Suspension questions - SC-10

742 Views 16 Replies 8 Participants Last post by bengelp, Sep 30, 2006

QWIKWHIP

Discussion Starter · Sep 29, 2006

Hi all, I have another question. The more I play around with this sled the more things I find to ask. lol

This is on my 99 MXZ 670HO with 3700 miles on it. I notice that on the rear suspension there is a good 3" of "free play". What I mean is that when the sled is sitting on the ground I can actually lift the rear of the sled at least 3" before the track lifts off the ground. Then when I set it back down it drops down that same 3" before the springs hold the weight. And once it's down, the remaining downward travel seems very tight. It doesn't appear to compress any more when I sit on it. And I'm about 160 pounds. Does this sound normal, could the springs be shot or could it just be way out of adjustment? Thanks in advance.

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tughillterror

· #2 · Sep 29, 2006

QWIKWHIP said:
Hi all, I have another question. The more I play around with this sled the more things I find to ask. lol

This is on my 99 MXZ 670HO with 3700 miles on it. I notice that on the rear suspension there is a good 3" of "free play". What I mean is that when the sled is sitting on the ground I can actually lift the rear of the sled at least 3" before the track lifts off the ground. Then when I set it back down it drops down that same 3" before the springs hold the weight. And once it's down, the remaining downward travel seems very tight. It doesn't appear to compress any more when I sit on it. And I'm about 160 pounds. Does this sound normal, could the springs be shot or could it just be way out of adjustment? Thanks in advance.

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3" of free play is a little much, but should be fine for your weight. What setting are your Torsion springs on? You can tighten them to make it sag less, or loosen them to provide a softer ride. also, you might just want to get a set of new Torsion Springs from a dealer. I imagine they are pretty worn out by now.

There's quite a few adjustments you can make on your rear suspension to make it ride the way you want, but the best thing you can do is wait until you get out on the trail to see how she rides.

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QWIKWHIP

Discussion Starter · #3 · Sep 29, 2006 (Edited by Moderator)

tughillterror said:
3" of free play is a little much, but should be fine for your weight. What setting are your Torsion springs on? You can tighten them to make it sag less, or loosen them to provide a softer ride. also, you might just want to get a set of new Torsion Springs from a dealer. I imagine they are pretty worn out by now.

There's quite a few adjustments you can make on your rear suspension to make it ride the way you want, but the best thing you can do is wait until you get out on the trail to see how she rides.

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I'm pretty sure they are on the softest setting. But your right, I should just wait till I can ride it to mess around. It just seemed a little much for free play and was curious.

Maybe I'll look into a new set of springs anyway. Like you said, they've gotta be pretty tired by now.

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bengelp

· #4 · Sep 29, 2006

How long since the shocks have been serviced?

QWIKWHIP

Discussion Starter · #5 · Sep 29, 2006

bengelp said:
How long since the shocks have been serviced?

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Honestly don't know. They could be original for all I know.

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Doomanmxz99

· #6 · Sep 29, 2006

I was going to say look at the shocks also. I have 4000 miles on my sled and I just brought the shocks in for service and I had about the same problem as you. I do have new springs in the rear and that did not seem to help much. Maybe a 1/2 inch but I will let you know on the shocks when I get them back and put it back together.

Got2go

· #7 · Sep 29, 2006

To test the springs spin the rear torsion spring cam adjuster to its highest pre load position then do your "free play" test agian. If there is little or no play those springs should be ok for your weight. If the suspension is pinned ot its max extension go down one position on the cam at a time until you get your desired height / free play. If your cam is allready at max before you start your srings are finished. Those look like the original shocks, if they are, they are completely rebuildable. If they have never had the oil changed and new gas they are way over due.

Highlander809

· #8 · Sep 29, 2006

Have somebody move it up and down and look at your ACM...film @ 11:00

icestew

· #9 · Sep 30, 2006

mine was the shock the exact same thing......

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QWIKWHIP

Discussion Starter · #10 · Sep 30, 2006

Thanks for the info guys. I'll move the cams and see what that does. I'm almost certain they are on the softest setting.
As far as the shocks, they do appear to be the original rebuildables. However, I'm not saying they don't need to be rebuilt cuz they probley do, but I'm not convinced that would cause the rear to sag. I've been working on cars for many years and in my experience a shock is a damper, not a spring. The condition of the shocks should have no effect on the height or weight capacity of the suspension. The shocks are there to keep the springs movements even and smooth. Or is it different for a snowmobile?? Just curious as I'm still learning all this snowmobile stuff. As you all can probley tell by all the questions. lol

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bengelp

· #11 · Sep 30, 2006

Ok.... Shocks won't cause sag? As a former alignment tech, would you like me to tell you how much a car can sag if the shocks are shot? Around 1/2" to 3/4"! And that is in a car that weighs over a ton. Imagine what it can mean to a sled that weighs 500lbs? Any GAS charged shock has a lifting force to it.

I'll use some nice round numbers to explain why. Suppose your shock has 100PSI of nitrogen pressure, and the piston in the shock has an area of 2 square inches. That is 200 lbs of force acting on the piston, right? Now, subtract the area that the shock shaft takes up on the rod end of the piston.... say it takes up 3/4 of a square inch, so the area of the rod end of the piston is 1.25 square inches. 100PSI x 1.25sq/in is 125 lbs of force. So you have a difference of 75 lbs of force between the two sides of the piston, which gives your shock 75 lbs of lifting force from just the gas pressure alone. So, when your shocks bleed off the nitrogen pressure over time, you lose any lifting force they would have given.

Hope that helps you understand why worn out shocks cause sag.

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QWIKWHIP

Discussion Starter · #12 · Sep 30, 2006 (Edited by Moderator)

4

bengelp said:
Ok.... Shocks won't cause sag? As a former alignment tech, would you like me to tell you how much a car can sag if the shocks are shot? Around 1/2" to 3/4"! And that is in a car that weighs over a ton. Imagine what it can mean to a sled that weighs 500lbs? Any GAS charged shock has a lifting force to it.

I'll use some nice round numbers to explain why. Suppose your shock has 100PSI of nitrogen pressure, and the piston in the shock has an area of 2 square inches. That is 200 lbs of force acting on the piston, right? Now, subtract the area that the shock shaft takes up on the rod end of the piston.... say it takes up 3/4 of a square inch, so the area of the rod end of the piston is 1.25 square inches. 100PSI x 1.25sq/in is 125 lbs of force. So you have a difference of 75 lbs of force between the two sides of the piston, which gives your shock 75 lbs of lifting force from just the gas pressure alone. So, when your shocks bleed off the nitrogen pressure over time, you lose any lifting force they would have given.

Hope that helps you understand why worn out shocks cause sag.

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I understand what your saying, but have to kindly disagree.

This is a good read, but a bit long.
http://www.monroe.com/tech_support/tec_shockabsorbers.asp
This is why I don't feel the shocks are my main issue.

But take note of these two paragraphs.

Let's start our discussion of shock absorbers with one of very important point: despite what many people think, conventional shock absorbers do not support vehicle weight. Instead, the primary purpose of the shock absorber is to control spring and suspension movement. This is accomplished by turning the kinetic energy of suspension movement into thermal energy, or heat energy, to be dissipated through the hydraulic fluid.

And this is what it says about gas charged shocks.

An additional benefit of gas charging is that it creates a mild boost in spring rate to the vehicle. This does not mean that a gas charged shock would raise the vehicle up to correct ride height if the springs were sagging. It does help reduce body roll, sway, brake dive, and acceleration squat.

And if replacing the shocks increase the height, then that's a good sign that the springs are about shot. The springs should carry the weight of the sled, not the shocks. But either way, I need to get a few miles on the snow first and start tinkering from there.

I did just notice this at the end of that article. Is this in fact what these shocks are? Mono-tube design? If so, then I admit I was wrong.

These are high-pressure gas shocks with only one tube, the pressure tube. Inside the pressure tube there are two pistons: a dividing piston and a working piston. The working piston and rod are very similar to the twin tube shock design. The difference in actual application is that a mono-tube shock absorber can be mounted upside down or right side up and will work either way. In addition to its mounting flexibility, mono-tube shocks are a significant component, along with the spring, in supporting vehicle weight.

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cbrburns

· #13 · Sep 30, 2006

I just put the SC-10 in my FIII last week, I thought I screwed up the measurements when I moved the rear mounts because the suspension was extremely stiff. Turnes out the ACM is rusted solid and can't slide on the shaft to allow the suspension to squat. Check your out, that may be why the ride feels so stiff. As far a sag goes I can't help ya much there, but I'd probably get my shocks rebuilt if I were you.

bengelp

· #14 · Sep 30, 2006 (Edited by Moderator)

QWIKWHIP, you can't compare an automotive shock which has a limited amount of gas pressure to a ATV, Motorcycle, or snowmobile shock that has 150-250lbs of nitrogen charge. That's apples and oranges. Even if your springs are brand new on a sled, going from a cheapy hydraulic shock or a worn out gas shock to a properly serviced gas shock WILL increase the ride height. And there isn't a reputable shock guy in the world who would argue against that statement. We have quite a few of them who are members on this site if you feel like asking.

Do an experiment for yourself. At 3700 miles, I personally guarantee that your shocks are toast. Try this... have your shocks serviced, ALL of them. Don't do anything else to your sled until you get the shocks done and installed... don't even change the spring preload settings from what you had. Then check your ride height.

When my '02 700 had about 1500 miles on it, I had the shocks serviced and revalved. Before the service I was running the springs as stiff as they went on the rear just to keep from bottoming on normal trail moguls. Afterwards, I could run them on the 2nd setting in most cases, third setting if conditions got rough. Try it for yourself.

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QWIKWHIP

Discussion Starter · #15 · Sep 30, 2006

bengelp said:
QWIKWHIP, you can't compare an automotive shock which has a limited amount of gas pressure to a ATV, Motorcycle, or snowmobile shock that has 150-250lbs of nitrogen charge. That's apples and oranges. Even if your springs are brand new on a sled, going from a cheapy hydraulic shock or a worn out gas shock to a properly serviced gas shock WILL increase the ride height. And there isn't a reputable shock guy in the world who would argue against that statement. We have quite a few of them who are members on this site if you feel like asking.

Do an experiment for yourself. At 3700 miles, I personally guarantee that your shocks are toast. Try this... have your shocks serviced, ALL of them. Don't do anything else to your sled until you get the shocks done and installed... don't even change the spring preload settings from what you had. Then check your ride height.

When my '02 700 had about 1500 miles on it, I had the shocks serviced and revalved. Before the service I was running the springs as stiff as they went on the rear just to keep from bottoming on normal trail moguls. Afterwards, I could run them on the 2nd setting in most cases, third setting if conditions got rough. Try it for yourself.

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Thanks, I will defenitly have them done then. It sounds like that's my issue. Like I said I'm learning all this sled stuff, but sometimes I have a hard head. lol About what should I expect to pay to have this done?

bengelp

· #16 · Sep 30, 2006 (Edited by Moderator)

QWIKWHIP said:
Thanks, I will defenitly have them done then. It sounds like that's my issue. Like I said I'm learning all this sled stuff, but sometimes I have a hard head. lol About what should I expect to pay to have this done?

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Prices usually range from $28-35 per shock for a basic service. Another tip for ya... find someone who uses aftermarket seals and a good synthetic oil. The OEM seals and oil are junk.

Note: seals are extra charge.

bengelp

· #17 · Sep 30, 2006

Doomanmxz99 said:
I was going to say look at the shocks also. I have 4000 miles on my sled and I just brought the shocks in for service and I had about the same problem as you. I do have new springs in the rear and that did not seem to help much. Maybe a 1/2 inch but I will let you know on the shocks when I get them back and put it back together.

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You're going to dump a load in your shorts when you see (and feel) the difference it makes.

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