Harbor Freight (type) Trailer Suspensions

rnArmy

Adventurer
I thought I'd start a thread about Overlanding DIY trailers based on the HF-type 4' trailer frames (also applicable to their 4'x8' frames). These trailer frames are also sold at places like Northern Tool. Specifically, I thought we'd focus on their suspensions, and modifications that can be done to improve the suspension.

All this and more can be found on this thread below (the thread is quite long; there's actually a table of contents in the first post):

Mini Harbor Freight (type) Trailer Ultimate Build-Up Thread - JeepForum.com

These lil' 4' trailer frames come factory with a short slipper-spring configuration. While they hold up the weight of the trailer, they are overly stiff, overly arched, and they just don't flex (I think they suck actually based on my experience on-and-off road with them). They're kinda ok at best if you're just sticking to smooth pavement (and no potholes or dips), but how many Overlanders here stick to just smooth pavement? My trailer would go airborne sometimes before I swapped out the suspension.

Generally these trailers come in red or black (as shown in the left picture below in red). Others came in black with the front tongue reinforcements (as shown in the right picture below in black). Mine was the type in the right. Other than those minor differences, the slipper spring suspensions are the same. Both pictures are shown with the factory 12" rims and tires.

four foot trailers.PNG

Leaf spring suspensions and straight axles are simple, and they work great on and off pavement (when properly set-up once you ditch the factory slipper spring set-up). And this suspension swap is actually fairly cheap and easy to do.

Below is a picture of the factory slipper spring set-up (with the axle mounted under the springs).

Trailer with wheel off.png

Pictured below is me with the Jeep and trailer up in Canada (in Atlin as I recall) on a trip with the factory slipper springs still on the trailer (205/75/15" tires on a slightly wider axle). I learned a lot about the trailer on that trip (and areas for improvement!):

Alaska%20remainder%20of%20trip%20004.jpg
 
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rnArmy

Adventurer
So what can be done to make the suspension better on these little trailer frames? Three things actually:

1. Swap out the stiff slipper springs to some longer springs with a mild arch (they'll still provide a bit of lift over the factory slipper springs) with a shackle at the end (as pictured below). Once you have done that, consider...

2. Adding shock absorbers.

3. Adding bump stops.

Let's start with swapping out the factory slipper springs. The factory slipper springs are 1.75" wide. Which is a common spring width for little trailers, and is also the same width as the old Willys flat fender Jeep springs (that will come into play later when talking about shocks). Here's a picture of the slipper springs removed, and a better flexing suspension mounted up in its place. Notice the fixed spring mount up front (1), the shackle mount attached to the frame (2), and the shackles (3). This picture shows a 26" long two-leaf spring which was rated at 575lbs each. Even with the axle shown mounted on top of the springs, I still gained an inch or so in height compared to the picture in the previous post with the slipper springs and the axle mounted under the springs.

Trailer suspension mounted up.1 - Copy.JPG

So to swap out to new springs, you need new mounting hardware. This is all a bolt-on affair. No welding is necessary.

Hardware (as shown above):

#1 and #3 (front frame mount for spring, rear shackles, and bolts to attach springs to both):
Single-Axle Trailer Hanger Kit for Double-Eye Springs - 3-1/4" Front, 9/10" Rear Redline Trailer Leaf Spring Suspension APS5

I like this kit because it uses longer shackles, and drops the springs a little further from the frame. Longer shackles allow for more flex in the spring because there's a longer arc with the longer shackles. You always have the option of mounting the axle on top of the the springs (shown), or underneath the springs.

#2 (rear spring frame mount for shackle - don't use the one that comes with the kit above):
H-110 HANGER TYPE = 2-EYE , A = NB-1 , B = , WIDTH = 1.75 (stengelbros.net) (I did have to drill two holes in each of these bracket to bolt them to the frame.) You need two of these.

Springs:

I get mine from Stengel Bros: Double Eye Trailer Leaf Springs (stengelbros.net)

You want either 26", 27.75", or 28" long & 1.75" wide springs rated between 540lbs to 975lbs each (depends on how heavy your trailer is, and how hard you plan on beating on it). Heavier is not necessarily better! You want them to be able to flex! Over the years I've actually swapped out my springs a couple of times as I've increased the trailer's weight (and more cargo) and in an effort to try to fine-tune it (and I just like messing with it).

Then it is just a matter of figuring out where you want the axle in relation to the frame, measure where the brackets will go, and drill & mount. In my experience, say I'm using 28" springs. If drawing a line straight down from the frame, I will have the bolt by #1 and the bolt by #2 28" apart. When there's weight on the suspension, the shackles will flex back a bit. That gives the springs plenty of room to flex and for the shackles to allow the flexing.

Obviously the shackle goes in the rear. If the spring only has one spring clamp, put the clamp up front.
 
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rnArmy

Adventurer
Shocks.

Some folks will tell you you don't need shocks on a little trailer like this. I'm not saying they're wrong by any means. My thinking with shocks on little trailers like these: can't hurt, might help. Shocks definitely won't help on a trailer with the factory slipper springs. This is also an inexpensive project.

Mounting shocks:

The old flatfender Jeeps had 1.75" wide springs. They also had shock mounts attached to the spring plates. I used two of them (a left and a right). The nice thing about these, is if you decide to move your axle from above the springs to below the springs (or vice-versa), you can just swap the plates to the other side and they'll still work. You'll most likely have to redrill these plates to match the axle width's U-bolts. I believe I got these from Summit racing, but Quadratec or Kaiser-Willys Jeep should have them.

Trailer shock.7.jpg

Trailer shock.6.jpg

So what about the upper shock mount? I use stake pockets from Tractor Supply, and shock bolt kit from the auto parts store:

Dorman HELP! Shock Bolt Kit 31001 | O'Reilly Auto Parts

Trailer shock.9.jpg

Trailer shock.10.jpg

Trailer shock.11.jpg

Trailer shock.12.jpg

They fit inside the frame rails quite nicely. Now you just have to figure out where to mount them. I mount the shock on the spring plate mount, compress them about half-way (with weight on the trailer's suspension), and that's where the upper shock mount goes. The picture below also shows the shackle mount mounted to the frame with the shackles attached.

Trailer shock.17.jpg
 
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rnArmy

Adventurer
What shock did I use (as shown in the previous post):

Monroe Magnum RV Series Shock Absorber - 555002 (jittruckparts.com) (found in lots of places - a common shock).

Additional Details
  • Boot Included: Yes
  • Compressed Length (In): 8.625 Inch
  • Extended Length (In): 12.750 Inch
  • Lower Mount Sleeve Inside Diameter (In): 5/8 Inch
  • Lower Mount Type: Loop
  • Stroke (In): 4.125 Inch
  • Upper Mount Sleeve Inside Diameter (In): 5/8 Inch
  • Upper Mount Type: Loop
They're designed for little trailers - roughly 12" fully expanded; 8" collapsed (so 4" travel). They also have a 5/8" hole in the upper and lower shock bushings.

Later on I painted my shocks blue. Because I like blue.
 
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rnArmy

Adventurer
Bump stops:

Bump stops definitely won't help on a trailer with the factory slipper springs (since the slipper springs don't flex).

On my last Overlanding trip, I actually snapped a spring. My fault - I was abusing them hard over the last year, and possibly overflexing them. So in addition to putting in a little heavier spring pack (four leaves now instead of three), I added some bump stops to the equation. I put a piece of angle iron under the frame to reinforce it, then got some Jeep TJ bumpstop cups, and some factory type foam bumpstops. These mount with just one bolt each.

Trailer repair.11.jpg

I put grease on them because I figured I'd be taking them in-and-out a couple times. The square things are shims to get the cups spaced down exactly where I wanted them. I also trimmed the sides of the cup (one is shown trimmed in the picture above) to increase the space between the cup and the shock. The bumpstops are positioned to hit on the axle/spring plate. You also have to remember that when springs flex, they also lengthen (that's why there's a shackle on the end of the springs) so you have to take that into account when positioning the bumpstops on the frame above the axle. Here's how it looks all installed (note I'm currently running with the axle under the springs):

Trailer repair.13.jpg

Trailer repair.6.jpg
 
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rnArmy

Adventurer
Here's my trailer when I started out (2009?). It started out as a little 4' HF frame with stake sides (which I made out of 1x4 pine boards), and the factory 12" rims and tires.

Jeeptrailer005.jpg

The first trip we took with the trailer was after I came back from Iraq the second time. My buddy and I took my TJ and trailer around the Olympic Peninsula in WA. We wrapped our gear in a tarp, and the trailer was running the factory slipper springs, factory axle, and 12" rims and tires. We had fun (it rained a lot though), and I knew I'd never want to go camping with the Jeep without the trailer again (I didn't know about the term "Overlanding" back then, but that's what we were doing).

Paul and Keith Jeep beachside81 (2).JPG

The trailer has since evolved and been modified over the years until it became what you see below (and I'll probably always be tweaking it somehow). I have thousands (and thousands!) of miles on it, and a lot of it off-pavement. I have added a good bit of weight to the trailer since I first began. The swapped-out suspension works! It makes a difference. The trailer and contents are no longer taking a beating. It has crisscrossed the country multiple times, been up to Alaska and Canada more than once (even did the Dempster in Northern Canada), and has performed superbly. I did snap a leaf spring once (recently), but I blame that on me (abuse and over-flexing). I have learned a lot about these little trailers during that time. I have extended the frame to put a cooler tray up front, swapped out the axle for a 3500lb axle with electric brakes, 235/75/15" tires, added a diamond-plate aluminum tub, put a Cabela's tent-cot on the lid as a RTT, and a whole lot more.

Overland Adventure.1 (2).jpg

Below shown as I'm getting ready to head up into Canada. Since here I have a kayak on the TJ's roof, I put the X-Bulls on the trailer's lid. I can (and sometimes do) watch the suspension on the trailer doing its thing. I can watch out the sideview mirror the distance between the top of the trailer's tire and the underside of the trailer's fender changing as the suspension flexes (even on the highway!). You'd think on a "smooth" highway there'd be no suspension movement, but you'd be wrong. It sounds dumb, but if I know a bump is coming up, I'll be watching the trailer suspension doing its thing out the side view mirror as the trailer goes over the bump and the springs soak up the bump.

arctic prerun.3.jpg

Willys and trailer.7 (2).jpg

One nice thing about building a little 4' HF-type based overlanding trailer, is it can be lightweight. Lightweight enough to where I can pull it with my Willys (but I feel better with the trailer having electric brakes - the brakes on the Willys are adequate at best). And it is amazing how much "stuff" you can put in even a little 4' trailer. I don't leave home without it.
 
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Goatdog

Member
We spoke on EP a few years ago. With your help I switched to the same wheel/tire combo as you. I'm now thinking of going to a 3500 lb axle. Can it be done by leaving the build intact and using jacks and jackstands?

Sent from my SM-N960U using Tapatalk
 

rnArmy

Adventurer
Yes it definitely can.

It would be best if you emptied the trailer first. You'll need to support the trailer frame on jack-stands. Depending on if you'll be mounting the axle above or below the springs may determine if you need to drop the springs at one end or not. I usually use four jack-stands - two for the back of the trailer, and two to support the axle as I'm mounting it to the springs (lifting and lowering the axle with a jack).

You will need some additional parts just to mount the axle to your current springs. I'm betting your new 3500lb axle will have a larger axle diameter than your current axle. If so, you'll need new spring plates and U-bolts. Stengel Bros or E-trailer should have them (my go-to places for things trailer related), or even TSC may have them in stock. If you're getting your axle from a local trailer place (or you have a local trailer shop), they should stock them.

If you're no longer running the stock slipper springs, now would be a good time to consider getting a pair of early Willys spring plates with the shock mount tabs already installed to use for your spring plates. In case you might want to add shocks at a later date. Just saying....

Check out this thread post for other things you will probably need when converting your trailer over to electric brakes (and your vehicle to be wired for an electric brake controller). These are what I used; it doesn't mean this is the only option.

Mini Harbor Freight (type) Trailer Ultimate Build-Up Thread - Page 173 - JeepForum.com

You may have to get the axle perches mounted on the axle (they will often come loose with the axle) - any welding shop can do it (if you don't weld). If getting your axle from a local shop, they should do this for you once you tell them the axle perch center measurements (taken from your existing axle). Some mail order axle places may weld them for you at an additional cost.

You may be asked if you want a straight axle, or one with a camber. You want a straight one for these little overlanding adventure trailers. If you were building a trailer for hauling cars and such you might consider an axle with a camber.

Some newer vehicles come pre-wired for an electric brake controller. If so, you're ahead of the game. Mine weren't. So far I've wired four vehicles with the universal kit from E-trailer (linked in the link posted above) to pull my lil' trailer with great results. E-trailer may also have some vehicle-specific kits for wiring your particular vehicle for a 7-prong wiring harness.

I usually recommend carrying a spare hub and already greased bearings with your trailer in case you have issues in the field. With these types of axles, the brake drum is the hub. So consider when purchasing your new axle, getting an additional brake drum with already greased bearings installed, and find a place to keep it in/on your trailer if venturing far from home.

You can pull a trailer with a flat tire if you have to (I recommend always having a matching spare tire for your trailer); you can pull a trailer with a broken leaf spring if you have to (once you've ratchet-strapped the axle in place with a block of wood between the axle and frame - I did it for a couple hundred miles). If you ruin a set of bearings you might be stuck - and you don't want to have to leave your trailer (and all your gear) unattended in the middle of nowhere while you go off trying to find replacement bearings or a hub. Cheap insurance.
 
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Goatdog

Member
Thanks!

I do have a spare tire as well as a hub. Suspension and axle have been fine for over three years now, but figured upgrading to 3500 wouldn't hurt anything but my wallet. And I'm on your very long thread at Jeep Forum. My posts start at #3022

Sent from my SM-N960U using Tapatalk
 

rnArmy

Adventurer
Thanks!

I do have a spare tire as well as a hub. Suspension and axle have been fine for over three years now, but figured upgrading to 3500 wouldn't hurt anything but my wallet. And I'm on your very long thread at Jeep Forum. My posts start at #3022

Sent from my SM-N960U using Tapatalk

I went back and looked at #3022. I remember that conversation now. Glad it is still working out for you. Please post pics and a short write-up when you do your axle swap (what-all you needed to complete the swap, etc.). Maybe post both here and on the JF!
 
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rnArmy

Adventurer
Amazing thread!

Thanks! I hope it will be helpful to some folks. It is amazing what you can do with these little 4' trailer frames to allow you to make your overlanding adventures better; even more so when you swap out the suspension! Usually when someone gets a vehicle to go overlanding with, one of the first things they swap out (or upgrade) is the suspension. It should be the same with these little trailers.

Mounting brackets and springs for the project can be had for around $100 (depends on your spring choices) and will make a huge difference in how your trailer rides.

Double Eye Trailer Leaf Springs (stengelbros.net)

I don't work for StengelBros or E-trailer (rnArmy... Army Nurse... get it?), so shop around - but make sure if you're buying springs you know the spring rating! There are lots of 2000lb (each) rated spring packs out there for sale that are way too stiff for these types of trailers. Even 740lb (each) springs might be a little stiff for a lightly set-up/loaded lil' 4' trailer.

Example:

Two 26: long springs rated at 575lbs each ($28.00 each spring) = $56.00
US-1001 Type EE (Eye/Eye) Utility and Boat Trailer Spring 1.75 inch Width; 26 inch Overall Length; 575 lb rating per spring (stengelbros.net)

Two 28" long springs rated at 740lbs each ($30.00 each spring) = $60.00 (remember... heavier is not necessarily better! You want the springs to flex!)
US-1030 Type EE (Eye/Eye) Utility and Boat Trailer Spring 1.75 inch Width; 28 inch Overall Length; 740 lb rating per spring (stengelbros.net)

Mounting kit = $31
Single-Axle Trailer Hanger Kit for Double-Eye Springs - 3-1/4" Front, 9/10" Rear Redline Trailer Leaf Spring Suspension APS5

Two rear shackle mounts ($8.00 each) = $16.00
H-110 HANGER TYPE = 2-EYE , A = NB-1 , B = , WIDTH = 1.75 (stengelbros.net)

Total: $103.00 - $107.00 (in this example)

You still need to add spring plates and U-bolts into the cost if your axle diameter has changed (otherwise reuse what you've got), but they're not expensive. Sometimes folks do an axle and suspension upgrade at the same time.

spring_plates | etrailer.com
 
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john61ct

Adventurer
What would you suggest for a trailer that needs to haul 12000lbs sometimes including off road

but most of the time only 3-4000?

Thinking a re-positionable tandem axle-less setup, only add the second pair when needed. . .
 

rnArmy

Adventurer
What would you suggest for a trailer that needs to haul 12000lbs sometimes including off road

but most of the time only 3-4000?

Thinking a re-positionable tandem axle-less setup, only add the second pair when needed. . .

Interesting question. Totally out of my scope of experience, but I'll try and give you a few thoughts.

1. Sounds like you need two separate trailers; one for the big loads, and one for the lighter loads (especially if going off-road). I can't see having a trailer with a removable axle set-up being practical. Even if you could or did, the remaining axle's suspension would still be very stiff (half of the rating needed to haul 12,000 lbs) to have any suspension at all flex off-road.

2. By axle-less set-up, I'm assuming you're thinking about a Timbren system?

Axle-Less Trailer Suspension – A Discussion With The Mechanic (mechanicalelements.com)

They do make them up to a 7000lb capacity (I still can't figure out if that is per side, or per pair):

Axle Less Trailer Suspension Systems, Trailer Axle Kit by Timbren (sdtrucksprings.com)

But to make them work on a really HD trailer like you're talking about, the frame needs to be reinforced and/or the two sides tied together.

3 Questions about Tandem Axle Trailer Suspensions (timbren.com)

Axle placement in relation to the trailer's frame is important. You don't want it (them) too far back or too far forward. Seems like if you remove one of the axles, now the remaining axle is either too far forward (trailer will sway) or too far to the back (too much tongue weight).

Sounds like you're wanting the best of both worlds in one package. Like wanting a full-size 4x4 dual cab one-ton dually truck that is light and nimble off-road and gets good gas mileage. Good luck.
 

rnArmy

Adventurer
Speaking of Timbren suspensions, here's an interesting read about installation and such:

Timbren Heavy-Duty Axle-Less Trailer Suspension - Straight Spindle - Wide Tires - 1,200 lbs Timbren Trailer Leaf Spring Suspension ASR1200S03 (etrailer.com)

if you wanted to put one on a little HF-type trailer, the frame would need to be heavily reinforced (or a 2" square tube run from side-to-side). Seems like they make them with a 4" lift for running taller tires. I haven't checked to see how far out they can go (thinking wheel backspacing and such so the tires don't rub on the frame or tub).

ASR2KHDS03 Timbren AXLE-LESS Trailer Suspension Off-Road Kit - 4 Lift Spindle with Brake Flange for Off Road Tires - 2000lb Capacity [ASR2KHDS03] | $694.87 | SD Truck Springs | Leaf Springs, Helper Springs and Suspension Parts

One nice thing about leaf spring suspensions is they spread the load along the length of the frame. These Timbren systems focus the load on a smaller section of the frame (think fulcrum on a beam). Could it possibly cause the frame to bend in the middle? Theoretically maybe. Would help to run a piece of angle iron along the length of the trailer's frame before mounting up the Timbren system. These HF-type trailer frames are made of a somewhat thin C-channel (plenty strong for most applications - I've had no issues). When folks home-build a trailer frame, they usually use square tubing.

These Timbren systems are not cheap either. Seems like overkill for these little HF-type trailer frames. But part of the fun of building one of these little HF-type trailers is making it your own the way you want it.

I've got 33" tires on my Jeep TJ. On the trailer I've got 235/75/15" tires and a straight axle. I've got 3-4" more clearance under the trailer's axle vs. under the pumpkin of my Jeeps rear Dana 44. I've yet to have a clearance issue with my trailer's axle.

And with leaf springs you have many more options of spring weights to customize your trailer's suspension, and an infinite amount of choices of axle widths. With the Timbren system... not so much. With a leaf spring set-up, you can do a trail repair if needed if you break a spring. With a Timbren axle-less set-up, if something breaks, I think you're stuck.

Overland adventure.10.jpg

And not to be saying anything bad about Timbren - I'm running these on the back of my Dodge Truck:

1996 Dodge Ram Pickup Vehicle Suspension - Timbren (etrailer.com)
 
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