Help - Clunking under car due to ZR-1 shutdown ??

[Volunteer]

I have a 90 ZR-1 that I purchased from a dealer and I picked it up yesterday and all was fine until I got home and shut the car off. There was a noticeable "clunking" from what seemed to be directly under the drivers door location of the car. The dealer mechanic says thats the way ZR-1's are. That the car's either do that when they start up or when they shut down. Is there any suggestions on what this may be off hand before having to dig into it ???

Thanks to those who resonded to my previous ZR-1 question since I am new to both the site and the car.

 

[Steel Half-Shafts]

Could be the "Dual-Mass" Flywheel making that noise on shutdown due to the springs getting old and loosing some of their tension.
Sometimes the heat shields on the cat's can loosen up and make a rattle.
Most ZR's seem to make some noise at idle or shutdown due to the flywheel or the 6 speed tranny design. I don't think it's anything to really worry about.
Also a lot of the ZR's will have "Cam Chain Rattle" on startup until the oil pressure builds up.

 

[ArtZR1991]

That is indeed the dual mass flywheel and very normal. In a dual mass flywheel, the springs (normally on the clutch disk itself) that isolate the cluch disk from vibrating on take up are located on the flywheel itself, not the clutch disk. So the flywheel is actually two disks, hence "dual mass". The idea is to put more mass on the springs to quiet the lower gears of the ZF 6 speed. That's because, as a result of packaging issues and the need to have more power handling capacity, the (lower) gears are "square cut", to allow greater strength in a small space. Same thing is done in high performance marine outdrives.

But back to the rattle on shutdown. Because the flywheel has more mass on the springs, when the engine stops suddenly (try a stall as well as a shutdown), the sprung part of the flywheel moves and makes the sound... normal.

Ironically, on the later 405 hp ZR1's the gears were handled a bit differently in an attempt to quiet them. And they are less strong (but still plenty strong enough).

With the door open at idle, if you let the clutch out in neutral, you will likely hear the gearbox. Also "normal", though the level that is normal can be subjective. But it is there.

You are OK.

Regards,

 

[secondchance]

Hi, Art,
There was a post, possibly in ZR1.net, which was a letter written by one of ZF engineers. In the letter, he indicated that, contrary to popular belief, all ZF6s gears were cut helical. Later in production, due to complaints over excessive noise, clearance between lower gears were tightened resulting in reduction of noise but this reduced the max. torque rating. As you have indicated, torque capacity is still plenty high.

 

[Volunteer]

Thanks for you help and thank you to Rob who also made suggestions. This site and members have been helpful with the couple questions that I have had about particular items on the ZR-1 that I am not familiar with. I appreciate your help