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Understanding why shock performance degrades


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#1 Saber

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Posted 15 May 2020 - 09:05 AM

 I have done a lot of trail riding in Quebec over the years.  Rode with many high miler riders.  Never met anyone who felt their shocks had deteriorated to the point of making them unacceptable.  Of course reading Doo talk one sees that many people feel their shocks are spent in a couple of thousand miles, requiring rebuilding.  Maybe that has to do with they way they ride their sleds.  I thought I would do a closer look at shocks this off season as I have a nitrogen tank and regulator from my motocross days and lots of time on my hands.

 

Can someone explain how take apart shocks with separate gas and oil chambers degrade and thus impact their function.  Additionally what life in miles should one expect before their function is noticeably impacted for saddle bag touring on groomed trail in Quebec?   Also would using aftermarket shocks or XRS shocks with multiple adjustments allow one to adjust the shock characteristic as the miles add up to compensate for the shock deterioration?

 

Correct me if I'm wrong but it seems to me that two things are changing in the shock as the miles add up.  One is material is worn off the various parts turning the oil into a mixture of oil/metal/oring.  I would guess this makes the oil thicker.  Two, as the internal seal wears, gas must start to cross over into the oil, emulsifying it.  I would guess the oil/gas mix starts to act like thin oil.

 

Thanks for your input

Saber


Past Sleds:

1969 skidoo Olympic

1972 Polaris Charger 400

1976 Polaris TX 440

1979 Polaris TXL

1981 Polaris Indy 500

1984 Polaris Indy 400

1986 Polaris Indy SP 488

1992 Polaris RXL

1993 Polaris SP 500

1996 Polaris XLT

2004 Skidoo Rev 500

2005 Skidoo Rev 500

2007 Skidoo Blizzard 600 SDI

2009 Skidoo Renegade 600 Etec

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1980 Polaris Indy 500 Factory Prototype

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#2 600dooagain

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Posted 15 May 2020 - 09:50 AM

seal failure and heat(lots of high speed shock cycling)



#3 stealth bomber

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Posted 15 May 2020 - 11:33 AM

Night and day difference in a set of shocks that are spent compared to a set that are fresh.

Small amounts of moisture enter the shock along with the shaft, contaminating the oil.

The oil degrades due to moisture and heat, looses its viscosity, making it run through the valves easier and the shocks feel weak.

The contaminants in the oil collect on the valves, and they don't do their job properly.

The nitrogen bypasses the IFP and contaminates the oil.  Some of the nitrogen also escapes the shock, making them weak.

 

I'm no expert.  We just got involved with basic rebuilds last year but much enjoy it. 

If you have the equipment it's totally worth it.

IMO only really hardcore riders would need to service them every year, every two would be good for the average trail rider.  Although how does the average guy know if the shock has lost nitrogen unless it's serviced? 

I don't believe that adjustments could compensate for shocks that require service.  Maybe you could mask problems, but probably going to create another problem by doing that. 



#4 12/3

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Posted 15 May 2020 - 01:10 PM

Well said Stealh. Our family rides 95% trails and my interval for service is 3000 miles. All of our shocks are mono tube KYB’s. Remote resi shocks will experience less shock fade as the day goes on but I would guess that the the oil looks similar to monos with the same mileage?

I started changing oil and seals in our sleds two years ago and the challenge of learning the tricks to shock rebuilding has been rewarding. I still have lots to learn but glad that I can perform this maintenance on our sleds.

The biggest obstacle I have encountered while trying to learn the “trade” is finding someone who is willing to share a few pointers or tricks to rebuilding.

#5 stealth bomber

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Posted 15 May 2020 - 02:56 PM

^^^^ I think that's what took me so long to take the plunge and learn basic rebuilds.  Lack of good info, of at least not easy to find it.  I was lucky enough to find a dootalk member willing to give me a quick rundown on the basics and answer a few questions when I got hung up.  At the end of the day it's not that difficult to take apart a shock, clean, inspect, new seals, oil, bleed it out and charge it.  Doing it quickly and overcoming obstacles that may arise, that's where experience comes into play.  Knowing how to fix problems and change valving, that's the real talent.  I don't aspire to get into valving, just the cost savings from being able to do our own service makes it worth it.     



#6 Saber

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Posted 15 May 2020 - 03:49 PM

I'm learning!

 

So just plan on seals every rebuild.

 

Find factory directions for the 3 types of shocks in your sled.  Buy specialized tools.

 

Realize the rebuild will take some time as you lack experience and you would only do once (at 2 years) as the sled would have 12 to 20 k miles after 4 years and be sold off.

 

Next sled may need some new tools.

 

OR

 

Buy new sled for me every 2 years and give 2 year old sled to wife.  Don't concern myself with shocks


Past Sleds:

1969 skidoo Olympic

1972 Polaris Charger 400

1976 Polaris TX 440

1979 Polaris TXL

1981 Polaris Indy 500

1984 Polaris Indy 400

1986 Polaris Indy SP 488

1992 Polaris RXL

1993 Polaris SP 500

1996 Polaris XLT

2004 Skidoo Rev 500

2005 Skidoo Rev 500

2007 Skidoo Blizzard 600 SDI

2009 Skidoo Renegade 600 Etec

Vintage:

1980 Polaris Indy 500 Factory Prototype

1997 Polaris Ultra

1983 Yamaha Enticer 300


#7 mxzscotty

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Posted 15 May 2020 - 05:11 PM

you tube .



#8 stealth bomber

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Posted 15 May 2020 - 05:24 PM

There’s really not much in the way of special tools to service KYB shocks. If you have nitrogen, a regulator and safety needle filler that’s the main expense. I wanted to purchase collets to clamp the bodies in the vice, but they just don’t seem to be available anymore, everyone must just clamp them by the eyes. So that’s what we’ve been doing. Also wanted the bullet seal protectors to protect the seals when installing them on the shafts but they were backorder so we’ve been improvising with plastic tubing wrapped with tape to bring it to the shaft size. I’m sure someone with a lathe could make some pretty easy.

#9 Saber

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Posted 15 May 2020 - 08:31 PM

Safety needle filler...is the needle a tip from a syringe?  If so I could make that.

 

Seal protector... I have a lathe and use to design tools to insert orings so that is doable.

 

Vice blocks... Alu block, mill a specific size hole then split it with a saw.

 

OK it can be done with only investment being time.  If one does all that then might as well rebuild every year.


Past Sleds:

1969 skidoo Olympic

1972 Polaris Charger 400

1976 Polaris TX 440

1979 Polaris TXL

1981 Polaris Indy 500

1984 Polaris Indy 400

1986 Polaris Indy SP 488

1992 Polaris RXL

1993 Polaris SP 500

1996 Polaris XLT

2004 Skidoo Rev 500

2005 Skidoo Rev 500

2007 Skidoo Blizzard 600 SDI

2009 Skidoo Renegade 600 Etec

Vintage:

1980 Polaris Indy 500 Factory Prototype

1997 Polaris Ultra

1983 Yamaha Enticer 300


#10 A7M266D

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Posted 15 May 2020 - 09:17 PM

Started doing my shocks after 500 miles then again at 2000. Huge difference. If you ride every weekend you adapt and don’t really notice them degrade. Once you freshen them it’s like wow the difference is instantaneously noticeable.

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#11 hemidoo

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Posted 15 May 2020 - 09:25 PM

I'd say setting up for a nitrogen charge is probably the biggest expense . Like Jamie i refresh my shocks about every 1500-2000 miles so typically 2 times a season 8c9f13855ded0df0799fd1dfe83675cf.jpgd68d16bf08e90cccedc381e6ff33a833.jpg

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#12 12/3

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Posted 15 May 2020 - 11:39 PM

Try Carvers Performance for some of the tools that you are looking for. Mike has the bullet end to cover the threads when removing the seal head. He also sells the aluminum blocks for holding the shaft.
https://www.carverperformance.com/

#13 skippydoo

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Posted 16 May 2020 - 07:20 AM

Try Carvers Performance for some of the tools that you are looking for. Mike has the bullet end to cover the threads when removing the seal head. He also sells the aluminum blocks for holding the shaft.
https://www.carverperformance.com/

Carver also has IFP  listings and many parts.

https://www.carverpe...es.php?pageid=6



#14 nub1111

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Posted 16 May 2020 - 05:13 PM

I like to do my own, send them out to Ian performance, always spot on.



#15 RVJ

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Posted 17 May 2020 - 11:28 AM

As long as the ride is comfortable for me, I don't usually change or have my shocks rebuilt until I can't keep up with the other riders or I feel like I'm bouncing all over the place.  That typically seems to be at about 3 seasons at around 1,000 - 1,500 km a season (3k to 5k total). I have about  4,500 km on a 2005 renegade X. I really noticed it was riding rough this last spring. I dropped the skid, removed the shocks and am sending them out for a rebuild this week.

 

I bought this sled in 2015 with only 400km on it. kept inside in showroom condition. That's why I have a 2005 with only 4,500 km on it.


Edited by RVJ, 17 May 2020 - 11:33 AM.





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