Truck Conversion & Toterhome Community - View Single Post

Doug · 03-01-2004, 07:50 PM

I would say that is correct. I note for example that the 380/410 Mack delivers 1560 ft-lbs. That is probably more than enough, even with a tandem and building your Class 8 RV to the max (as I probably would, using it for more or less full timing). I strongly suspect that even the 310/330 would have enough torque for such a unit.

The 9 speed Mack with the low gears has only one disadvantage. If one drives over the entire country, cruising speed and speed limits can vary from 55 to 75. Gearing for one end means one is either racing or lugging at the other, or at least has that risk. While most motors are more tolerant than they were 20 years ago, they have a sweet spot where they give their best fuel economy for a given speed.

I did the math playing with the Roadranger road speed calculator some time back, and I concluded that the 13 speed could address that range best due to the small split (and since the 18 is fundamentally the same as to this issue, one could do it with that tranny, such as when buying a used truck, although I would find it hard to justify getting one if ordering new for RV use). With the figures I used, the difference in cruising speed at the same RPM was about 10 MPH or a little more. Set it for 58-60 in 8L and you have about 68-71 at the same RPM in 8H. Not bad, eh? And, if you don't need the extra flexibility of the 13, you don't have to split it, which means it's a 9 speed with an extra button.

In case anyone is thinking I am advocating for Mack over others, the answer is no. It can be a PIA to get a Mack worked on sometimes, and Mack parts tend to be more expensive. I am, however, looking at either a Mack or a Western Star, due to the ease of special odd orders for these makers. I think I want a driving front axle, depending on what I learn from a dealer, and that could be a controlling factor. The Mack website no longer mentions them.

These are of course, options based on my preferences. I hate to fly, need room for the dogs, might be functionally full timing, etc. What YOU need for YOUR life is a different issue, and in spite of my pontificating, I am not living your life. I used to run OTR, and generally hate automatic transmissions. I doubt that applies to most here. Some of these issues are personal preference - I prefer certain breeds of dogs, with certain attributes of size, hair length etc. That doesn't make Rotts or certain obscure Mastiff breeds right for you.

The issue at hand was the suitability of this used truck for this member. While it might not be the truck any of us would order, if it is a good condition used truck and he feels confident in that, the transmission would not be the reason I would pass on buying this truck.

03-01-2004, 07:50 PM	#26
Doug Member Join Date: Dec 2002 Location: Cheney, WA, US Posts: 61	I would say that is correct. I note for example that the 380/410 Mack delivers 1560 ft-lbs. That is probably more than enough, even with a tandem and building your Class 8 RV to the max (as I probably would, using it for more or less full timing). I strongly suspect that even the 310/330 would have enough torque for such a unit. The 9 speed Mack with the low gears has only one disadvantage. If one drives over the entire country, cruising speed and speed limits can vary from 55 to 75. Gearing for one end means one is either racing or lugging at the other, or at least has that risk. While most motors are more tolerant than they were 20 years ago, they have a sweet spot where they give their best fuel economy for a given speed. I did the math playing with the Roadranger road speed calculator some time back, and I concluded that the 13 speed could address that range best due to the small split (and since the 18 is fundamentally the same as to this issue, one could do it with that tranny, such as when buying a used truck, although I would find it hard to justify getting one if ordering new for RV use). With the figures I used, the difference in cruising speed at the same RPM was about 10 MPH or a little more. Set it for 58-60 in 8L and you have about 68-71 at the same RPM in 8H. Not bad, eh? And, if you don't need the extra flexibility of the 13, you don't have to split it, which means it's a 9 speed with an extra button. In case anyone is thinking I am advocating for Mack over others, the answer is no. It can be a PIA to get a Mack worked on sometimes, and Mack parts tend to be more expensive. I am, however, looking at either a Mack or a Western Star, due to the ease of special odd orders for these makers. I think I want a driving front axle, depending on what I learn from a dealer, and that could be a controlling factor. The Mack website no longer mentions them. These are of course, options based on my preferences. I hate to fly, need room for the dogs, might be functionally full timing, etc. What YOU need for YOUR life is a different issue, and in spite of my pontificating, I am not living your life. I used to run OTR, and generally hate automatic transmissions. I doubt that applies to most here. Some of these issues are personal preference - I prefer certain breeds of dogs, with certain attributes of size, hair length etc. That doesn't make Rotts or certain obscure Mastiff breeds right for you. The issue at hand was the suitability of this used truck for this member. While it might not be the truck any of us would order, if it is a good condition used truck and he feels confident in that, the transmission would not be the reason I would pass on buying this truck.