How To Replace An Old Square Boat Trailer Axle
Updated 02/03/2026 | Published 07/07/2024
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Question:
I need to replace a boat trailer axle. The axle tubing is square so would i need to replace the ubolts and all? also it looks like my spring hangers are at 75 inch centers not 74 and the springs set on top of the axle and not underslug. What do you suggest? Also I know it had brakes on it but i do not need them I need an idler axle instead of a brake axle.
asked by: Tracy D
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Expert Reply:
Hey Tracy,
In order to get the right axle we'll need to know the axle capacity, hub face to hub face measurement, and spring center measurement. I'm assuming the trailer is pretty light and you most likely have a 3,500lb axle. We can try to verify that with any part numbers you can get off the bearings, grease seal, or hubs. You can measure for the bearings and grease seal using a caliper # PTW80157 and the diagram below. For the hub face measurement you and a helper can run a tape measure across and it sounds like you already measured 75" for the spring centers.
You would need to replace the u-bolts since you're switching to a round axle, and because you typically would have to cut off the u-bolts since the nuts tend to seize up from rust over the years.
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Product Page this Question was Asked From
Dexter Trailer Axle w/ Idler Hubs - EZ-Lube - 5 on 4-1/2 Bolt Pattern - 89" Long - 3,500 lbs
- Trailer Axles
- Leaf Spring Suspension
- Standard Grade
- Idler Hubs
- 3500 lbs
- 5 on 4-1/2 Inch
- 74 Inch Spring Center
- 89 Inch Hub Face
- No Drop or Lift
- Dexter
more information >
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Lazer S.
2/3/2026
Hey Tracy, were you able to get the axle capacity and hub face measurement figured out for your trailer? Once you had those numbers, did the new idler axle line up well with your 75-inch spring centers? Sharing what worked could help others replacing a similar setup.