Popping sound when accelerating

[andrewwynn]

Sound stops when no power to front axle. No logical connection.

I get thump from rear when under power due to subframe bushings.

Is the thump sound possibly synchronized with bumps in the road and you are getting some suspension bushing movement that only happens when the front axle is loaded?

It sounds similar to the rear subframe moving that only happens when I hit a bump while going up hill or accelerating.

There has got to be some equivalent bushings up front to isolate the front subframe and the diff possibly motor mount.

The theory is: when under load from front axle under power the diff/motor are being torqued back at the top. When you hit a bump it hops off the mount and gets pushed back from the wheel torque.

If you get a longer video it can be examined with software to see if the pops are evenly spaced hinting at gear or they are not and it can't be.

[X5chemist]

Check all the mounts. One may be loose or broken. Use a BFP bar. It’s going to a challenge. Which side is the noise loudest?

[Thaniel]

Sounds like it could be the transfer case chain. Doing the transfer case chain on mine right now. the change slacks over time then slips over the sprockets. Not necessarily going to see any flakes as the chain is stretched not fragmented. If caught early enough the sprockets don't need replaced. There are some vids on youtube demonstrating the sound. See if it's the same.



CV's typically sound more like clicking and in all the car's I've had, if the boots don't tear I've not had them fail.

[nick325xit 5spd]

I will note that Cardone axles are generally just rebooted and regreased used axles. At least in the E30 world, they are also typically *damaged*. And if they are actually new, they are definitely garbage. I'd take rebooted stock axles any day over a $50 new axle.

I also made the mistake of buying a Cardone rebuilt brake booster once, and it arrived leaking.

I wouldn't assume that Cardone parts are good.

[bcredliner]

As I understand it the popping noise is only under acceleration. If that is the only time you hear the noise I would check the sway bar links and bushings, and the struts. And, I would do a complete check of the front suspension. Assuming you don't have a lift I would take it to shop that can do so and then they can check the components that need to be loaded or not loaded to do the troubleshooting.

[andrewwynn]

Since it's only happening when front axle is loaded, that should eliminate just about everything drive train except backlash. If there is backlash in the CV axle for example when you are under load and hit a bump/dip you have that also for spring action to pay out slack that is removed on re loading the spring. I get very very similar sound from my worn subframe bushing in the back. It only happens under load and when I go over "dips" that partially unload the springs.

That mostly leaves suspention parts and that means look into Etsy parts get torqued under load. Mostly that means shock tower and tension struts. Do some unloaded prodding for loose joints.

Since the problem is only happening under torque lift one tire off the ground remove the wheel and apply as much torque as you can (you can use 36mm socket on the axle nut to apply up to 300 ft·lb CW or put a bar between a couple lugs and hub to add a lever you can push with your foot.

Push hard CCW then CW and listen and look for motion.

Recently people have traced weird suspension sounds to the shock tower bearing and even a broken spring!

Oh final thought:

I did a complete front and rear suspension refresh and I still ended up with an occasional while braking wobble.

Turned out to be steering rack. The reason I bring it up is that after i finally figured out that was failing, I noticed it makes a thump sound pretty darn close to your "pop".

If your tires are 255 or wider, power application on front axle will torque the wheels toe out and hitting dips will cause the same relaxing of the springy tension that could slap into the rack backlash (that's what's happening on my car now).

Have somebody turn your steering left and right while engine off and confirm you don't have excessive noise in the rack mine i didn't notice with engine running but when off very obvious.

Also: do your recreation test like the video and try it while steering up a curve both left and right. If the sound goes away more likely rack.

Do you ever get shimmy under braking, especially if just rarely ?

[E53Envyy]

We’ll guys I finally fixed the issue!

It was the transfer case!!!

When I cracked her open the chain was flapping in the breeze. I decided picking up a used transfer case would be the easiest option and I had it back together in short order.

A couple notes if anyone has to do this job:

- On the ATC500 transfer case you cannot see if the chain is loose through the drain or fill hole.
- access to the torx bolts is much easier then on the NV125.
- Remember to buy the DTF-1 fluid, it’s expensive!

Here’s a good video on disassembly:

https://m.youtube.com/watch?v=M_qKif-KXGo


From my knowledge not many x5’s have had this issue. Knowing that my X has the tow package leads me to believe lots of heavy towing from the previous owners caused the failure.

Thanks everyone for the help! Really appreciate it!



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[andrewwynn]

Wow so was it the chain popping to the next tooth?


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[bcredliner]

Great video!

[Thaniel]

Glad you got it fixed. I replaced the chain and bearings in my t-case (185,000 miles). My case is the NV125 though.



From my reading trying to find more about the repair it seemed not uncommon for any 4WD (BMW or any other brand) to have the transfer case chain wear/stretch over time and there is no chain tensioner t-cases. Bit surprising it lasts as long as it does. How often the fluid is changed might have an effect too. The insides of mine were pretty dirty so it had not been changed often.