C3 - Bottoming Out

[Andrew Johnson]

I just bought a C3 and it seems that it takes very little down force to cause minor bottom scraping. I had the car fully checked out by a very reputable Vette dealer in MD and he never mentioned a need for new shocks.

I currently have 225/60/15 tires on the car, could this be causing the problem?

The handling is fine with no swaying in corners so I am not sure what to check or replace first. However, I will be upgrading to 225/70/15 tires. Will this help?

Regards,

Andrew

[Michael H.]

Re: C3 - Bottoming Out

Hey Andrew -

Your shocks are not the problem - it is most likely that your springs are shot. Metal springs have a definite life cycle and do wear out. Think about substituting a fiberglass composite rear spring if not concerned about correctness. The composite springs last a lifetime as long as they're shielded from heat.

[Mark #28455]

Re: C3 - Bottoming Out

the bigger tires will help also

[Duke W.]

Re: C3 - Bottoming Out

I disagree that springs "wear out". Though they have a fatigue life, it is typically well beyond the life of the car. What kills springs is corrosion, which removes material from the springs. Spring rate is a function of wire diameter to the fourth power, so it doesn't take much material loss to weaken them, and they will usually end up breaking if seriously corroded.

Your tires are not a issue, but Sharks have a low front air dam and it is easy to scrape entering steep approaches such as driveway.

The first thing you should do is measure ride height per the service manual or AIM. If it is out of spec, you could have a weakened or even broken spring. If the ride height is okay, Look for low hanging components on the car. You may not be "bottoming out" - just something low is scrapping.

If you want to check for bottoming, place a dab of grease on the front and rear bump stops, then after driving, check if there is grease on the frame where the rubber bumper contacts.

Duke

[Andrew Johnson]

Re: C3 - Bottoming Out

Duke,

I had the car thoroughly inspected by Tony's Corvette Shop in MD prior to buying it last week and he looked over the springs and made no mention of them being corroded or worn.

As a matter of fact the car had a frame on restoration 7-years ago and has had very little mileage since.

It doesn't bottom out when coming out of a driveway and the sound is a light metallic scrape that is somewhere between mid-chassis and the back mufflers.

It happens most when traveling at 20 to 50 miles per hour and going through valleys in the pavement such at the bottom of hills or on a country road where out of nowhere you kind of float up or down. Only in this car I get the scrape with the float.

I think the previous owner mentioned something about a U-bolt and exhaust?

Regards,

Andrew

[Duke W.]

Re: C3 - Bottoming Out

It sounds like either something on the chassis is interfering with something on the suspension as it goes through jounce and rebound, or something is hanging low and scraping on the ground on jounce.

It's not really bottoming out. A thorough under-chassis inspection should reveal the problem as there are likely wear marks at the interference point.

Duke

[Roger Legge]

Re: C3 - Bottoming Out

Check the positioning of the exhaust pipes at the low point just before they turn up to the mufflers. If they're not welded, meaning there are clamps, they can loosen and not be tucked up into the normal position. I ran into this with an undercar chambered setup on my '68.

Roger
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