[Marlinman]

Have you limited your boost by gear as well? Thank you for the response, it will be very helpful for others headed this route.

[zole2112]

Originally Posted by Marlinman

Have you limited your boost by gear as well? Thank you for the response, it will be very helpful for others headed this route.

I haven't limited the boost yet but I was running with the same mods, JB4 map 5 and the same mix of 93 octane/e85 since 2017 with no issues until after I lowered it. Not to say a boost limit wouldn't resolve the issue when it's lowered but if it is boost I know that at the normal height the boost wasn't the issue so lowering it may have made it less robust and unable to handle that same boost level.

[Marlinman]

Okay yea I see what you're saying. I'm just surprised it is just you we've heard about so far with all the other people running around with lowered xdrives! keep us posted!

[zole2112]

After reviewing one of my failed front right axles with our Mechanical Engineering guru we believe the issue that caused this is the length of the axle being too short to support my set up. The end of the axle shaft (labeled A in the attachment) has 3 bearings on the end and it rides inside the part labeled B which allows axle A to slide in an out as needed. As You lower the car the hub height on the wheel stays constant with the differential getting lower so the length between the hub and the differential gets longer. With my setup I lowered my car far enough that the end of axle A moved close enough to the end of the part B that one of the bearings was torn apart and the axle came out of part B with no noticeable damage to part B. To lower my Xdrive I would need a longer axle shaft A.
I plan to put my old axle back in the car temporarily so I can see where the bearings fall in part B (since there is no boot left on the old broken shaft) then I will know how much room I have for movement. In addition I can measure the lengths so I can calculate where the bearings fell when the car was another inch lower. I will also know how much longer the shaft would need to be to lower it as much as I want.

[JDuffy14]

What were the signs that the bearing was failing? If any? I'm worried mine might be but i can't tell between the axle or the hub

[zole2112]

Originally Posted by JDuffy14

What were the signs that the bearing was failing? If any? I'm worried mine might be but i can't tell between the axle or the hub

Unfortunately I didn't have any warning, it just failed on acceleration. When I get a chance to swap out a failed axle so I can measure everything then i should be able to calculate the maximum drop to go along with my wheel hub height. You should be able to use my calculations to at least know how far from the edge your bearings are with your setup.

Basically we believe the failure was not that a bearing was bad but that the bearing rode out too far but until I can measure it on the rack I won't know for sure. I'll report back

[zole2112]

Update: no issues since I raised my car 1 inch. Looking at the angle of the axle at ride height and the mode of failure I'm positive that the issue with lowering the car that much made the distance from the differential to the wheel hub long enough that the axle bearings reached the edge of the receiver they fit into. The fix to allow me to lower my xDrive more would be to have an axle made with a longer shaft between the outer CV joint and the receiver coming off of the differential axle.

I still plan to re-install my broke axle with no boot so I can measure exactly how far the bearing are into the receiver at current ride height. I'm paranoid that I'm right at the edge of failure all the time lol.

[Marlinman]

No issues driving regularly? How about smashing that throttle?

[alexng72]

So you're saying that we cannot lower our xdrive models more than 3 inches?

[zole2112]

Originally Posted by Marlinman

No issues driving regularly? How about smashing that throttle?

no issues, wot/mashing the throttle/driving like a madman..so far so good!

[zole2112]

Originally Posted by alexng72

So you're saying that we cannot lower our xdrive models more than 3 inches?

It appears that way based on the evidence I have but I still want to take the time to install the broken axle without the boot so I can measure how far inside the bearings rest when at my normal ride height. As soon as I do that I will also measure my ride height, differential height and axle length so that I can then calculate the effect on the axle bearing position for any given height. Stay tuned for that.

By the way the failure occurred, the axle A (in the above diagram) was completely out of the receiver B with basically no damage to the receiver. The only conclusion I could come to was that at that lowered height I would need the axle A to be longer.

[alexng72]

Originally Posted by zole2112

It appears that way based on the evidence I have but I still want to take the time to install the broken axle without the boot so I can measure how far inside the bearings rest when at my normal ride height. As soon as I do that I will also measure my ride height, differential height and axle length so that I can then calculate the effect on the axle bearing position for any given height. Stay tuned for that.

By the way the failure occurred, the axle A (in the above diagram) was completely out of the receiver B with basically no damage to the receiver. The only conclusion I could come to was that at that lowered height I would need the axle A to be longer.

Thank you. This is very helpful since I plan to put my xdrive on bags.

[zole2112]

Axle blew yet again. driving slow, about 15 mph immediately after turning a corner, just crazy. I am having a custom length axle shaft made and will be moving to that.

Has anybody else out there lowered their F30 xDrives? I can't be the only one to have done it.

[Polo08816]

Originally Posted by zole2112

I haven't launched at all and still on the stock turbo. I have about 80,000 miles on my car. I've been thinking about the design of the axle and I really don't see any reason lowering the car a couple of inches would put any extra stress on the axles so I think it's the miles on the axle bearings, all it takes is 1 of the bearings having a single flaw and it will go under stress at some point. With the JB4 and all of my mods as well as running e50 I'm sure I'm running significantly higher torque than stock. When Trebila does my tune he'll limit the torque/boost in 1st & 2nd gear.

This will not deter me, still looking to get to 700hp!!!

... but aren't you a mechanical engineer?

Originally Posted by zole2112

I'm going to talk to a couple of Mechanical Engineering gurus at work next week. I'm starting to think maybe the angle change with a 2" drop, which is about 5 degrees difference I believe, may change the direction of the load on the 3 bearings at the end of the shaft outside of the differential enough that the load they can handle is significantly reduced, that's all I can figure at the moment anyway.

[Polo08816]

Originally Posted by zole2112

Axle blew yet again. driving slow, about 15 mph immediately after turning a corner, just crazy. I am having a custom length axle shaft made and will be moving to that.

Has anybody else out there lowered their F30 xDrives? I can't be the only one to have done it.

Is this the 2nd or 3rd time?

It seems the MSRP on the axle is about $1363. You should just start saving up for the G80 M3 AWD instead of replacing front output shafts all the time.

You'll get better performance with a factory warranty.

[zole2112]

Originally Posted by Polo08816

... but aren't you a mechanical engineer?

No, I'm a Process Engineer.

[zole2112]

Originally Posted by Polo08816

Is this the 2nd or 3rd time?

It seems the MSRP on the axle is about $1363. You should just start saving up for the G80 M3 AWD instead of replacing front output shafts all the time.

You'll get better performance with a factory warranty.

Third time, car-part.com, got one this time for $113 shipped from a 2015, cheapest yet. I found a guy to make me a custom axle that is longer than the current one. I have one that is mostly disassembled, I have to finish disassembly and ship it to him. He'll make me one to my spec for about $500 so I'll have a custom axle when I'm done for about $700-750 total, then I should be set. I want this car a certain way and I will not give up!! I'm going to be picking up a RWD 135 later this year to build though.

[Marlinman]

Wait, what the heck is going on? I've read many posts about lowered xdrives with no problem. I'm lowered, albeit on ACS which is less than other companies but something has to be unique about your setup I would think? Aren't you also still on stock turbo?

[zole2112]

Originally Posted by Marlinman

Wait, what the heck is going on? I've read many posts about lowered xdrives with no problem. I'm lowered, albeit on ACS which is less than other companies but something has to be unique about your setup I would think? Aren't you also still on stock turbo?

I still am on stock turbo. I know, I knew there have to be other lowered xDrives. I don't know why I keep having this issue. I'm going to put it up on the lift on the weekend and see if I can find anything but I couldn't find anything last time. The axle is completely separated at the inside ball joint with the axle tripod hanging down and the rest of the axle assembly still in the differential as normal. This is bugging the shit out of me and I really need to figure it out before installing my turbo.

[Marlinman]

I hope you can find something definitive. I think there has to be a constant that you'll find that would keep leading to a broken axle downstream. There just has to be something we are missing! Good luck to you, keep us informed please!

[zole2112]

Originally Posted by Marlinman

I hope you can find something definitive. I think there has to be a constant that you'll find that would keep leading to a broken axle downstream. There just has to be something we are missing! Good luck to you, keep us informed please!

Thank you, I will. I agree with you, it may be a combination of factors which will make it harder to diagnose but I will keep on it.

[Marlinman]

Any new discoveries zole?