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Discussion Starter #1
Shock Absorber Primer

Shock absorbers (SA) control motion. They help control the rate at which the suspension moves up or down. Shock absorbers work in conjunction with springs (or torsion bars) to isolate, or reduce, the impact of surface irregularities upon a vehicle.

Without a SA the suspension bottoms easier and the smallest bump can cause it to oscillate wildly. That is the SA only task, to control compression and rebound.

When the suspension moves up (hits a bump), this is called compression.
When the suspension extends (after the bump or drop into a hole), this is called rebound.
These parameters are controlled by a piston on the end of the main shock shaft.
Different methodologies exist to accomplish this but the goal is to control the shock shaft speed for compression and rebound. This is what is referred to as valving.

There is no right or wrong when it comes to shock valving, only incremental differences. Typically a valve “stack” is used to control the oil flow from one side of the piston to the other. A valve stack consists of what are essentially small precision washers that flex once a fluid force is applied to them. Many different combinations can yield essentially the same action. This means your shock guy needs some experience or a shock dyno when you start to change the dampening characteristics of the shock.

Shock absorbers, like most things in life, come in different qualities with performance parameters or features that can vary widely. Typically, inexpensive sealed shocks are set-up for average conditions, or the engineers “best guess” on how it will be used. Take-apart shocks can be “tuned” for individual preference. Another advantage of take-apart shocks is that they can be serviced. Individual parts can be replaced and the oil can be changed to renew the function after hard use.

Take-apart shocks can be identified by (typically) a small brass fitting on the shock body or reservoir. This is where the shock is charged with nitrogen, a special tool with a needle fitting is required.

You cannot judge a book by it covers and neither can you judge a shock by viewing its exterior. A perfectly fine looking shock may have the oil contents of some prehistoric tar pit. They’re sealed so how do they get like that? Moisture, dirt, and air can get past seals and combined with wear on the internal bore will turn once high quality oil into goo. Cheap new oil is better than old expensive oil.

Service intervals go by time, use, mileage, or a combination of any of the three.

A high pressure shock is typically deemed superior to a low pressure shock as these shocks incorporate a floating piston or gas bag to separate the oil from the air. This eliminates foaming of the oil and increases the boiling point of the oil. Nitrogen is used instead of compressed air due to the low moisture content of the nitrogen. You cannot use a tire-type pressure gage to check the shock pressure (typically 200 -300 psi.) due to the low volume. Never recharge a shock without rebuilding first.

The shocks are usually referred to as having a high-speed dampening circuit and a low speed dampening circuit. This means shaft speed – not MPH. You can hit a square edge bump at 10 mph and use the high speed dampening circuit.

A dialed-in inexpensive shock (a shock that is tuned for your weight and riding style) is better than the trickest multi adjustable, triple rate, reservoir equipped shock that is not set up for your riding style. One mans soft is another mans firm so it is hard to generalize when describing shock action.

Keep spring preload to 1" or less. If you bottom or think you need to dial up the preload you probably need stiffer springs.

Servicing shocks can be done by the Do-It-Yourselfer with the right tools, a good tech manual, a few spare parts, and some mechanical aptitude – sometimes a little cursing helps also.

Happy Trails, JK
 

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I'd just like to interject about spring rates for a second, and also a warning.

First the warning to the newbies rebuilding shocks.

Its a good idea to remove the Fox Air Valve COMPLETLY after depressurizing, when servicing the removable style lower end cap type shock(old style used from the 90s). It allows you to see inside the shock. Should you find the IFP wedged against that lower cap, STOP!! Nitrogen migrated past the IFP O ring, and got on top of it. That could be potentially 200# of pressure on the TOP side of that cap! You will need to CAREFULLY crack the seal cap (rod end), and allow the pressure to bleed through the threads.

If you fail to heed this warning, that lower cap will come off from the shock like a rocket!

Pay 100% attention to this!





Spring Rates:
In a follow up to the previous explanation, shocks control motion, SPRINGS CARRY THE WEIGHT.

I disagree with the 1" preload. I will explain spring rates, and everyone can formulate their own opinion.

Lets use generic terms to make following the math easy.

A 100# spring means it takes 100# to compress it 1". So a 100# spring compressed THREE inches is pre-loaded 300# and every inch of further compression is an additonal 100#. Three inches of preload , plus 4 inches of shock compression equals 700# of stored energy.

A 150# spring compressed TWO inches is preloaded 300# Every inch of further compression is 150#. Say just TWO inches of preload (One inch less) plus the same 4" of shock compression now equals 900#!!

Following the "Stiffer is better" mantra, we'd be riding buckboards with no suspension travel. Also remember that heavier springs NEED MORE REBOUND VALVING to keep you from getting tail whipped!

The Canadian Crusiers (awesome groomed superhighway trails) would want a MUCH softer spring than a Tug Hill Terrorist who is bombing the trails that rival a snocross track just before they have to re-groom it.


The spring pressure ramp up in a heavy spring is too high for a groomed trail. Thats when valving must be softened on compression and stiffened on rebound.

And conversely, if the spring is too soft, you will need to stiffen the compression valving to a point where you can burn out a shock in 75 miles.


Basic parameters:

You need to set your "ride in" or Sag for your riding style and trails. This procedure is outlined in the manuals.

The spring needs a minimum of 1" preload to retain the spring. Springs CAN kick the retainer out for too soft of a setting.

Most sleds are designed for 180# rider in general conditions. If you are heavier, go heavier on ALL the springs, and tighten up the rebound valving to control the higher stored potential energy of the heavier spring. Same for aggressive riders, or beat up trails.

Your goal is to use as much suspension travel (without bottoming) as possible. Thats going to provide the most comfortable ride.


I know thats a ton to digest. Step back.

To get the most from your sled, you need to identify EXACTLY what you dont like. And what you DO like. And what tradeoffs you are willing to make.
Stutters? G bumps (slow rollers)? 2' hills spaced on top of each other? spread out 6'? What speed are you trying to cross them at? Orifice size plays into the equasion in 3 of those situations.


Focus on the ride, and then tell your shock guy or dealer exactly the problem area, and you'll get the ride you want much quicker.
 

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great info, can I pick your brain? I have a 03 F7 I had the shocks rebuilt using 2.5 weight silkolene had the IFP depth set correctly but I am bottoming out on rough trails and when I get off the machine after a ride the back sags and I lift it up about two inches and it drops back down. I have the cam adjusters on the heavy setting I weigh 185. I just ordered stiffer sno pro springs am I going to hate life riding the machine without compensating with valving?
 

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2 part question:

Resistance to bottoming:
Dump the 2.5 weight and go heavier. OEM Fox/ACT is 5 weight. Aggressive riders or heavier sprung riders do better with the 10 weight from AMSOIL. Poor mans revalving. Zero cost. By virtue of the heavier or more viscous fluid, it travels thru the valving slower. Slows the shaft speed down, reducing both the effect of the pent up potential energy from heavier springs(or harder hits) and adds resistanc eto bottoming. It also helps reduce nitrogen migration past the IFP seal.

Sag: It's been written a few places on here about this. Could be limiter straps, could be too stiff of ski shocks, unlevel ground, etc.


Pull the skid, rebuild the shock with 10# AMSOIL, reset your SAG, go thru skid to be sure nothing is binding or bent. Highly unlikely you need new springs. And newer heavier ones will make your ride problems worse, until you fix the shock.
 

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wat do you think about some <98 zr shocks on the front of a 98 jag 440 and and maybe just the shock of the zr on the back do you guys think that will help me to :trail: haha jk i jump alot and bottom the unajustable front socks once an hour practicly so i dont wanna kill my sled
 

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97 440 front shocks

man do i need help! i am replacing the front shocks on my boys 97 440. I have them off, dealer rebuilt, now, i cannot get them back on! The dealer said I have to compress the spring to make this happen?! is this correct? any and all help is appreciated. We just got another foot of snow, and my little gys want to ride. I am a newbie at this, so please be patient with me....
 

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man do i need help! i am replacing the front shocks on my boys 97 440. I have them off, dealer rebuilt, now, i cannot get them back on! The dealer said I have to compress the spring to make this happen?! is this correct? any and all help is appreciated. We just got another foot of snow, and my little gys want to ride. I am a newbie at this, so please be patient with me....
Should have posted this in the ZR section, but anyway, is the sled or at least the ski off the ground? Had no problem putting mine back in with the sled up where I can move the ski and spindle to where I need it to bolt up.
 

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Discussion Starter #8
Spring Preload

Spring preload – 101;

I continually read post saying “I cranked up my preload to stop the bottoming” and wonder where that came from. Preload has nothing to do with bottoming, and here’s why:

Here is a make-believe scenario and I have used round numbers to make things simple but the principle applies no matter how much travel or what springs you are using so lets start,

Let’s say you have a 5” travel suspension and you have a 100 lb/in spring. That means that if you compress the spring 1” there will be a resistance of 100 pounds, if you compress the spring 2” then you will have 200 pounds of resistance, and so forth up to the point the entire spring is compressed (5” = 500 lb).

So… you have your preload set to 1” and go out riding. You will need to hit a bump with at least 100 pounds of force before the spring will start moving, so far so good. Then you add a passenger to share your fun so you crank up the preload to 2”. You will need to hit a bump that enacts a minimum of 200 pounds before the spring moves.

Then you hit a really big bump and the spring just barely bottoms out (500 lb of force). It is going to bottom out no matter where the initial preload was set. Preload is mainly to adjust for rider weight and “sag”. Changing the preload does not change the spring rate; otherwise you would be changing physics. In the above example, if you did not want the suspension to bottom then you would use something like a 120 lb/in spring (which would yield 600 lb resistance at 5” - that math is 120 x 5 = 600).

This is one reason they make variable rate springs or double or triple spring “stacks” – soft on the small bumps but firm on the big ones. In some 2-up series Arctic Cats they actually have a helper spring (rear skid) that you manually activate when carrying a passenger, it effectively increases the spring rate.

The single biggest suspension tuning error is cranking up the preload too much, if you tend to think you continually need more preload you probably need a higher spring rate.

Happy Trails, JK
 

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I'm going to have to cry foul. If you are talking about fully compressing the spring then the previous post is correct and it takes the same amount of force to fully compress the spring. However, it depends on what is limiting the suspension travel. If the spring is the limiting factor then the previous post is spot on. If the spring is not the limiting factor then increasing the spring pre-load will indeed help out regarding bottoming. for example, lets take the front ski suspension. The shock has a rubber bumper on the shaft between the shock body and the eye at the end of the shaft. That is the limiting factor on the front. You can fully compress a front ski shock and the spring will not be fully compressed yet. In other words, the shock is limiting the travel. Lets just assume the shock has 5" of travel. If the 100 lb/in spring is set so that there is 0" preload then it will take 500 pounds to compress the shock/spring to minimum length ignoring the nitrogen charge. Now your 100 lb/in spring is cranked up 1" of preload or 100 pounds. So you need a load of 100 lb to even start moving the shock. The shock can still move 5 inches, so to fully compress the shock, the spring will have to be compressed 5 inches on top of the 1 inch preload, or 600 pounds to bottom the shock/spring assuming we haven't reached coil bind yet.

On the rear suspension, the rear shock can't fully compress because of how the suspension is designed. It has torsion springs in most cases and they do not limit the travel. The front shock on the rear skid can't be compressed to the limit either as the limit is determined by the rubber limit bumpers on the rails. Therefore I see no shocks on a typical snowmobile setup that are limited by coil bind.
 

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Discussion Starter #10
Now your 100 lb/in spring is cranked up 1" of preload or 100 pounds. So you need a load of 100 lb to even start moving the shock. The shock can still move 5 inches, so to fully compress the shock, the spring will have to be compressed 5 inches on top of the 1 inch preload, or 600 pounds to bottom the shock/spring assuming we haven't reached coil bind yet.

Sir, you need to re-read your statement. You started out with a 1" preload and then stroked it through an additional 5" of travel and came to the conclusion that this would yeild 600 lbs of force.

That means you started out with a 6" spring - not a 5" spring. Yes indeed, a 6" spring at 100 lb/in would be 600 lbs. but my example was for a 5" spring.

If you put a 5" 100 in/lb spring on an Instron or spring tester, at 5" it will read 500 lbs (+/- tolerances). It doesn't matter what is in the middle of the spring - the spring does not know. So I will stand by my original comments.

Regards, Jim

 

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Now your 100 lb/in spring is cranked up 1" of preload or 100 pounds. So you need a load of 100 lb to even start moving the shock. The shock can still move 5 inches, so to fully compress the shock, the spring will have to be compressed 5 inches on top of the 1 inch preload, or 600 pounds to bottom the shock/spring assuming we haven't reached coil bind yet.

Sir, you need to re-read your statement. You started out with a 1" preload and then stroked it through an additional 5" of travel and came to the conclusion that this would yeild 600 lbs of force.

That means you started out with a 6" spring - not a 5" spring. Yes indeed, a 6" spring at 100 lb/in would be 600 lbs. but my example was for a 5" spring.

If you put a 5" 100 in/lb spring on an Instron or spring tester, at 5" it will read 500 lbs (+/- tolerances). It doesn't matter what is in the middle of the spring - the spring does not know. So I will stand by my original comments.

Regards, Jim

No. You are wrong. I didn't say how long a spring I was talking about and it doesn't matter as long as it doesn't reach coil bind as installed. I don't care if the spring is 10 inches long, or 100 inches long. If the spring rate is 100 lb/in then 1 inch of preload is 100 pounds and 5 more inches of travel is a total compression of the spring of 6 inches or 600 pounds of spring force. If the spring is not limiting the travel then cranking the preload WILL increase the amount required to bottom out. The only way it works the way you said is if the spring reaches coil bind and that doesn't happen on our suspensions.
 

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Discussion Starter #12
preload

You are welcome to believe what you want. This is not about coil bind, I am not taking about coil bind. I am not talking about bump stops. I am not talking about linkages. Those are subjects all onto themselves but none of them care how much preload is applied to a spring.

If preload helped bottoming then there would be no reason to sell different spring rates. I will tune my sled with different spring rates, somehow you have talked yourself into thinking that preload makes the spring stiffer - it does not - nor will it help bottoming. That is a fact.


JK
 

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If preload didn't do anything there would be no reason to make preload adjustable. You are arguing that compressing a spring more doesn't take more force. This is a physical impossibility. I will continue to believe what is right and you can continue to be wrong.
 

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Discussion Starter #14
If preload didn't do anything there would be no reason to make preload adjustable. I never said that. Preload is to adjust for rider weight and to set sag, it also helps to take up tolerances in spring lengths.

You are arguing that compressing a spring more doesn't take more force. No I am not. I said:

Let’s say you have a 5” travel suspension and you have a 100 lb/in spring. That means that if you compress the spring 1” there will be a resistance of 100 pounds, if you compress the spring 2” then you will have 200 pounds of resistance, and so forth up to the point the entire spring is compressed (5” = 500 lb).

Somehow you think that increasing preload makes the spring stiffer. The amount of preload only changes when the spring first starts to move.

I am saying preload does not affect bottoming - Just what I said at the start.



 

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Here is a make-believe scenario and I have used round numbers to make things simple but the principle applies no matter how much travel or what springs you are using so lets start,

Let’s say you have a 5” travel suspension and you have a 100 lb/in spring. That means that if you compress the spring 1” there will be a resistance of 100 pounds, if you compress the spring 2” then you will have 200 pounds of resistance, and so forth up to the point the entire spring is compressed (5” = 500 lb).

So… you have your preload set to 1” and go out riding. You will need to hit a bump with at least 100 pounds of force before the spring will start moving, so far so good. Then you add a passenger to share your fun so you crank up the preload to 2”. You will need to hit a bump that enacts a minimum of 200 pounds before the spring moves.

Then you hit a really big bump and the spring just barely bottoms out (500 lb of force). It is going to bottom out no matter where the initial preload was set. Preload is mainly to adjust for rider weight and “sag”. Changing the preload does not change the spring rate; otherwise you would be changing physics. In the above example, if you did not want the suspension to bottom then you would use something like a 120 lb/in spring (which would yield 600 lb resistance at 5” - that math is 120 x 5 = 600).


Happy Trails, JK
In your story above you say that said that a 100 lb/in spring with 2 inches of preload and 5 inches of stroke will always bottom out the suspension at 500 pounds. There it is above in your words not mine. That is just not physically possible, not the way it works, and just flat out wrong. In that scenario, it will take 700 pounds of force to bottom out the suspension, 2 inches of preload and 5 inches for the travel of the suspension equals 7 inches of total spring movement. Plain and simple that is how much the spring is compressed in your scenario. If the spring is 100 lb.in and it is compressed 7 inches that is 700 pounds of force.

I never said changing the preload makes the spring change in any way, but it does change the starting and ending force of the spring as it is installed on a shock. In the example of a 100 lb/in spring and 5 inches on stroke IN THE SHOCK you have the following:

No preload - 0 lbs at start of stroke OF THE SHOCK - 500 lbs at end of 5 inch stroke OF THE SHOCK
1 inch preload - 100 lbs at start OF THE SHOCK - 600 lbs at end of 5 inch stroke OF THE SHOCK.
2 inch preload - 200 lbs at start OF THE SHOCK - 700 lbs at end of 5 inch stroke OF THE SHOCK.

So adding preload DOES increase the amount of force required to fully compress the shock/spring unit. No question about it.

I am talking about the stroke of the shock. 1 inch of preload already adds 1 inch of stroke to the spring before the shock even starts to move. Therefore , any preload you add increases the amount of force required to fully compress the shock/spring unit.

The reason you change spring rate is to have a different range from start to end. In the example with a 5 inch stroke shock, a 100 lb/inch spring means that you always have a 500 pound RANGE between starting compression of the SHOCK to full compressing the SHOCK. That could be 0-500, 100-600, 200-700, etc, the the RANGE is what is always 500. If you want to increase or decrease this range that is when you get a different spring.
 

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Have you ever run a spring tester or an Instron? I didn't think so.
Not that it matters at all, or makes any difference in who is right, but I have run tensile and compression testing machines of which Instron is only one brand. I also have a small spring tester for testing intake and exhaust springs on cars. However none of that matters. What matters is who is correct. Your statement above means absolutely nothing in regard to supporting your argument.
 

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I give up. Believe what you want. In your world, somehow compressing a 100 lb/in spring 7 inches (2 inches of preload + 5 inches of suspension travel) takes only 500 pounds. Never mind that it is in defiance of Hooke's Law as well as pure common sense. Believe whatever you want. I could really care less. This is the last time I will post here.
 

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I give up. Believe what you want. In your world, somehow compressing a 100 lb/in spring 7 inches (2 inches of preload + 5 inches of suspension travel) takes only 500 pounds. Never mind that it is in defiance of Hooke's Law as well as pure common sense. Believe whatever you want. I could really care less. This is the last time I will post here.

Cat happyRockerdudeClapNot worthy:
 
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