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So when I do this weld I am basically making the ring gear and planetary gearset spin as one unit?


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Discussion Starter #42
So when I do this weld I am basically making the ring gear and planetary gearset spin as one unit?


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Exactly. It'll also bring along the front-drive portion of the gears, so the output flange pointing back towards the engine will still spin (and drive). You could theoretically put the front driveshaft in and still be 4wd in a straight line. Good luck taking a turn with no center diff though. Its just all locked together.
 

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Very cool, The only thing I like about my xi is the handling in the snow and rain. Any other time I kinda wish I bought a rwd for the fun factor. Great experiment, perfect if someone wanted to track a budget xi for fun.
 

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Hmm, Wouldn't this be easier if you got a spare output shaft and welded up a custom locking plate?
Short version: Remove the front drive shaft, pull the output shaft, weld a locking plate (maybe something that could bold around the Tcase, or to the mounting bolt) then you can just crawl under and convert at will.

Just a thought...
 

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I've been working on a little side project and I've finally made enough progress to post about it here. I picked up a junkyard transfer case and welded up the planetary gearset inside. Not the prettiest welds, but there are more than enough throughout, and the final re-sealed diff spun smooth as new. With a locked center diff, I can run without a front driveshaft and enjoy the RWD. I swapped it in this afternoon and had a very successful ride home. No noise or vibrations way beyond highway cruising speed plus all the perks of rwd (noticeable power bump, oversteer under throttle, slip when I wanted it). DSC wasn't too happy with me when I did mess around, even with it "disabled", but I risked a few clutch dumps in the rain and got plenty of standing wheelspin. I'm going to unplug the unit soon and see what it can really do. The plan for now is to leave the front diff and axles in, the idea being to swap the old transfer case back when I put my snow tires on. But you never know...



Awesome! We are race prepping a 2003 325xi and I feel certain we will, at some point, find this mighty useful.

Yes, pride in pulling it off on your own. Carry on!

Cheers,
Bob
 

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Hmm, Wouldn't this be easier if you got a spare output shaft and welded up a custom locking plate?
Short version: Remove the front drive shaft, pull the output shaft, weld a locking plate (maybe something that could bold around the Tcase, or to the mounting bolt) then you can just crawl under and convert at will.

Just a thought...

Hmm....this is an interesting thought.
Leave front diff and CV shafts in place, remove front drive shaft and figure out how to lock the front output flange to the TC- the 4 bolt flange with the red plug in the center of the image.




 

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Discussion Starter #49
Appreciate it, guys.

As for this new design, you are correct, in principal. Holding the front output flange will ultimately send 100% of the torque to the rear. However, I see a few potential flaws.

The most glaring issue is the resulting gear reduction. I don't have it in me to do the math, but I'm thinking the ratio would be extreme. In my design, the power passes straight through with no differential action and no change in input/output rpms. By essentially holding the sun gear and putting power through the carrier, you're gonna work the planetary gears and spin the ring gear significantly faster than the trans output speed. A slight difference would be manageable, akin to moving to a higher rear diff ratio, but I have a feeling that the results from this mod would shorten the gears far to much for practical use.

Second, like I sad earlier, you'd be working that diff like crazy at all times. Those planetary gears are designed to spin as little as possible, only in use really as you steer the car, and even then at a relatively low speed. Those are straight cut gears designed for strength, not noise, and my guess is the transfer case would quickly develop a very loud whine (like a car speeding in reverse).

Strength seems like it could be an issue. I'm not sure where you could mount a bracket under there. It would have to be pretty large, which means cost and weight. And it would need to be able to handle a significant amount of torque, assuming some hard launches are in order. I feel like welding directly on the gears, right in the center of the driveline, provides the most reliable strength.

And really, is there any more ease to this design? If you can remove a transfer case, you can take one apart and re-seal it. There would be welding involved either way. To me, $100-300 for a second transfer case isn't unreasonable, versus the potentially cheaper cost of bracket parts. And I don't see this bracket being much easier technically.

If we're talking design, I've been mulling over having a custom gear made to simply replace the planetary carrier. I'm thinking the existing carrier/planets/sun/ring might be able to be scanned or measured and used to CAD blueprint a solid replacement, retaining the inner input splines but with full 360° tooth mesh into both the ring and sun gears (instead of 3 small points of contact you get with the planets). Strenth and balance would be excellent, and installation would be as easy as taking the transfer case apart. Could be marketed to any e46xi or e53 owner, and maybe even some in that GM crowd. I don't really have the spare cash to make exploring this feasible, but I might as well put it out there to the crowd(fund)...
 

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If we're talking design, I've been mulling over having a custom gear made to simply replace the planetary carrier. I'm thinking the existing carrier/planets/sun/ring might be able to be scanned or measured and used to CAD blueprint a solid replacement, retaining the inner input splines but with full 360° tooth mesh into both the ring and sun gears (instead of 3 small points of contact you get with the planets). Strenth and balance would be excellent, and installation would be as easy as taking the transfer case apart. Could be marketed to any e46xi or e53 owner, and maybe even some in that GM crowd. I don't really have the spare cash to make exploring this feasible, but I might as well put it out there to the crowd(fund)...
I assume those gears arnt pressed in? Once inside the TC they can be lifted out and swapped?

If that's the case, why not just have a second set of welded gears to swap in/out of 1 transfer case.
 

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Discussion Starter #51 (Edited)
I assume those gears arnt pressed in? Once inside the TC they can be lifted out and swapped?

If that's the case, why not just have a second set of welded gears to swap in/out of 1 transfer case.
You could. The planetary carrier lifts right out once the case is open. And you could probably put down enough welds on the carrier itself to do the job without joining it to the ring like I did. Two things though. One, the only planetary carrier I've seen for sale on its own was the same price as a full transfer case. Also, its just easier to swap transfer cases than it is to deal with pulling it, splitting it, re-sealing it, and fluid changes every time.

But to each their own...
 

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You could. The planetary carrier lifts right out once the case is open. And you could probably put down enough welds on the carrier itself to do the job without joining it to the ring like I did. Two things though. One, the only planetary carrier I've seen for sale on its own was the same price as a full transfer case. Also, its just easier to swap transfer cases than it is to deal with pulling it, splitting it, re-sealing it, and fluid changes every time.

But to each their own...

price wise, that's a good point- did not think of that.
I can go to the pick n pull today and come home with a TC for $75.
 

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This intrigues me. Though, with just a thicker rear sway bar, I've been able to get the rear to kick out just like with my old RWD E34. The main reason I would want to switch to RWD is to get the tighter steering ratio rather than the extra sensation of being pushed.
 

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i'd be careful talking so openly about your fwd desire around here lol pretty sure the thought of front wheel drive bmws is some sort of blasphemy


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Discussion Starter #57
I was gonna say, it was only a matter of time haha

From a purely mechanical standpoint, yes, it should work just fine. I'd have some concerns about the strength of the front driveshaft and diff, but the car should drive fine in fwd, at least under low loads.

Why you would want to do this is beyond me, and this is coming from someone who just justified a rwd conversion. The main benefits of fwd are related to the company's ability to design the car in a different way from the ground up. Smaller/lighter/cheaper/simpler drivetrains, larger cabins because everything is forward of the firewall, short axles means better mpgs, etc. You would get none of that by converting an e46, save for a slight fuel mileage bump. But you would lose so much more...
 

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i'd be careful talking so openly about your fwd desire around here lol pretty sure the thought of front wheel drive bmws is some sort of blasphemy


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So blasphemous that when BMW made a FWD car, they had to re-brand it as a MINI Cooper.
 

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Discussion Starter #59
Looks like I'll be parting out a 2004 330xi soon, which means I'll have another transfer case to play with. Any chance someone would want one made for them?
 
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