I'm looking for assistance with a disturbing clunk at the top of fork travel in my 1977 RD400E, even when going over small bumps at low speed.
The clunk is disturbing to the point of not wanting to ride the bike.
I've been refurbishing the bike, tip to tail, over the winter, added Vape ignition, many parts, paint, top end.
New fork tubes, have now added progressive springs, tried different weights and levels of fork oil.
The clunk is at the top end of travel when forks extended after a bump in the road, nasty clunk felt through the bars.
The steering head seems fine, new bearing, adjusted to specs.
I've owned 20 bikes over the decades, including an RD400 back in the day, and have never experienced anything like this.
Any and all thoughts would be much appreciated.
I'm stumped, as is John at Economy Cycle......
Hemi
What kind of tubes did you use? I had a similar complaint with a set of tubes from Forking by Frank that I never was able to resolve.
reduce the preload.
if theres a spacer, use a shorter one. (can make one out of PVC if need be)
I don't think it's any of the above. I ran into the same problem. There's some hardware at the bottom of the fork tubes that you needed to swap, correct? It's very important that you get that back in the right way. It will go together either way but I'm pretty sure it has something to do with dampening control in that direction. I couldn't tell you which way is right or wrong because I just figured it out by trial and error. It wasn't my bike so someone else did the swap, I noticed the "top out" problem and just started swapping and flipping parts. I would bet that's the problem. Maybe one side is right and the other is wrong or maybe both are wrong.
Thanks Jspooner,
Yes, the previous owner installed the new fork tubes.
Perhaps the damping rod was reassembled incorrectly?
Any other ideas out there would be appreciated.
There are no spacers with the progressive springs.
Either way, with progressives or the stock springs and spacers, there is about a 1" extrusion out the top of the forks before screwing the fork cap back on, which I believe is about the correct amount.
Hemi
It's not the dampening rod. Can't really do anything wrong there. What I'm talking about are actually at the bottom of the tube on the inside. If you pull it all apart and remove the dampening rod and look at the bottom of the tube you'll see s9me stuff held in with come c-clips. That's what I'm talking about. Normally you leave that stuff in tact when working on the forks but when you replace tubes you have to remove then and reinstall them in the new tubes.
Also,
The fork tubes were supplied by HVC Cycle- part number 1A0-23124-00-00, 1A1-23124-00-00
Hemi
Ok,
Thanks Jspooner,
Looks like it time to disassemble the forks.
Hemi
In all honesty, I thought it was all of the obvious stuff too. Before you remove that stuff see if you can fine a diagram that shows it. If I remember right it can go together a few different ways as far as the actual order of the parts and which way they are flipped, but only one way is correct.
Hemi, I'm reassembling my fork tubes right now and i'm also using the progressive springs. On both Economy and HVC site it says to cut the springs 1.5". I have cut mine.
However, there is no mention of not using the spacers. With the top fork tube fully compressed into the lower tube, I have about 4" of spring sticking out. With the top fork tube fully extended, my spring is not exposed at all. In fact, it's about 1.5" down inside the tube.
STLMike,
That's very interesting.
Let me know how that works out for you when you ride your bike after reassembly.
I've been talking to John at Economy Cycle. He sold me the progressive springs.
He has 2 personal RD400's, one with progressives and the other with stiffer springs for the track.
He hasn't mentioned cutting the springs, and I believe the spacer is supposed to be removed with progressives, leaving about an inch of spring above the tube with forks extended prior to replacing the caps.
Before I switched to progressives, the forks had the spacers and stock springs, and had the same problem, a nasty clunk at full extension.
Hemi
1" extension, or less, sounds about right coming out of the top. lack of sag on ft end would be a big indicator of an issue. 4" is WAY too much to have to compress to put the cap back on.
I cut the 1.5" off mine and just reassembled. There was no way the spacers were going back in. I also emailed John to be sure.
Quote from: Jspooner on April 13, 2024, 02:42:46 PMIt's not the dampening rod. Can't really do anything wrong there. What I'm talking about are actually at the bottom of the tube on the inside. If you pull it all apart and remove the dampening rod and look at the bottom of the tube you'll see s9me stuff held in with come c-clips. That's what I'm talking about. Normally you leave that stuff in tact when working on the forks but when you replace tubes you have to remove then and reinstall them in the new tubes.
I think it's called the top out valve. It causes real strong damping the last 1/4" of topping out. Remove the snap ring on the inside of the fork tube and pull the piston/bushing out and it should be in there, aluminum valve and spring.
(https://i.ibb.co/9YyfMQR/20240414-074827-1.jpg) (https://ibb.co/BsT7108)
Quote from: 1976RD400C on April 14, 2024, 07:58:54 AMQuote from: Jspooner on April 13, 2024, 02:42:46 PMIt's not the dampening rod. Can't really do anything wrong there. What I'm talking about are actually at the bottom of the tube on the inside. If you pull it all apart and remove the dampening rod and look at the bottom of the tube you'll see s9me stuff held in with come c-clips. That's what I'm talking about. Normally you leave that stuff in tact when working on the forks but when you replace tubes you have to remove then and reinstall them in the new tubes.
I think it's called the top out valve. It causes real strong damping the last 1/4" of topping out. Remove the snap ring on the inside of the fork tube and pull the piston/bushing out and it should be in there, aluminum valve and spring.
<a href="https://ibb.co/BsT7108"><img src="https://i.ibb.co/9YyfMQR/20240414-074827-1.jpg" alt="20240414-074827-1 (tel:20240414-074827-1)" border="0"></a>
Thats what I'm talking about.
Thanks Jspooner!
That gives me something to work with.
Found a couple parts diagrams.
Looks like there are several parts that come together in the bottom of the forks.
Perhaps the previous owner re-installed incorrectly.
Hemi
Jspooner,
I've checked several parts diagrams and I don't see the springs you noted at the bottom of the forks?
I can't seem to paste a photo here.
Hemi
Quote from: Hemi on April 14, 2024, 01:10:59 PMJspooner,
I've checked several parts diagrams and I don't see the springs you noted at the bottom of the forks?
I can't seem to paste a photo here.
Hemi
I took that picture this morning of the fork pieces. I don't think they were ever available?? Yamaha had the fork tube come as an assembly with them installed.
There are several possible contributing causes to this "top out clunk" phenomenon:
- Too much spring preload and/or too stiff spring rate
- Not enough rebound damping (Oil too thin, or someone may have modified or messed with the damping rods/ valving)
There should normally be significantly more damping on the rebound than in compression. Just remove the spring, add
a little more oil, and test by hand.
- Excessive unsprung weight. Like a heavy aftermarket fender, a second brake disc and caliper.I had this "clunking"
during accelleration on my then totally stock "Euro" XS650, with extremely heavy OEM dual front discs and a heavy
OEM chrome front fender. After upgrading to a much lighter brake setup, etc, I lost around 10 lbs of unsprung
weight, and the "clunk" was gone.
- Some bike also have a "top out spring" that will give the forks a "soft stop" as they extend fully. These are often
20-30 mm long, and sit on the outside of the damper rods. Just google "top out springs".
the top out springs aren't in the 400 forks... but they are in the xs650 ones. just as a point of interest.
Thanks Dvsrd,
I've tried more fork oil, thicker oil, less oil.
With more oil, the forks seemed a bit more extended at rest, felt stiffer, less sag, still had the clunk.
I'll check the other things you mentioned.
Hemi
Quote from: Hemi on April 15, 2024, 04:43:28 PMThanks Dvsrd,
I've tried more fork oil, thicker oil, less oil.
With more oil, the forks seemed a bit more extended at rest, felt stiffer, less sag, still had the clunk.
I'll check the other things you mentioned.
Hemi
I'm still going to say its the "top out valve" as 1976RD400C calls it. As I said, you can assemble the parts MORE than one way, but it only works ONE way.
Jspooner,
Appreciate your advice. Seems you've experienced the very same issue and found a fix.
Fingers crossed that's the issue.
Sounds like it took you a few attempts to get the parts inserted correctly.
Hemi
Quote from: m in sc on April 15, 2024, 03:52:35 PMthe top out springs aren't in the 400 forks... but they are in the xs650 ones. just as a point of interest.
Mark, yes the later years of XS650 had top out springs, but my 77 XS650D does not. It is really a bit weird that the rather wheelie prone RDs did not have them :)
so, is there any consensus on the forks with top out springs being preferred over those without? If so, maybe an easy bolt on improvement?
IMHO it doesn't matter. i've never had this issue unless the preload spacer was too long or the wrong parts were in there. somebody did some 'creative' shit to the 70 R5 and one was way longer than the other and used to do this. stuffed regular RD internals in it and swapped the tubes and haven't had an issue since. It's not a common problem on rds unless somebody was mucking about in there.
Jspooner,
You nailed it!
Disassembled the forks today, and found the top out valve had been reassembled incorrectly by the previous owner.
The oil flow ring that contains the spring was upside down, easy to see how that could happen.
No more clunk at extension, hard to believe that little spring and ring make such a big difference.
Many thanks!
Hemi
Quote from: Hemi on April 19, 2024, 07:49:19 PMJspooner,
You nailed it!
Disassembled the forks today, and found the top out valve had been reassembled incorrectly by the previous owner.
The oil flow ring that contains the spring was upside down, easy to see how that could happen.
No more clunk at extension, hard to believe that little spring and ring make such a big difference.
Many thanks!
Hemi
Glad you figured it out. I remember thinking the same thing when I figured it out.