Mac trailer tandem axle conversion

[Bob 04 H260]

I am considering adding a second axle to my trailer (stock, 1991) because I carry too much weight in the boat and have am starting to have a problem wearing out the inside edge of the tires. Has anyone on this list done this conversion ? if so how are the two axles positioned ? was the original axle moved ? was trailer frame extended ? What is your tongue weight ? are you happy with how it tows ? did your gas mileage go down ?

thanks Bob

 

[Timo42]

Wear on the inside

is more likely caused by a bent axle than overweight. You can do a rudimentary alignment check with a level, and a tape measure. Make sure both wheels are vertical and measure the distance between the wheels at the front and at the rear at the edge of the rim, should be within 1/16". Check at the rim not the tire. You should weigh your rig to make sure you aren't overloading your tow vehicle, those don't have a lot of tow capacity There doesn't appear to be a lot of frame behind the existing axle to add a second wheel in your picture, most people just relocate the existing axle to the rear so it tracks better. Tim

 

[Bob]

thanks for the tips

The trailer and boat were weighed on a truck scale at 3800 lbs, the Pathfinder has 255 hp and is rated to tow 5200 lbs so no problem there. I towed the boat from Canada to Florida Keys this winter (1800 miles one way), truck easily hauls it in overdrive except for bigger hills if you keep the revs above 2000 rpms (60 mph).
MacGregor claims the trailer is rated for 2750 lbs so the trailer is well overloaded. I started to notice some wear on inside surface of the tires. Looking at the trailer carrying the boat from behind you can see the tires are canted in on the top out on the bottom. When the boat comes off, the trailer looks normal, so axle is flexing under weight. I usually have about 300 lbs on the tongue.
You are right there is not enough room behind the original axle unless I extend the frame. My concern is if I move the front axle forward I will not have enough weight on the ball. I would really like to make the axle position adjustable so they be easily moved along the frame to adjust tongue weight, it would be a fairly easy solution. I would need to know beforehand how far back to extend the frame and what other issues this extension might generate.
I am also concerned about the trailer frame itself, it does have some flex, maybe that is a good thing ? My trailer frame is 4" open channel (some newer ( 93 to 95 ??) Macs are only 3"), I could weld a plate on the inside of the channel to form a box frame, much stronger, but will add another 100 lbs or so. Also a closed box is more of a rust problem. Lots of decisions to make.
As far as trailer wheel alignment is concerned, most trailer axles are bowed up in the center when manufactured so that when they are loaded the tire will sit flat on the road. They also have a bit of toe-in to improve towing stability.

Bob

 

[walt]

tires

I think a lot of trailer tires (which fit on a 26C) are also rated for something like 1600 pounds. How interpret this... not sure but if it implies that the boat and trailer should weight less than 3200 pounds, hmmm. Ive never had my boat weighed but am guessing Im a little too close to this also.

 

[kendall]

axle

The axle on the boat should be a 3500lb axle.

If planning to buy a new axle, it may be cheaper and easier overall to mount a heavier duty axle in it's place and then sell the old axle. A 5200lb drop axle runs under $200 on line. Ready to bolt on (springs mounts hubs etc) are around $250. (Use existing mounts)

Tandem axles have a few disavantages, harder to manuever and accelerated tire wear in tight quarters because one set of tires will tend to skid around instead of rolling which makes it very hard to turn by hand with a trailer dolly or on the tongue jack.

Ken.

 

[Timo42]

Maybe start with a heavier axle

An axle sized for the load wouldn't bend as much, eliminate excessive toe possibility, this one comes with springs. The amount of toe built in probably isn't discernible with a tape measure, given the play in axle bearings and variation in the wheels, although I used to work with a guy who was too lazy to setup the alignment machine and used a tape measure and eyeball to do alignments until they caught him at it. *yks I did mean to check camber loaded. Just checked my trailer tires, they are rated at 1850lbs, Walt, yes the rating is what you think. Sounds like you need to put the boat on a diet. I am a firm believer in overkill for tow vehicles, I haul with a 3/4 ton diesel, I will trade 19mpg highway for peace of mind any day. ymmv What shape is the rest of the trailer in? One of the other guys here had issues with rust at the hitch area, the p/o on mine built his own out of 4" channel, talk about overkill, but a beautiful job he said the old one was rusted away. Tim

 

[mrBill]

mount new axle behind stock one

I saw a mac 26 at the homestead ramp, with 2nd axle behind 1st. spoke to owner and he said it worked great,,, he had drove 1000 miles to get there..

I moved my stock axle back 13" a year ago to stop the trl sway and add tongue weight. that was best thing I did to the stock trailer.


you can also box the steel to add strength

 

[Bob]

trailer

Thanks for all the information. The trailer is in good shape, it has only been used in salt water a couple of times. I'm the second owner, the boat was usually kept on a lift most of its life. I have the MacGregor engineering drawings for the trailer, they specify a 3200 lb. axle, the plate on the trailer frame indicates a maximum weight of 2750 lbs. The tires I have are 3 years old, they are identical to the original tires (I have those too) and they are rated at 1760 lbs each.

It is easy to reduce weight if I was only trailering it for a day or weekend sail. The problem occurs because my boat is normally in a slip but when it is trailered it is to go on a long drive and a cruise of one week to a month. I admit I have a tendency to take too many tools, spares, extra fuel, food, water, ice etc.

Anyone I know that has put a Mac 26C on the scales has reported a weight around 3500 lbs. I think I could get down to around that level.

MrBill do you know if the frame was extended to mount the second axle behind the first ? I looked at 2 mac trailers recently that had the original axle moved forward to allow the second axle to be mounted as close to the back of the frame as possible. I was not able to ask the owners how they handled or the tongue weight issue.

I have s/s disk brakes on these hubs. If I decided to use a heavier axle and tires I would also have to replace these brakes. A second axle might be cheaper.

I just bought a 3500 lb axle (made in USA) with hubs and bearings for $129 and two fenders for tandem axles $50. I have a set of 3500 lb. trailer springs. A bit of steel and an afternoon of welding would get it done. I know there are a lot of disadvantages to tandem axles, however those that have done the conversion seem very pleased. Some have told me tongue is much less of an issue with two axles.

Bob

 

[Bob McL]

Trailer Mod

Bob, Just so the answer is on this board too:

I have a tandem axle on my Venture 25. It is not the original trailer but the application of the axles works very well. There are two pieces of angle that go fore/aft on each side. Then two pieces of rectangle tube welded across ("V" shaped) that Kinda' form a box. The spring mounts are welded to the fore/aft "L" pieces, springs and axles attached. The actual trailer sits cradled in the "L" angle held by three "U" bolts on each side. It is easy to adjust the balance by just moving the axle assembly under the trailer.

 

[mrBill]

trailer was not extended

if you think about me moving my axle back 13", and adding a new axle... if you leave the original axle where it is, and add a new one behind the stock, I think you'll be about 12'-16" back.

thats what I saw, original trailer, with a new axle added behing the original.

-I think chamipion trailer makes a slider for the leaf springs and hangers to allow sliding the axles front/back...

-if it were me, I'd add a new axle behing the stock one, and call it a day.

best of luck!!!