Transmission clunking noise?

Does anyone else get a "clunk" sound when they shift their i-MiEV back into Park after returning from a drive? It doesn't happen all the time for me. I'd guess around 30% of the time. It's pretty loud and obvious. It kind of worries me that something might be wrong with the transmission.

RobbW said:

Does anyone else get a "clunk" sound when they shift their i-MiEV back into Park after returning from a drive?

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Yes. And it didn’t sound good. Maybe other miev’s are slightly different.
My sound comes if the brake pedal is lifted within a few ms after I put it into P. So to stop the clunk, I wait 2 seconds before I lift up and off my brake pedal (after it’s in P).

Happy cruising,
-Barry

RobbW said:

So to stop the clunk, I wait 2 seconds before I lift up and off my brake pedal (after it’s in P).

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I think it's the park lock. If I'm on a level surface, sometimes the clunk will happen immediately, sometimes as I'm getting out of the car (jostling it a bit with my fat, American ass). Many drivers of automatic vehicles rely exclusively on the park lock to keep their car from moving, rather than using the parking brake.

Mine happens as I'm shifting into park. I'll pay better attention when I'm parking from now on to see if I can determine the conditions that cause the clunk. Sometimes I engage the parking brake before shifting into park; sometimes I engage it after I shift into park. Sometimes I'm in a hurry and run the shifter all the way up into park really fast. Other times I'm slower and more deliberate. I can't remember off-hand when it usually happens. So, I'll just have to pay close attention here on out.

Would constantly shifting between all the drive modes and neutral while your driving have any effect on the transmission? Could I be messing up some mechanical component?

I'm in the habit of using my parking brake in addition to the park lock. Someone told me years ago that it would help save wear and tear on your transmission as the parking brake will hold the weight of your vehicle and keep it from moving rather than putting all that pressure on the trans. I don't know if that is true or not, but it has stuck ever since. However, if my car is going to be sitting unused for an extended period of time, I will not use the parking brake. I will park on a level surface and only use the park lock. The reason for this is an experience I had last year when trying to sell one of my ICE vehicles. We had purchased our minivan and were trying to sell our Hyundai Tucson. Since we were driving the minivan all the time and I wanted to keep the Tuscon nice and clean, I parked the Tucson in the street, engaged the parking brake, and it sat there for a about a month, maybe a little longer, before it was driven again. Once we had a buyer, I wanted to take the Tuscon out to get it one last clean and vacuum so it was all nice and pretty for its new owner. I started her up, disengaged the parking brake, and put it in drive. When I pressed on the gas, the car wouldn't budge. After several attempts, the car started to move slowly but the rear wheels were seized up. With the parking brake engaged for an extended period of time, it had gotten stuck in the lock position. It took several cycles of engaging/disengaging the parking brake and then one final stomp on the gas to break the wheels free. Ever since then, I will not use the parking brake if a car is going to sit unused for a long time.

There is no "transmission' in the traditional sense of the word, as the motor is directly attached to the "transmission" and no shifting takes place. Putting the iMiEV into Park merely shoves a pawl into the drivetrain to lock it. The clunk is normal, and I typically keep my foot on the brake and engage the handbrake before putting it into P. Same goes for disengagement: I keep my foot on the brake pedal when releasing the hand brake when taking out of P to minimize/eliminate the clunk.

For long-term storage, the hand brake should never be set as the brake shoes can stick to the drum. I even avoid engaging the hand brake after driving in the rain for that same reason.

Thanks, Joe! Once again, I'm relieved to hear that my experiences are completely normal. I will be more methodical with my parking procedures to avoid this unnerving noise in the future.

I understand that there is no transmission in the traditional sense. The shifter is a software switch but Mitsu left the "shifting" in place to give drivers that tactile feel. I just want to make sure that I am not messing the shifter up at all with my constant shifting. I have significantly reduced my use of the service brakes by careful use of coasting and regen. However, I am probably shifting from N->D->Eco->B and back up through the gates more times than I can count during a driving session.

Our "clunks" maybe 10% of the time. I think I first heard it when I killed the car while it was still in neutral then moved it into P and heard the clunk. It doesn't sound good when it happens. Anyone know if this is a poorly adjusted parking lock or normal?

A lot of the time, the pawl either falls into place when shifted to park, or it sits between the cogs and the tires hold the car in place. You hear the clunk when the car is in park, and movement causes the pawl to fall in place (snaps into lock position). Quite often, I'll park, and it'll clunk when I get out. Other times it clunks when I let off the brakes after putting it in park. Usually, it doesn't clunk at all since I park on level. If I park on a hill, I set the parking brake before putting it in park. I hear people in other cars that don't do this, try to get their car out of park with a literal bang, and I can't help but wonder how the pawl lasts without getting sheared.

PV1 said:

A lot of the time, the pawl either falls into place when shifted to park, or it sits between the cogs and the tires hold the car in place. You hear the clunk when the car is in park, and movement causes the pawl to fall in place (snaps into lock position). Quite often, I'll park, and it'll clunk when I get out. Other times it clunks when I let off the brakes after putting it in park. Usually, it doesn't clunk at all since I park on level. If I park on a hill, I set the parking brake before putting it in park. I hear people in other cars that don't do this, try to get their car out of park with a literal bang, and I can't help but wonder how the pawl lasts without getting sheared.

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I've never heard of this before. Do all cars have this issue?

Some aren't as bad, while others are worse. It mostly depends on how and where you park. If you're moving slowly and put it in park, you most definitely hear it, as well as coming to an abrupt stop. If you set your parking brake before putting it in park, you'll never hear it.

PV1 said:

Some aren't as bad, while others are worse. It mostly depends on how and where you park. If you're moving slowly and put it in park, you most definitely hear it, as well as coming to an abrupt stop. If you set your parking brake before putting it in park, you'll never hear it.

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Thanks! This would have been good enough to know ahead of time. That first clunk freaked me out.

olagon said:

Thanks! This would have been good enough to know ahead of time. That first clunk freaked me out.

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Me too! I thought I had broken something!

What freaked me out is the bang the front suspension made when I hit a pothole. Definitely sounded like something snapped. It was low speed, just deep. Fortunately, everything looks good.

PV1 said:

What freaked me out is the bang the front suspension made when I hit a pothole. Definitely sounded like something snapped. It was low speed, just deep. Fortunately, everything looks good.

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What you may have heard/felt is the ASC kicking in. It's a horrible sound+sensation which for me regularly occurs on sweeping curves with rough surfaces (I have no qualms pushing our iMiEV hard in corners).

olagon said:

PV1 said:

A lot of the time, the pawl either falls into place when shifted to park, or it sits between the cogs and the tires hold the car in place. You hear the clunk when the car is in park, and movement causes the pawl to fall in place (snaps into lock position). Quite often, I'll park, and it'll clunk when I get out. Other times it clunks when I let off the brakes after putting it in park. Usually, it doesn't clunk at all since I park on level. If I park on a hill, I set the parking brake before putting it in park. I hear people in other cars that don't do this, try to get their car out of park with a literal bang, and I can't help but wonder how the pawl lasts without getting sheared.

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I've never heard of this before. Do all cars have this issue?

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No - In more than 13,000 miles, I've never once heard anything remotely like what's described here

Hard to say (since I've never heard anything) but could it be that some of you are shifting into Park without the brake pedal fully depressed? If you recall, there is a position where the car is not moving, but the motor is still drawing the 'creep current' and if you depress the brake pedal just a bit harder, that creep current goes away. I never engage Park without the brake fully depressed

We never use the handbrake. 98% of the time, we park on level ground, so there's seldom any pressure on the park pawl which locks the 'transmission'. Not using the hand brake is a habit carried over from always driving manual transmission cars. With those, I always put the trans in 1st gear to park

Anyway, no clunking, banging or crunching here when engaging Park . . . . ever

Don

If the car is moving, or if you are on a hill or a slope so that the car has not fully "settled", then that could easily put enough stress on the park lock to make a noise.

JoeS said:

PV1 said:

What freaked me out is the bang the front suspension made when I hit a pothole. Definitely sounded like something snapped. It was low speed, just deep. Fortunately, everything looks good.

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What you may have heard/felt is the ASC kicking in. It's a horrible sound+sensation which for me regularly occurs on sweeping curves with rough surfaces (I have no qualms pushing our iMiEV hard in corners).

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I experienced ASC several times. It definitely wasn't that. I'm pretty sure it was the suspension fully extending and leaving the road for a split second.

I noticed yesterday that the clunk can happen, but it's quieter and masked out by the sound of the shifter.

I had the reduction gear apart today and took a look at the parking pawl. It's similar to type of pawl used in most automatic transmissions but it is really oversized for the I-MiEV. When you shift into park the pawl tries to engage a slot cut into the first gear in the geartrain. This is the gear the motor shaft is connected to. If the pawl hits a slot, fine. If not, it compresses a spring that will force the pawl into a slot as soon as the car rolls a slight amount. I would think it would be fairly loud when the pawl drops into place especially if you had already opened the door to step out. I am really impressed with the quality of the reduction gear, the size of gears and bearings, and the design of the lubrication system.

siai47, nothing like taking it apart for first-hand knowledge!

There's a link here to an exploded view of the transmission on this thread in our very own technical reference section:
http://myimiev.com/forum/viewtopic.php?f=19&t=244

I like their very proper terminology: "Sprag"

Finally, a little more information about the transmission is here: http://myimiev.com/forum/viewtopic.php?f=19&t=552

EDIT 8/29: Oooh, found this link with more transmission details and a beautiful drawing: http://myimiev.com/forum/viewtopic.php?f=22&t=232