Help Please: Strange sound during break in period

aa909 · #1 (**permalink**) 10-10-2014, 07:16 PM

Hi Guys

Have a new backdraft cobra with a smeding 427 Cobra and TKO600. Car is new, only has 30 miles on it and drives perfectly. However today I took it for a 15 mile drive on the side streets to work the clutch and transmission a bit and after about 25 minutes of drive I came to a stop light and heard a loud "SNAP!" sound from the drivers side. sounded like a piece of metal snapping. Quickly pulled over checked oil pressure and temp, all was in normal range. Turned off engine and inspected the engine bay and under the car. No leaks, smoke, smells etc.

Got back in and car started up perfectly, drove for another 10 minutes and everything was operating fine, engine sounded perfect and pulled strong. Came to another light and another metallic "SNAP!" but this time from the passenger front side. again pulled over and inspected everything and again no issues.

Decided better to drive home and drove 20 minutes back with no issues. Got home and listened to the engine at idle and no tapping, clanking or any odd sounds. No smoke, leaks, pulled strong in 2nd, 3rd, 4th and sounded normal.

So what could this metallic "SNAP!" be? My current thought is that since the car and components are new maybe its a result of the heat cycling of the connection between the side pipes and headers. I checked the bolts etc and no cracks. They were all about 1/4 turn loose.

I also let the engine cool for an hour, started it back up and ran through some RPMs and then let it idle for a bit. Again no issues, smoke or clicking, tapping etc

Thank you in advance for your thoughts and feedback

Mr Jody · #2 (**permalink**) 10-10-2014, 10:55 PM

I don’t think heat cycling would give you the single loud snap that you are hearing. This is usually a series of smaller, less intense snaps.

I may not be telling you anything you haven’t already thought of, but just in case, since so far nothing indicated it is engine related. Since it seems to be related to stopping or low speeds, to check out the possible causes, try to find somewhere where there is a slight decline and with no traffic like a parking lot or quiet side street where you can turn the car off and let it coast. Then apply the brakes. Maybe try it several times at different intensities, with and without depressing the clutch, and moving the gearshift lever if you were moving it as you were making stops when you heard the noise before. Also try a few tugs on the parking brake if nothing else yields any sound. With the car not running, you may be able to hear similar but less intense sounds that would otherwise be masked by the engine noise.

You could also get it up on jack stands so you can get under it to look for moving parts and listen while an assistant performs actions similar to those above. And of course check for anything loose while you are under there, and to see if there is any contact between any moving parts and the body and frame. Check motor mounts and the transmission support, shift linkage. and shocks and their springs and mounts as well. The only downside to this is the suspension geometry is changed when it is on jack stands, so if there is somewhere you can take it where you can get under it with the weight still on the tires would be good. While on the stands, you could also manually rotate each tire to listen for sounds, with and without the above actions, or even crank the car and let the drive train run at low speeds. I wouldn't operate it at higher speeds while on the stands if the u-joints appear to be overly angled from the norm.

Like I said, maybe nothing you haven’t already thought of, just trying to help in recreating the scene, or sound, of the crime.

Rick Parker · #3 (**permalink**) 10-10-2014, 11:14 PM

Front springs ??

Sawdust · #4 (**permalink**) 10-11-2014, 06:47 AM

Quote:

Originally Posted by Rick Parker

Front springs ??

I agree with Rick it sounds like it's the front springs especially since it was heard on the left front then on the right front. I've had that same loud snap on my SPF several times. Scares the crap out of you.

LMH · #5 (**permalink**) 10-10-2014, 11:25 PM

I was thinking front springs too or possibly brake pads or calipers. Might be something to check out.
Larry

Cashburn · #6 (**permalink**) 10-11-2014, 05:53 AM

Did you have the car jacked up? It was the front coil springs resetting in the saddles... You can avoid this and the scary handling until they reset by guiding them in when you lower the car.

aa909 · #7 (**permalink**) 10-11-2014, 12:06 PM

thank you everyone. You all may be right about the springs, the car was in for alignment a day or two before so it's possible when they lowered it off the lift the springs weren't seated properly. Surprised it would take 6 or 7 miles of driving for them to "pop" into place but I suppose that is possible, especially since it happened on both sides independently.

That first "SNAP!" was right next to me and scared the bejesus out of me LOL!! I half expected to be covered in smoke and sitting in a puddle of oil.

In any case, I checked and the springs are currently seated properly. Will take the car out for a test drive later this weekend and see if I can reproduce the sound (hopefully NOT!)

Cashburn · #8 (**permalink**) 10-11-2014, 01:27 PM

Quote:

Originally Posted by aa909

thank you everyone. You all may be right about the springs, the car was in for alignment a day or two before so it's possible when they lowered it off the lift the springs weren't seated properly. Surprised it would take 6 or 7 miles of driving for them to "pop" into place but I suppose that is possible, especially since it happened on both sides independently.

That first "SNAP!" was right next to me and scared the bejesus out of me LOL!! I half expected to be covered in smoke and sitting in a puddle of oil.

In any case, I checked and the springs are currently seated properly. Will take the car out for a test drive later this weekend and see if I can reproduce the sound (hopefully NOT!)

Hope they did the alignment with the springs properly seated...