What Solenoid do I Need For My 2005 MRI Boat Trailer to Fix Clunking Noise After Braking?
Updated 10/30/2025 | Published 02/01/2025
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Question:
I have a 2005 MRI boat trailer for a Yamaha ar230 and I’m thinking the master break solenoid is having issues. It clunks pretty hard when accelerating after breaking. How do I know which master solenoid to replace it with? It has a manual reverse magnet. But looks like it may have been set up with an automatic reverse at some point. I would like to use an automatic reverse if it’s not too hard to switch over. Do I also need to do the brakes lines at the same time?
asked by: Dan
Expert Reply:
Hello Dan,
Sounds like you have done your research, or have dealt with this issue before. I do not have a database that supplies me with what is put on what trailer, in my research I see that you most likely have the UFP A-60 (you will want to confirm this, if you are not sure feel free to send me some pictures so I can identify what you have). Your boat trailer's hard clunk after braking is likely due to a faulty reverse lockout solenoid or a worn shock in the surge brake actuator. The solenoid should release the brakes when you shift into reverse, but if it's failing, the brakes may stay engaged too long, causing a clunk when you accelerate. For a new solenoid you will want # T4748800, this solenoid will automatically engage when the car is put into reverse. I would also inspect the shock absorber as that could be causing the clunking noise as well. If you find that it is worn or damaged you will want # TK71-758-00 (I attached an image so you can confirm fitment).
If those parts are going out it's just a matter of time before the master cylinder does as well. If you wanted to spend the extra money you could just replace the inner member with the Replacement Inner Member for Dexter DX7.5L # DX99FR for tandem axle, and # DX39FR for single axle.
I never understood the Boat = Bill out another thousand until I bought a boat =) Are you getting things geared up for nice weather, or are you in a part of the U.S. where it is always boat season? I am in Missouri and just as long as I can get the boat down the ramp, I'm going in the water!
(click to enlarge)
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Kate F.
10/30/2025
Hey Dan, how did things turn out with the new reverse lockout solenoid on your MRI boat trailer? Did replacing it help stop the hard clunk after braking? Your update could make it easier for others dealing with the same issue.