2004 600HO Rear Suspension Help?

My 2004 600HO rear suspension has kicked my *** since I bought it, great in the deep powder and pretty tough to ride in all other conditions. Based on the manual recommendation of sag 3 to 4 inches of sag, and this forum I decided to see if the Hawk could be improved. Checked my sag and basically there was none with me on it, 220 lbs, checked the preload on the shocks this and found the vertical shocks at zero preload and the front shock was set at 33mm from the base of the threads to the locking ring. Took all the preload from the front shock and maybe got about one inch of sag with rider, so it is way too stiff, just as I have always suspected but never did anything about it since I mainly only rode it when the snow was deep.

Will be trailering the 600 home and pulling the shocks and replacing the springs with lighter springs. Any recommendations would be greatly appreciated.

Thank you.

This thread should get you in the going in the right direction...

http://www.snowest.com/forum/showthread.php?t=56894

So is this the correct set up?

"The 2004 / 2005 600 Hawks All Ran A 320 Lb Rear Spring Rate On The Rear Skid Vertical Shocks, 2006 All Ran A 280lb Rate Spring On The 3 Shocks. 2006 600 Valving Was Different By 2 Shims In Each Rebound Shock Stack. We Set Up Quite A Few Older 600's To 2006 Stack Specs With Good Results. I Never Removed The Front Shock Completely, Just The Spring. The 2008 Models All Run Without The Front Skid Shock. This Set Up Is Very Very Soft. By Leaving The Front Shock On The Bike Seems To Take The Chop Better Without Packing Up The Rear. These Shocks Seem To Loose Nitro Charge Over Time, All Require A 300lb Charge. I Also Run All Hawks In The Lowered Position And Drop The Front In The Forks. I Currently Run A 2007 800 With The Front Spring Removed, The Bike Feels About Right, Very Predictable On And Off The Trail. Just A Few Thoughts On The Subject."

Still not clear on what spring rate to use.

It looks to me that you need to get the two 280lb springs for the back two shocks,remove the front coil from the front shock and revalve all three to the 06 specs(changing or removing) two shims from the rebound stack and recharging them all to 300lbs of nitrogen)

JAYHAWK was the original poster of this info-he works at a HawkDealer,contact him for the correct parts to get you fixed up.

Thank you

This is what I'm going to do!

I have the same issues with the rear suspension - stiff as a board on initial travel - no sag. I did some research - here goes.
The hawk suspension is a "falling" rate set up - i.e. - the leverage of the swingarm increases aginst the spring as the rear sags, making the spring rate DECREASE as it compresses. This is NOT a good thing. Straight rate springs will ALWAYS feel to stiff at first then also bottom out on the big stuff - worst of both worlds. I Took off the middle spring, lossened the preload felt OK on the trail, but would stay stuck compressed after a big hit.
The 503F had a progressive spring of 185/465 with NO middle shock. Still feels kinda stiff at first and to soft at the end.

I talked to arep from works shocks, going to order a set of triple rate springs for my 05 600HO. Did a little trig last night and roughly worked out this info on the rear suspension

Measured from the swing arm end we get about 14” of travel with about 6 inches of total shock travel.

First 4” of compression of the swing arm yields about 3” of shock travel. - Effective spring rate is ~3/4 of spring rating

Middle 5” of travel of swing arm yields about 2” of shock travel – Effective spring rate is about ~2/5 of spring rating

Last 5” of travel only yields the last 1” on the shock - Effective spring rate is only 1/5 of spring rating!!


I am replacing each 280 in/lb spring with three shorter springs – 100 in/lb; 250 in/lb; 500 in/lb, and still leave the middle spring out.

Predicted results

First 4 inches

-Before (280 in/lb x 2) x ¾ ratio = 420 in/lbs = STIFF
-After (100 in/lb x2) x ¾ ratio = 150 in/lbs = comparably soft (maybe too much!)

Middle 5 inches

-Before (280 in/lb x 2) x 2/5 ratio = 224 in/lbs = getting better
-After (250 in/lb x2) x 2/5 ratio = 200 in/lbs = progressively stiffening!

Last 5 inches

-Before (280 in/lb x 2) x 1/5 ratio = 112 in/lbs = why my machine was staying fully compressed!
-After (500 in/lb x2) x 1/5 ratio = 200 in/lbs = same as middle

This yields a very gentle progression as opposed to way to stiff at first and then WAY to soft at the end

This three piece spring assembly is about 1 inch longer than my originals. Means you can crank down the preload and really make a difference when the springs transfer to the higher rate.

This may totally suck, and it’s gonna cost about $600.00 and I sure my damping will be all wrong, BUT If I can make this thing supple in the back this thing will rule the whoops!

WORKS shocks sell a “Heart transplant” for the KYB’s which changes the piston out to a clicker type damping setup. It is a service where you send out your shocks 5-6 week turn around. Click it for the trail - then click it for the deep! Doing that this summer.

Please post results.

The progressive spring makes sense, please post your results.

The first thing I am doing is removing the shocks and measuring the rate, if they are the 320# that will explain a lot. Guessing some combination of the proper spring and re valve will get me close.

Will post results as changes are made and tested.

holy grail !

stay tuned for all the answers u will need for the "perfect" suspension for the hawk, i will get pics and explain very soon!

Holy Grail Batman!

877snowhawk said:

stay tuned for all the answers u will need for the "perfect" suspension for the hawk, i will get pics and explain very soon!

Click to expand...

Lets us know what you did!

Thanks.

877snowhawk said:

stay tuned for all the answers u will need for the "perfect" suspension for the hawk, i will get pics and explain very soon!

Click to expand...

Yes! Please save me from myself and the mess I am about to create

2004 600HO Actual Spring Rates

Had all three springs from the shocks in the rear suspension tested and the results are:

R Rear Springs: 348 lbs @ 1 inch, 697 lbs @ 2 inches
L Rear Springs: 348 lbs @ 1 inch, 697 lbs @ 2 inches
Middle Spring: 296 lbs @ 1 inch, 584 lbs @ 2 inches

Force required to compress the rear shocks ONE INCH equals 992 lbs.

Force required to compress the rear shocks TWO INCHES equals 1,984 lbs.

More research needed.

Response from AD Boivin

Hi Carl,

Your testing is right. The front shock is a 280lb/inch and the rear spring are 340lb/inch. The thing that you don’t take in consideration is the leverage from the single swing arm instead of the short one like a regular suspension. If you don’t jump around and a drive more like a Enduro Bike. There is what you need:

The first thing to do is to soft the valving in the front shock of the rear suspension. With a softer valving, like a DB-05, you will enter the bump better and soft the geometry of the suspension.

If this is not enough, We can replace the 340 lbs/inch spring with 280 lbs/inch that we have in stock.

Just be carefull with the softer spring set-up, You may end up bottoming because the suspension is a falling rate suspension.

You don’t want to much sag with this suspension because the suspension get softer the more it compress. So yes it fill stiff at the beginning but after you have it start to work, it will soft up on you. So don’t get to crazy on the spring for a softer ride.

Want I would do is send you 2 x 280lbs/ inch spring with a shock valving sheet for the front shock.

If you can’t valve your shocks, We can do it here for you, just send me you shocks and I will do it for you, in house.The 280lbs spring are 67.22$ / each . The valving should not be that expensive, the oil is what is expensive.

Let me know what you think about this,

Jean-François Couture
Ventes / Service à la clientèle
Sales / Customer Service
AD Boivin Design
jfcouture@adboivin.com
(418) 838-3783 ext 221 / 222
Fax : (418) 838-3957

I have 280's you can have after this summer

After reading this, it only confirms the main issue - FALLING Rate suspension system. After looking at the zx2 it also is a falling rate unless I'm totally missing some hidden linkage. The only real soloution is multi rate springs! Soft at first and then WAY Harder to make up for the falling rate. I will have my 3 280's for sale after i convert mine to different springs.

I can see why they may want a falling rate suspension. It allows the machine to stay up in its travel on smoother trails thus keeping the weight forward on the ski. I would be afraid of losing ski pressure with a more progressive system.

The reason is..

Because of the shock has to sit in side the track, and has to lay flat with the swingarm when full compressed as not to interfere with the track. All the old motorcylces with dual rear shocks have a falling rate suspension. Early in the suspesnsion revoution, manufacturers went with a progressive spring to offset the falling rates of the conventional dual shock suspension. Only problem - falling rate dampneing (built in by the design) combined with a progressive rising rate spring still not very good.
EVERY current suspension on every highend machine - dirt bikes, street bikes; F1 race cars, hell even accords have a LINKED suspension system that is progressive by design. This allows a straight rate spring and dampning to have a soft initial spring rate AND soft dampning for small defelections and very aggressive spring rates AND dampning for those big gullys. The physics is simple. Finding a real world engineering soloution that is both functional and reliable is a whole nother animal. Hence the cunumdrum we find our selves in. One thing for sure falling rate = BAD.
I took the middle spring out of my 05 600HO, was really concerned about ski pressure, I liked the increased transfer on the ski, blip of the thottle and it's gone, but I don't have the trail adapter, which seems much more affected by ski pressure...

SeattleSnowHawker said:

Because of the shock has to sit in side the track, and has to lay flat with the swingarm when full compressed as not to interfere with the track. All the old motorcylces with dual rear shocks have a falling rate suspension. Early in the suspesnsion revoution, manufacturers went with a progressive spring to offset the falling rates of the conventional dual shock suspension. Only problem - falling rate dampneing (built in by the design) combined with a progressive rising rate spring still not very good.
EVERY current suspension on every highend machine - dirt bikes, street bikes; F1 race cars, hell even accords have a LINKED suspension system that is progressive by design. This allows a straight rate spring and dampning to have a soft initial spring rate AND soft dampning for small defelections and very aggressive spring rates AND dampning for those big gullys. The physics is simple. Finding a real world engineering soloution that is both functional and reliable is a whole nother animal. Hence the cunumdrum we find our selves in. One thing for sure falling rate = BAD.
I took the middle spring out of my 05 600HO, was really concerned about ski pressure, I liked the increased transfer on the ski, blip of the thottle and it's gone, but I don't have the trail adapter, which seems much more affected by ski pressure...

Click to expand...

Well an air sprung shock is what we need. I believe there is another thread where someone found an air sprung set up. Have you seen that thread?

http://www.snowest.com/forum/showthread.php?t=47779

these guys use air i think!

http://www.teamfast.com/index.php?main_page=HOME

If I am understanding what a "falling rate suspension" means, as the suspension travels the force on the spring becomes less.

Is this correct?

Its more than force...Its about rate of change of applied force

say at the beginning of the suspension travel you move 1 unit at the swing arm and that same movement on the shock shaft is also 1. So the leverage ratio at the beginning of travel is 1 to 1.

If the suspension was a straight rate you would expect the last unit of swingarm travel would yield 1 unit on the shock shaft. leverage ratio 1/1
This ratio doesn't change.. Ideal for coil springs which are usually one rate.

If the suspension is a falling rate the last unit on the swingarm would yield less movement on the shock say .5 units.. so you have something like .5/1 or 1/2 so the suspension can move more easily through the last unit because it only has to compress the spring half as far.
So the rate falls. from 1 to 1/2. You need a spring that is progressive, some springs are wound to be progressive or you can use air as a spring which compresses in a progressive manner.

The opposite is true for Rising rate, the suspension moves the rate in which the shock shaft travels falls, 1/1 at start goes to 2/1 at the end.
So the rate rises from 1 to 2.

not the most technical explanation but thats how I see it.

so whats the verdict

a buddy of mine is going through all the same issues and experiments on his 06 600 shorty, just wondering what some of you guys have settled on?