Over-rev ---> Odd sound at 3,000rpm.

[romancer]

Hello everyone,

2008 GT.

On the way home about a month ago I mis-shifted from mid third into second gear. The car revved to a very high rpm for a short time. It didn't sound good and I was ready for the worst. Currently waiting for a replacement shifter as well..

Thankfully everything ran fine on the way home. After the instance, I tested my car around town and noticed a slight buzzing sound in first gear. It is noticeable in the other gears, but it seems to be really pronounced in first. If you listen closely, you can hear the sound reverberate outside of the car...but it isn't anything serious or very loud.

I can pinpoint the sound @ 3,000 rpms...roughly the point where the valves open, no? It is a slight buzzing sound that can be heard (if you are listening closely) at that time. Any thoughts on what it is? Implications for the future? I'm going to call and have Ford check it out this week. This afternoon I sat and revved the car in neutral and the sound consistently happened at 3,000 rpm. The car does this when it is completely warmed up, so I ruled out the cold engine rattle.

Performance seems exactly the same. I feel no drops in power or anything like that. Not even at the point where the sound is made. I first thought (and still am considering) it to be valve rattle or valve float, but wouldn't performance be compromised? I must admit that I'm legitimately confused, as I would think it to be valves after an over-rev instance.

Any thoughts?

 

[bradleyem]

You say that you are replacing the shifter? When you mis shifted, did you jam it in gear? I highly doubt that you did anything to the engine. The rev limiter is designed to cut power way before any damage would be done. Most likely you bent something in the shifter linkage or messed up a bushing. The shifters in these cars are notoroiusly noisy to begin with, and if you messed up a bushing or bent something, it would result in more play, which would make the vibration from the shifter worse, or more audible.

Another possibility, although very unlikely, is that it's the throwout bearing or something in the clutch assembly. This might happen if you panicked and dumped the clutch. But I highly doubt that thats the issue. If you're already changing the shifter, then do that and see how it affects the sound. What kind of shifter are you getting? Be aware that many aftermarket shifters will actually be more noisy, and read up on the threads on using dynamat to help dampen the vibration.

 

[Sparty92]

You say that you are replacing the shifter? When you mis shifted, did you jam it in gear? I highly doubt that you did anything to the engine. The rev limiter is designed to cut power way before any damage would be done.

There is no rev-limiter really, it's more like a fuel cut-off...at redline. On my Honda Civic Si, I had a rev-limiter. If I accelerated past 8,000rpm the needle would bounce on the tach but the car would still get fuel and go.

If you took your Mustang to redline and beyond (while in gear), the fuel would cut and the car would slow down. The tach would not bounce on the redline, and the car would just die of fuel starvation.

That said, if you are shifting from say, 4th gear at 110mph down to 2nd gear and actually engage 2nd gear and get off the clutch, I think the engine would mechanically over-rev and blow right past the redline, and that's where damage is done.

It's one thing to accelerate INTO a rev/fuel limiter. It's another thing to mechanically force it into/beyond the limiter by missing a downshift.

I'm just guessing at all this, of course. I'm not a mechanic, I'm a photographer.