Just had a scary incident with what may be a problem with the ZF 9-speed transmission in my SH-AWD TLX. I am very interested to hear if anyone else has experienced anything similar. I'm including all the details I can, though some may end up not being relevant, in case someone has an idea as to what happened.

Midday, mild temperature (~50 degrees F), clear weather. IDS set to normal. Started car and drove secondary roads to Interstate. After approximately 10 minutes I exited the Interstate to an off-ramp so that I could turn left onto a secondary road. Light at end of off ramp was red and there were several cars stopped and waiting. I came to a normal stop behind the last car and the TLX performed an idle stop as expected. Light turned green and all cars except one directly in front of me proceeded. I waited a few moments then honked the horn to get them to go, after which they took off. I pressed on the accelerator to follow and as expected the engine started and I began to roll. I probably got up to about 10mph before they began to stop somewhat suddenly again because the light turned yellow. I put on the brakes to also stop and simultaneously I got the BRAKE and flashing heads up warning. I was applying brakes moderately hard but definitely not enough to trigger antilock brakes or anything like that.

Here's where the problem occurred. While braking and while warning light flashing, a loud, grinding, metallic gear-on-gear sound emanated from the front of the vehicle. I believe I also felt vibrations through the floorboard. Again, I am familiar with the feel of anti-lock brakes and this was very different. The "click-click-click" sound, machine-gun rapid at first, slowed as the vehicle speed slowed and finally ended with a definitive "clunk" just before the car stopped. There were no additional dashboard lights or indicators, and the engine continued to run normally afterwards. The stoplight went green again and both I and the car in front proceeded normally through the intersection.

I immediately turned into an empty parking lot and tried in vain to reproduce the problem by starting and stopping in the same way. I could not get it to happen again.

The ordeal was very disconcerting and didn't sound like it had done any favors to whatever engine parts were involved. My best guess (and it is only a guess) is that it had something to do with the way in which the ZF 9-speed transmission "dog clutch" operates (see here). It certainly sounded like a bad synchronization or someone "grinding the gears" in a stick shift. What doesn't make sense, though, is that I had not accelerated nearly long or hard enough to get anywhere near the first dog clutch shift point, which the above link says happens from 4th to 5th gear.

Has anyone experienced anything like this? Not what I expected from a 1 month old car with 1000 miles on the odometer!

 

First of all I'm not an owner of the TLX, but I'd take it to the dealer and have them see if it threw any codes and document the report from you on the incident. There may be some repeat in the future.

But the dog clutches don't come into play until the shift from 4 to 5 and at 10 mph you probably weren't using the dog clutch. Not to say there couldn't be some issue.

 

I was under the impression that the 4-banger has the ZF tranny, whereas the v6 J engines are coupled to the home-made 9-speed.

Regardless, if the lights on the dash went on, chances are there are codes logged in the computer. So, since you are under warranty, take it to the dealer to take a look.

 

It's actually the other way around. The V4 uses a home grown 8-speed double clutch, and the V6 like in my car uses the ZF 9-speed.

A second hypothesis I've had is that the tranny somehow was between drive and some other setting (neutral, park, reverse?)

 

^i4.

 

because it happened while you were braking, i honestly believe it has something to do with VSA or however the TLX implements ABS, VSA , etc.

 

Was there any strong seat belt retraction? You mention the heads up "brake" warning engaged, so wondering if the Collision Mitigation Braking System was at the point where it would do strong brake application.

 

^sounds more plausible than the tranny

 

No, there wasn't any seat belt retraction. I believe the BRAKE warning came on solely due to proximity to the vehicle ahead. I certainly wasn't feather braking, but it wasn't hard braking either, and it was relative to my own foot pressure (meaning, there was no noticeable additional automated braking applied). While it felt to me like the grinding sound went on forever, I estimate it occurred for at least 2 seconds, ending in a "clunk" before I stopped rolling.

When I tried to reproduce in the parking lot I tried braking very hard to be sure I was familiar with the ABS feel in this car. I got the ABS to momentarily engage and it neither sounded like nor felt like the problem.

 

ABS makes a grinding noise exactly as you are describing. Speed up to 35MPH and SLAM on the brakes. You'll get ABS to engage until you are at about 0MPH and you'll hear the machine gun sound that you mentioned along with the grinding.

 

Thanks for the note, though I'm nearly certain that it was not ABS:

1. I am familiar with the sound/feel of ABS - this was nothing like it. MUCH faster (at first), metal-on-metal grinding sound.

2. I was going no faster than 10MPH and provided moderately hard braking on dry pavement - nothing that should have come close to endangering tire slippage. In fact, I'm quite surprised in my subsequent tests of just how hard the brakes have to be pushed to get ABS to activate. I was nowhere near that hard on the brake. I came to a fairly normal speed stop.

3. The metal-on-metal grinding sound slowed as the car slowed down, ending in a clunk. I'm not familiar with an ABS system that slows its pulse rate with travel speed, though I'm not certain on that point.

I've checked my ODBII port and there are no stored codes, so the mystery continues.

 

You said the car had the BRAKE symbol pop up, does your TLX mash the brakes to avoid a collision? If yes, that's why VSA + ABS kicked in causing the sound. I've gotten the clunk when stopping with VSA on my MDX, easily duplicated over speedbumps with the front wheels! ABS may have been working in combination with the VSA system altering pulsing rates as VSA controls individual brakes to my knowledge.

Go to acura anyway! They can hook the car up to HDS (very useful software for these cars) and see if they can pull the event information up or the logs in your car to see if an internal computer documented it that wouldn't show up on your typical OBDII scanner.

 

Any chance you were on a metal grate or manhole cover when you initially hit the brakes? That can cause ABS activation, but not the typical feel or sounds.

 

Thanks for the thought, but this was on an interstate off ramp and one that I regularly drive on. Nothing but pavement there.

If this instead only happened a few weeks from now I would have captured sound and video on my newly ordered dashcam.

 

I think this is exactly what happened. With all of the safety features in the cars today like ABS, VSA, CMBS, TCS, LDW, and LKAS (just to name a few), there are lots of conditions that will trigger one or more of the systems which will create noises/vibrations the driver is not used to seeing.

I don't know if I would waste the time making a separate trip to the dealer, especially since it only has happened one time and you are not able to duplicate the concern. Even in the unlikely event that there is something stored in the computer (which I suspect there will be no codes found), all you are going to get is that they have cleared the codes and will want to wait and see if the codes return.

If I were going to have the dealer look at it, I would wait until the next oil change is due and then have them look into it while they are completing the oil change. You still have a lot of warranty left so if there is really something going on, it will come back long before the warranty is up on the car.

 

i called it post #6

 

Thanks to everyone and their input as to what may have caused the disconcerting noise. With ice on the roads today I was able to test the antilock brake sound/feel multiple times, and I can say with 100% confidence that this was not in play during the mystery incident. There is a night and day difference in the two, with the ABS causing a dull ~5 pulse per second sound/feel, while the sound I heard last week was loud and grinding, with a click rate at least 4 times that of the ABS.

 

^you are just accounting for ABS.

there are other mechanics at play here.
heisnuts explained it, ABS, VSA, CMBS, TCS, LDW, and LKAS all work together.

 

I have had this issue... but only when Brake Hold is engaged. I know exactly the sound you're talking about; it doesn't sound at all like ABS, but rather like a ratcheting sound, not unlike what this might make: http://www.technologystudent.com/images7/crnky2.gif

I am able to reproduce it regularly with my car (SH-AWD Tech) by doing the following:

1. Engage brake hold.
2. If not already moving, accelerate to ~5 mph. If already moving, slow down to ~5 mph.
3. LIGHTLY press the brake just enough to slow down the car such that it will eventually come to a complete stop.

The noise will occur as soon as the car's forward motion stops entirely and the brake hold system engages. You should try these steps and see if you can replicate it.

I'm taking my car into the shop Friday to get it checked out.

 

Thank you - I believe we're experiencing the same problem. I was unable to reproduce by your steps, but your description is spot on. Please let me know what your dealer says.

 

so, it does have something to do with braking.

 

So I just got back from the dealer, and they confirmed that the sound comes from the system that controls the brakes for any system that uses it automatically. So, in my case, only the brake hold uses that system, but for the Advance package, the CMBS also uses it. Therefore, what djsteve experienced is likely the CMBS engaging. I believe the parking brake is also the same system, but it's not like I use that while driving...

They didn't have any solution for me, but the service adviser said he will do some research and see if he can figure anything out. For most people, it seems rare enough that it's not that big of an issue, though. Even though I'm able to replicate it on demand, I really have to try to get it to happen, so I'm not worried.

Knowing this, though, you could probably try to trigger the CMBS to get it to make the sound again. I really wouldn't recommend it though, since you'd probably have to drive at something and be ready to hit it -.-'

 

DJSteve, Mine has done this before as well. i know the car will apply the brakes for you and it does downshift the tranny to help do it. Mine made a grinding noise as well when someone pulled out in front of me(i was going a little fast) and i felt the car actually apply the brakes on it's own. the seatbelt was jerking and lights were flashing on the dash. I think that this is just part of their safety systems. Although the noise didn't sound right, i've had no issues with the tranny(other than shifting hard into 2nd on cold mornings).

Hope this helps.

Dan

 

Thanks, Dan. Although I was applying the brakes at the time and there wasn't any noticeable additional stopping power, I'm convinced that it did have something to do with the collision avoidance. I've not been able to reproduce in the month since (and I've tried many times!), so I'm just going to file in my memory in case it happens again but otherwise not let it bother me. Like you and others, I am happy with the car except for the hard shifts from 2-3, which I understand there is now a software fix for.

Thanks again,
djsteve