fork antidive removal

[chixson]

Hi all, just wanted to say that you guys rock with all the knowlage and info on here. My new adventure involves the removal of the anti dive feature that I read should be removed. Any thoughts and how to's??? I've noticed that my  bike  ('86) really noses under hard traffic brakeing. My best friend has an "83 XJ 750R seca and his does the same thing, thought maybe I could kill two birds with one stone..lol
thanks

[racerman_27410]

the real cure is a new set of fork springs for the bike..... anywhere from .95kg up to 1.10kg depending on your weight.  add in some fresh fork oil and you will love the difference.


Kookaloo!


Frank

[andyb]

Actually getting damping effect makes a bigger difference.  Moving up from 10w to 15w, and running a larger amount of oil (smaller air gap) will help significantly.

If you're riding roughly, you'll be able to bottom nearly anything, so consider your riding style first.

[chixson]

I'm not riding rough or anything, just a lot of stop and go traffic. I didn't know what the reason was for removing the antidive on the bottom of the forks though. If the antidive where the cause of the excessive diving under braking or just the need for the fork modification as posted on the site.
thanks, great info.

[racerman_27410]

Actually getting damping effect makes a bigger difference.  Moving up from 10w to 15w, and running a larger amount of oil (smaller air gap) will help significantly.

If you're riding roughly, you'll be able to bottom nearly anything, so consider your riding style first.

this is not the way suspension works.... this is a damper rod fork.... the fork oil flows thru holes in the damper rod..... the object is for the oil to be just thick enough to control the movement of the springs without being so thick it will lock up the front end on bumps.

thicker oil cannot flow thru the holes fast enough.........the forks lock up.... sure it will help with the forks not bottoming but at what cost?     thicker oil is not the answer.

the way a fork works.... the springs support the weight of the rider and motorcycle
the oil's job is to damp the movement of the springs.    the right springs with the thinnest oil possible will result in the plushest ride without bottoming out or excessive pitching on the brakes.

remember the forks also have to extend after the bump (rebound circuit) so by putting thicker oil in the forks will be slower to extend after a bump meaning the next bump is gonna make you feel it ..... no we want the suspension to properly support the weight of the bike and rider and move as quickly as possible (in both directions) during its action without pogo'ing/bouncing back (the oil weight controls this in a damper rod fork)

you've got to start with the springs


Kookaloo!

[the fan]

What frank said.

[chixson]

Ok, that all makes perfect sense. So once i get the right combination of spring and oil for my weight, should I still let the antidive on or take them off?? Sorry, I'm a little slow..lol

[andyb]

Don't agree at all.  Yes, if you put 90w or something in there, most certainly!

If you're putting a 700lb package (bike + rider) and grabbing a boatload of brakes, that all ends up on the front wheel, plenty of force being thrown around to bottom nearly any spring that'd be usable.

Slightly increasing the damping simply means that you go through the stroke more slowly and at a more controlled rate, so things move around less.  Using a thicker oil (and more of it) never gave me any issue with the wheel skidding (which is what would happen if it was locking up), and felt fairly good otherwise.

You're both missing some key items:  What shape are the forks currently in?  Has the oil been changed in the past.. uh... 5 years, say?  Ten?  Is there enough oil in there?  Etc.  Throwing money at it is all fine and well, but I'd be quite surprised to hear someone complaining of excessive front end dive anywhere but a racetrack with a stock suspension working the way it's intended.

[racerman_27410]

its a proven fact the fj has weak fork springs...... you need to do some reading on basic suspension and how it works mate.


literally hundreds of people have complained over on the yahoo list for the last 10 years about this very thing....

just cause you 're a moderator dont mean you know everything


Kookaloo!

[chixson]

I bought the bike three yrs ago and the guy I got it from told me he had just gone thru everything and it was good to go. I know, shame on me... I took him at his word..the out side of the forks look great. No leaks or rough edges and nicks.they move smoothly through the range of motion. Maybe its a old rubber hose problem, that I have to apply more force than needed due to expansion in the old hose and it gets to acertain  point and then dives under excessive preasure.  I'll check the levels and see where they are before removing anything, and maybe new hoses are in order.
thanks for the great advice..  

[chixson]

Thanks, will do
chris

[the fan]

I know a few things about how suspension works....

[andyb]

Nevermind, obviously you guys are right.

Every time I've touched my (originally sprung) FJ's brake, the front end dives, the wheel locks, and i'm thrown off.  Bummer, really.

The solution is to tear the front end off and replace it all with something else.  Spend as much as possible, it works best that way.

[racerman_27410]

Nevermind, obviously you guys are right.

Every time I've touched my (originally sprung) FJ's brake, the front end dives, the wheel locks, and i'm thrown off.  Bummer, really.

The solution is to tear the front end off and replace it all with something else.  Spend as much as possible, it works best that way.

that sounds about right.  

seriously... how much do you think fork springs cost ?   a hundred bucks is cheap for the improvement recieved.




Kookaloo!

Frank

[andyb]

Oh, no.  It's not remotely enough to make it work well.  I'd suggest pulling the forks off and replacing them with a minimum spec of WSB forks from no older than the 2005 season.

Three year old fork oil will likely come out even cleaner than it went in.  Sometimes I use my forks to clean oil, it comes out sweetly scented and lovely and clear. 

I'm sure that the brakes having an uneven feel wouldn't cause roughness on the suspension and induce additional dive from the jerky input. 

Of course, it's good to have a PO that rebuilt everything so well, making no mistakes and taking no shortcuts.  Periodically I sell bikes to random folks, so that I can buy them back improved from the care that others lavish on them.