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  #1  
Old 05-23-2021, 05:19 PM
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rear wheels trying to keep forward movement, front wheels fighting to stop

A few notes for some background..

*2003 E53 Pre-facelift X5 4.4i (non xdrive)
*While seemingly solving my trifecta problem in my last thread I noticed that the front left cv axle appeared to be new and have been very recently changed.
*While using PA Soft I noted that there is a mileage descrepancy between the EWS and every other module, (no tamper dot is present), and the VIN on the EGS belongs to a 1998 BMW 7 Series. I checked the part number on the transmission(ZF5HP24) plate, and the part number, 1058 000 029, cross references with the ZF part installed only in the E53 4.4i, so I feel that the TCM has been changed and this replacement is from the 1998 7 Series.

(see attached)

Now the rest of the story...

The road test.. I drove approx 1 mile and then after a quick acceleration, a problem, the best way to describe it is it felt like the rear wheels were trying to keep forward movement but the front wheels were not cooperating and fighting trying to stop the vehicle and not like a brake lock up, almost like a winding up then release of the front wheels over and over. I was able to get it back home at very slow speed with no real acceleration. Into the garage, up on 4 jack stands. Started it up put into D and while to back wheels were spinning the front were not and neither was the shaft from the TC to the front differential until I stepped on the accelerator pushing the RPM's up to over 1500rpm then the front wheels moved barely, like stuttering, and what seemed like a shutter while moving seemingly fighting the movemnt to the point of when i released the accelerator they immediately stopped and snapped back a few inches. Now, during this time I can move the front wheels freely with my hands and the shaft from the TC moves accordingly, left front is a little stiffer than the right.

I could really use the forums help in determining what my next step is to determine the cause. Anything I should try? Any correlation to the 1998 7 Series TCM? The apparently recently changed LF cv axle? Any specific relationship to free spinning the wheels by hand with movement of the TC shaft either in P, N, or D?
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  #2  
Old 05-23-2021, 08:12 PM
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I don't think 7 Series BMW were ever four-wheel or AWD vehicles. Perhaps replace the TCM with one that was made for you X.
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Old 05-23-2021, 08:19 PM
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The TC is open dif but 2/3 the torque goes too the rear so when off the ground the rears only turn will be normal.

Bind and pop can be a problem with the spline coming out off the TC.

A problem with the abs sensor can cause some problems that match your symptoms.

To eliminate DSC from the equation, pull the plug on a sensor and it will auto disable.
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Old 05-23-2021, 11:46 PM
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Quote:
Originally Posted by andrewwynn View Post
The TC is open dif but 2/3 the torque goes too the rear so when off the ground the rears only turn will be normal.

I am not sure about the rest of what you said, but unless there is something braking the fronts, they should rotate when the car's in the air just the same as the rears. And if the fronts are not turning then the rears would need to be turning twice as fast as they would normally be. Unless there's something braking the fronts and not the rears (or something like a spline popping out), I don't think this would happen.
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Old 05-24-2021, 01:04 AM
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Incorrect.

Twice as much torque goes to the rear wheels so unless you apply braking force on the rears or some way (eg rev enough) to overcome the torque bias, the fronts won't turn. The DSC system may see the rears "spinning on ice" and clamp three binders and get power to the fronts. Until that happens the rears should spin much more freely than the fronts.

The TC is torque split not speed split so the speed of the input is not divided like you are thinking.

I'm not sure exactly how that works but consider the x-drive system: if you stop the front output entirely by removing the front drive shaft, it doesn't take double or half the rpm to drive a particular speed: it's exactly the same as before.

Take some video when reproducing the problem or do some reverse testing: turn one front wheel at a time and track what happens at the TC output. If things are binding at the differential you should be able to tell
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Old 05-24-2021, 10:54 AM
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It sounds to me like the DSC is braking the fronts. I was going to say the front diff, driveshaft, or halfshafts were binding, but if the front wheels turn freely in the air when the car's off, AND the front driveshaft turns freely with them, it sounds like the DSC might be erroneously braking the front wheels. I agree with Andrew, binding should be obvious if it is happening, but it sounds like it is not happening.



After all, the pre-X-drive cars just have a simple open center diff, and use individual wheel braking in lieu of limited-slip differentials.
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Old 05-24-2021, 11:02 AM
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It is possible why I suggested to unplug abs sensor (or fuse) to disable.

When my abs sensor was misaligned, the abs would kick in at every stop for about 6 stops until it disabled itself.
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Old 05-24-2021, 03:03 PM
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The pre-xdrive E53 uses a NV125 transfer case. I'll say it is so different vs the xdrive one that discussing the xdrive here adds nothing other than confusion.

As said, the NV125 can be considered to work as an open differential does. That's really all you need to know.

It is designed to nominally operate with the front and rear drive shafts turning at the same speed; just as a differential is designed to have both left and right wheels turning at about the same speed. Due to the geometry of the gearing, there is a 38% front : 62% rear torque split. Pure mechanical geometry of the gears gives this split ratio. No clutches, circuits, computers, etc. It's like having levers of different lengths.

If you jack just the front, so the rear tires are on the ground and the front ones are in the air, it will work just like on a 2WD car when the driven wheels are jacked. For example, you can turn the left front wheel forwards, and the right front wheel will turn backwards at exactly the same rate and angle. So you cannot turn both front wheels forward at the same time.

The front differential enforces this, and the front driveshaft (from the TC to the front diff) is fixed due to the rear tires being on the ground. That front driveshaft cannot move because the rear tires are on the ground, so the rear driveshaft cannot move, and then the TC will not allow the front drivehaft to turn while the rear is fixed ... because it's just like an open differential.

This is all a carefully explained description that just says that the NV125 TC acts like an open differential. It really does.

The traction control on these things work with the purely mechanical TC+diffs by applying braking to the slipping wheel(s), sending torque to wheels that still have traction. So disabling that system would remove that as a possible source for the OP's problem.
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Old 05-24-2021, 03:34 PM
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Quote:
Originally Posted by oldskewel View Post
The pre-xdrive E53 uses a NV125 transfer case. I'll say it is so different vs the xdrive one that discussing the xdrive here adds nothing other than confusion.

As said, the NV125 can be considered to work as an open differential does. That's really all you need to know.

It is designed to nominally operate with the front and rear drive shafts turning at the same speed; just as a differential is designed to have both left and right wheels turning at about the same speed. Due to the geometry of the gearing, there is a 38% front : 62% rear torque split. Pure mechanical geometry of the gears gives this split ratio. No clutches, circuits, computers, etc. It's like having levers of different lengths.

If you jack just the front, so the rear tires are on the ground and the front ones are in the air, it will work just like on a 2WD car when the driven wheels are jacked. For example, you can turn the left front wheel forwards, and the right front wheel will turn backwards at exactly the same rate and angle. So you cannot turn both front wheels forward at the same time.

The front differential enforces this, and the front driveshaft (from the TC to the front diff) is fixed due to the rear tires being on the ground. That front driveshaft cannot move because the rear tires are on the ground, so the rear driveshaft cannot move, and then the TC will not allow the front drivehaft to turn while the rear is fixed ... because it's just like an open differential.

This is all a carefully explained description that just says that the NV125 TC acts like an open differential. It really does.

The traction control on these things work with the purely mechanical TC+diffs by applying braking to the slipping wheel(s), sending torque to wheels that still have traction. So disabling that system would remove that as a possible source for the OP's problem.

Yes. The pre-X-drive E53 just has a planetary differential with no slip-limiting mechanism. Like you said, it can be considered identical to any other open differential. The sum of the front and rear driveshaft speeds will be twice the speed of the transfer case input shaft, at all times. The center diff may send more torque to the rear driveshaft, but they are mechanically geared together just like any other differential.



Likewise, if you were to disconnect the front driveshaft, the car would go nowhere. You would have to weld or otherwise lock the center diff.
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Old 05-25-2021, 10:32 AM
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When off the ground, engine off, I can freely spin the 2 front wheels, spinning either wheel will spin the front shaft. Spinning the front shaft by hand spins the left front wheel.
Engine running the rear wheels spin the second it is in D, the front wheels or front shaft from the TC do not spin unless I increase the engine speed upwards of 1500 rpm and then they barely move as if being braked or binding but when this is happening I can spin either wheel by hand easily.
I thought about the DSC causing this so I pressed the DSC button on the console, the yellow light came on the instrument panel but it did not have any effect on the problem.. I didn't think about unplugging or a fuse.
My next thought was the recently replaced left front cv axle as it does not spin as freely as the right front. I checked to make sure it was inserted fully, multiple times and it was. So, I removed it. After getting the clip to release I grabbed the shaft to pull it out and it easily extended at the inner boot, much more than I thought it should. I have replaced 5 or 6 on different vehicles and not one has extended like this. When I finally got it out I could not easily get it to retract back. I had to hold it vertically with that end on the ground then lift the axle up and then down smacking the ground, think of slide hammer, doing this multiple times until it finally retracted. I have it in my vice and when I extend that end I feels very rough, and the same goes for when I push it back, like there are notches or its catching inside the boot. I thought about removing that boot to inspect the joint and the cage but have not done so yet. I did order a new axle.
Can I run the vehicle, in the air, in drive, with that cv axle out of the differential to see if the issue still exists?
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