02-05-2018, 10:19 PM | #1 |
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AWD to RWD via pulling a fuse?
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 Last edited by DuSh; 02-05-2018 at 10:37 PM.. |
02-05-2018, 10:51 PM | #2 |
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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. |
02-06-2018, 12:13 AM | #3 |
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Would be cool if possible. Especially for you v8 guys
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02-06-2018, 01:25 AM | #4 |
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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.
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02-06-2018, 08:57 AM | #5 | |
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02-06-2018, 09:14 AM | #6 |
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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.
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02-06-2018, 10:21 AM | #7 | |
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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 |
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02-06-2018, 10:52 AM | #8 | |
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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! Last edited by DuSh; 02-06-2018 at 07:17 PM.. |
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02-06-2018, 10:56 AM | #9 | |
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02-06-2018, 07:11 PM | #11 |
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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 |
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02-07-2018, 06:40 AM | #12 |
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That's an easy way of damaging the transfer box.
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02-07-2018, 04:56 PM | #16 |
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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. |
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02-07-2018, 05:34 PM | #17 | |
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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.
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02-07-2018, 09:20 PM | #18 |
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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 |
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02-08-2018, 12:16 AM | #20 | |
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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
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02-08-2018, 04:05 AM | #21 |
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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. |
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02-08-2018, 08:48 AM | #22 | |
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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!
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