The Dodge Diplomat / Plymouth Gran Fury
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Throughout the 1980s, the Dodge Diplomat and Plymouth Gran Fury were extensively used as both pursuit and detective cars. Though the standard 318 could not hold a candle to the old 440, it proved to be extremely durable, capable of taking much abuse, and sufficient for most uses. The optional 360 was more powerful and better suited to pursuit cars; dropped from civilian cars in 1981, it remained available for the police until 1984.
Most Diplomat 318 squads (including municipal cars) seem to have been fitted with a standard two-barrel carburetors, as well as the usual electrical, suspension, and transmission upgrades, for use as detective cars and low-performance patrol duty. The state police tended to favor the four-barrel carburetor, which added some horsepower but had about the same torque; Danny Moore reported that cars equipped with the 318 four-barrel had roller cams and 360 heads.
Police could also order a slant six model, useful in cities (where Motorola was more important than motorpower) and detective work, in some years. Slant six powered M-bodies could (in 1981) muster a 21 second 0-60 time, with a top speed of under 100 mph. Gas mileage was around 18 mpg, far higher than the 318 four-barrel V8s, which got around 14 - 15.5 combined city-highway miles per gallon.
The V8 models, with 318s and four barrel carbs, were doing 0-60 in around 12-13 seconds; 100 mph came up in around 40 seconds, with quarter mile times of around 19-20 seconds. (Times are from MSP tests.) The 318 four-barrel was rated at 165 hp and 240 lb-ft of torque.
The E48 option was the 318 four-barrel; the E45, the 318 two-barrel; the general squad package, A38; and the 360, E58. In 1984, the squad package became AHB, and the two and four barrel 318s became, respectively, the ELD and ELE. The AHB would provide tigher, firm-feel power steering; extra heavy duty suspension with front and rear sway bars, heavy duty front and rear springs, strut bushing, and shock absorbers; and wide-ratio TorqueFlite automatic.
In 1984, the Michigan State Police tested the 318 two barrel and the four barrel, and found that the extra 35 hp and 5 lb-ft of torque in the four-barrel cars led to a hefty improvement. The Gran Fury two-barrel managed 0-60 in 13.1 seconds, with a stunning 61 second 0-100 and 19.5 second quarter mile; gas mileage was, however, with a 2.94:1 ratio, 16.5 mpg. The Gran Fury four-barrel, weighing just 35 pounds more, ran 0-60 in 10.9, 0-100 in 34 seconds, and the quarter mile in 18.2. Gas mileage with the same axle ratio was 14.6 mpg, though.
The two-barrel car had a 106 mph top speed; the four-barrel, 121 mph. Numbers varied each year depending on conditions, but aside from a 2.24:1 axle ratio on two-barrels in some years, they were moderately similar. (With the two barrel and 2.24 ratio, the 318 sucked down 14 miles per gallon, and did a 15-second 0-60 in 1989; but the top speed was up to 111 mph and quarter-mile time was 20 seconds.)
The heavy-duty A-727 automatic transmission was dropped at the end of 1982, leaving the A-904 or A-999 in its place. Danny Moore wrote that the A-998 had four or five clutches while the A-904 had three; by 1975, the A-998 was used with the 360 two barrel, and by 1983 the A-727 was changed to the A-904 in squads. (Torqueflite details
The "economy" rear gear ratio of later squads (2.24:1) reduced acceleration and top-end speeds (the 2.94:1 ratio was optional); the result was a V8 powered squad car (Gran Fury, 2-barrel 318) that had the same acceleration as the 2.2 liter Plymouth Reliant. The Diplomat never saw the Magnum head, cam, manifold, and fuel injection treatment. At the end, the standard 318's gas mileage was rated by the EPA at a lowly 15 city, 19 highway.
Duane Hughes pointed out: "The 360 police engine was identical in output to a standard 360, but toughened for continuous high speed use with a double roller timing chain, forged crank, and windage tray. These engines were also standard in the Volare Super Coupe."
The 360 two-barrel was capable of 155 hp in 1977 - compared with the 150 hp of the 318 two-barrel in 1976 Valiants. Former police officer and fleet manager Curtis Redgap wrote,
The Diplomat (Gran Fury) really did well against the Ford Crown Victoria, in part
because it was a better police package. Chrysler Fleet knew then how to meet
and beat bidding. Straight up in 1984 (the last year I was Fleet Manager), the Gran Fury outpointed the Impala and the CVPI in Michigan, and Los Angeles. The
only shortcoming was those front shock suspension towers with the weakened front end braces. If Chrysler had redesigned the front
suspension to the older style parallel torsion bars, the cars would have
been far more acceptable.
For the time, the 318 equated itself well.
While it may not have been as powerful as the old school guys (like
me) liked, it was fast enough, and rugged enough to fulfill 50-60,000
miles of police constant abuse without whimpering. Once the front
suspension weakness was identified, and fixed, (the problem did not cross over to the civilian models) the Diplomat and Fury really were great
In 1989, Chevrolet launched a new fuel-injected Caprice, which bested the Diplomat and Gran Fury in every category but braking and interior egonomics. The writing had been on the wall for years; and in 1989, the last Dodge Diplomat and Plymouth Gran Fury ran their way down the Kenosha line.
Another source, unconfirmed, wrote around 1999:
(A) county in Florida took several 1988 and 1989 Diplomats and worked them over to become drug interdiction cars. The 318 was replaced by the new crate motor from Direct Connection. Rumored horsepower was a manageable 350 net with about 425 foot pounds of torque. Top speed was in the neighborhood of 145 with these cars. The chassis and brakes were changed. The units are still being used sparingly for special cases.
The suspension towers could be a problem; all of a sudden you got some squirrely handling. LA banned the transverse torsion bar suspension from participation in the bidding process. To make matters worse, the K-member of the frame where the suspension was mounted, cracked, allowing further degradation of the sagging due to low quality tensile strength steel. This was particularly evident in the 1984, 85, 86 and 87 cars.
Once the suspension exhibited the nasty habit of going out of alignment within hours of having been reset, the only cure was replacement of the K-member and the shock towers. A rather expensive fix.
This "out of alignment" problem was directly proportional on the type of driving it had received. The NYC police, operating on the bombed out streets of the Bronx and Manhattan, had suspension problems. A Nevada Highway Patrol might never had exhibited any problem at all. No civilian vehicles were ever reported with this sort of problem. Chrysler did solve the situation by 1986. The tower mounts had to be replaced, and the K-frame as well.
As for why the cars were discontinued, the new fuel-injected Chevrolet Caprice was probably a major reason; launched for 1989, the car reflected a major investment in a dying market, full-size rear wheel drive near-luxury cars. Mercedes and BMW could survive with their sales figures, given higher prices and worldwide distribution; Chrysler could not, and the Diplomat, Gran Fury, and Fifth Avenue were probably all surviving on a "until we need the factory space or have to put money in" basis. The Dodge and Plymouth versions of the cars had barely any sales outside of the police market, and the Chrysler only sold well in 1978, 1979, 1985, and 1986. In the end, the company used the factory to keep the Omni and Horizon going for another two model years, allowing the Belvidere plant to make the far more popular front wheel drive Dynasty, New Yorker, Imperial, and Fifth Avenue.
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Note: December 2022 revision, removed unsupported speculation.