Technical Inquiries: February 2004

Backward Boxster

Q: I want to use a tow dolly and pull my 2004 Porsche mid-engine Boxster with its drive wheels on the dolly. Your article states not to pull backward. Is this true for a mid-engine rear-wheel-drive car?

Bob Gorshe, F294988
Flat Rock, North Carolina

A: It’s true for any towable. While some emergency tow trucks haul vehicles to repair shops on their front tires, this is for a short duration by a professional driver. It’s too easy for the steering to become uncontrolled, which could cause an accident. I’d recommend an enclosed trailer or a low-bed car-hauling trailer with a bra or some type of debris shield in front of the Boxster.
“” J.B.

Q: In a past article in FMC magazine (“Dispelling Diesel Myths,” page 65, February 2003), you stated that an owner shouldn’t start a diesel engine and allow it to run for too long, and that a walkaround prior to leaving the campsite should be long enough.

This statement may not be true for all coaches. We have a converted 1983 MCI-9 with a Detroit Diesel GV-92TA engine. The bus does not move until 100 psi has built up in the brake system to release the parking brake. Depending on how long the coach has been sitting and how much air has leaked out of the brake system, this can take up to eight minutes. The coach will not move until I hear air release.

Also, the shop foreman at the service center that maintains my coach said “Idle for three to four minutes to cool off the turbo.” And because of our local weather conditions, I keep the engine block heater plugged in whenever we get ready to use the coach.

I can’t believe the value of FMC magazine for the price!

Roy Ranum, F215226
Silver Bay, Minnesota

Q: liked Jim Brightly’s article “Dispelling Diesel Myths.” These types of articles help motorhome owners use good practices when operating their rigs.

I have heard about not needing to cool down the engine from a Cummins rep before. However, I’m reluctant to follow this advice without actual test measurements showing how quickly the turbocharger cools down. Surely some type of data like this should be available. Do you know of or have any information about this?

Ron Swanson, F236512
Salem, Oregon

A: The “Dispelling Diesel Myths” article was a compilation of information from manufacturers’ reps from Caterpillar, Cummins, and Detroit Diesel who provide the same advice to seminar audiences at FMCA’s two international conventions each year. The article was not aimed at the sophisticated, long-time diesel-pusher owner, but rather at members who are considering buying a diesel pusher or who have just purchased one. In Mr. Ranum’s case, the design of his air brake system obviously requires a longer pump-up time. I’d also suggest that he leave the block heater connected whenever the coach is parked, not just when he plans to use it.

Concerning the cool-down period, which is mentioned in both letters, the engine manufacturers’ representatives who I’ve spoken with at convention seminars all say the same thing: the time between highway and campsite should be more than sufficient time to allow the turbocharger to cool.

Finally, thanks for the kind words about the magazine.
“” J.B.

Q: We have a 1998 Safari Trek on a Chevrolet chassis. We found out the hard way that if the fan belt breaks or the engine stops for any reason, there are no power brakes or power steering.

We were in heavy traffic in Tampa, Florida, when the fuel pump stopped working, which killed the engine. Thankfully, we were a good distance from the cars in front of us and barely moving or we could have wiped them out. The P-30 chassis model used for our motorhome does not even have a parking brake to use in an emergency.

According to the Chevrolet service manager I spoke with, the “hydraulic parking brake” would cause the universal joint to separate or the driveshaft to twist in two if it were engaged while moving. I found out that a later version of the P-30 chassis has an electric-hydraulic power steering pump that supplies steering power even when the engine is not running. Unfortunately, Chevrolet denies its existence. Could you help me with a solution to this problem before I get into real trouble?

John Kinder, F252118
Hobe Sound, Florida

A: The service manager with whom you spoke may not be familiar with motorhome chassis. Chevrolet stopped manufacturing them in late 1998 when Workhorse Custom Chassis purchased General Motors’ motorhome and commercial chassis division. Federal law mandates that all vehicles must have some type of parking brake that is exclusive of its service brakes, so there should be one on your motorhome.

You didn’t mention what the gross vehicle weight rating (GVWR) is on your P-30 chassis. For 1998, there were three Chevrolet motorhome chassis produced with different weight ratings; a 12,300-pound GVWR, a 14,800-pound GVWR, and a 16,500-pound GVWR. All were equipped with output-shaft-mounted parking brakes. The 16,500-pound-rated chassis was equipped with an auto-apply parking brake that operates in “an absence of pressure” situation when it senses that the engine is shut off. While the engine is running it supplies electrical power to a small frame-mounted motor that applies pressure to the parking brake assembly to keep it from applying its brake shoes to the output-shaft-mounted drum. When the engine is shut off, the pressure is released, allowing the shoes to push against the brake drum by spring action.

The 12,300-pound-rated chassis and 14,800-pound-rated chassis are equipped with a foot-actuated pedal and cable assembly that’s applied by the driver in the same manner that the cable-operated parking brake works in your car.

Your reference to the parking brake possibly causing a U-joint or the driveshaft to separate upon its application is an absolute worst-case scenario. If your motorhome were traveling at a high rate of speed when the parking brake was applied fully, there would be an opportunity for separation to occur; however, this is extremely unlikely to happen and would depend largely on the condition of the components involved. A more likely event would be for the brake to overheat and slip rather than lock up. However, at the slow speed you said you were traveling, a separation probably would not occur. Plus, you still can use the service brakes; you just don’t have power assist, so you have to push extremely hard on the pedal to actuate them.

Since Chevrolet is no longer in the motorhome chassis business, questions about Chevrolet P-series chassis can be directed to Workhorse Custom Chassis by calling (877) 294-6773. We have been told that the company values all owners of the Chevrolet chassis and will continue to support that product in any way possible.

Q: I would like to know how I can get more power out of my Detroit Diesel 8.2-liter diesel engine. I haven’t been able to find any aftermarket products for it.

Dave Morse, F253343
Grants Pass, Oregon

A: According to Frank Stranzl of Detroit Diesel, how to increase an engine’s power is a question engine manufacturers frequently receive. But without knowing the engine’s current horsepower rating, he said it would be difficult to make any recommendation. He did say that you should take your motorhome to a Detroit Diesel distributor who can test the engine and determine whether it is operating at maximum efficiency. The distributor also can suggest possible changes to increase its performance.

Before making any changes that will affect an engine’s horsepower, you should realize that boosting the power also will result in more engine heat. You will need to determine whether your motorhome’s current cooling system can handle the additional heat.

You may hear people talk about an inexpensive computer chip that is said to increase an engine’s horsepower and performance. Mr. Stranzl said there is no such thing, and any major increase in horsepower will be costly. Such changes could include new injectors, a turbocharger, and other things. If your motorhome requires a major upgrade in power, he said your best solution may be to invest in a new, more powerful engine.
“” J.B.

Q: I am going to buy a flatbed trailer to haul a car and two motorcycles. I have a two-part question.

1. I understand weight distribution, load securement, etc., but I don’t know overall length regulations. I have a 40-foot motorhome, so how much length in trailer can I tow, and where can I find these regulations? The federal motor carrier safety regulations are not specific for non-commercial vehicles and say nothing in regard to motorhomes, etc.

2. Of the trailer manufacturers that I have researched, most offer spring or torsion suspensions, and all of them proclaim their product to be the best. What is the best type suspension for a full-time trailer, with radial tires and a GVWR of approximately 7,000 pounds? Should brakes be electric or hydraulic surge? And again, who is an authority on these subjects?

John McCoy
Via e-mail

A: Each state has different combined length laws, just as they do commercial trailer laws. There are state and federal laws on federal highways; state laws on state highways; and local (county, municipal, etc.) laws for local roads. Most of the time the regulations are consistent within a state, but many times they are not consistent with the federal laws. Length regulations “” for both the motorhome itself and the motorhome and towed vehicle combined “” for each state and Canadian province can be found in the “Motorhome Regulations” chart published in FMC’s January 2004 issue (page 110). This information also is available online at FMCA.com.

To answer your second question, suspension choice is a matter of personal preference and economics. Leaf spring suspensions are less expensive and more prevalent; however, a trailer with a torsion bar suspension may last longer, have better stability, and be slightly easier to tow.

As far as choosing between surge and electric trailer brakes, the decision should be fairly simple. If you plan to tow the trailer with your motorhome only, select the electric brakes. Install the controller in your motorhome and you’ll enjoy many miles of worry-free towing. If you plan to use different vehicles to tow the trailer, surge brakes will mean that you don’t have to install a controller in each tow vehicle. These days, however, you’d be hard-pressed to find a car hauler with surge brakes; they are usually found on rental and boat trailers.
“” J.B.