C15 fork improvements

[DAVE BRADY]

Hi,

Has any one found a way to improve the standard C15 forks?  Specifically improved rebound damping of which there is non in a standard set up.

Dave.

[rhyatt]

I've only resorted to different grade oils, nothing mechanical

[limeyrob]

Are the dampers in correctly and in good condition (40-5025)?  There is probably not wear in the stop nut 40-5030 but its worth a look.  How about the washers 40-5047?  I can't remember, do these help rebound damping?
As above, start with a flush then refill to the correct level with the correct oil.
When were they last drained?  They are notorious for filling with water. 

[DAVE BRADY]

Hi,

Oil replaced recently and what came out looked quite good.  The fork action feels fine but on bumpy roads they top out on the rebound.
I thought of fitting external dampers but they would look wrong.  There are kits, believe it or not, for Honda C50/90 type bikes.

Dave.

[V500]

Many BSA tele forks top out. It's mildly annoying, but at least it's possible to fit Dow dampers to bigger BSA's, and they work well. 

[rhyatt]

from memory the correct C15 grade is sae20 - which i use - and they occasionally top out with a mild clunk.
in normal use they are fine - I have been tempted to use sae30 which is on my list of jobs to do next summer - no point in trying it over winter

[limeyrob]

BSA forks top out, you get used to it .  Thicker oil helps a bit because they compress less.

[scifi]

Try eating less sandwiches...  But seriously, they have hydraulic bump stops so the 'bottoming out' impact is reduced.   It is more likely a problem with the spring rate, being matched to skinny 1950's riders.  At least you know you are getting the full amount of movement, that they were designed for.

I have tried to find a silicon oil (for trials bike forks.) but the grade is usually not mentioned, and I guess it would be more like a thick runny grease.

[DAVE BRADY]

Hi,

It is on the rebound rather than compression and there is no rebound damping.  My be I will try a slightly heavier grade of oil.

Dave.

[limeyrob]

Looking at the parts in detail I think there is some rebound damping, just not much.  The A/ B series forks are often described as having no rebound damping and there are mods / kits (ie Eddie Dow) which put in proper rebound damping but reduce overall travel.  But I don't think its fair to say there is none, one the A / B forks the oil is sucked between the fork bushes and has to be pushed back out.  On the C15 the whole of the damper tube is in oil and when the forks are fully compressed its all up in the fork leg having to make its way back through the holes in the bottom of the stanchion.