axle upgrade

Why not contact Morryde to make sure you get the correct part?

I see you have a 2018 RV. Was the axle replacement covered by the warranty? What a shame that you have to do a modification because the RV had an insufficient suspension to begin with. It seems criminal that Grand Design would build an RV with a GVWR of 7500# and a dry weight of 5860#. By the time you add water, propane, and any accessories not included in the specs, you are down to a cargo capacity of just a few hundred pounds. I would also worry about upgrading the tires!

Yes I'll upgrade the tires but for my research i need to make sure I have the correct wheelbase dimension.

Center to Center spring perch is the critical dimension.Face to face of hubs also critical depending on wheel offset, if any.
We replaced our 7k 12" x 2" brakes Dexter axles with 8k. forward self adjusting 12 1/4" x 3 3/8 shoes ordered from Redneck Traler supplies with perches loose, welded them on myself with pre and post heat to minimize HAZ ( heat affected zone ) so I could vefify alignment with lasers. Tire wear and braking much improved,. 40 k mi., no issues.
If you do mot have the ability to do it yourself, consider ordering the axles with loose perches, then have a local shop weld them on. Welding procedure to minimize stress, warpage will be superior to the factory.

best measurement is hubface to hubface, the part that the wheel is bolted flat to, usually the brake drum with the studs poking out. Center-to-center will bring in variables like wheel/tire width that is not unique to the axle.
Easy to just call them after you take many measurements including the leaf spring perch, which you can do center to center.

ajriding wrote:
best measurement is hubface to hubface, the part that the wheel is bolted flat to, usually the brake drum with the studs poking out.

That is also commonly referred to as WMS, aka "wheel Mounting Surface"