$200 rwd conversion

That's pretty cool being able to swap between the two types of drive. I live up in a snow state too, so I feel your pain. Keep up the creativity, and wrenching.

Awesome post man

Originally Posted by inline.6ix

Awesome post man

Haha thanks

As for an update, I'm over 5k miles in with no issues. I swapped my 3.07 rear diff for a 3.46, which is pretty great. I have the matching front diff too, if I want to go back to 4wd.

Any electronics guys out there? I've been researching a work-around for the single stage xi DSC. I found a thread that seems to confirm the later e39 Bosch 5.7 units will bolt right in with a few swapped pins in the connector. I'm wondering if the new unit will bring fully disable-able DSC to the car, or if coding it will force it to act like a normal xi unit.

Originally Posted by Manchicle

Any electronics guys out there? I've been researching a work-around for the single stage xi DSC. I found a thread that seems to confirm the later e39 Bosch 5.7 units will bolt right in with a few swapped pins in the connector. I'm wondering if the new unit will bring fully disable-able DSC to the car, or if coding it will force it to act like a normal xi unit.

This is really the last remaining issue to tackle to make this a viable swap so I'm very interested as well. I have other priorities right now, but sometime soon I'd like to look into whether we can just code the DSC unit we have using NCS Expert instead of swapping it with one from an E39. There's a thread where someone with a ZHP was able turn off the system that emulates an LSD using the brakes. I know that's a different unit entirely, but we may have similar options.

If we can turn off our DSC units' longitudinal differential-lock function (braking the slipping axle as previously discussed), then this mod can be done without any risk to drivetrain components.

Originally Posted by xi46

This is really the last remaining issue to tackle to make this a viable swap so I'm very interested as well. I have other priorities right now, but sometime soon I'd like to look into whether we can just code the DSC unit we have using NCS Expert instead of swapping it with one from an E39. There's a thread where someone with a ZHP was able turn off the system that emulates an LSD using the brakes. I know that's a different unit entirely, but we may have similar options.

If we can turn off our DSC units' longitudinal differential-lock function (braking the slipping axle as previously discussed), then this mod can be done without any risk to drivetrain components.

I'd be willing to guinea pig if we can get some definitive info on the coding. I recently did my own EU2 tune. The fact that rwd e39 cars shared the same DSC unit makes me hopeful. I'm capable, I just don't have enough confidence in my understanding of coding to dive in without some expert guidance.

Originally Posted by Manchicle

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...

Hi! Congratulations for the good idea

Do you think that it's possible to obtain the same result like in the following picture? I'm thinking to weld all the space inside the red arrow, and completely remove all the other gears (yellow arrows). Because there is no more reason to leave connected the central/front gears (less components, less friction and less heat).

What do you think about?

I'm not really sure how you would accomplish the extra welds you're talking about, and they seem unnecessary if you're going to start by following in my footsteps. That input gear you're pointing to (red) is already locked in place while in constant mesh with the welded planetary unit on the other side of the case. As for removing the other gears for weight and friction reduction, I thought about it but it seemed like more trouble than it was worth. The outer of the two gears is involved with retaining the front output flange. Removing it would bring up a new problem of sealing the case. Removing the big intermediate gear is more feasible, but getting it out would have required major disassembly of rest of the internals, including pulling bearings, and I didn't want to mess with it. Also, you could end up with lubrication issues without those gears there to carry oil up to the carrier and bearings. But hey, this is all speculation anyway. I say go for it. Tell us how it works out...

I will receive the spare transfer case in next few days... I let you know

Back to 4wd just in time for the first snow day of the year. I put about 10k on the car in rwd with the front diff and axles still in place. No noise or vibrations on the ride home. I'd say this first season was a success.

Originally Posted by Manchicle

Back to 4wd just in time for the first snow day of the year. I put about 10k on the car in rwd with the front diff and axles still in place. No noise or vibrations on the ride home. I'd say this first season was a success.

Thanks for the update. I haven’t had time to explore the traction control issue discussed previously, but hopefully sometime this winter so I could try this out during the summer.

I was thinking about this recently. My thought was a disconnect like the front axels on the YJ jeeps. But, I am curious now. What happens if you just remove the front drive shaft without welding anything. In the real world, this would be the equivalent of having the front tires on ice, and the rear on pavement. Looking at drawings of this transfer case, it doesn't resemble a differential at all. Again, just curious and looking for a conversation, not a debate. let me know what you think.

The manual states "The transmission ratio of the planetary gearset provides a fixed torque transfer of 38:62 (front:Rear). The output speeds to the frontand rear axle are the same (1:1).

https://www.manualslib.com/manual/80...page=54#manual

Originally Posted by drehart

What happens if you just remove the front drive shaft without welding anything. In the real world, this would be the equivalent of having the front tires on ice, and the rear on pavement.

If you were to remove the front driveshaft without welding, the front driveshaft output would spin freely and the car wouldn’t move. This is not equivalent to having the front tires on ice and the rear on pavement because without the front driveshaft in place, the car is unable to force power to the rear wheels by braking the front wheels. Our AWD system would be worthless without the DSC module.

Originally Posted by drehart

Looking at drawings of this transfer case, it doesn't resemble a differential at all.

Totally understandable, if you're looking for your traditional ring/pinion/spider gear setup. A planetary gearset actually acts in the same way. In that pdf you found, look at the diagram of the gearset. The three little "planets" take the place of the spider gears. Power is applied to the carrier that houses them, much like the diff carrier in the rear. In an ideal situation (no differential action), the planets themselves don't spin (like spiders), and the whole sun/planet/ring unit spins locked in unison. Equal output speed to both front and rear, same as equal output speed under normal conditions in the rear. As differential action is naturally induced by the changes in wheel speed front-to-rear (in turns, during loss of traction), the planets begin to spin to allow a speed differential between the sun (front output) and ring (rear output). Same concept in the rear; as one wheel accelerates beyond the other, the spiders provide differential action between the two sides. And just like in an open rear, without any clutches or other gears to limit slip, the planetary gearset is more than capable of providing full differential action and sending 200% speed to the bare front output shaft vs. 0% speed to the still-connected rear.

The "torque split" is the natural result of the sun and ring gears being different sizes. The planets are providing power to the sun and ring simultaneously. When a differential action occurs, the X-many-tooth planets rolling on the Y-tooth ring versus Z-tooth sun creates two different torque ratios, hence the rwd bias. This only occurs when the planets are spinning for diff action, so under normal conditions its really 50/50.

In essence, by removing the front driveshaft, the traction of the rear wheels would "hold" the ring gear. Applying power to the planets inside a held ring gear would just spin the crap out of the "free" sun gear. Again, to compare to the rear, if you pull one wheel off and leave the other on the ground, you're essentially "holding" one of the spider gears and sending power through the diff, making the "free" side go extra fast.

Thank you both for the explanations. I appreciate your time.


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I purchased a TC today and plan to do the same conversion.
Plenty of time to wrestle the old TC free while the car is away for the winter.

I will document as much as I can.

I just bought a 2001 330xi and my front differential basically exploded the night I bought the car. This should be very helpful. Thank you

Found one from an AT which is the same PN as the MT, and i thought were going for cheaper than ones from a MT.
Not sure about the "adapter shaft" though. If I have a MT I assume I already have that- any ideas?

http://www.realoem.com/bmw/enUS/show...diagId=27_0013

My children, unplug abs brain in drug bin. remove front half shaft, remove tranny, tcase, add a rwd trans, plus this custom trans mount. This custom trans mount is for sale, uses all oem mounting locations on xi's, direct swap. With this custom mount, you can make your xi rwd. I sold my old rwd swap xi, working on a new project. GL, if you guys have any questions lmk. To the guy above me, yes if you have a manual tc laying around you have that small shaft.

Where you been hiding with this!!
How much does this sell for?
You fabricate it your self?

Originally Posted by 332

My children, unplug abs brain in drug bin. remove front half shaft, remove tranny, tcase, add a rwd trans, plus this custom trans mount. This custom trans mount is for sale, uses all oem mounting locations on xi's, direct swap. With this custom mount, you can make your xi rwd. I sold my old rwd swap xi, working on a new project. GL, if you guys have any questions lmk. To the guy above me, yes if you have a manual tc laying around you have that small shaft.