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BMW 3-Series (E90 E92) Forum
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does the 335Xi have the option to be RWD like an STI?
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11-16-2010, 06:09 PM | #89 | |
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If this works :| I will be very very happy...I love RWD...and def do not need the traction control in the summer |
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11-17-2010, 04:58 PM | #91 |
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One thing we need to check is if our brake lights still function after pulling this fuse....I just scanned my car and pulled/replaced the fuse on Monday.
I had an error with a description something like brake light input to ECU. BTW FOR THOSE WITHOUT A WAY TO CLEAR CODES OFF YOUR CAR!!!!!! THERE ARE TONS OF HIDDEN FAULTS STORED THROUGHOUT MULTIPLE MODULES!!!!!! Last edited by fdriller9; 11-17-2010 at 05:07 PM.. |
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11-17-2010, 05:03 PM | #92 | |
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So I don't see how power would be traveling from side to side. Also I beleive the rear diff is always engaged and since it is electronically controlled, pulling the fuse disables the ability to disengage the rear diff. That's my theory as to why the rear diff is "locked." EDIT: So the xDrive system can only transfer power from the rear to front axles...not side to side. I beleive braking is applied to slow down a wheel so it can match torque on each side. However, as per the BMW website: "In addition, brake force courtesy of DSC is used when there is traction difference between the two sides of the vehicle and wheel spin is likely. " So I think ABS is part of DSC and both are disabled by pulling the fuse. So no braking is applied and that's why we can spin both rear wheels. Last edited by fdriller9; 11-17-2010 at 05:27 PM.. |
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11-17-2010, 05:31 PM | #93 | |
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With an open diff and no e-braking you'd just spin one wheel. |
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11-17-2010, 05:36 PM | #94 | |
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We have open diffs but I don't think the diffs ever disengage a wheel....that's why the car uses the brakes to balance torque, hence side-to-side but not really lol. |
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11-17-2010, 05:38 PM | #95 |
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And here is our answer...
http://auto.howstuffworks.com/differential2.htm This is why the guy who pulled a 180 turn thought the inside wheel was spinning at a different speed.. So in a STRAIGHT LINE our rear diff is indeed locked. |
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11-17-2010, 06:47 PM | #96 | |
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I think its in open diff mode. |
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11-17-2010, 06:50 PM | #97 | ||
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Hitting the brakes will cause you to lockup like a mother. ABS is out. |
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11-17-2010, 07:27 PM | #98 | |
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11-17-2010, 08:10 PM | #99 | |
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I'm not sure what a procede is. Last edited by fdriller9; 11-17-2010 at 08:16 PM.. |
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11-17-2010, 08:22 PM | #100 |
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11-17-2010, 08:31 PM | #102 | |
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Btw, procede is the turbo tuner for 335 owners. |
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11-17-2010, 08:36 PM | #103 |
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11-18-2010, 06:20 AM | #105 |
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SO, i tried this on a 2011 sedan yesterday, and it works the same. But my car is a lease, so can someone tell me the easiest way to reset the error codes that will show? whats the best scan tool to buy simply to read and reset codes on my car?
very interesting thread, the reason i registered. Thanks! |
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11-18-2010, 09:37 AM | #106 |
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What is this e-LSD you guys are talking about? I'm pretty sure our cars cannot disengage wheels on either side of the axle...especially the rear.
The xDrive system can ONLY transfer power from front to back and vice versa with a 40:60 split(rear bias). ABS (I think) applies brake to each wheel to balance torque on each side. A mechanical wet clutch pack is used to transfer power from the front to rear...I think this is the e-LSD you guys are referring to. However with the fuse pulled, the e-LSD never engaged the front. An with the behavior of traditional open diff, the rear axle locks up, in a straight line....I think the front wheels have to be parallel with the rears for the diff to lock up. Also our wheel angle sensor is disabled by pulling the fuse(hidden fault) so I don't know how the car knows we are turning. Maybe this is why the rear diff acts invariably. Also because the wheel angle sensor is disabled, our turn signal does not automatically turn off after coming out a turn. Last edited by fdriller9; 11-18-2010 at 09:51 AM.. |
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11-18-2010, 02:06 PM | #107 |
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In certain situations, an open diff can be made to behave like a limited slip diff by applying the brakes to the spinning wheel. That is because an open diff will always send torque to the wheel with less traction and spin it. So by braking the spinning wheel, TQ gets sent to the wheel with more traction, electronically simulating a limited slip diff (LSD). Xdrive uses this feature on both the front and rear axles. RWD 335 cars have a similar feature for the rear diff only. It is not an optimal solution, a conventional LSD is better. M3 has a true LSD, and I think X6 gets an xDrive with true LSD ("torque sensing").
Xdrive has three layers of software, DSC, DTC, and then both off. DTC is a subset of DSC, lighter stability control and no engine power reduction, but traction control is still on though a bit more agressive, allowing a bit of oversteer. With DTC/DSC off completely, in xDrive you still have the front and rear e-LSD (via brakes) and the transfer case working. So IN THEORY as far as I can tell, with DTC and DSC off you may be able to spin all four tires on ice. Have not tested this yet as I have not had the car in winter. As I have said in other threads, BMW is very cagey about how all this works. BTW ABS and "e-LSD" both work through the brakes of course, but one works by modulating (cutting) pressure in the lines on lock up, the other actively applies the brakes based on sensors and electronics to stop wheel spin. So in theory they are totally separate systems, both of which act on brakes but no need for them to be in the same fuse circuit or even same control algorithm. They have nothing to do with one another as one works when you apply the brakes the other is when you give it gas. Then there's stability control which another system entirely. They all talk to one another of course. I personally would not want to yank a fuse out of the middle of all this, disable ABS and all layers of DTC/DSC/e-LSD, and then push around dead rotating mass of front AWD system. But I admire the spirit of experimentation it represents. Proper solution is for Shiv or someone similar to do this w/o messing with the other sytems (if that even can be done). edit: the above is as far as I have been able to figure out, reading a lot here and on other forums. Anyone has any knowledge to the contrary please chime in. |
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11-18-2010, 02:52 PM | #108 | |
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Have you ever jacked up your car on all 4 wheels? The front wheels can spin freely while the back is locked up. I think because the front can spin freely, it is disengaged from the rest of the drivetrain. When the car is on, the wet clutch pack in the xDrive system engages the front diff. and the axles can only go in a 40:60 split with rear bias. I wonder if you can spin the front wheels with the car on, off the ground in neutral? Obviously in drive the wheels would be spinning and the front diff would be engaged. Also when you reach highway speeds, no power is going to the front so I would assume the xDrive system disengages the front axle so less parts are moving and the front wheels are just rotating because the rear wheels are pushing the car. |
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11-18-2010, 03:19 PM | #109 | |||
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Also there is a very confusing case described where on glaze ice, when the rears both have zero traction and the fronts have some, BMW says xDrive sends almost all TQ to the front, which is impossible unless you write science fiction for a living. Or write politcal speeches. |
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11-18-2010, 03:31 PM | #110 | |
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I've heard the front disengages around 70mph.....again can't confirm either. I don't know about your last statement lol....I do agree though. How can 100% of the power go to the front if the rear is always engaged? |
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