Bearing Kit for 2021 Grand Design MB31 Trailer Axle

Updated 09/15/2025 | Published 09/05/2025

Question:

Hi, I think there is a mistake on your website. I used the vehicle search to find grease seals for my 2021 Grand Design MB31. The options it gave me for MB31 were 2.125 ID when Im pretty certain the Dexter 5200lb axles have a 2.25 ID. Im pretty confident that Im correct to the point of buying seals and a bearing kit with 2.25 ID seals. Just wanted to let you know incase it is a mistake. thanks, Mike

asked by: Michael B

Expert Reply:

Hey Michael, the 5,200 to 7,000 lb trailer axles are odd in that the seal diameter is hard to nail down. Some of them have the 2.125 inch diameter and others have the 2.25 inch diameter. To our knowledge there isn't a way to know exactly for sure when it's one way or the other. Best solution we can provide would be to check yours and let us know. Or if you already did and you know that you need the 2.25 inch seal then you'd want the part # BK3-300 which is bearing kit that includes that seal.

expert reply by: Jameson C

Michael B.

9/15/2025

Hi Jameson, I pulled my first hub today and the seal is definitely 2.25 ID. Thanks, Mike

Jameson C.

9/15/2025

@MichaelB That would make sense. One would think that if any of the capacities between 5.2 and 7k would have that seal size it would be the 5.2k axle since it would mean the spindle is slightly smaller.