RD400F fork mod

[car91r]

OK, here is the second part to the fork rebuild. When I dismantled a second set of RD400F forks, I found they had Gold Valve emulators installed. The damper rods also had been modified. The 2 top holes and one of the bottom holes had been filled. Seems to me I have seen this done to older Yamaha dirt bike forks in the past. May be a common mod to old Yamaha forks or something done when adding the emulators? I have never used emulators before.
Also noticed one set of forks (stock looking) had long progressive looking springs with no spacer. Only required about 10mm of compression to install caps. Other set (modified) had shorter springs with long, about 5" spacer. Required about 2" of compression to install caps. Also had Goki air caps.

[IR8D8R]

Installing Gold valves for an RD 350/400 involves enlarging original holes in the steel rod and drilling extra holes in the bottom to increase fluid flow to the valve. That lets the emulator handle the flow control instead of the hole size. Some versions require drilling the cast piston "head" at the end of the rod or cutting off the top.
I don't remember any part of the instruction calling for plugging holes in the steel rod, if that's what you're saying.

https://racetech.com/ProductSearch/12/Yamaha/RD400F%20Daytona/1979

https://racetech.com/page/title/DRod%202-2%20KYB%201970s

They work very well. The install is a little fiddly but not too challenging if you have a drill press.

IR8D8R

[paul1478]

Chuck had a how to at one point, not sure if it is on this form or the old one. I don't see it on his page but it was step by step.

[car91r]

Thanks for the info. Looks like I will need to modify the stock damper rods for the emulators and move the modified dampers to the spare set. Then a comparison will be in order. I'm rather slow with my projects, but will get there eventually.

[teazer]

The two holes at the top are rebound damping and most forks came with insufficient damping, so the answer was to fill one with bronze weld.  The Emulator takes care of compression damping, and that requires additional holes at the bottom of the damper rod plus on some forks the top of the damper rod needs to be modified to allow the oil free access to the emulator.

Details on the race-tech site.

[sav0r]

Rebound damping is the most important of the damping. You have to control the spring. If you can control the spring in rebound to a satisfactory degree, then you get to play in compression. In your example, Rich, you might be dealing spring rates a good bit higher than stock, which would require more damping. It's worth a check anyways.

[car91r]

OK. Have the damping rods switched. Modified the ones to use the emulators by drilling the damping rod holes correctly. The directions refer to a DVS set up. Being as I am not the original purchaser, I do not have this info. It would appears these valves were never set up. They have a silver spring with no paint mark I can see and were adjusted one turn in. Enough to hold the assembly together it seems. Only one bleed hole. I emailed Race Tech Support to see if I could get the DVS info. Haven't heard back. Maybe someone that has set these up can offer some advise.

[RDRoy]

Daytona 35mm,400 34mm, i installed emulators i got at mikes xs they work fine hope this helps,i think chucks mod was for 34mm.?

[car91r]

Race Tech responded with the info I needed. Many thanks! These were obviously never set up by the previous owner, just dropped in and run. They are set up for the Daytona correctly now. Just need to finish the rest of the bike now.