Clunk at engine start up and shut down
 

Ok, I have searched and searched and have come up empty. Here is my story:

I broke down and took my car to an Indy for ball joints, new belts and to check out the motor mounts. I just wasn't finding the time to do this and now my garage is 100+ degrees every day :eek:

Indy said the motor mounts were fine. Other work was done and I was glad to be rid of the squeeking from the front end.

Next day I go out to start the car and notice a definite clunk from somewhere around the tranny area (best I can tell sitting inside). Noticed it on shutdown, too. Nothing unusual while driving, starting, stopping etc.

Took the car back to the Indy and asked them to check the mounts to see if someone loosened something and forgot to re-tighten. Sure enough, the right side was slightly loose. He also pointed out a 1/2" weld that has let loose on the driver's side, just inboard of the lower control arm bushing. He said that might be contributing. I will have the weld re-done, but it doesn't seem like I'd be getting a clunk in the center of the car when I do, from that busted weld.

Anyway, the tightening of the motor mount made no difference. I had to leave as I was late for a meeting. I really suspect the tranny mount and plan to take the car back at my first opportunity to have them check the tranny mount and do some welding. It seems like he would have checked the tranny mount, but after I heard the clunking and gave it some thought I realized he never mentioned looking at the tranny mount.

Any other ideas of possible causes that I might suggest the Indy look at?

Thanks guys - I appreciate your time!

Tim

Replace your motor mounts. That is the problem. You can't tell they're bad by inspecting.
Steve

I agree... also check the two engine shocks. Mine had no lower bolts when I bought the car.

Check to make sure your air cleaner housing is tight. Mine had the same problem, after replacing motor mounts. My bracket was broken. Those things are louder than they appear they should be.

check the exhaust.. make sure all the hangers (donuts) are there and solid

There is also a mount on the tail end of the transmission. I had the two bolts on mine strip out. It sounded similiar to what you describe.

TimK

I've had this happen before.

It turned out to be a crack in the flywheel, after replacing motor mounts, and going through everything else, the dealership found it.

The crack, started at the center hub/hole of the flywheel, and made it's way over to a bolt hole...

They showed me the old flywheel, and I could not believe what I was seeing..Pretty serious crack, about a millameter wide, and a few millameters.

Thanks - new bracket two weeks ago!

I should have thought of that.

thanks,

Tim

The Indy said they looked like new (PO must have done them relatively late in his ownership). Could he really miss it by that much?

Sounds like I really need to get this thing back in the air...and maybe have a different tech look at it this time.

Ok, now you're scaring me :eek:

:D

hwo could a crack in the flywheel cause this...?

Not exactly sure, but the mechanic told me that the torqueing of the engine, uppon start-up, and shut down, causes the flywheel to sort of "Dance"...Like when an airplane engine shuts down, and both the first and last motions of the prop. actually seem to bounce back in the opposite direction of the engine's rotation. You can actually see this happen, by watching the front pullys of the engine when you shut it down, they sorta bounce back the other way for a second. The higher the compression, the more serious the bounce will be..

I guess this causes the flywheel to be highly stressed, especially where it is attached to the crankshaft. This caused the crack..

The noise you are hearing, is the flywheel popping back into it's position, or flexing, with the tranny torque converter's weight pushing against it.

Turns out my engine shocks were shot.

She is all better now!