[DaanBMW]

Originally Posted by HP Autowerks

Sounds like something internal with the transmission not syncing up and depressing the clutch long enough did the trick.

Yes, I'm just not sure if it's the clutch or the tranny that is causing this behavior, let alone that none of these were touched during install so I'm unclear about how this became an issue only now.

While keeping the clutch pressed in longer before shifting into gear avoids the noise/thump and the feeling that the drivetrain closes a gap/slop 100% of the time, most of (but not all) the time once I let the clutch back out there is a feel of jerkiness as if the torque transmitted thru the drivetrain closes a gap/slop before it finally finds the resistance of the wheels on the ground. So while the initial noise/thump is avoided by keeping the clutch pressed longer, the feel of a gap/slop closing is not always avoided.

(I did not yet find a rule as to when this feel of a gap/slop closing is avoided. Seems to be related to a pre-existing load on the drivetrain which thus does not allow this gap/slop to open up, but I'm unclear how this sometimes load "stays" in or not).

[HP Autosport]

Originally Posted by DaanBMW

Yes, I'm just not sure if it's the clutch or the tranny that is causing this behavior, let alone that none of these were touched during install so I'm unclear about how this became an issue only now.

While keeping the clutch pressed in longer before shifting into gear avoids the noise/thump and the feeling that the drivetrain closes a gap/slop 100% of the time, most of (but not all) the time once I let the clutch back out there is a feel of jerkiness as if the torque transmitted thru the drivetrain closes a gap/slop before it finally finds the resistance of the wheels on the ground. So while the initial noise/thump is avoided by keeping the clutch pressed longer, the feel of a gap/slop closing is not always avoided.

(I did not yet find a rule as to when this feel of a gap/slop closing is avoided. Seems to be related to a pre-existing load on the drivetrain which thus does not allow this gap/slop to open up, but I'm unclear how this sometimes load "stays" in or not).

Do we know where the backlash is set to?

[DaanBMW]

Originally Posted by HP Autowerks

Do we know where the backlash is set to?

Unfortunately no. It was hard to get the last snap ring in, but obviously that's not a measurement.

That is why I wanted to know what the effect of too tight of too loose backlash are. Given that once you drive there are no issues I am inclined to think the backlash is not an issue, but no one seems to post what the effects of too tight or too loose backlash are.

[crypticc]

Am told. Tight =whine. Loose = knock when loading and unloading the gearbox while already in gear.

[DaanBMW]

^ Thanks !

The tranny oil change actually did help after a couple of days (as it also took a couple of days for the noise to become so obnoxious). I am a convert to the "do not use RedLine" crowd. The Pennzoil Synchromesh is all that it is advertised to be (great on synchros for those not aware of it.)

I also reverted to the stock trany mounts, and did the center brg preload (5mm). Seems some sloppiness is required by design...

Overall, while the noise/thump is still there, it's not as invasive as before. So I guess I'll have to subscribe to the overall idea that an LSD comes with downsides and try to live with it...

[DaanBMW]

Originally Posted by crypticc

Am told. Tight =whine. Loose = knock when loading and unloading the gearbox while already in gear.

criptic - yours sounds a bit more logical, but is that knock maybe the thump I am describing here, but after a longer pressed clutch ? I've no idea. I def have no noticeable drivability issues.

It is quite disturbing to me how little actually seems to be known about the manifestations of incorrect backlash. Read what wavetrac is telling me:

"Gear whine is most pronounced on loose backlash (too much backlash) setups.
Tight backlash doesn’t often manifest itself in short term, again, unless it is extremely tight, preventing free rotation of the gearset – causing drag and heat issues. Gear whine can also come from a tight setup, but usually it is more of a vibration than a whine."

To me this is a bit confusing. So whine or whine ?

Last but not least: say your backlash is not within range. WTF do you actually do ? The snap rings ASAIK don't even have part no's, realoem doesn't even show them, supposedly BMW does not consider the innards of the diff serviceable.

[HP Autosport]

Originally Posted by DaanBMW

Unfortunately no. It was hard to get the last snap ring in, but obviously that's not a measurement.

That is why I wanted to know what the effect of too tight of too loose backlash are. Given that once you drive there are no issues I am inclined to think the backlash is not an issue, but no one seems to post what the effects of too tight or too loose backlash are.

Too tight = gear whine
Too loose = clunks during shifts

[DaanBMW]

Originally Posted by HP Autosport

Too tight = gear whine
Too loose = clunks during shifts

reviving this after along time... (been out of pocket for while.)

Sooo, doesn't this mean then that the backlash is too loose ? The jerkiness I was describing when upshifting ?

[Joey911]

Originally Posted by DaanBMW

reviving this after along time... (been out of pocket for while.)

Sooo, doesn't this mean then that the backlash is too loose ? The jerkiness I was describing when upshifting ?

Hi there, came to your thread now. I read everything, and we've got the same problem...

it seems like it only happens on MT car. I got mine from DiffsOnline. We double check the backlash many times. Then we swap a new unit from wavetrac, and tighten the backlash even more. Thump still pretty fxxxxxx violent.

When I take my car to drift or so, the thump will be minimal for a short period (cause stuffs heat up)

I sigh everyday I shift, sigh

[DaanBMW]

yeah... i now think the diff manufacturers are not supporting their product as they should. if they'd make clear how involved a full install is, ppl wouln't do it, so they'd lose sales. instead, they say it's install&play then blame the installer, or your car, etc...