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Old 10-23-2002, 08:45 AM   #1
Join Date: Sep 2002
Location: Arizona
Posts: 37

Very glad this site popped up. The holes in my Class 8 knowledge are getting fileld up! (that's a good thing).

I have a couple of questions regarding the number of axles. My primary interest is an RV Hauler, not a full motor home conversion. Pulling a 20k#+ fiver/garage/worksite is the goal in the next few months.

A lot of folks seem to grab a Class 8 and rip out an axle, leaving it as a single. I'm curious of the reasons everyone has (need to confirm my own newbie theories).

My questions:
1) Why a single axle?
2) What does it take to convert?
3) What Class 8 machines should NOT be converted to single (too expensive, can't do it, not worth it, etc)?
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Old 10-23-2002, 07:11 PM   #2
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Join Date: Aug 2002
Posts: 193

Good question Chris,

Most OTR tandem axle tractors have a 38 or 40K rear axle rating. This means that when crossing weigh scales, a commercial vehicle can legally weigh the respective amounts above on the rear axles only.

When one axle is removed from a tandem, so is 1/2 of the rear axle GVW rating. A single axle will be rated as either 18 or 20K.

When towing a fifth wheel travel trailer, the most anyone usually has on the hitch is around 4K. If you chose to carry a couple of motorcycles, tools etc., on a custom bed, you would still be hard pressed to exceed the 18K capacity of the remaining single axle. The second axle is therefore unnecessary.

Then there is the overall tractor length consideration. Removing an axle and shortening the frame allows for better maneuverability in tight spots.

However, some folks want something different. Some are towing fivers with factory tandem axles. Some drop out the front axle, lengthen the driveshaft, add a carrier bearing, install a custom bed, and haul various items in front of the fiver.

In general, a Kenworth is the only tractor that cannot be converted to single axle due to the unique suspension arrange Kenworth utilizes on most of their tractors.

To give you a better idea of a single axle conversion, below is the URL for my latest conversion. The Volvo depicted in the site is already sold, but I have already purchased another one exactly like it which has not yet been converted.

The Volvo on the site below has a 202 inch wheelbase. Concerning the other Volvo I have not yet converted, If I were to remove the front axle, and retain the rear axle in its current position, the wheelbase would be about 256 inches. This would really provide lots of room to haul whatever in front of your fiver, I would also sell it with the tandems intact as it now sits.

There are 21 large pictures and text on the site below. If you have a dial up connection, it may take up to 8 minutes to load.

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Old 10-24-2002, 07:43 AM   #3
Junior Member
Join Date: Sep 2002
Location: Castle Rock,CO
Posts: 5

Although I saw Larry's Volvo last month.I really didn't consider the leaving of the rear axle to get more length for a bed...I was impressed with the turning radius of the one with the rear axle gone..I didn't measure it but it seemed that it turned as short if not shorter than my Dodge dually.
Now the question..the increase in wheelbase would surely have some impact on turning radius..
The cost would also be higher(I suppose).With the shorter wheelbase..could you still haul a
full size motorcycle?As I remember,you could. But, just wondering if the downside of the longer wheelbase would be worth it.
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Old 10-24-2002, 01:03 PM   #4
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Join Date: Oct 2002
Location: Cincinnati Ohio USA
Posts: 286

....ah what about the weight of the tractor?....wouldn't the back axel have 1/2 to 1/3 the weight of the tractor so if a tractor weighs 16,000# take off the rear axel we are talkin' about 14,000# divide that by 3 equals 4666# plus tools M/C & hitch plus the 5th wheeler we are adding up some here.....see what I mean?... maybe 10,000# total?.....what do you think?....I want a 12,500 watt ONAN generator on the tractor also...that addss some too.....geof
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Old 10-24-2002, 02:34 PM   #5
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Join Date: Aug 2002
Posts: 193

Hi guys,

There is plenty of room to haul two full size motorcycles behind the sleeper in front of a fiver with a 202 inch wheelbase.

The shorter the wheelbase the shorter the tractor will turn. I don't have a formula for this but there probably is one.

The 202 inch wheelbase turns real well, but not quite as short as the 185 inch wheelbase Volvos I have had. The differenc is not really significient though.

Only the buyer can dicide how long a WB he wants.
It really depends on what he plans to carry on the bed if a bed is installed. For example, a flatbed could be installed that extends back only as far as required.

An air slide hitch will slide about 24 inches back from the forward position. That alone creates considerably more usable space.

One might consider sketching out a bed, then measuring space requirements to carry whatever he would like to take with him. This can be done with chalk on a cement floor for example. Measure the length and width of the items as they might sit when fastened down to the bed for travel. That makes it easier to determine the amount of space required.

Removing the forward tandem axle and leaving the rear axle in its current position on this Volvo would result in a 256 inch WB. This would cost maybe 1K more than moving the front axle forward and shortening the frame. That's because a carrier bearing and two new driveshafts would be required. The cost for the parts to do this would probably run somewhere around $1,200 plus the labor.

These last Volvo I weighed full of fuel single rear axle weighed about 9600 on the front axle with an M 11 Cummins and about 5300 on the rear axle.

If a bed is to be built, I reccommend steel rather than aluminum. Steel is cheaper and heavier. A 1/2 steel plate could be added to the frame if one wants to add even more weight.

If the highway is slick, driving bobtail requires more care than driving a car for example. In such conditions, I always leave extra room between me and traffic in front of me.

If a bed is to be built and installed, I reccommend sketching out the entire bed. That way you can sketch in side toolboxes, the number and location of eyehooks you will want for tie down purposes, where you will hook a ramp to load motorcycles, where the ramp will be stored when not in use etc. I also reccommend beveling the the rear corners of the bed and rounding off the front of the bed so it extends inside the rear farings to 4 inches from the back of the sleeper. A headache rack can be fabricated and welded onto the bed also.

I designed and had a bed built for the FL60 I had. I made some mistakes. I would be happy to discuss some important details I failed to consider when anyone is ready to have a bed built.

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Old 10-25-2002, 12:41 PM   #6
Join Date: Sep 2002
Location: Arizona
Posts: 37

Great information! Thanks!

I'll echo what has been said many times on this site, that is one Gorgeous Volvo.

Onezman: you mentioned shortening the frame. Is that something commonly done? Would a dealer / truck shop normally handle that?

If shortening a frame and dropping the axle is only a couple grand, that opens up all sorts of options for picking the right truck.

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Old 10-25-2002, 07:16 PM   #7
Senior Member
Join Date: Aug 2002
Posts: 193


I haven't seen any dealers that do frame work. Any frame shop should be able to handle it though.

A far more important item is knowing what to look for when buying a used tractor. There are numerous pitfalls, even for an experienced tractor driver.

It is not uncommon a for company tractor driver to quit his job, buy a used tractor, and become an owner/operator. Too late he discovers his tractor needs 10 to 15K worth of unexpected repairs.

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