1. Trailer Leaf Spring Suspension
  2. Universal Group
  3. Leaf Springs
  4. Springs
  5. Slipper Springs - 1-3/4 Inch
  6. 30 Inch Long
4-Leaf Slipper Spring w/ Flat End for 3,700-lb Trailer Axles - 30" Long

4-Leaf Slipper Spring w/ Flat End for 3,700-lb Trailer Axles - 30" Long

Item # SP-040275
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Trailer Leaf Spring Suspension
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Universal Group Springs - SP-040275
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Slipper leaf spring acts as part of a trailer's suspension system by providing an attachment point for a 3,700-lb axle. Spring flexes to resist shock and also ensures a smooth ride. Includes bushing with 9/16" inner diameter. Lowest Prices for the best trailer leaf spring suspension from Universal Group. 4-Leaf Slipper Spring w/ Flat End for 3,700-lb Trailer Axles - 30" Long part number SP-040275 can be ordered online at etrailer.com or call 800-298-8924 for expert service.
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  • Reviews (63)
  • Q & A (18)
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Universal Group Trailer Leaf Spring Suspension - SP-040275

  • Leaf Springs
  • Springs
  • Slipper Springs - 1-3/4 Inch
  • 30 Inch Long
  • 3700 lbs
  • Universal Group

Slipper leaf spring acts as part of a trailer's suspension system by providing an attachment point for a 3,700-lb axle. Spring flexes to resist shock and also ensures a smooth ride. Includes bushing with 9/16" inner diameter.


  • Leaf spring acts as part of your trailer's suspension system
    • Provides attachment point for your trailer's axle
  • Multiple leaves allow flexibility to absorb road shock
    • Allows for a smooth ride
    • Reduces wear and tear on trailer
    • Ensures level ride on bumpy and uneven surfaces
  • Sturdy steel construction
  • Nylon bushing included
  • Pre-mounted hangers or aftermarket hanger kit (sold separately) required for installation
    • Eye of spring attaches to hanger mounted on trailer frame
    • Slipper end slides into hanger or equalizer


  • Quantity: 1 leaf spring
  • Spring capacity: 1,850 lbs
  • Axle capacity: 3,700 lbs
  • Length from center of spring eye to end of spring: 30"
  • Spring width: 1-3/4"
  • Eye diameter with bushing: 9/16"
    • Eye diameter without bushing: 7/8"
  • Leaf thickness: 3/8"
  • Number of leaves: 4
  • Additional dimensions: see table

Flat End Slipper Spring

Part NumberABCDE

Note: To ensure proper axle alignment and suspension performance, leaf springs should always be replaced in pairs.

Leaf springs are an integral part of your trailer suspension system. The leaf springs provide the attachment points for your trailer's axle, suspending it from the frame of your trailer. Each spring flexes to absorb road shock as you travel, allowing the axle to move somewhat independently of the rest of your trailer. This helps to reduce wear and tear on the trailer and also ensures a smooth ride.

Slipper leaf springs attach to hangers that are welded onto your trailer. The eye of this spring will attach to the front hanger with a suspension bolt. The flat slipper end of the spring will slide into the rear hanger. If you have a tandem- or triple-axle trailer, the slipper end will slide into the equalizer that connects multiple springs. The shape of the slipper end of a leaf spring may vary slightly due to differences among trailer manufacturers. Because of this, it's important to check your leaf spring's slipper end before purchasing a replacement spring.

To mount this spring, you will need hangers, a suspension bolt, and possibly a spring keeper bolt, depending on the design of the rear hanger. If you are simply replacing a spring, you may still have hangers welded onto your trailer, but it would be wise to replace the bolts as they can experience wear. It is also recommended that you replace the other leaf spring in your setup at the same time. Because springs can sag and elongate as they wear, this new spring may not exactly match the old one, and the alignment of your trailer could be affected.

If you are fabricating a trailer, you will need to purchase a hanger kit for installation. To determine the type of hanger kit that you need, you must know the specific type of leaf spring that you have, as well as your axle capacity. Depending on the hanger kits used with them, springs can be configured to work for single-, tandem- or triple-axle applications. Hangers and other suspension components can also be purchased separately if there isn't a complete kit that works for your setup.

UNA-040 Universal Group Slipper Trailer Leaf Spring - 4 Leaf - 1,850-lb Capacity

Replaces WIG4

Video of 4-Leaf Slipper Spring w/ Flat End for 3,700-lb Trailer Axles - 30" Long

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Universal Group Trailer Suspension - Leaf Spring Suspension - SP-040275 Review

Today we're going to be taking a look at the 4 Leaf Slipper Spring for 3,700 pound trailer axles. It's made from a durable steel construction. It's going to flex to absorb road shock and provide a smooth ride. It really helps reduce wear and tear on your trailer, and it's going to ensure a level ride on bumpy and uneven surfaces. This is designed to mount to the trailer frame with a hanger or a hanger kit. Those items are sold separately, so if you're in need or interested in something like that you can check out your options here at etrailer.com.

It's got 1 eye on it and then it's going to feature a slipper end. The eye is going to include the nylon bushing. This is a 4 leaf spring, it's going to have a spring capacity of 1,850 pounds, and again it is designed for 3,700 pound trailer axles. A few measurements to go over with you real quick. We want to go over the spring length, I'm going to give you 2 measurements with the spring length. First one we're going to measure from the center of the eye to the end of the spring and on the second one we're going to measure from the center of the eye to the top portion right here of the bend, or of the curve.

Measuring to the end of the spring from the center of the eye, that's going to give us a measurement of right around 30 inches. Then to the top portion about right here that's going to be right around 28 inches. The width measuring edge to edge is 1 3/4 of an inch. The eye is going to have a diameter of 9/16 of an inch. Please keep in mind that in order to ensure proper axle alignment and suspension performance, leaf springs should always be replaced in pairs.

That's going to do it for today's look at the 4 Leaf Slipper Spring for 3,700 pound trailer axles.

Customer Reviews

4-Leaf Slipper Spring w/ Flat End for 3,700-lb Trailer Axles - 30" Long - SP-040275

Average Customer Rating:  5.0 out of 5 stars   (63 Customer Reviews)

Slipper leaf spring acts as part of a trailer's suspension system by providing an attachment point for a 3,700-lb axle. Spring flexes to resist shock and also ensures a smooth ride. Includes bushing with 9/16" inner diameter.

- SP-040275

I ordered a fender, springs,8 and misc parts for my magic tilt boat trailer to get it back in good condition. Everything was exactly what I ordered and worked great. The order was delivered in two days with free shipping The customer service was also very helpful (thanks Taylor ) Only place to go for your trailer needs. 656436

- SP-040275

Works great hasn't had any problems 748748

- SP-040275

product delivered early all goo, box was ripped in transit but all ok Great survice and follow up support1 723335

- SP-040275

I just cant say enough good things about my experience. Along with a great product, the service and support are unbelievable. Thanks from a first time but multiple future customer. 708476

- SP-040275

Great product.Fits perfect 698222

- SP-040275

price was good, shipping was fast and installing the springs was easy. What more can I say. 693728

- SP-040275

Very good product. My mechanic told me to go get the same thing I had on my trailer, only more leafs. Knowing very little about these, I couldn't find what I thought I needed...then etrailer came up on Google search. I got what I thought would be needed and all the mechanic had to get were ubolts etc to connect to axle. These leaf springs should be strong enough to help me save fuel when hauling wood and mulch no matter what vehicle I am using. Thanks for helping me get what I needed. Emily 682988

- SP-040275

We initially ordered the wrong size spring leaf and Rebecca made the exchange easy. The correct ones came very fast! Thank you! 682211

- SP-040275

You Da Man!!! Perfect fit, boat and trailer has never pulled that smooth before.. thank you for the speedy shipping also. 673726

- SP-040275

Very good , help full, and fast shipping. Thank you. 664630

- SP-040275

Just installed it, not driven with it yet, but no problems. 602439

- SP-040275

Really happy with product 600138

- SP-040275

Great service product and price........nuf said 585398

- SP-040275

Holding up just fine 584260

- SP-040275

Product was exactly as described and arrived in a timely manner. Customer service was great too. Web page was easy to navigate and I would recommend etrailer to anyone looking for trailer parts. They have it all. 571298

- SP-040275


- SP-040275

Very good I’d buy again from etrailer 550208

- SP-040275

Great looking quality, fast fast shipping ??, gives my trailer a higher tire clearance from the deck which is what I needed. My only recommendation to etrailer is seeing if their supplier can start making this same spring in a 32" version due to that's what this 30" spring is replacing. I made some modifications to make this spring work. Overall this is a nice spring pack assembly. 544719

- SP-040275

Quality parts for a great price. I now have a trailer with better suspension than when I bought it. I am confident it will carry the loads I haul in it for years to come. 519951

- SP-040275

It’s a leaf spring. Dimensions were acc urate. 496451

- SP-040275

The first set of springs I ordered had been discontinued (but still on website). However, their customer service was extremely helpful in correcting the order and recommending a similar spring that will work just fine for me. 484220

- SP-040275

additional items to update a 38 year old trailer 484126

- SP-040275

Very fast shipping. Package got alittle damage with shipping but everything was there in great shape. 482788

- SP-040275

I bought these leaf springs about a year ago. Not only did they get here fast I have zero concerns about them. Good stuff! 436128

- SP-040275

Very helpful taking my order and great pricing . Also free shipping at $100.00 is a great money saver based on the weight of trailer leaf springs and all the hardware i received shipping would have been a killer . I will be using this place again for sure !! 426029

Show More Reviews

Ask the Experts about this Universal Group Trailer Leaf Spring Suspension

  • Replacement Slipper Springs to Replace 32 Inch Long Springs
    The 30 inch slipper springs we carry don't have a measured radius but the 28 inches you're looking for will work just fine. Your 32 inch springs were likely a little shorter than that originally and have flattened over time. Although probably not the full 2 inch difference but enough that our 30 inch springs will work on your trailer. We carry three different weight capacities that are 30 inches: 4-Leaf for 3,700 pound axles # SP-040275 3-Leaf for 2,900 pound axles # SP-039275 2-Leaf...
    view full answer...
  • 30 inch Long Slipper Spring Recommendation for Boat Trailer
    We have a few options for 30 inch long slipper spring that is 1-3/4 inches wide. For a 3,700 lb axle option we have the part # SP-040275. For a 2,900 lb axle option we have the part # SP-039275. For an 1,800 lb axle you would want the part # SP-038275.
    view full answer...
  • Recommended Spring Seat for a Square Axle Tube
    Correct, you will need to have a spring set installed on the axle tube to hold the leaf springs in place and prevent them from sliding back and forth. That said, although we do not have any spring seats specifically for a square tube axle you can use the Spring Seat part # TRSS300 by grinding the ends down and then welding it to the axle tube.
    view full answer...
  • Replacement Leaf Springs for 1989 TeeNee Boat Trailer
    As leaf springs become worn, they tend to flatten out, which would explain the slightly longer dimensions of your existing slipper spring. The correct replacement spring you need will depend on the capacity of your axle. If your TeeNee boat trailer uses a 3500 lb axle, then the # SP-040275 is the correct replacement. For a 3000 lb axle, use # SP-040275. Leaf springs should be replaced in pairs.
    view full answer...
  • How to Find Axle capacity of a Trailer to Choose the Right Replacement Slipper Springs
    The leaf springs on a trailer will need to meet or slightly exceed the axle capacity. So if you know the axle capacity then each spring should be rated for at least 1/2 of that capacity on a single axle trailer. The axle capacity may be listed somewhere on the trailer frame near the front of the trailer. Another option is to pull off a hub and retrieve the inner and outer bearing numbers stamped into the sides of the bearings. With that information I can determine the likely hubs that...
    view full answer...
  • Replacement 32 Inch Leaf Springs for Trailer
    The closest leaf springs we have available to the specifications you mentioned is the Universal Group 4-Leaf Slipper Spring # SP-040275. These slipper springs have a 30 inch length from the center of the spring eye to the end of the spring. Leaf springs will stretch over time, so it's possible that the leaf springs on your trailer originally had a length closer to 30 inches. These are designed for axle capacities of 3,700 pounds and have a width of 1-3/4 inches. The eye diameter with...
    view full answer...
  • Looking for Spring for Model R1828 Yacht Club Boat Trailer With 1-3/4 x 30 Leaf Slipper Springs
    As long as a spring is of the correct weight rating, size and type (slipper or double-eye), the number of leaves in a spring isn't important. This is especially true since springs should always be replaced in pairs. If you are confident that your trailer has a 3500 lb axle, the # SP-040275 slipper spring should work just fine for you.
    view full answer...
  • Can Bottom Leaf be Removed When Replacing 3-Leaf Slipper Spring with 4-Leaf Slipper Spring
    You can easily replace a 3-leaf slipper spring with a 4-leaf option like the Universal Group Slipper Spring # SP-040275 that you referenced. You should definitely not remove the bottom leaf from this as that would lower the weight capacity plus the center bolt that holds all of the leaf springs together would need to be modified. All the extra leaf spring will affect is the height of your trailer but that will be very minimal. Just be sure that the leaf spring is rated properly, has the...
    view full answer...
  • Are 5-3/4 Inch U-Bolts Long Enough for a 3 Inch Tall Axle and Slipper Spring # SP-040275
    The internal length of u-bolts # SP01-160 is 5-3/4 inches so you would not subtract 9/16 inches from that length. The u-bolt plate # 117594-G is 3/16 inches thick. The spring stack for # SP-040275 I just measured and it is 1-7/16 inches thick. Adding in the 3 inch height of the axle and the total comes to 4-5/8 inches. So all of these parts will fit your trailer axle.
    view full answer...
  • Trailer Leaf Slipper Spring Hardware
    The Trailer Leaf Slipper Spring, part number SP-040275, is not galvanized or coated it is a solid steel leaf spring. The leaf springs are shipped with a light coat of paint for rust protection but are not rust proof. Coating or treating the springs would not work because of the flexing and rubbing the springs are subject to under the trailer. The leaf springs can be painted but the paint will not last long with the constant flexing and road debris hitting them. The mounting hardware...
    view full answer...
  • Replacement Leaf Springs and U-Bolts for a 1987 Shore Line Boat Trailer
    Thank you for submitting the photo of your setup. Considering the height of your axle and the amount of clearance you currently have from the axle to the frame of your trailer you wouldn't have enough room to put your axle above the leaf spring. You would barely have a couple of inches of suspension travel. For U-bolts you would want the part # SP01-160 and then for plates you would want the # 117594. Based on the dimensions of your current slipper springs the # SP-040275 that you...
    view full answer...
  • Thickness of the 4-Leaf Slipper Spring SP-040275
    I went and grabbed a 4-Leaf Slipper Spring # SP-040275 from our warehouse to measure it and found that it is 1-7/8 inches thick if you only look at the leafs. If you add in the bolt that runs down the center you would add 1/2 an inch to the overall thickness.
    view full answer...
  • 4-Leaf Slipper Spring Recommendation that is 1-3/4 inches Wide and 30 inches Long
    I believe the closest spring we carry to what you are looking for is the 4-Leaf Slipper Spring part # SP-040275. This is a 4-leaf spring that is 1-3/4 inches wide that is 30-1/4 inches long. This spring is designed for a 3.500 lb axle. If the axles you have on your trailer are 3,500 lb capacity this spring would work well for you. I attached an FAQ article on slipper springs for you to check out also.
    view full answer...
  • 4-Leaf Slipper Spring Recommendation for a 3,500 lb Axle Boat Trailer
    As long as the capacity of the spring matches what the trailer needs it won't matter at all if there are a different number of leaves on the spring. Based on the weight of your trailer and the fact the # SP-040275 matches up dimensionally this spring would be the perfect spring to use. I attached a review video for you to check out as well.
    view full answer...
  • How To Choose Correct 3,500 Lb Axle for Slipper Spring Setup
    In order to determine which axle is correct for your trailer we need to find out what your hub face (HF) and spring center (SC) measurements are. If you take a look at the photo I have attached for you that should then help with obtaining the above two measurements. The most important thing we need to look for is the hub face as the spring center can then be moved (within a range) if we need to. I have attached a list of the 3,500 lb axles we offer in the varying hub face and spring center...
    view full answer...
  • Replacement Slipper Springs for 1985 Harding Boat Trailer
    I do have options for you but exact replacements for old boat trailers are hard to come by. In the majority of cases, items will need to be altered for an exact fit which I assume is what is going to need to be done on your trailer as well. We don't have a slipper spring that is 1-3/4" wide x 28" long (center of eye to end of spring) with a 2,500, 3,000, or 3,500 lb capacity. However, leaf springs will fatten out over time which means the leaf spring that was originally installed on the...
    view full answer...
  • How to Select the Correct Leaf Spring Size for a Tandem Axle Trailer with Slipper Springs
    To determine the correct slipper springs for your tandem axle trailer, the axle capacity will need to be determined. Selecting a spring by length alone could cause the selection to be under or over capacity substantially. If your spring is shaped like the 4-Leaf Slipper Spring for 4,100-lb Trailer Axles, # SP-264275, and each axle capacity is 4,100 lbs or just below that, then this spring should work for you. This is the only spring we have with the slipper end shaped this way. If...
    view full answer...
  • Replacement Slipper Springs for a 2,100 lb Trailer
    The most important factor in picking out a new leaf spring for a trailer is to match the capacity needed. Going with a 3,500 lb spring for a 2,100 lb trailer is going to give you a very harsh ride. For a spring similar to the # WIG4 that is better rated for your trailer we have the # SP-039275 which is for a 3,000 lb axle or part # SP-038275 for a 2,000 lb axle. If you need all 2,100 lbs of your trailer's capacity you would have to go with the # SP-039275. If you have a 2 inch square...
    view full answer...

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Info for this part was:

Expert Research:
Michael H
Expert Research:
Jameson C
Installed by:
Cole B
Updated by:
Sarah W
Written by:
Alexander C

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