Rear end feels like it's grabbing or binding under load HELP! - Page 3

Albear · #21 12-20-2018, 02:28 AM

Highly doubtful, I'm sure the shop spun it to make sure it didn't sound "rough", installed it and filled it. I know they took the output flanges off the old one and the input yoke off the old one and used them on the new one. I can drive it initially without issue, after a short drive (5-10 min) it will start.. buck, good.. buck, pause for 2 sec, buck again etc.. doesn't matter how hard on the throttle I am (granted I haven't used more than half pedal or less due to not wanting to grenade anything), off throttle, not noticable. It doesn't seem to do it when it's first cold (if so, nowhere as noticable). I have data logged engine systems and nothing to note.. o2 readings are constantly similar between banks so no miss, weak coils, fouled plug or anything like that.. no codes (except when I first got it it had both banks below threshold for catalyst.. but hadn't been run in months prior and hasn't flagged again since I cleared them).

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EODguy · #22 12-20-2018, 03:01 AM

To be honest it's sounding more and more like a lash problem between ring/pinion and if it changes depending upon temperature... To check the lash takes feeler gauges and a little wax to see the contact surfaces. I have never bought a diff set that wasn't a "custom" order that didn't need to be adjusted (although never had to shim one either)

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Albear · #23 12-20-2018, 09:01 AM

This was a used low mileage original diff out of a donor vehicle. It wasn't rebuilt or a reman.. (which is why I don't think that's the problem.. (unless this new one was on its way out too..). But I can't see that being the case either as the x5 isn't known for blowing them up and they usually stand the test of time. Going to see if I can disable power being sent to the front wheels.. if I can that will tell me for certain that the problem isn't compatability between diffs and is in the rear end. In a few min going to pull fuse 46 and see if I can stop power going to the front wheels, if not try to disconnect servo on transfercase and see if that does it. I know I can't disconnect the front driveshaft. . So I hope this helps to isolate the issue.

andrewwynn · #24 12-20-2018, 09:38 AM

Has the FRONT dif ever been replaced? Maybe PO replaced the front with the wrong ratio and that was the reason the rear blew. Pull the fuse to disable the front and if the problem goes away that's where the smart money is.

Or: are the wheels staggered where that car is not designed for a non square setup, that's the same as different ratio differentials. Door sticker should show the stock tire sizes.

Albear · #25 12-20-2018, 09:44 AM

Wheels are stock, pulled #46 fuse yet front wheels are still spinning under power (unloaded on hoist) so it could just be parasitic power, no abs or tc lights on dash..so not sure if it really did anything. Now going to try and pull the tc accuator connector itself off and see what that does.. barring that, pulling the front driveshaft off and will see what happens...lol. running out of options.

andrewwynn · #26 12-20-2018, 10:47 AM

The whole pull the fuse thing is confusing to me. Does the TC disconnect and reconnect every drive cycle? I would look into that motor operation also with the DSC disabled there is more to the equation what necessary components aren't functioning?

Maybe the TC disconnect motor can be jumpered to activate it and disconnect the front drive train.

Albear · #27 12-20-2018, 12:44 PM

Update.. disconnected servo on tc.. front wheels are still powered. They're going to pull the front driveshaft at this point, requires the stabilizer bar to be moved out of the way etc.. will update when they're finished. But so far all the means to disable front drive on a xdrive system listed are fantasy and don't stop wheels from being engaged #46 fuse, even servo motor disconnect.. still runs front wheels. Am I missing something?

crystalworks · #28 12-20-2018, 01:09 PM

I did not remove front sway bar when I removed my front shaft for guibo replacement and spline greasing. Just fyi.

Edit: nm, you said moved, not removed. After removing the reinforcement plate the sway bar has plenty of movement to it. But honestly I don't ever remember it being in the way.

andrewwynn · #29 12-20-2018, 02:06 PM

Quote:

Originally Posted by Albear

Update.. disconnected servo on tc.. front wheels are still powered. They're going to pull the front driveshaft at this point, requires the stabilizer bar to be moved out of the way etc.. will update when they're finished. But so far all the means to disable front drive on a xdrive system listed are fantasy and don't stop wheels from being engaged #46 fuse, even servo motor disconnect.. still runs front wheels. Am I missing something?

If the TC is sending power forward pulling the drive shaft won't help it will just spin the output spline. (Just like on pre xdrive, if one CV pops out you just spin the differential)

It seems like the problem is in the TC at this point. The elecro-mechanics that are supposed to disable the front axle aren't. Maybe something went haywire inside the TC to cause the original problem.

I still would try to get that motor to do it's job or pull the motor and turn the gear manually that disengages the front axle.

Maybe somehow the TC has something locked up or binding inside that is not allowing it to split the torque from the transmission properly. The fact there are systems that read things like the transmission rpm to function are disabled, I would want to get those online and maybe you'll get some codes that tell you what is going on.

My TC is a relatively simple differential that is designed to output the same speed on the two outputs but split the torque 2/3 and 1/3. The xdrive TC I don't know how it works it's magic because if you locked one output shaft on mine the other will turn twice as fast so clearly it works on a different method if it can operate outputs at different speeds.

The tech info says the xdrive can transfer power front to back in milliseconds, so maybe a solinoid is kicking on and off disconnecting the front drive and the speed doesn't match causing the bucking

Albear · #30 12-20-2018, 03:37 PM

Because my truck is 08/2004.. (when they first rolled out the xdrive system for the first time). We're there any differences in the very first production models by any chance (like for example it was possibly powered off a different fuse, used a early model adaptation of the current controller that worked a little differently etc.)? My truck doesn't seem to respond like all the posts I've read and dug through regarding making a x5 rwd. I'm getting a little frustrated throwing hours of labor at this problem at $100/hr. Lol

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