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Class A motor homes roll on new Ford chassis

October 28, 2005|by JEFF JOHNSTON/Motor Matters

Buyers of Class A motor homes have been able to choose a Ford chassis as an option for many years now. Ford's F53 Super Duty Stripped chassis, as it's officially known, has developed a popular following and is available on many new motor homes on the market.

A new five-speed TorqShift automatic transmission highlights the chassis for the 2006 model. While the company has made other improvements over the years, adding an extra gear selection is one way to dramatically improve a rig's powertrain.

The challenge of getting the power to the road in an efficient, effective manner is significant in a heavy rig like a motor home. You need power at the low end, for starting from a dead stop and climbing hills, as well as speed to accommodate today's highway travel. Fuel efficiency is a must, since single-digit mileage is common in RVs and every little bit helps. Extra transmission gearing can help accommodate those mileage and power-delivery needs.

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Another significant TorqShift feature is its tow/haul mode, which is switched on and off by pressing a button in the end of the shift lever. This setting not only changes the shift point schedule to better accommodate the extra demands of towing a load, it also engages the grade braking feature.

Grade braking is an automatic feature that shifts the transmission down, and holds that gear, when certain downhill driving situations are encountered. The alternative is manually shifting down to a lower gear to better use engine compression and avoid overheating the rig's brakes.

Ford powers the chassis with its popular 6.8-liter Triton V-10 engine rated at 362 horsepower and 457 lbs.-ft. of torque. Solid axles front and back are supported by conventional leaf spring suspension hardware, and the disc brakes all around are augmented by four-wheel ABS.

Our first drive with the new transmission was in a Holiday Rambler Admiral SE 30PDD, a 30-foot coach built on the 20,500-pound GVWR chassis.

Engine noise is related as much to how the coach is built as it is to the powertrain specifics, and the Admiral was as quiet as a front-engine gas-powered coach could be.

It accelerated from a dead stop quickly - relatively speaking - and quietly. The shifts are perceptible as crisp and firm but not harsh. A 0-to-60 mph run consumed nearly 21 seconds, and the more-important 40-to-60 mph "passing speed" run took 11.4 seconds. Despite the rig's 16,920-pound weight, it moves along just fine. Freeway speeds generate minimal underfloor and underhood noise, and the transmission holds Overdrive very well. Some powertrains tend to hunt a lot between OD and 4th (direct) gear, but the Ford seems to lack this problem.

Hill climbs seriously test a motor home's powertrain. We tackled several Cascade mountain grades in the 5 percent range, both uphill and down, and came away impressed.

Overdrive gear goes away almost immediately on starting up a hill, and the coach purrs along in 4th gear for a long while as the rig fights gravity and slowly loses speed.

It's a bit of a surprise the first time the transmission shifts down to 3rd gear when you're moving at a reasonable speed. A sudden and unavoidable roar under the hood is verified by the tachometer, which climbs immediately into the high end of the scale. A built-in limiter is there to avoid engine over-rev damage, and would automatically shift up if called for. Part of the high engine rpm-nervousness is a habit that those accustomed to big blocks from years back need to break. The Triton V-10 is made to run up faster than its elder counterparts, so although 3,500-rpm sounds bad, it's quite comfortable running at that point, and higher.

We averaged 54 mph at 3,300 rpm in 4th gear upgrade, and extra throttle produced another shift down to 3rd gear at 4,500 rpm while holding 53 mph.

Downhill, the Grade Braking feature pops the gear down into 4th or 3rd as needed. As we ease down on the brake, the transmission electronics tell it to drop down a gear. The controls only allow this to happen if the engine would not exceed its safe operating rpm range.

In 3rd gear, we averaged about 43 mph at 3,500 rpm downgrade on the 5 percent hill. That's slow enough to save a lot of brake pad. Our fuel economy averaged 6.9 mpg overall, or about the same as before.

Shoppers looking for a coach on a Ford chassis may well find the new five-speed transmission is a useful tool in the powertrain department.

Copyright, Motor Matters, 2005

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