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The Gentleman's Express: Tech-Tips from the JIOC

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Retorsion Rear Springs and Add Leaf

Author: Joe Sicignano

This tip is dedicated to Ron Jacobson who had the temerity to deviate from the traditional in experimenting with and succeeding in improving his suspension. I recently followed his recommendations and had Dick Gulstrand Enterprises of Culver City CA 90230 do their thing. They have a solid name in custom suspension fine tuned from long experience in racing.

Prior newsletters listed replacement shocks for the Interceptor including Gabriel and Monroe as well as Koni, the latter (a high-priced import) was also mentioned by Jim Cummings. He also pointed out the problem with rear leaf spring sag which adversely affects the ride, causes the car to bottom out quite easily and contributes to the problem of understeer in the Interceptors which began when the heavy 440 block was introduced.

I began to note that I would scrape the spare tire carriage coming off a steep curb, after 20000 miles. The problem becomes most annoying with two people in the back seat unless I added four pounds of pressure to the back tires.

The pounding and scraping also required the rewelding of the bolt assembly needed to crank down the spare. I have 30000 miles on the adjustable Gabriels (set on regular as the firm and extra-firm settings were unbearable) but the rear end would shimmy after bumps such as railroad tracks. The sag in the rear was easily noticed by the eclipsing of the rear tires under the fender as compared to the front.

Gulstrand pulled the rear leaf springs, had them retortioned (rearched) to lift the car to proper height and added an additional leaf. Dick no longer recommends Koni’s which he feels give too much of a rough ride and are over-priced. His recommendation for the state of the art is Belstein gas-filled shocks, used in some high priced imports and off road vehicles. Mickey Thompson manufactures gasfilled shocks utilizing Belstein patents custom fit for the Interceptor. The price is $75 per pair for the front and $85 per pair for the rear.

The results for the job, which ran $489 total, are quite satisfying. The ride is firm but not jarring. The steering is neutral, and the extra weight under the hood now appears to have gone. The cornering, even with my GR70 Michelin X with 30000 miles on them, is again sports car like. There is less rear squat and wheelspin in open throttle acceleration, and less front dip on hard braking.

I had looked into adding a rear antisway,bar and increasing the size of the front one but the consensus at Gulstrand was that the present modifications were optimal. Gulstrand, like A K Miller, did not recommend the expense of high priced import tires except for status. A 60 series tire is still a possibility but it would be a tight fit at best.

Gulstrand reports good results with the Goodyear GT radial on their high performance machines. I am still waiting for reports on the new Pirelli P6, their off-shoot of the state of the art P7 which is a 50 series tire. The P6 will be available as a 65 series tire which might be worth waiting for in 1979.

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Contents copyright 2008, 2009 - Jody F. Kerr

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