How much does shock oil break down?

[Casper250]

The other day i'm at the track and my shock felt like it was bottoming out when I was trying to seat bounce some jumps. I go to adjust the compression only to find out that i was all the way in on the compression. My suspension was revalved in the spring and I have been riding on average of 8 hours per week, plus racing on sunday. Could the shock oil break down that much that the dampening could loosen up to the point of no more adjustment?

Also, how hard is it to do an oil change on a shock? I'm pretty good with a working on my bike but it's something I have never done.

Lastly, I was thinking of switching to Mobile 1 ATF instead of using suspension oil. I read here that the AFT has a higher viscosity then suspension oil(or at least feels like it does) which would be good for me so I would move the adjustment of the compression back toward the middle of the adjustment range. Does this sound right?

 

[MXTex]

Yes, shock oil can break down and change the dampening characteristics. I suppose if you went long enough, it could break down to the point you have described. The oil change frequency I've heard most often is every 8 to 15 hours of operation. So I would say you are due a change.

Servicing a shock is not difficult but takes some know-how. I ordered a shock servicing video from Eric Gorr and read my service manual closely before doing so. Now I can do it fairly easily. There are some specialized tools that make the job much easier. As often as you ride, it may be a good idea to get tooled up.

The subject of utilizing Mobil 1 ATF as suspension fluid has been discussed quite a bit in this forum. If you perform a search you'll receive a huge amount of information. I've used it in both my shock and forks. My personal opinion is it's better in the forks. But felt like I experienced more shock fade with it in the shock. I now use Motorex 5wt in my forks and Motorex 2.5 in my shock.

Good luck,

 

[Casper250]

I was looking around on the internet and found this: http://www.motocross.com/motoprof/moto/mcycle/shock/shock.html

From reading that, it doesn't seem that hard to just change the fluid. To me it looks like i just bleed off the nitrogen, remove the bladder cap, drain and fill with oil, put the bladder cap back on then have it recharged with nitrogen. I didn't see the need for any special tools. What special tools do you have for servicing your shock?

I have used Mobile 1 ATF in my forks before and liked the results. I'm a little bit more sesitive to settings in my shock then my forks though. I guess I should just give it a try.

 

[russ17]

Casper,

Here is some good info on oil
http://www.allthingsmoto.com/forums/showthread.php?s=&threadid=8675&forumid=157

 

[JohnScott]

From reading that, it doesn't seem that hard to just change the fluid. To me it looks like i just bleed off the nitrogen, remove the bladder cap, drain and fill with oil, put the bladder cap back on then have it recharged with nitrogen. I didn't see the need for any special tools. What special tools do you have for servicing your shock?

That's not right. You have to take the shaft out of the shock and bleed the air out before sealing the piston side and charging with nitrogen. I think step-by-step directions can be found on the net.

John

 

[JTT]

Your correct John, it's not that simple. If your going to do it, do it right. Everything should be taken apart and thoroughly cleaned, then reassembled, carefully bled and recharged. I think Jer still has a step by step instructional manual on his website www.mxtech.com

 

[Casper250]

I was reading my service manual last night and I still don't see the need to take apart the whole shock. The manual says that I can release the nitrogen, then I can take the compression clicker assembly(for lack of a the real name of it) out and drain the oil from there. If the spring is taken off, I don't see how this would be any different then doing an oil change in the forks? Just fill up with oil, pump the shock until no more air bubbles come up.

I read the article on the mx-tech site but that is for a rebuild. I figure if i follow the point of where he talks about filling with oil I should be good.

 

[JohnScott]

You will need to remove the shaft (that holds the piston), so basically you have to take the shock apart. I believe taking the compression adjuster out is a waste of time. You need to (short, no detail version):
- release the nitrogen
- push down the bladder cap & remove the retaining ring
- pull out the bladder
- push down the seal head & remove the retaining ring
- pull out the shaft and piston
- pour out the oil
- clean everything well
- pour in new oil in bladder side
- reinstall bladder and retaining ring allowing oil to spill out while inserting
- fill piston side with oil to within 1/2" of top
- gently insert piston & cycle up and down to bleed air
- when no more air bubbles exist, top off with oil and push seal head down and reinstall reaining ring
- charge with nitrogen

I have left out a lot of important details like when to partially air up the bladder and when to let the air out during the reassembly process but I wanted to demonstrate to you that there's a little more to this than what you've described. It's easy to do it right and will only take you about an hour or less. I would use Wilkey's directions for a rebuild but ignore the parts replacement portions if your components are still in good shape. If you don't clean things up after you've removed the old oil you're just wasting your time.

John

 

[Casper250]

It's easy to do it right and will only take you about an hour or less. I would use Wilkey's directions for a rebuild but ignore the parts replacement portions if your components are still in good shape. If you don't clean things up after you've removed the old oil you're just wasting your time.

John

Are there any special tools involved with this?

 

[JohnScott]

With the exception of the nitrogen charge, no. The most challenging part of this is removing the retaining rings. You'll need a small sharp flat blade screwdriver or something similar. Be careful not to nick anything in the process. I use oderless mineral spirits to clean everything up - it's cheap and seems to work.

 

[JTT]

John is right, it's no big deal. Removing the shaft and piston is only a circlip away, so you'd be silly not to do it. No special tools required.

I find it easy to remove the clip using a thin flat scewdriver to lift the edge, then a small hook to gently pull the ring out as the screwdriver holds it out of the groove.

 

[Casper250]

So i dove in and did this last night and I still don't see the need to take everything apart to do an oil change. FYI it's a showa shock from a crf250.

So I take the spring off and drain the nitrogen and remove the bladder and drain the oil. I fill it up and reinstall the bladder and let the excess oil spill out. I then took out the clicker assembly and it drained out both the new oil I put in and the old oil from the dampner side.

I filled up the shock through the clicker assembly hole and pumped the dampner rod till there was no air bubbles comming up. Once both sides were filled, i reinstalled the clicker assembly and now I just need to get it charged with nitrogen.

From the service manual, it shows that the shock is just the bladder side, and the dampner side separated by the clicker assembly. If you take out the clicker assembly and hold the shock at a 45 degree angle, the hole where the clicker assembly screws into is the highest point on the shock for air to go.

This is a diagram of the shock: http://www.servicehonda.com/hard parts/off road/crf250r '04/rear shock absorber.htm

If you look where 49 and 50 is, that's the piece that I'm talking about comming out.

 

[marcusgunby]

You can do it that way-i would suspect small airpockets will exist but no worse than a badly bleed shock, its just you cannot inspect the parts doing it that way, i have found brand new shocks with problems, eg on a new 2003 KX125 the shock circlip holding the seal head wasnt installed correct-it could have done major damage.

 

[Casper250]

I understand about not being able to inspect the parts but I was just interested in the oil change. I had it revalved in the spring when it was about a month old and I plan on sending it back in the fall for a rebuild.

"i would suspect small airpockets will exist but no worse than a badly bleed shock"

Why would you say that? I bled the dampener side of the shock the same way you would bleed fork dampener, by filling it up with oil and keep working the dampener up and down till no more air bubbles come up. The bladder side I just had to fill up and I tapped it with screwdriver to work any small bubbles up.

Another quick question. When I put the bladder back in and the whole shock was back together, I read that you should fill the bladder with regular air to pop the bladder back up agaist the circlip. I drained that air out after I did that. Now when I go to get it filled with Nitrogen, will that small amout of air effect the shock at all or do they vacuum out the air in there before filling the shock with Nitrogen?

 

[russ17]

Yes you can do this this way ! but the draw back to this method, is there is still unwanted contaniments in the shock body that cling to the walls piston ect. I would have to think that you would be contaminating the new oil and at the prices that you pay for a good oil why waste your money! to save miniutes really.

 

[DW]

No special tools. Two tricky steps.

My perspective: if you are going to vent the nitrogen, take the shock apart for a good cleaning and an inspection. You may even want to replace the seal head. If you are not recharging the shock, there are no special tools required. There are, however, two steps that require the right "technique":

#1 - removal of the circlips from the reservoir and the shock body (I use a small pick to force the circlip down and then place a screwdriver underneath it to act as a ramp as I force the circlip back up and over the retaining groove)

#2 - final insertion of the of the shaft and seal assembly into the body is messy (see MX Tuner's description at the weblink below). It is important that you release the 40 - 50 pounds of shop air from the bladder for the final push of the seal head to expose the circlip groove.

I have been using Mark Klein's advice since 1999. It is well written.

Good luck,

DW

http://www.off-road.com/dirtbike/mar99/db101/db101shock.html

 

[JohnScott]

Now when I go to get it filled with Nitrogen, will that small amout of air effect the shock at all or do they vacuum out the air in there before filling the shock with Nitrogen?

I'd be more worried about the large amounts of contanimates that still exist in your shock...

Your way might not hurt you this time but it will in the long run if you were to do it this way everytime.

and I plan on sending it back in the fall for a rebuild.

I bet you feel a big improvement in your rear suspension after the rebuild in the fall. :)

John