Rear differential upgrade to 3.73,have questions

[Heebs84]

Hello everyone I’m fairly new to the forum. A little background purchased a 2007 E86 3.0si last September manuel and love every second driving it too! I’m doing a few upgrades to her and already purchased a new Quaife lsd, it’s sitting at my house waiting to be put in. I planned on changing my gear ratio cause if I didn’t do it now I’d regret it later on soooo. I’m going to go with a 3.73 gear ratio. Now I’ve been looking on eBay for just the gear & pinion but the few there are I’m not sure they would work. Are people just buying the whole rear diff just for the gear & pinion ??? Also are people buying the diff and putting the lsd in the newly bought one then swap them out? I’m just a bit confused on what vehicles are interchangeable. It seems the cars that have the 3.73 are the 330i or something around there. I could really use everyone’s knowledge to help me figure this out. Thanks for your time in this matter

 

[M@_]

Just throwing this out…. It’s possible you’d need a different carrier if you are going from 3.07. Again, I don’t have the details on your car, and my experience was with wavetrac, but there were two different sizes of carrier for different ring gear sizes. My 03 3.0i 6 speed used the smaller.

 

[Heebs84]

yeah my plan is to install Quaife lsd into rear diff & if it’s not to big of a headache install a 3.73 gear & pinion otherwise I’m just going to use my original which should bolt right up I believe. Then reassemble, but was thinking of getting a rebuild kit for the bearings & seals might as well since I’d have it apart.
Does this sound reasonable or am I missing something? I have a 2007 3.0si manuel has the 3.46 gear ratio too. Thanks again for the ideas & suggestions.

 

[Heebs84]

Did you change your gearing as well?

 

[M@_]

Based on your response you should be good to change out the gear-set. The size transition happens at 3.1. So going from 3.46 to 3.73 has the same carrier. Just know you'll need to adjust the lash and pinion if you are swapping gears.

For mine, I just needed to remove the open carrier, remove the OEM bearings and ring-gear. Then install the ring gear and bearings onto the Wavetrac carrier. After that I had to grind the case a smidge to get it all back in, but no messing with gear-lash or pinion bearing stuff. Just check the pattern and lash then seal it back up.

 

[Heebs84]

Thanks for the input. I’m looking at a rear diff it’s from a 2008 z4 e85 3.0i with gear ratio of 3.73. But I’m not sure if it will work. Would you know by chance? Also another one I’m looking at is a rear diff from a 2006-2011 E90,e91,e92 325,328, it has the 3.73 gearing. I’d appreciate the input