School me on rear suspension set up

[Marmot MB]

2008 Arctic Cat M8 Fox Float air rear shock. coil over front rear shock

I have been trying to figure out the set up and reasons of the front rear skid shock.

Mine at present it set to have the spring as tight as possible. (done by previous owner)

My rear seems to sag alot, I checked and set the rear shock pressure to 150 PSI settled (cold)

I have no idea how to set up the front rear shock and what a tight spring VS a loose spring will provide in handling etc....

Also I am not sure what the brass screw at the bottom of the shock does, I tried searching found very little info on the front rear shock. I suspect rebound ?

 

[CatMan16]

I had the same sled and never ran my spring on the front skid more than half way. Those sleds transfer weight off the skis easily and I would suspect if your spring is that tight you have very light ski pressure. Unless the limiter straps are pulled down really tight that might compensate the spring pressure. How does it ride on trials? Does it want to push through the corners and not turn? On my float I ran it at around 120psi and I didn't have any sag issues. I sold the sled last year with 2400 miles on it and it was still fine and rebounded properly. The float rear shock has been know not to be the best setup for a rear shock and some may have been better than others.


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[sc800]

My front skid shock is cranked right up and I generally run 145-150 psi in the rear. Very little sag. If your getting sag your back shock is likely shot.

 

[Marmot MB]

The limiter straps are not slacked at rest, but they are set to the longest they can be with what is available right now.

On the trails is hard for me to say, this is my first sled I have ever really ridden on trails. I found standing up others seemed to make corners much easier with out having to transfer any weight over on most corners (Doo Summits) If I leaned accordingly in corners I could keep up to others, but noticed they did not have to make the same movement.

I found if I sat down on trails and just shifted my weight to the side a slight amount I could fly around corners without much effort but it was always a fight to keep it from drifting outward. (lots of steering input)

Front shocks are probably 60% tightened for spring tension, they were 85% and I loosened the spring and it handled alot better. may try loosening spring some more ( I am only 160 #)

of note it seems to dart about on trails, I noticed last night one ski is pointed outward more than the other, easy fix of the knuckle joint, and I am going to try to toe it inward slightly.

So am I correct that if the front skid shock has a compressed spring it causes less front ski pressure ?

I read that adjustment of this can assist with trenching ? but is loose spring or tight spring less trenching ? I found I got trenched a few times when I really thought I should not have.

I had the same sled and never ran my spring on the front skid more than half way. Those sleds transfer weight off the skis easily and I would suspect if your spring is that tight you have very light ski pressure. Unless the limiter straps are pulled down really tight that might compensate the spring pressure. How does it ride on trials? Does it want to push through the corners and not turn? On my float I ran it at around 120psi and I didn't have any sag issues. I sold the sled last year with 2400 miles on it and it was still fine and rebounded properly. The float rear shock has been know not to be the best setup for a rear shock and some may have been better than others.


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[Marmot MB]

if the rear shock is shot it should not hold pressure ? IE set it to 125 PSI and in a ride or two it is greatly reduced ?

of is the rebound ability separate to the pressure in the chamber ?

My front skid shock is cranked right up and I generally run 145-150 psi in the rear. Very little sag. If your getting sag your back shock is likely shot.

 

[X-Treme]

Don't toe it in. Snowmobiles are supposed to have a very slight toe OUT.

 

[CatMan16]

I should have mentioned also that even set up properly those sleds aren't great on trails but they aren't really made for trails either. I would loosen the spring some and see how it rides. Pretty easy to mess around with this setting while you are out riding unless it gets iced up. The more compressed the front skid spring is will increase the down pressure of the the front of the skid. This will result in less pressure on the skis. Not sure about the trenching and the relation to spring tension but I was told to keep the limiter straps loose to help get the sled up on the snow easier. Which would mean it wasn't trenching but my old sled did trench compared to my friends Dragon. When you are working on the front end to align your skis check your a arms for bends and for cracks in the bushings. I bought my 08 used and the skis were out of line when I got it. I straighten the out and rode it for a season the noticed the bushings were cracked and when I pulled it apart to change them I found that both my left side a arms were bent. When you set your ski alignment you want a 1/4" toe out.


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[CatMan16]

This is what I found when I took mine apart.

 

[Marmot MB]

Thanks for the toe tip. I set mine to 1/4" and re-aligned the steering to ski set up. it was way out. one ski 1/2" toed out the other nearly 1". squared it all up with the track using a straight 2 x 4 against the track on each side, bars ratchet strapped exactly straight, and set each ski the same against the 2 x 4. then re-measured from backcarbide bolt to front carbide bolt.

each ski is 1/4" toed out from center, giving 1/2 Total.

Reduced front skid shock spring tension, likely by 1/4" of thread. it is sitting just above half way now of the total thread length.

re-checked rear fox float pressure and it is at 150 PSI. I think i will leave it there, easy enough to trail reduce it as needed.

with the garage warm now it seems to creep back up, wouldn't say it springs back up like dirt bike or road bike rear shocks raise up after loading, but it is going back to full extension.

Now I just need to get out and test ride it.

Don't toe it in. Snowmobiles are supposed to have a very slight toe OUT.

 

[Marmot MB]

Thanks for the pics, I checked mine and they all look okay, the previous owner certainly gave the front some sort of impact as the alignment was way out when I got it. there is some sign of stress but not terribly bad.

If I stumble across new uppers and lowers for cheap I will replace them just to know it is square.

This is what I found when I took mine apart.

 

[CatMan16]

You may have a bit too much toe out still. I think it is suppose to be a total of 1/4"

 

[X-Treme]

1/2" of toe out is too much. You want 1/8" - 1/4" TOTAL toe out. 1/16" - 1/8" toe out per ski.

 

[Marmot MB]

Crap ! I had a feeling !

Back to the man cave I guess.

There is worse things in life than wrenching !

You may have a bit too much toe out still. I think it is suppose to be a total of 1/4"

 

[HILCLMR]

Loose limiter straps do nothing for getting on top of the snow, think of it like this. When your hard on the gas the driveshaft is pulling on the track, when it does that, it's pulling from your rear idler wheels, this causes the front of the skid to extend fully, causing a steeper approach angle. If the center spring is jacked up tight then there is no way the snow will compress it and let the sled climb on top...alla trenching.
You need to describe what you want your sled to do, Wheelies? loosen limiters all the way and crank the center spring right up. Climb mountains with limited ski lift and get on top of the snow? Tighten straps and soften center spring.
There are other options as far as set up also, however concerning your rear shock sagging out, how much sag does it have? you always want a little bit of sag, because when your riding you want the rear to extend to help soak up bumps, look at desert racer suspensions. They cycle down almost as much as up for a reason. I'm not saying your shock is good, it may need a rebuild. But super stiff spring settings won't get you what your after.
My $0.02