going up for sale!
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