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      06-12-2021, 09:41 PM   #71
proboner
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Drives: 2003 Z4 3.0 6-speed
Join Date: Feb 2017
Location: Mountain View, CA

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Well... I have had quite an interesting day!

This afternoon I set out on the task to swap in the LSD diff. Got the car up on stands and began removing all the braces and shields that are the first line of defense.


With those out of the way I could clearly see our target, but there was still much to do before she was accessible.


As mentioned in my previous post, I had purchased replacements for the wear items in the drivetrain as "while-you're-in-there's", so this wouldn't be one of those jobs where you try to find the shortcut to get the diff out... everything had to go. While unbolting the exhaust from the downpipes, I noticed one of the bolts was missing. Surely causing some sort of exhaust leak, which I'd actually kind of been suspecting recently. Sure enough, with the exhaust removed it's clear there had been exhaust gasses slipping across the flange


I would also like to point out, I know everyone says there's no power to be gained by the mid-pipes, but that squeezed down section seriously drives me nuts. I just do not see how that doesn't cause a huge restriction and destroy HP.


With the exhaust fully removed, I could now scratch an itch that had been bugging me since I purchased the car. A rattle. I remember hearing it the first time I drove the car when out in Washington to buy it. I was 99% sure it was the valve rattling in the passenger muffler, which was actually part of the reason I ended up going aftermarket. But after moving to new mufflers the errant noise persisted. In one of my videos someone suggested they thought it was wastegate rattle, which scared me for a moment, but it just didn't sound right and the turbos are too new. Finally, several weeks ago I got under the car to inspect and find the source. I couldnt see anything that could be the culprit, but upon hitting the passenger most secondary cat, I could hear something in there rattling. With the exhaust now off, this was my time to see if my theory was right. I lifted it up from the muffler until fully vertical when a small black something came falling out the pipe inlets


I was right! The PO, who notably did a TON of performance work to this car before I got it, must have accidentally dropped a bolt down in there and either didn't realize or didn't want to deal with dropping the exhaust again to fix it. I am SO HAPPY that this was the actual reason.

It was now as easy as removing the last heat shield to have access to the driveshaft tunnel and the secrets it held. And what a secret it was! Back when I was deciding what replacement parts to buy, I was doing research to find pieces that would be upgrades from stock but wouldnt increase NVH. One of the items I did a good little bit of searching on was a metal giubo that sits between the transmission and driveshaft. I coulnd't help but think that with my now basically doubled hp/tq, that thing had taken a beating. I'd read about a metal giubo that was an upgrade for certain e90 335is', which started in about 2010 but was discontinued a few years later. There seemed to be a lot of uncertainty about this piece, but I happened upon a thread on *********** that convinced me to just buy a stock rubber replacement. Well wouldn't you know, upon pulling the heatshield, it turns out I have a metal giubo!


Now I'm not sure if this is stock, and honestly I kind of doubt it is, but it's so curious to me! I know the PO installed a 335is clutch, so maybe he went ahead and bought one of these unicorn giubo's as well?

Anyways, I decided to stop there for now, as I'm at a bit of a crossroads. I had theories that despite only having 50k miles, all the bushings were perhaps shot due to the massive increase in power. But upon close up inspection they all look totally fine. The giubo appears to be in great shape and I'm not sure if I want to replace it with a potentially less durable version. The drive shaft center support bearing rubber looks pristine, and if the giubo isn't coming off, it seems like a lot of work to replace a part that still looks new. As well, the diff bushings don't seem to be too bad either. I'll certainly replace the rear bushing, as it's easiest to get to and I had an upgraded Meyle HD version, but the 2 front bushings look fine and I believe will be noticeable harder to get access to. Choices choices. Tonight will be one of contemplation.

edit: you know what? Now that I think about it I'm willing to bet the PO already went through the drivetrain a few thousand miles ago when he did the clutch. Along with all the performance mods he performed, he was also way on top of preventative maintenance and had pretty much every possible wear item in the engine bay replaced. Seems pretty par for the course that he would have upgrade the giubo and replaced the center support bearing when the trans was out. I almost wouldn't be surprised to pull the diff and find that it was LSD already, haha!

Last edited by proboner; 06-12-2021 at 09:52 PM..
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