Front Drive Solution

An Alternative Choice For All-Wheel Drive

Choosing the chassis on which to build wasn’t that difficult to figure out. All the information we gathered pointed us to the Volvo VHD as the best choice. It’s the vocational platform that Volvo uses for dump trucks, cement trucks and other vehicles that would see heavy and even abusive use. We liked the look of the truck, and it had a very comfortable, almost plush interior. At least by truck standards anyway. But there was one option that Volvo didn't offer, a factory installed all wheel drive solution. We just couldn’t buy a ready built 4x4 or 6x6 right from Volvo. Nor could we from any of the other North American truck manufacturers for that matter. The only way we could get one was by having it installed by an aftermarket truck modifier.

But here’s the rub. In order to get a conventional front drive axle installed, the truck had to be raised up from the suspension by almost a foot, so the axle’s differential housing would clear the engine oil pan. There simply was no other way. That meant over a foot of clearance between the top of the front tire and the inside edge of the fender, and that would look ridiculous. Not to mention the problem of a substantially higher center of gravity, and an increased overall height that would present many problems with overhead obstacles when using the truck offroad. And then there was the inconvenience. We’d need a step ladder to get into the cab. There had to be a better way.

After discussing these concerns with various truck modifiers, one asked if we had considered using the EZ-Trac solution. Never having heard of this, we asked for more information. What we learned was that there was a unique solution for a driven front axle that wouldn’t require raising the vehicle even an inch, and it would give us on demand front wheel drive when the going got tough. There were several advantages for us if we opted for the EZ-Trac system. We could keep the overall height for the build much lower, and we’d get around having to add an extra eight hundred pounds of equipment to the truck. There would be no front differential, no front drive shaft, and no transfer case.

But it gets better. Two important factors for a truck that’s going to travel many thousands of miles and navigate through difficult terrain, is fuel economy and a tight turning radius. With EZ-Trac there is no conventional mechanical front drive train. Translated, this means no differential gears, drive shafts, CV joints or extra gearboxes to rob us of the usual 15% fuel economy inherent in a conventional front drive solution. And since there are no CV joints to transfer the power from the axle through to the wheel hubs, we don’t sacrifice our 50º wheel cut for the more restrictive 30º one. It couldn't get any better than that as far as we were concerned.

So how does the EZ-Trac system work if there are none of the conventional components? Well it’s quite simple really. It’s hydraulic. Each of the front wheel hubs are replaced with ones that have a built in hydraulic motor, and the hydraulic force is provided by the transmission’s power takeoff and a large hydraulic pump. A valving system is used to provide forward and reverse motion, and the whole system is controlled by one simple button installed on the dashboard. Sensors installed on the rear axle(s) tell the system how fast to turn the front wheels so they always drive at the same speed as the rear axles. The system turns on as soon as you push the button, and starts the front wheels turning as soon as you step on the accelerator. They continue to operate until the truck reaches about 20 miles per hour, or shifts out of first gear, and then the system automatically disengages so only the rear axles are driving. If the vehicle speed slows down to about 10 mph, then the system re-engages to give you all wheel drive once more.

Some might think the top speed limitation might be a real drawback, but our experience of driving a Land Rover Defender, offroad, all over the western U.S. has shown us that all wheel drive is only necessary for slow speed operation. If you can drive the vehicle over 20mph, then you certainly don’t need front wheel drive. Unless of course you are a highways truck snow ploughing the interstate at high speed. For us, it sounded like the perfect solution.

Reliability and Service

However, we did have concerns about reliability, and the ongoing support for parts and maintenance. The system is, after all, an aftermarket solution. Sometimes these aftermarket companies can run into trouble and go out of business, leaving everyone in the lurch. So I did some research on just where the system comes from.

As it happens, hydraulically driven axles are nothing new, and are used all over the world. The agriculture industry has been using them for decades on tractors, harvesters and the like, and they are also used in industry for things such as excavation and specialty trucking. In fact, the EZ-Trac system is manufactured in the U.S.A., by a company in Indiana called Terra Drive Systems (TDS). They are a world leader in hydraulic drive axle solutions, and have been making them since 1976. So by no means a new startup. Terra Drive Systems (www.tdsdrive.com) pioneered the use of hydraulic drive axles on agriculture combines with their Mudhog System, and it is this system that is in use today by most major agricultural equipment manufacturers such as CNH, Agro, Claas, John Deere, Oxbo and Rostelmash to name a few.

What was important to us was the fact that the TDS EZ-Trac system was specifically engineered as an on/off highway drive solution for class 5, 6, 7, and 8 trucks. It’s used by major companies in the utility industry such as Duke Energy, Southern Cal Edison and many more, and it's being installed on all the major truck brands like Freightliner, Ford, Western Star, Mack, Hino, Peterbilt, Volvo, Kenworth and more.

But wait, here’s what gave us the warm and fuzzy feeling. EZ-Trac is also used for mission critical purposes such as Fire/Rescue, Military, snow clearing, emergency vehicle recovery and more. These are all areas where equipment reliability and performance are absolutely paramount. If EZ-Trac is good enough for these first responders to put their trust in, then that’s good enough for us! Our needs should be well served.

Cost Comparison

But what about the cost... how does it compare with the conventional system? Well that’s the good part. The EZ-Trac system works out, after installation, to be about the same cost as a conventional front drive train. So to us it was a moot point. But because there is less weight added to the truck, and the rolling resistance is much lower, we gain the cost advantage of better fuel economy. And that keeps money in our pockets mile after mile.

Experience so far.

We’ve had the finished truck for several years now, and on our very first trip, which was to the Canadian Rockies in January, we made use of our front drive axle. We had started pulling into a small, snow covered parking lot, when we thought better of it. The front wheels were in snow about a foot deep. The rear tires were still on the hard packed snow of the street, which unfortunately was uphill from the parking lot. So as we started to back out, the rear wheels started to spin. Even after engaging all the rear differential locks, the rear wheels just kept spinning. A simple push of the EZ-Trac button on the dash and the front axle engaged, and because the front wheels were in deep unpacked snow with a lot of weight on them, the tires gripped and the front drive easily pushed our 17.5 tonne truck backwards up the hill and back onto the street. There was no shifting of transfer case gear levers, or selecting of a particular gear range as with a conventional front drive axle. Just a simple push of a button was all that was needed.