Hi chouston,
Welcome to Sunline Owners Club! And congrats on your Sunny!
Now to your axle. Odds are high you will not find in the Sunline info the dimensions you are looking for to order a new brake axle. I myself went through this on mine to buy new axle tubes as the original ones where made wrong and had excessive toe out in them. That and the hangers where welded on wrong.
Some of my work may help you here. Since you are going with a new axle, I recommend you go Dexter. The quality and the before and after the sale tech support is very good. They have a staffed tech line even.
You will need at least 3 dimensions to order a new brake axle.
1. The machined surface of brake drum to brake drum.
2. The left to right distance of the axle seat where the leaf spring mounts.
3. The axle and spring capacity.
You did not say if you are adding new springs, it might be cheaper with new springs. I found you can buy the axle ass'y in parts or a whole assembly and the assembly often wins being cheaper.
Other dimensions,
4. Wheel lug nut bolt circle diameter and number of lugs.
5. Straight axle or drop axle and how much drop. Odds are high you might have a drop axle as Sunline used them often to lower the campers.
I looked up the 1985 1350 from our brochures in the FILES section on the forum. You have access to this too. See the word "FILES" on the tabs across the top of the forum. Click it and go into the brochures area and look for 1985 and download a copy.
It is fuzzy but it looks like the GVWR of the camper is 1,610 lb. Dexter makes a 1,000 to 2,200 # axle they call the D20 There are several brochures on this site
1,000 - 2,200 lb capacity. You can get the 2,200# axle tube with reduced capacity springs if wanted. I would recommend the heavier axle tube at least. They may not have a 1,610# spring pack but more sizes close. Make sure the springs and axle tube can hold the entire weight of the camper. An 1,800 # spring set on a 2,200# axle tube would work or what ever they have close to at or above the GVWR of the camper. Your tires may end up being the weakest link.
Next is where to buy. I bought my axles tubes from Axle Inc. in Elkart IN. I gave them my dimensions and they ordered a made up axle to fit my dimensions. In my case, they shipped UPS right to my house.
These folks know axles and can walk you through the ordering process.
Axle Inc. - trailer axles, axles and service, brakes and drums They have a form you fill out here
Sprung Axle Order Form - Axle Inc. of Elkhart
I had to measure my own to get the info.
Hope this helps.
John
PS. When you install the new axle, the axle alignment needs to be checked on the trailer with the new axle and corrected as needed. Some thrust angle alignment can be moved from the play in the axle spring seat hole and some may need a hanger moved. If the axle is out of alignment with the trailer frame, you will wear tires a lot faster. This post may help, it is on a much larger camper, but the measuring process to the tow ball (thrust angle) and which side of the axle tube faces forward are the same. (yes, the axle tube does have a front and back, the toe alignment can be wrong if installed backwards.)
http://www.sunlineclub.com/forums/f71/tt-axle-alignment-details-long-with-lots-of-pics-10043.html
