the sound of rock impacting fiberglass?

[Slick61]

newbie owner here... with a paranoid question... was out driving on some country roads tonight & a couple of times heard a loud, cracking sound. Is this just a rock banging around underneath? Sounded like the car was going to split in two. It really freaked me out. Pulled over & opened the hood... everything seemed fine... running smoothly (a relative term), good oil pressure, running cool, no fluids leaking, nothing missing, no smoking, yada yada yada. I try to keep enough distance from cars ahead of me so that nothing will be kicked up into mine, though I suppose my own tires may have caught something. Anything in the front end I should be watching for, as far as loosening up? I usually do a pre-flight before each outing, though I may not be thorough enough. I welcome your suggestions...

P.S. I have the Pete Jackson timing gear set, & have heard (from some) that it goes out with a bang, so that was my first thought. Seems to be fine tho...

Now that I think about it, the oil pan is so low that it wouldn't take much to hit that & maybe ricochet around a bit. Dunno...

yea, that's me... the Nervous Nelly...

just want to keep the learning curve as short as possible...

[trularin]

The gear drive alone would scare off most.

I live on a country road as well. YOU need to go very, very slow and avoid washboard sections at all cost. They will crack your windshield.

If you are going to stay on that road ( live there ), I will suggest spats for the rear fenders.

You should preflight every time you take her out. Keeps the wife from loosing her mind if the car dies because you forgot to do something.

Well, good to see someone else had these thoughts.

[eschaider]

Don't mean to be an alarmist but a loud cracking sound could be a weld on a stressed chassis component breaking! Did the sound repeat or was it a one time occurrence? Usually stones into fiberglass are very stealthy in their mission. We don't necessarily hear them but we see their work as stars in our fiberglass sometime later.

You might want to check things like motor mounts that might loosen up and ride up on a couple of threads and then settle down again into their correct locations accompanied by a loud sound. Did the noise occur under power, decelerating or coasting?

Suspension components like shock mounts might break loose under the right conditions (very unusual) but they would create a loud cracking sound when they let go. You should notice it immediately however, in the handling of the car.

If you can you should either provide some crash protection, like a skid pad, for the oil pan or better build a lower profile pan that doesn't get as close to the ground. It's not hard to do your own pan. Look at some of the pictures of good comp pans from builders like Avaid who did the original pans for Shelby.

Even if you don't have access to welding equipment you can still draw up a new pan with some of the low cost to free 2D drafting software available today. Take your drawings to the local sheet metal shop buy the sheetmetal and farm out the welding job to a local welding shop. It's smart and its good insurance!

By the way, ditto Trularin's comments about the windscreen. Do a search on the site for broken windshields and you will find a wealth of information. They are tender and expensive so be protective.

Hope your mystery noise turns out to be no big deal.

Ed

[uncltodd]

Hey, Slick61!

Get used to strange "impact" sounds from under the car that you can feel in your buttocks.

I'm in rural Oklahoma and have to pull into 55MPH (Yeah, right) US Highway traffic to go anywhere!

I hate truckers, sorry. They don't look, they don't obey the speed laws, they don't care. They own the highway and don't Habla Ingles.

Our little cars are almost invisible, I WILL NOT drive at night!!!

Trucks throw rocks at highway speeds, their mudflaps are a cruel joke when you drive a car that is only 4 inches off the ground. A 1-inch rock bouncing off the bottom of a fibreglas body sounds like a gunshot! Been there, done that.

BackDrafts are built hell-for-stout, I wouldn't worry about a chassis or frame failure.

Gunrack is a driver, rock chips are kinda like tick bites, where I live they can't be avoided.

Gilroy? As I recall, that's the hottest place in California, year-round!

Watch your coolant level in your preflight.

UT

[Slick61]

... actually, it happened while accelerating away from a stop light... was probably doing about 40-50 mph. There was a car in front of me, tho I thought I kept a safe distance. Wasn't a single impact... it banged around underneath a couple of times. Just couldn't figure out what could've come loose (if anything actually did).

It wasn't really a country road per se... is a 2 lane highway out in the sticks (Sierra Highway- from Canyon Country to Acton) Not the best road, but not the worst either. I'm sure there's some loose rubble from time to time.

Took the freeway back home... was fine... no issues, tho I'll still probably crawl underneath & doublecheck...

am curious to know what everyone's pre-flight regimen is...

[BRYCE]

Slick61 Where in Valencia do you live? Would love to see your car. Haven't seen to many other Cobra's out here. Get back to me and lets compare notes. Leaving for Laguna Seca wednesday morning ( historic races, car show ect.) give me a shout after the 22nd.

[Sledge]

Here's my checklist, developed specifically for my BDR:

ONCE PER WEEK

Oil Level--Above minimum
Spark Plug Wires--Attached (both ends)
Alternator Belt tension
Pedal Hanger Nut--Secure
Heat Shields--Secure
Side Pipe Mounts--Secure
Battery Mount--Secure
Electric Fans--both operating
Horn--function and security (I've had one fall off)
Lights, signals, brake lights, etc. (I've had lots of issues with the lights)
Tire Pressures
Knockoffs and Wheels--Secure
Wind Wings and Visors--Secure
Radiator for Debris


ONCE PER MONTH

Brake Fluid Level--above min
Coolant Level--above min
Cooling System Hoses
Throttle Cable--secure
Windshield Bolts--secure
Bumpers--Front and Rear--secure
Oil Pan Plug--secure
Trunk lid attach bolts--secure

Cheers,

[trularin]

Wow Sledge, that about covers it.

[MaSnaka]

I like your checklist...perhaps to add is fuel level...check. Clean windsheild...check. Wipe down with car duster while warming up...check. Let's go! Not too far from Valencia either.
John

[BDR530]

Slick61,
I live on a gravel road and everytime I drive out it sounds like its raining rocks. I never go more than 10 MPH until I hit pavement but those sticky tires throw rocks everywhere. Its really an "audible illusion" because it literally sounds like rocks are falling from the sky. I wouldn't worry too much about it. Its just the nature of the beast!

[cbreez]

I have heard the same(similar) terrible cracking sound in mine...on smooth paved roads...sounded like it was in the trunk...I have yet to figure it out...almost like a tremendous electrical arcing sound....my car looks good though...????

[Smoking Cobra]

With those wide deep groved tires your bound to pick up rocks etc.
joeg