What kind of torsion axle is this?

Thanks for a good topic to discuss. There's many different kinds of suspension besides leaf spring sprung and torsion axles. As you would expect, it's not a black and white choice. Both styles have their advantages, and drawbacks.

Lets break it down. Your photo shows a "trailing arm" type axle and I cannot tell in your photo if it has the coil wound spring, or a rubber spring unit, they both do the very same thing. One of the disadvantages is show in your photo. Since the trailing arm is so short in length, as it moves through it's arc, the wheel base shortens. You arm "has settled" from it's straight back 9' O'clock position.

You tend to see torsion axles used on original equipment, and leaf spring axles used as aftermarket replacements. I believe this is because it's very hard to determine the spring rate on a torsion axle. If you order a replacement axle assembly, and "you order", or "they manufacture" the replacement with the wrong rate you have no recourse other than ordering another replacement assembly ($500 to a $700 mistake).

On a leaf spring style, you order the leaf springs separate from the weight rated axle and brake assembly. When or if a mistake occurs, you remove the spring packs, and have your local spring shop remove some, or add leaves to change the spring rate. Not a very big problem, as long as you catch it before you cutoff the new U-Bolts to length.

One of the many options you have in ordering a replacement torsion axle assembly is specifying your desired trailing arm angle. Basically, it's usually straight back at 9' O'clock. down slightly at 7' O'clock, or up at 10' o'clock. Even with a tape measure, it's really difficult to figure out how much weight spring sag you will have an a new axle, much less complicating the order sheet with trailing arm angles.

About 12 years ago, I built a new very "high end" 5' by 10' custom teardrop for my son. He towed that trailer all over Baja California watching the off road races while camping. That trailer was built with a 8" Dexter torsion axle with electric brakes. I'm guessing now, it might have been a small 2000# rated axle. It worked flawlessly, and never gave a minutes of trouble inspite of the abuse we gave it towing off road.

In conclusion, torsion axles work fine, are more difficult to correctly order and service, leaf spring axles are easier to order, and  service locally.

On your Boles Aero, I would use a Dexter 3500# or 5000# axle assembly, with the 10" to 12" brakes, and it has the larger axle bearing. I would use six lug Dexstar 16" trailer wheels, and 16" Maxxis ST radial trailer tires in the weight rating that suits your trailer weight allowing a 25% to 50% safety margin.  Is you Boles 14' body length, or overall 14' trailer length?

Was your Boles Aero's frame built by Zeman Trailers in Whittier, CA.?

You can find lots of good trailer axle specification information in the Dexter site. Make sure you order the correct hub face and spring center distances on your new axle. I like to order my spring seats loose (un-welded) to give me more fudge room.

John

Zeman, (maybe it's actually Zeiman) is a commercial trailer builder, still today. They manufactured the frames and suspension used on the Boles Aero trailers for a long period. Not sure when they started, or ended. They built the frame on my 1967 Boles Mira Mar 24'. The frames built by Zeiman were stamped with an VIN# that began with "Z" since they were the California frame manufacturer, and not Boles.

Looking at your bare floor, makes me think that you are at the perfect point to do your frame modifications. All vintage camper trailers were originally built with very short frame tongue's. They did not require the longer tongue because the current tow vehicle was a 1948 pick up truck with a narrow 4' bed, and "step fenders". Move up 70 years and look at the pick up trucks we tow with today. They are six feet wide, and have square back beds with tail lights that extend all the way out to the corners. When you back up a vintage trailer, with a modern truck, it's "very easy" to jack knife the the corner of the bed into the front of the trailer. Don't believe me, just walk around a vintage trailer rally and count how many "unrestored" trailers have vertical dents in their front skin panels.

You only need maybe six to eight inches in extra length to fix the problem. If you do choose to extend the tongue, please spend some time reviewing designs, and not just have a local welder come up with a poorly designed addition. It can be done, so you would not even know it was extended unless someone told you. My current Spartan frame is extended.

If you live in, or ever plan to sell your trailer in California, do not extend the frame past 17', which places the trailer in a different DMV classification. Basically $125/per year (CCH, coach) vs. $25 for five years (a CMP PTI).

At your small trailer length and weight, I would suggest a 3500# axle with 10" brakes. If your nervous, they offer thick wall axle options at a very small up charge to give you a larger safety margin. You wheel wells, and fenders will determine how large of a wheel and tire you can fit under the trailer. Remember, you have to be able to remove and install the tire. If I remember correctly some of the Boles models do not have a very large wheel opening?

John

I've looked more closely at how this torsion axle works. It's got 2 long pieces of spring steel attached perpendicular (along the "axle") to each trailing arm. This spring is held fixed at the center of the axle. The opposite side trailing arm has a similar arrangement. As the trailing arm moves up and down the spring steel twists to absorb the load.

I also took a closer look at the electric brakes and will create a separate post on them. They are unlike anything I can find with a simple google search.

Yep, getting a quote on a Dexter and Flexiride axle this week. Turns out there are a couple minor frames welds that cracked and need to be mended (seems like the factory missed a couple gussets on one crossmember) so will be a convenient time to weld in new axle side mount flanges. Better now than after I get the floor back in!

I'd assumed this torsion axle was a retrofit, but I can't see any evidence of leaf spring attachment points. All the other Boles I've seen have leaf springs. Do you think this axle is original equipment?

Ordered a Flexiride torsion axle today with side mounting plates. 3500lb axle derated to 2500lb. 3 features that helped make the decision: 1) adjustable start angle; 2) unidirectional, replaceable spindle and arm (I ordered a spare); 3) price (about 20% less with shipping). Mom always said you get what you pay - hope she was wrong on this purchase!

I went with the side mounting plates because my C-channel frame is too narrow to drill mounting holes through. Also the dimensions look compatible with other axle brands (Dexter) and will make any required future replacement easier.