2009 GL450 w/ 159k miles

Last fall I was driving and came to a stop sign that was on a bit of an incline. After stopping I went to go again in the car moved forward a few feet and then all of a sudden started rolling backwards and there was a loud grinding clicking noise coming from the transmission. It would not go into any gear, even park. Called a tow truck and had it towed home and ended up driving it off the tow truck and drove it around my yard just fine like there was nothing wrong with it.

Parked it and then came back out later to start digging into it to see what was going on and it was like before, it would not go into any gear again but instead makes a loud grinding clicking noise. It has not worked since. I performed a fluid flush but it has not helped. I do not see any error codes in the transmission with my MBII icarsoft computer.

I let it sit because I did not have the money nor the time to work on it until now. I’m about to pull the transmission to see what’s going on but was wondering if anyone knew what the problem could be? It’s weird that it went out on me but then worked just fine once I got it home and then hasn’t worked since. Hoping it’s an easy fix, but I’m ready to put a replacement transmission in if necessary.

I added a video of the sound it makes when trying to put it into gear.

any help is greatly appreciated, thanks!

What was the fluid like when you drained it. Have you cut open the old transmission filter to see if anything in it

when you came to the stop sign did you just leave it in D or did you put it in N or P. The noise video is very short. Trying to work out if it is in selector ISM or inside transmission

wasnt there a malfunction message that came up on dash or is it just the suspension one.

I did not cut open the old transmission filter but the fluid did not look too terrible. I did not put the transmission in to park upon stopping at the stop sign, I simply stopped and then went to go again, it move forward about 5 feet and then just started rolling back and that’s when the clicking noise started. I had to make the video extremely short so I could upload it as this site only allows a maximum of 20 MB files. The message that came up was that my door was open while the vehicle was not in park. I had the door open to easier hear the noise.

One other thing I wanted to mention was that I replaced the chain in the transfer case about a year and a half ago. I don’t believe it would have anything to do with this though, because if that went out I should still have rear wheel drive.

Sounds like something on the output side or past the output of your tranny, in that the sound changes in pitch when you go from drive to reverse, indicating that the tranny itself is shifting from one ratio to another; but it’s obviously not transmitting the power to the wheels.

Have you checked your transfer case for a broken chain? If the input shaft to it rotates in drive or reverse you have a broken chain.

if no rotating shaft from
tranny output, it’s something in the power output side of the tranny.

Agree to previous but not sure why you had it working after you got towed for a bit.

might be worthwhile draining transfer case and see what that fluid like. (Run magnet in fluid. Can’t remember if drain plug magnetic)

if you had broken chain you should be able to lift a wheel and rotate wheel with it in park.

If you still have old transmission filter cut it open and look for metal but normally on magnets

if transfer oil bad then maybe that is only problem. Hopefully. Transmission is a pain with having to use old computer etc

is it just AWD transfer case or locking/low range etc?

Think if chain broken you would have no drive unless you have a locking centre diff and locked

You can hear that it goes into gear in the video.
shifts from Park to reverse fine
grrrrr in reverse
shift into drive, the pitch of the grrr changes.
so it is shifting. The indicator wouldn’t move out of park if it wasn’t.
2nd forward and 1st reverse are two different ratios iirc.

also check for rusty splines on input and output shafts from tranny on out. Also that park pawl isn’t holding the vehicle indicates failure of it or some component downstream of it.

OP, you currently have no forward or reverse drive?

I like your logic of downstream of park lock

that is correct, I have no forward or reverse drive at all.

no it’s just the regular all-wheel-drive transfer case. Seems like that would be the place to start then seeing as I just replaced that chain about a year and a half ago, it’s possible something broke in the transfer case I guess.

So if you have standard tcase, I believe you should have at least rwd with a broken chain since the input axle isn’t split as it is in the hi/lo range variant. I may be wrong about this though.

get under the car and check for any broken driveshaft bolts or obviously rusty splines on input/output shafts. Since there’s no diff lock in this system the power will take the path of least resistance, which a broken connection or spline is.

yeah, I was thinking the same thing on the broken chain, the rear wheels are in a direct line so those should move when in gear. I won’t have a chance to get under the car today, but hopefully tomorrow I will. Thanks for the info!

and if you put it in park, will it roll?

yes, it will roll freely while in park

Park lock is the last item in the power path fwiw.

it has to be on transfer case or output shaft of transmission

with standard transfer case I still think if chain broken the rear wheels are not locked to the transmission. Centre diff should find path of least resistance

ok thanks. Hopefully I can dig into it tomorrow, if not definitely this weekend.

What luck?

I haven't had a chance to dig into it yet unfortunately. :\ I'll post an update when I do. Definitely gong to check the transfer case first. Thanks!

Here's my guess - had the same thing happen to me... Check your axles where they go in to the diffs. If one of the axle shafts has dislodged from the differential (it's only held in by a circlip?!) You will get the same result you are describing. Grinding, no gear engagement, rolls while in park. I had this happen on one of the front axles and it happened while at a stoplight. It's some sort of safety mechanism so you don't do any further damage if the axle had been damaged. If it (the axle) got pushed back in far enough when it was loaded on the tow truck, it would have driven normal again, as you described - then it worked it's way back out. As little as a 1/4 inch can engage/disengage the drive system. It happened twice before I had a new axle installed. A word of warning, don't get a cheap aftermarket part - they don't always meet the spec. and you'll end up in the same boat. If the axle is not damaged, you might only need a new $2 circlip. The expense comes in installing it! The axle needs to be completely removed, so youre looking at a couple of hours of labor.

thanks for the reply! I finally got it up off the ground this afternoon and have been checking it out. What you describe definitely sounds plausible, but as far as I can tell the axle shafts seem to be firmly engaged into the differentials. Is there an easy way to tell if it’s not engaging all the way? I tried to move the axleshafts laterally from the large part that engages the differential and it does not seem to move any. If I rotate a tire it will rotate the prop shaft for a little bit and then start rotating the opposite tire in the opposite direction. If I stop and reverse the wheel it will rotate the propshaft again for a little bit and then rotate the opposite tire in the opposite direction again. Both the front and rear wheels do the same thing. Also, with all four wheels off the ground I started the vehicle and put it in gear and neither of the propshafts spin. Thanks for the help!

In my case, I looked at the end of the axle where it goes in to the diff - there is a metal lip on the axle-side portion, and it is supposed to sit completely flush against st the differential housing. On mine, there was about a 1/8-1/4" gap there - it was not flush. I was able to shove it back in place and drive it, but it soon worked itself back out. I had the grinding g noise as well -it was the splines on the axle barely touching the splines in the diff as soon as I engaged Drive or Reverse. It would make the noice and slowly go away. If you can get good access, try to move the axles in-and-out of the diff. If you see any movement at the diff/axle connection, I would bet that's your bad one. It's possible your transfer case is bad, but I honestly don't know how it would work/not work/work again... If the T-Case goes, it should be a permanent failure. When you take it back down and attempt to drive it, if it happens again- stop and look at the axles. That's when i could see the gap on mine. Good luck!

Well my drive shafts are not turning at all with the car running, in gear, and the wheels off the ground so it doesn’t sound like that would be it then. The noise is coming from the transfer case/transmission area. I don’t think it’s the transfer case because when I rotate a tire it will turn both the front and rear propshaft together, indicating that the chain is still attached and functioning. I replaced the transfer case chain about a year and a half ago so I was concerned something could’ve happened with it, but that doesn’t appear to be the case. The only thing I seem to be left with is the transmission itself.

Sounds right. Let us know how it turns out.

It might be an easy check to to drop the transfer fluid (into a clean container) and see what the drain plug and fluid looks like. Chunks?

any chance of while in park with back wheels locked (handbrake) then lock one front wheel and put as much torque as possible on other wheel. Eventually it should release through the failure you have.