Index

SJ23 Tandem Axle Conversion - Bob Schimmel
(or The Rebirth of a Trailer in 1998!)

INDEX - Overall weight, Tongue weight, Brakes.

I started off by doing some investigative work, talking to several local axle manufacturers and finally settled on McCoy Brothers in Edmonton.  The staff in the Axle Division (unfortunately no longer in business) were very helpful.  We discussed the pros and cons of a spring axle versus the new rubber torsion axle, comparing them with assembly diagrams and they explained the installation process fully.  Either style of axle was good for my application but I opted to add a spring axle for a smoother ride.  Factors that convinced me were; deterioration of rubber over time, the wider temperature operating range of a metal spring, repair possibility of a spring while on the road, and the lower cost.  I also learned the benefits of using a center rim for the wheels as this design is the strongest and therefore less likely to fail from stress fatigue.  (The bolt plate of a center rim is located equidistant between the inside and outside beads of the rim.  This results in minimal flex on the bolt plate, the studs and the rim).  The net result is a wheel and studs that operate cooler.  I also had a friend who was very familiar with welding horse trailers.  Since a horse trailer is very demanding construction, I felt pretty confident with him.  Without a good retailer and a welder, I wouldn't have tackled this upgrade. 

When I bought my tandem axle conversion kit it included a "walking bar."  This triangular bracket is bolted to the middle spring hanger and connects the front and back springs to each other.  The walking bar makes the two axles perform in tandem, transferring the weight smoothly from one axle to the other.  Consequently the ride is smoother than two independent axles.  So when you order your axle kit, take a close look at your existing trailer to match the kit to your axle and hangers.  The absolute best way to accomplish this is to haul the trailer to the axle shop so they can confirm the parts requirements.  For example, the axle guy may advise you that it is less expensive to trade your old axle in for two new ones, just to create a matching set.  While this is good I was able to add the new axle to the existing one by buying springs and hangers for both axles so they rode at the same height with equal spring rates all around.  I have never regretted this decision.

ONLY 3000 POUNDS YOU SAY! - "The design weight of a San Juan 23 is just under 3000 pounds.  The cabin liner and the interior pan (floor) were made with a chopper gun that sprays resin and glass, similar to a paint sprayer.  It is very difficult to maintain a uniform thickness with a chopper gun unless you have the touch of a Rembrandt.  If you have this touch you don't need to build boats for a living!  The result is that SJ23s varied widely in weight.  An extreme example of this was the last boat I handled, which weighed 4000 pounds, empty.  This was 1000 pounds over weight, which is an example of why the people who built it did not stay in business long.  As a dealer, who was the last 10' of the assembly line, I got to install the second axle on the occasional trailer.  The 3000 pound design weight is right at the upper edge of how much weight a single axle trailer can support.  If your boat happens to be on the heavy side, you need two axles." Gene Gardener.  TOP
 

CONSTRUCTION - Armed with the installation instructions and diagrams we chose to weld the spring hangers to (3x1/4)" flat iron (mounting rails) and then U-bolt the assembly to the bottom of the trailer frame.  (It is much easier and stronger to fasten spring hangers to the mounting rails by welding downwards than to weld permanent hangers to the bottom of the trailer frame by welding upwards.  This also eliminates any chance of accidentally "blowing" a hole in the frame with the torch.  It is also much easier to fabricate accurate symmetrical left and right mounting rails for the springs.  I am a firm believer in, "If it's easier to do, you are apt to do it correct, the first time").  The advantage of this design is that the axle assembly can be slid forward or backward under the trailer without affecting the axle to axle alignment.  (The position of the spring hangers is determined by the length of the springs, the mounting requirements of the axles and the desired hitch weight.  Use the instructions that come with your tandem axle kit).  

1. The spring hangers were welded to two suitable lengths of (3x1/4)" flat iron, one for each side of the trailer. 
   While we wanted to weld cross pieces to the rails to keep them square to each other, this was impossible due to other cross members on the trailer.  So we opted to bolt one in the correct position then matched the other to it so the trailer didn't dog rack.  Neither has ever moved. 
2. The springs were bolted to the hangers. 
3. The axles were U-bolted to the springs. 
4. After a thorough check of our work, the tandem axle assembly was rolled under the trailer frame.  Having previously determined that the trailer frame was square, (i.e.: side rails parallel to each other and on the same plane) the axle assembly was aligned to the trailer frame using the following guidelines; 
   - Axles are parallel to each other. 
   - Each axle protrudes the same amount on each side (i.e.: front and back wheels run in the same track).
   - Axles are perpendicular to the center line of the trailer (i.e.: trailer not dog tracking). 
   - Spindles are equidistant to the coupler.  (i.e.: trailer not dog tracking). 

Finally the U-bolts were slipped over the trailer frame and tightened to lock the tandem assembly in place.  To verify the wheel alignment we took the empty trailer for a road test on a dry dirt.  Dry dirt or sand is very effective at revealing axle misalignment or dog tracking.  If the dirt on either side of the track drops in an equal amount then the tires are aligned to the direction of travel.  If more dirt drops on one side than the other, the wheel is not aligned to the direction of travel.  You require bone dry fine dirt or dry sand to see this effect.  In addition, if the tread marks leave equal left/right track patterns in the sand, the alignment is also OK.  These are the patterns you are looking for.  If the tires "dog track," then the track on the ground will be wider than the tread on the tires (1 tire width plus a bit from the other tire).  The pattern of the track may also be unsymmetrical.  One final point, I replaced my old springs on the original axle with new ones to have four matching springs.  The axle manufacturer, McCoy Bros, recommended this for proper tandem operation. 

TONGUE WEIGHT - I positioned the center hanger of the tandem axle directly where the old single axle was.  In this way the trailer tongue weight remains about the same as with the single axle.  The tongue weight should be about 10% to 15% of the trailer weight.  As such the front of the window will be about 2" ahead of center of the tandem axle assembly.  You can use this guideline to position the hull pads.  See Tech Tip A10.   After 25 years of towing the trailer with the boat over various terrains, I have never experienced a problem with too little or too much tongue weight.  The coupler never lifts off the ball.   TOP

BRAKES - In Canada, brakes are mandatory on trailers exceeding 2000 lbs carrying capacity.  I equipped all four wheels with electric brakes for the extra safety factor for emergency stopping or traveling down long mountain hills.  Panache's trailer brakes are controlled by a Tekonsha Voyager 9030 inertia activated brake controller.  The unit is equipped with level control (brake timing) and gain control (braking power) so the inertia sensor (pendulum) can be adjusted for very smooth breaking action, down to almost crawling speed.  It is far superior than my previous direct coupled hydraulic controller that was popular in the 1960/70s.   A nice safety feature is the LED that monitors circuit continuity to the brakes; green light on = brakes OK, The green changes to red to indicate increase of power to the brakes. If the green light is off = NO BRAKES.   Very handy if you are about to go down a long grade or enter a congested roadway!  A properly adjusted braking sensor applies trailer brakes at the same rate of deceleration as the tow vehicle. 

If you launch your boat in salt water it's an excellent idea to add a flushing kit to the brakes and brake drums.  This consists of a garden hose fitting on the front of the trailer interconnected to water lines connected to the backing plate on each wheel.  Immediately after the trailer comes out of the water you run fresh water through the lines to flush the salt water off the drums and actuating coils.  This prevents corrosion to ensure continued operation of the brakes.  Bearing Buddy is one such example of this product.  Remember to drain these hoses dry for winter.  Also see Tech Tip A09, Tow Vehicle Considerations   

On the other hand there are many people who have good success with hydraulic brakes.  I have been told they operate well on flat land with minor hills.  If you choose this system consider the following advice from the folks at Road King trailers in Texas.  They said the reason most hydraulic brake systems fail are as follows: 

1. Rust in the system is usually associated with older actuators that had cast iron fluid reservoirs.  Since brake fluid has an affinity for water its easy to see that this is a bad combination.  Most every major manufacturer has switched to aluminum or composite metal to eliminate this problem. 
2. After backing up a trailer you should always roll it forward a bit until the actuator moves forward all the way.  Don't just park it.  In most systems part of the plunger remains exposed if not rolled forward.  A covered plunger prevents rust on the exposed surface when sitting idle for long periods.  It is also suggested to spray some light lubricant on the actuator and bolts if exposed to weather. 
3. Always pay the extra money for stainless steel break lines and install them so they are exposed for inspection and washing.  DO NOT install them inside the box frame of a trailer. 
4. Disc brakes perform much better than drum brakes if the load is over 2500 lbs (the SJ23 trailer and all others easily qualify).  They also rinse easier. 
5. Lastly, Road King does get requests for electric trailer on a boat trailer but they will not warranty them partly due to failure when launching in salt water.  If the electrical short should happen it may have an adverse effect on the tow vehicle electrical system.  TOP

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