Front-end diving

[Evan]

35 miles on the 82 V, and with having been riding the 82 Honda CB900F as a reference point -- Is it normal for the Vision to have so much dive? 

It has the stock single disk, but with the Stainless Steel brake line (and rock solid feel), it seems to brake well.  When braking (even moderately), it seems to dive 3-4 inches!  I am not sure of the state of the fork oil, so I have been thinking of just changing the oil to see if that improves things (the procedure under the Yamaha manual's maintenance section looks fairly straight forward).

I know there will be a ton of opinions on this, but I am 5'9" (can stand flat footed -- which is not the case with the CB900), 200lbs (and Houston is hot) -- should I stick with the 15W oil?  How much time does this take to do the first time (never drained/filled forks before)?

[h2olawyer]

Some front end dive is normal on a Vision.  However, you could be experiencing worn out springs.  The 15W fork oil is considered by some to be too heavy.  I suggest you check your fork springs length to see if they've passed their prime & replace them with a set from Progressive.

H₂O

[kwells]

a good stock spring will still dive too much IMO.  I am running 15wt oil with progressives and found it a much better front end

[YellowJacket!]

Check to make sure you even have fork oil.  When Lucky and I did my tapered bearings last year, we decided to changeth the fork oil too only to find out that there was almost none in one of the forks and none at all in the other.  About 1 month before that, I thought it handled REALLY well on the Dragon....much to my surprise.  :o

David

[Evan]

I read somewhere that swapping the fork oil should take around an hour the first time -- for me it took over 2 last night.  The left fork definitely had ATF (since it was red), and quantity look about right.  The right fork did not have ATF (brown/black), and the quantity looked about right.  When I stopped by the stealer yesterday to get some fork oil, he did not have any 15w, so I went with the Bel-Ray 20w (since it is fairly warm in the USA's 4th largest city).  Despite the fact that the price on the carton said $8.59, it rang-up at $12.xx ("guess that sticker did not get changed"!!!), so he discounted it by 10% -- definitely earned the title "stealer"!

With 20w the ride this morning was definitely firmer.  Will have to wait and see if they are too stiff or about right.

What is ATF equivalent to ???

Sure wish my convenient choices were not limited to stealer, AutoZone & Walmart!

[Lucky]

ATF is 7.5 wt

[Cdnlouie]

The key area of concern for front end dive is to stiffen up the springs as mentioned by going to the progressive springs or setting the proper sag for the front end.  The 82 Vision is way too soft on the front and way to stiff on the rear.

The 83 corrects this with a new rear spring and air on the front.  You can also increase the spring preload by adding different lengths of PVC spacers in the front end until you get the stiffness that you would like.  Just adding a heavier weight oil is going to create some pretty nasty wheel bounce at higher speeds because the fork is real stiff and not likely to absorb the shock.  You are making a trade-off here unless you get the right pre-load on the front spring, to handle your weight.  I wouldn't go over 15wt as that is stiff enough for even hot areas.  Your ATF is definitely way too soft unless you like the big "caddy" feel, and drive it like one.

Then again, you can add air to your front forks (install air valves) and stiffen them up as well, so you do have some choices  :).

[QBS]

What would be the result of just adding air to stock '82 forks?

[h2olawyer]

Exactly the same as adding air to 83 forks.  I put some air valves on my 82 caps a few years ago.  Stiffened them up quite nicely.  Have since swapped to 83 forks, but air in the 82s is a fine improvement.

H₂O

[QBS]

Seems like air should be the first modification made in search of better forks on the '82.

[h2olawyer]

Air valves are inexpensive & easy to install.  When combined with progressive springs, you won't even recognize them as the same forks that came from Yamaha!  (Yes, that's a good thing!)

H₂O

[Night Vision]

can you explain the theory of air forks?  :-[

I don't understand how the air stays in the forks.
are fork seals air tight?
there's always a slight oil film on the tubes.
is that oil film enough to seal the air in?  ???

[YellowJacket!]

Its like a bicycle pump.  They are effectively sealed up and when pushed down on, the air gets compressed...
except in a bicycle pump, the air goes out the hose. I was playing around with one of my 82's when I was doing the 83 upgrade.  It had no spring or oil in it but it was capped off and still would compress and rebound back up.  I think the oil seal expands as the pressure increases.  The slight bit of oil on the tubes si like a lubricant and seals the gap between the piston and the outer tube.
Just look at the tubes on a big dump truck or back hoe, they have a film on them too.

David

[Cdnlouie]

The forks are 'air-tight' as long as the seals and o-rings are sealing properly.  It does not take very much air pressure to make a compressible 'air spring.'  There is a lot you can do with that 'air spring' which is similar to increasing pre-load on the steel spring.  Of course the behaviour characteristics are a bit different (between air and coil steel) but each supplies something to the suspension equation. Air has the convenience of being easily adjusted when you change your riding needs such as adding two-up and maybe some luggage.  It's a lot easier than changing your fork spacers  >:(.

When you increase the air pressure you increase the pre-load on the 'air spring' so you stiffen up the suspension for carrying heavy loads.  Now you lose your soft ride as you increase air.  You can even adjust the 'spring rate' of the 'air spring' by lowering your fork oil to give you a larger air pocket (or higher for stiffer forks) which can give you sofer ride for small bumps and yet still be good when hitting larger obstructions.

You need to assess what your handling need is for the type of riding you do and make the adjustments that give you that result.

Enjoy your ride,

Louie

[Lucky]

Yup ,i have a balance tube installed between my forks (1/8" copper tubing with fittings tapped into my tubes between the tripple clamps) and a small air guage in place of one of the fill caps. 

i use a sports pump to fill them to 6 psi unloaded. it sits at 11 psi with me on the bike.  this way, adjusting the air pressure is easy. overfill to 10 psi, when you remove the pump you will lose some air, it's unavoidable, but then i can press in the shrader valve with a pointy object & carefully bleed down the air to 6 psi.

i installed the balance tube over 2 years ago & it's still holding at 6 psi. i haven't needed to add air since.

i do get dirty rings on the tubes, but it's still holds pressure.

--Lucky

[GT @ oh.]

Can you post a pic of all the fittings you used once you tapped the 82 fork caps? This is something I would like to try while I'm replacing the sightglass and fluid...... as it shouldn't cost me to much to do.....Right? I think the balance tube is the way to go.         This post was a good post it answered most all      the q's I had in mind to ask