What makes a 1979 RD400 Daytona Special

[IR8D8R]

 Get the adjustable preload caps from Economy Cycle. It makes setting the preload 10x easier. While you have it apart you should consider the Gold Valve conversion and new springs. There are cheaper knockoffs online (Mikes XS) but I used the originals. https://www.mikesxs.net/yamaha-xs650-damper-valve-pr-front-forks-77-84-oem-1t3-23170-00-00.html
 The Race-tech kits come with some pieces of 1/2" PVC pipe to use as preload spacers. You can use that instead of the stock spacers. If I recall correctly the stock spacers are around 3-1/2" long? They are just rolled sheet metal like a big single-slot roll pin. The length is spring dependent so you really need to set the preload instead of just using the stock spacer. Stock springs are probably going to be shorter than they were in 1979.
 The Race-tech spring kits come with a handful of fender washers to use for shims on top of the PVC if you need to add more preload. Basically you measure the fork cap threads and subtract that from the amount the spring and cap stick up above the top of the fork. If you have at least 5mm of preload to start you can set it with the adjustable cap.

The "too much preload" photo shows how to measure preload. It's a bad example because it's way too much preload.
I copied the text from the RaceTech instructions:

11 - Setting the fork spring preload is done by making the correct length preload spacers.
Find the recommended preload in Product Search or on your DVS Setup Sheet. [I don't have that info but  correct preload is somewhere between 15 and 35 mm or 15% of sag (% of the suspension depression from the bike's weight)]
 
1. If your forks have Preload Adjusters set them to minimum.
2. If you have a fork with an Emulator. Drop the Emulator down the tube. Install the Emulator Adapter first if required. It sits on top of the damping rod with the Emulator Valve Spring facing up and is held in place with the main fork spring. Visually check to make sure the Emulator is sitting squarely on top of the damping rod or the Adapter.
3. Extend the fork tube all the way.
4. Insert the fork springs into the fork tube on top of the Emulator (No emulator, no problem).
5. Install a steel fork spring washer
6. Install the fork spring spacer tube (1/2" PVC or any size that will fit inside the fork tube). Any length that goes above the top of the fork tube is ok for now.
7. Install another steel fork spring washer (washer-spacer-washer)
10. Adjust the spring spacer tube length (or PVC) to achieve the proper preload.
In this example using the image:
If you are looking for 15mm preload you would shorten the spacer by 46 - 15 = 31mm length of spacer (I guess the 15 mm is the desired preload? Doesn't matter as much if you have adjustable preload. You can start with 5mm and increase by 10 easily).
NOTE: You must have steel washers on both ends of the spacer. The spacer must not rest directly on the spring or the cap.
12 - If there is very little preload the thread on the cap will hit the thread in the fork tube before touching the washer.
Measure from the top of the fork tube to the Steel Spring Washer.
13 -  Measure the Fork Cap Height In this case 18mm.
Calculate the Preload
(Fork Cap Height) - (Top to Washer) = Preload
18 - 11 = 7mm Preload (the 18 is the distance the threads will close when you screw the cap down).
Adjust the Spacer Length or add washers to get the recommended Preload.

The adjustable caps have a self-centering spring washer included. Any washers used as shims go under it.

Hope this helps
IR8D8R

[Andrew S]

Thanks, that does help.  I'll start with a 3.5" spacer and work from there.  If I can outride the stock forks, then I'll pursue some of the emulators.  I've often thought about trying emulators on other bikes, but have been happy in the past with some tuning of fork oil and preload.

[Andrew S]

I realized today that the passenger peg brackets have been cut off, as well as the loop on the left side.  Any chance I can talk somebody into tracing their brackets and loop so I can re-create them here?  Or even better a bent Daytona frame and I can buy the sections I need.  (yeah, right.)