Saturday, 12 July 2014

The San Juan Scenic Skyway

Driving North out of Durango on Highway 550, it became clear that once again I would have to adjust my presumptions on how long journeys would take in Colorado. The 50 miles to Silverton included a 1,300m climb to Molas and Coal Bank passes, and a 600m descent into the town, and in a heavy truck like Jim, these kind of journeys take while. It would be reasonable to assume that the upwards climb would be the slower section, but this is not always the case. Whilst lighter vehicles can descend steep grades using the engine to slow them down, in a heavy truck this is not always enough.

Even in first gear, Jim needs additional braking force to prevent him running away on steep downhill grades; on a short descent, it would be fine to use the foot brake, but on long descents the brake discs would become dangerously hot, and I would risk warping the discs or suffering dangerous brake fade. Thankfully Jim has an engine retarder, which partially closes the exhaust, and creates a braking effect through the driveline. Using the exhaust brake uses the engine to slow the truck down, and means that on long descents the brakes do not heat up, saving wear and improving safety. Many big truck have multi-stage retarders, either of the exhaust brake or jake brake type, which allow the driver to apply a different amount of braking force depending on the situation. Unfortunately the retarder on Jim has only one stage, and on steep mountain grades it poses a problem.

In first or second gear, the retarder on Jim is sufficient to hold the truck at a constant speed on all but the most absurd grades, but this limits top speed to around 15mph. If the road conditions and speed limit permit faster speeds, I must to go into a higher gear, and in places like the Rockies, the retarder is no longer powerful enough on its own to prevent the truck running away. At one end of the scale I can drive at antisocially slow speed and avoid using the foot brake entirely, and at the other end of the scale I can drive at the speed limit, relying almost entirely on the foot brake to slow the truck down. Most of the time I find a suitable compromise; I’ll put the truck in a higher gear and periodically use the foot break to slow the truck down. If there are no vehicle queuing behind me I drive slower and rely more on the retarder, and if there are inpatient motorists on my tail I drive faster and use more of the foot brake. Either way, I usually descend at speeds well below the posted limits.

Mercedes offered trucks like Jim with a magnetic retarder, which wraps around the prop shaft and uses strong eddy currents to slow the truck down. It was not a popular option in the UK for obvious reasons, and so I rarely see them, but in the future I can explore the option of fitting one from Voith or Telma to add additional braking force.

After a slow descent into Silverton, we parked in town and enjoyed a walk around this rough-around-the-edges historic mining town. We stayed for a beer at the awesome Handlebars Restaurant, before getting back on the road and heading up into the mountains.

There are a huge number of scenic backcountry roads around Silverton, but on the whole they are 4x4 only, evidenced by the huge number of vehicle rental places in town, all offering extremely capable vehicles such as Jeep Rubicons and dedicated off-road ATVs. We had been told that the road up to the ghost town of Animas Forks was passable in most vehicles, if not the mountain passes beyond, and so we headed out of Silverton, following the Animas River.
The road starts as a well graded gravel road, and until we reached the campsite at the old mining town of Eureka we travelled at highway speeds in relative comfort. Beyond the campground the road starts to ascend more sharply, and the quality of the road surface deteriorates considerably. The road becomes fairly rocky, and even on the decent sections we couldn’t get beyond second gear. There were a few sections with high and low spots in the road which made for uncomfortable swaying, and one section with fallen boulders which required Naomi to spot me to avoid a long fall into the river. In general the road is passable in any high clearance vehicle, but is at the limit of what Jim and we are comfortable with. At Animas Forks we had had enough of the punishment (thick leaf springs and a rigid chassis do not make for a comfortable ride on rocky roads), and we parked for the night near the partially restored remains of the old mining town.

We enjoyed our visit to Animas Forks, and the site certainly made the uncomfortable drive worthwhile, but in the morning we were ready to move on. Not wishing to risk attempting Cinnamon or Engineer Pass in a heavy two wheel drive truck, we descended the way we had come. At the campground in Eureka is a large parking lot where people can unload the toys and continue into the mountains in Off-Highway-vehicles. We pulled into the parking lot and I did a thorough check of the rear tyres, looking for rocks wedged between the twin tyres so that we didn’t end up with another expensive bill. I was grateful that we did, as there was a large rock wedged between the tyres on the left of the vehicle, the side which was spared in the previous incident.

Hitting the rock with a lump hammer did nothing but send chips of rock into my face, and so I had to look at more drastic measures for removing the rock. I have heard of people using chains or ropes wrapped around the axle, or tied to a tree, to remove an offending rock, but I was too scared of tearing a gash in the sidewalls attempting a manoeuvre like this. Instead I opted for the slower option; I jacked the wheels off the ground, and loosened each of the ten lug nuts holding the wheels to the hub. Thankfully I didn’t have to wrestle the heavy tyre off completely, loosening all of the nuts allowed sufficient movement for me to yank the rock out, saving me some back ache. The rock had made a visible mark on the sidewall of both tyres, but thankfully the damage was shallow, and had not cut to the reinforcing wires.

I threw to offending rock angrily into the bushes, retorqued the wheel nuts using the large torque wrench which we carry with us in the boot, and we continued onwards. We passed back through Silverton, and spent the next ten miles climbing upwards, peaking above the tree line at 3,375m on the mountain pass, before descending to the next historic mining town on our route, Ouray.

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