AWD to RWD via pulling a fuse?

[DuSh]

Would love to do some burnouts occasionally, but not sure if it's even possible to temporarily disengage front axle on x5? (I mean without physically removing shafts)

I remember reading that during some specific malfunction when DCT/ABS/4x4 combo error pops up - car goes into safemode and becomes RWD essentially. Maybe we can pull some fuse to reproduce that scenario just for some RWD fun?

P.S. I feel like I'm the only idiot who posts such nonsense here

[CeeTeeX5]

Originally Posted by DuSh

P.S. I feel like I'm the only idiot who posts such nonsense here

Someone has to do it

I was close to looking in to this too but for the purpose of doing some dyno runs. A friend of mine was setting up a dyno day and the dyno is only 2wd. Decided against it as I'd rather get realistic numbers based on all 4 wheels spinning.

[Wavy]

Would be cool if possible. Especially for you v8 guys

[Doanster]

OMG, you're like a kid jacked up on Pop Rocks and Jolt Cola (remember that one kiddies?)!
Your actual drive-time vs mod-thinking ratio is skewed in the wrong direction.
Your prescription: take two spirited drives with no music on and windows open, then call me in the morning.
That's exactly what I did after putting the summer wheels/tires back on yesterday.

[CeeTeeX5]

Originally Posted by Doanster

OMG, you're like a kid jacked up on Pop Rocks and Jolt Cola (remember that one kiddies?)!
Your actual drive-time vs mod-thinking ratio is skewed in the wrong direction.
Your prescription: take two spirited drives with no music on and windows open, then call me in the morning.
That's exactly what I did after putting the summer wheels/tires back on yesterday.

Summer wheels back on already??

[Doanster]

Originally Posted by CeeTeeX5

Summer wheels back on already??

This is the PNW. No snow on the ground this year. A few trips up to ski and that's it. 18s with 255/55 tires gets old to look at real quick.
It did give me a chance to finally fix a really curb-rashed wheel though. Amazing work considering the machined face. Will post a sep thread with before/afters. I keep hijacking DuSh's threads.

[CeeTeeX5]

Originally Posted by Doanster

This is the PNW. No snow on the ground this year. A few trips up to ski and that's it. 18s with 255/55 tires gets old to look at real quick.
It did give me a chance to finally fix a really curb-rashed wheel though. Amazing work considering the machined face. Will post a sep thread with before/afters. I keep hijacking DuSh's threads.

I know it's the PNW, I'm just a few hours North of you It has been a warmer/milder winter so far and I'm also contemplating putting my summers on. Just got my 22s and tires delivered. Just feels early!

Dush, to keep things on topic, here is some info that I had previously found. it's for E70 but should be similar: https://xoutpost.com/bmw-sav-forums/...sfer-case.html

[DuSh]

Originally Posted by CeeTeeX5

I know it's the PNW, I'm just a few hours North of you It has been a warmer/milder winter so far and I'm also contemplating putting my summers on. Just got my 22s and tires delivered. Just feels early!

Dush, to keep things on topic, here is some info that I had previously found. it's for E70 but should be similar: https://xoutpost.com/bmw-sav-forums/...sfer-case.html

Interesting read! So somebody correct me if I'm wrong, but it seems like disconnecting transfer case servo/actuator plug will essentially make our cars RWD?

As it was mentioned in that thread you linked - there is no preloading spring inside transfer case and if motor/actuator is switched off - front axle will not get much force if any at all!

[CeeTeeX5]

Originally Posted by DuSh

Interesting read! So somebody correct me if I'm wrong, but it seems like disconnecting transfer case servo/actuator will essentially make our cars RWD?

As it was mentioned in that thread you linked - there is no preloading spring inside transfer case and if motor/actuator is switched off - front axle will not get much force if any at all!

Yah, that's my understanding of it.

[fosterelli]

Damn it DuSh, quit trying to make me young again...now I want to yank the plug and power brake this 6 banger into oblivion just for fun.

[DuSh]

Some fun video (disclaimer - I'm against such irresponsible driving on the public roads), but it just shows x5 can drift:

And a famous "if you are happy, I'm happy" x5 jump - just for fun, if someone didn't watch it already: https://www.youtube.com/watch?time_c...&v=oNXo8E5cOeU

[CatalinP]

Originally Posted by CeeTeeX5

Someone has to do it

I was close to looking in to this too but for the purpose of doing some dyno runs. A friend of mine was setting up a dyno day and the dyno is only 2wd. Decided against it as I'd rather get realistic numbers based on all 4 wheels spinning.

That's an easy way of damaging the transfer box.

[CeeTeeX5]

Originally Posted by CatalinP

That's an easy way of damaging the transfer box.

What is? Putting the car on a dyno?

[CatalinP]

A 4wd car onto a 2wd dyno.

[CeeTeeX5]

Originally Posted by CatalinP

A 4wd car onto a 2wd dyno.

Do you know from experience?

[CatalinP]

The transfer box is not designed to deliver 100% of the torque to 1 axle for prolonged time.

Read the manual, it is clearly stated in the section about towing the car with 1 axle suspended.

[fosterelli]

Originally Posted by CatalinP

The transfer box is not designed to deliver 100% of the torque to 1 axle for prolonged time.

Read the manual, it is clearly stated in the section about towing the car with 1 axle suspended.

Towing requires flatbeds on AWD vehicles because both axles are typically connected at the transfer case by some sort of coupling, clutch, or hard connection. In fact, in a pinch tow companies w/o a flatbed available have been known to simply remove one of the drivelines and pick the vehicle up with the disengaged wheels on the ground.

The rule is not because one axle is not supposed to have 100% of the power, it's about doing damage to the clutches and other components when some drive wheels are on the ground and some are in the air.

There are many AWD systems that can transfer 100% of the power to the front or rear of the vehicle, and some can even put 100% of the power to any one wheel when necessary.

By design this clutch system (or coupling) is disengaged and engaged electronically. In theory (I haven't personally tried it) you can unplug the harness at the transfer case, which should prevent the activation of the clutch lever that engages the front output shaft.

The BMW xDrive can place virtually 100% of the power to the front or back, and is normally 60:40 rear biased. So this transfer case is totally okay with almost 100% power front/back by design, before you unplug the transfer case and prevent forward output at the shaft.

I'm sure someone will jack up all four corners of their rig and put it on stands, then try this out while in the air...then we'll all know for sure how much, if any, power is moving to the front.

[DuSh]

Yes, just to add to this - BMW techs use this method of unplugging transfer case actuator plug for test purposes to rule out front drivetrain/axle/shafts and/or transfer case issues - basically if noise/jerking stops when unplugged - then it's a positive diagnostic sign and they can narrow it down further more. Of course they don't test customer cars with unplugged actuator on dyno, but that's another story (I'm not 100% sure it is because of risk damaging something, but more because of any engine revving or drifting done by techs in customer cars is frowned upon in dealerships)

As for topic - I decided to maybe take driving courses down the road before trying anything like this, it's just too dangerous for me and everyone around me lol

[CatalinP]

It is designed to transfer 100% of the torque (not power) to any axle, BUT NOT FOR SUCH A LONG TIME as when you do a dyno.

[fosterelli]

Originally Posted by CatalinP

It is designed to transfer 100% of the torque (not power) to any axle, BUT NOT FOR SUCH A LONG TIME as when you do a dyno.

I think you're not following some of our points...I'll try to be more helpful if I can.

To simplify, torque is a twisting force which causes rotation (measured in N m). Horsepower = torque x RPM.

To transfer one, the transfer case transfers both. You cannot transfer torque without power, and power without torque. You're talking about two measurements of semantically equal points. One does not say "transfers torque not power", or power not torque. They intertwine not unlike the engine output. Does an engine produce horsepower or torque? Both. So how would a transfer case move one without the other? It doesn't and cannot.

The whole purpose of the engine is to create power, which is transferred from reciprocal to rotational via the crankshaft, which spins the transmission, whose job is to control the power output to the drive shaft/s and transfer cases, which feed the differential/s, which turn the axle/s, and eventually the wheels. You cannot separate power and torque.

A dyno distance typically is less than a couple of miles. A long time on a dyno would be strange for any car short of a racing program.

And if the clutch is not engaged to activate the front output shaft, how would the transfer case (1) know that there isn't an output to the front shaft (2) where would the damage occur? From my understanding of transfer cases, and from the BMW diagram on the previously posted link, it doesn't appear that any damage could occur from a disengaged front shaft due to the coupling not being electronically activated.

If we're wrong, please set us straight or show us the data you're drawing from, because I cannot find, nor distinguish from my own research, what you're referring to. We're all here to learn.

From my point of view, as long as the disabled front shaft is fully disengaged, I cannot determine how any damage could occur. But I would definitely test my theory on stands like I suggested, prior to engaging in full blown drifting and tire smoking!

And for what it's worth, here's BMW's statement: If wheel slip is detected by the ABS/DSC system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle

[CatalinP]

On any car all 4 wheels will have roughly the same rpm during normal conditions, what is different is the torque, which gets distributed by the transfer box.
The clouch you mention is not totally disengaged, and the wear on it is quite high when the angular speed difference is so high.

[fosterelli]

Originally Posted by CatalinP

On any car all 4 wheels will have roughly the same rpm during normal conditions, what is different is the torque, which gets distributed by the transfer box.
The clouch you mention is not totally disengaged, and the wear on it is quite high when the angular speed difference is so high.

The whole point of AWD (and 4WD) is because there are times when the wheels are spinning at different speeds, slipping, etc. so the power is reduced or removed from the wheels that are slipping, and redistributed to the wheels that are achieving traction.

As BMW says, up to 100% of the power can be moved front/back.

So you're saying BMW is wrong by this statement? "If wheel slip is detected by the ABS/DSC system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle"

Are we still talking about power vs torque? Don't you think it's synonymous in this situation? I'm pretty sure everyone describes AWD systems as a method of power distribution/redistribution.

Very curious how have you confirmed that the front output shaft is still engaged (or isn't 100% disengaged)? Again, if you have knowledge you can share on this please let us know. Otherwise someone here will run a test soon I'm sure of it!