“The Heartbeat of America” the ads for Chevrolet, General Motors’ flagship brand of cars, used to boast. For better or worst, as the US auto giant celebrates its 100th anniversary this month, the company’s health has never seemed more tied to the country’s economic health.

At a time when the US economy is spluttering, the country’s most venerable car brand seems to be running out of gas.

“General Motors is closely related to the old economy, the manufacturing economy that America was largely based for the good part of the last century,” said Karl Brauer, editor-in-chief of automotive website Edmunds.com.

As manufacturing declines in the new century, so has GM, that potent symbol of US industry.

The company was founded in 1908 in Flint, Michigan — the hometown of filmmaker Michael Moore, whose first documentary ‘Roger and Me’ focused on GM plant closings in Flint in the late 1980s.

At its start GM was known for being an innovative industry leader.

GM started as “pioneers,” and kept it up for quite a while, said Leslie Kendall, curator of the Peterson Automotive Museum in Los Angeles.

The electric self starter was a GM first, introduced only four years after the company’s founding.

Independent front suspension, the V12 and V16 engines, fins, flaps, the Cadillac and the Chevrolet Corvette — a global automotive icon for 55 years — all came out of Flint, Michigan.

But, Kendall noted, the company “went from being a leader to becoming a follower, from setting the trends to following the trends.”

The oil crises of the 1970s saw the company’s market share begin to slip, as frugal Japanese models overtook GM’s muscle cars like the Pontiac GTO and the Chevrolet Camaro.

In these decades GM “seemed to have lost their ways, they became ponderous, all the creative enthusiasm seemed to have been drained,” said Kendall.

“There’s nothing wrong with following the trends, if you do it right, in a timely way and profitably, but they had trouble with that,” said Kendall.

The big shots of this era were the Chrysler Voyager minivan in 1983, and the Ford Explorer, the first family SUV, in 1993.

But GM had trouble keeping ahead of the curve.

“Cadillac was offering a S75 limousine along with the Cimarron, which was a Chevrolet Cavalier in a party dress, and not a pretty one,” Kendall said, adding: “They started to squander the public confidence.”

Even when the company had the good ideas, they came at the wrong time.

For example, the revolutionary battery-powered EV-1 in 1996 could have turned the company’s fortunes, but it was “too far ahead of its time,” according to Brauer.

Brauer attributes GM’s current state to a lack of diversity.

“When SUVs and big trucks are selling well, that’s fine … but the company didn’t plan enough variety in the product line-up,” he said, adding that “when the market shifted they didn’t have anywhere to go.”

GM however has not remained stagnant in the face of soaring oil prices.

In Europe the company’s Opel brand hopes to corner the market for smaller, more fuel efficient models.

For the 2009 model year GM have introduced the Chevrolet Volt, an electric car that hopes to take off where the EV-1 crashed.

But is it too late?

“I find it somewhat ironic that in the same week as GM is celebrating its 100th anniversary, the other biggest headline is, “Will the government bail out the domestics in order to prevent them from going under?” commented Brauer.

Kendall offered a philosophic take: “Nobody can be on top forever. Everything is cyclical, GM is cyclical too.

“The time may come, hopefully soon, when GM and US car manufacturers will return to world marketplace dominance. But who knows when that’s gonna be?”

General Motors (GM Quote - Cramer on GM - Stock Picks) announced Friday it intends to draw down the remaining $3.5 billion of its $4.5 billion line of credit.

The automaker said the move is aimed at maintaining a “high level of financial flexibility” as it continues to restructure during uncertain times in the capital markets.

“Accessing the funds available to us is a prudent liquidity measure. Drawing on the revolver now improves our liquidity position at a time when the capital markets have become more challenging,” said Walter Borst, GM’s treasurer.

The company set up the secured revolving credit facility in July 2006 with a consortium of banks.

Also Friday, GM announced the completion of a $322 million debt to equity exchange that the company says will improve its liquidity by reducing debt and interest costs. GM issued 28.3 million new shares of its common stock in exchange for $322 million principal amount of its 1.5% Series D Senior Convertible Debentures, which mature in June 2009.

GM shares finished Friday up $3.15 at $13.08.

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This article was written by a staff member of TheStreet.com.