Time to service the shock, etc

A service reference
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AZRickD
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Time to service the shock, etc

Post by AZRickD »

I've had the bike since last June and have been riding at least once a weekend since then. I just got done with a few punishing rides including a Destry Abbott clinic. Video of me (and a mo betta rider) going over whoops and climbing hills shows my back end bucking pretty severely.

I've adjusted everything with little improvement. Last night I sat on the bike in the garage and found that it was squeaking from somewhere down below. Could be the linkage, the swing arm, the shock? I don't know. Sounds like the metalic version of fingernails down a chalk board, or the kickstand rubbing against the concrete (only it was up). Squeak-squeak-squeak-squeak.

So... what the heck. It's been nearly two years since the last shock service, so I'll remove the shock again (as I did to install the 5.2 spring), and dissemble the linkage and swing arm and lube it up.

I'll go through the manual thoroughly. Anything I should do or look out for (including losing some of those pesky needle bearings)?

Thanks,

Rick
I done KX-ed QuailChaser's KDX220R
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Post by AZRickD »

I took the back end of the KDX apart and got the shock to the suspension shop for service. The conventional wisdom is that the shock is no longer a shock, thus allowing the spring to be the only active component of my rear suspension, hence the recent boinginess over whoops and hill climbs.

I've lubed all of the points of rotation and bolted most of the parts together. I await the completed shock on Friday.

Rick
I done KX-ed QuailChaser's KDX220R
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Post by AZRickD »

The suspension guy called today.

He said the shock oil was black and I had some warn parts.

He also questioned why I had my clickers all the way out. I told him it didn't seem to matter where I had them. :mrgreen:

Rick
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Post by scheckaet »

Is it pricy to send your shock? The reason I ask is because I wonder if I should rebuild mine myself (it's supposedly easier than the forks) or send it.
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Post by strider80 »

I think it is easy to do, but usually it is ~$100 for a rebuild to send it out.
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Post by AZRickD »

At this particular shop, it is $79 for a basic service which is...

Completely dissemble
Clean
Inspect and measure for tolerances
Add oil & reassemble

In addition to that, I needed the following replaced...

Piston ring ($13)
Rubber bumber ($13)
O-Ring -- 37.5 x 2.0 ($2.50)
Rod Guide ($18)

For a total of $130

If all you are doing is changing the oil, you can do that yourself.

However, mine was behaving in a manner that suggested major blow-through, so I decided to have a professional go through it. I wouldn't have any idea what to replace (although buying a rebuild kit that swapped out all of the friction components would have taken the guess work out of that).

Here is all the parts that he took out and replaced...

Image

After having installed the components and given the boingers a good bounce, I can safely say that I haven't had a working shock in a few months. The bike sits higher (even after the shop reduced the pre-load some), and the rear end smooshes slower.

I had to spin the spring nuts a bit more to get my free sag from .75" up to about 1.25". Keep in mind that just prior to getting the shock repaired, my free sag was about 1.3". That tells you something about how the old shock was working, and how my geometry might have been thrown off.

I think I might know when the shock failed. I was riding Sycamore which is 40 miles east of Phoenix. Mid-way through the ride, I found that my bike was sitting such that I was almost flat-footed instead of on my toes. My front end was lifting way too much as well.

I thought it was just my new spring settling in, so I just cranked the nut tighter to redo my sag. I'll bet my shock failed right then and there.

I'm going on a gentle ride tomorrow (teaching some newbie ladies how to ride). I'll try to take the opportunity to hit some whoops, crawl through a rocky wash, and climb a rock-strewn hill to see how the back behaves.

Rick
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Post by quailchaser »

Rick,

Please tell us that you are actually setting the "RACE SAG" at ~ 4" (~100mm) and not just "free sag". The "free sag" is a check for realative spring rate as related to having your "race sag" set properly.

Again "race sag" is what you want to set. "Free sag" is the check. Once your "race sag" is set, if your "free sag" is out of proper range, then you do not have the correct spring for your weight. Always set the "race sag" and then check the "free sag". If your spring is correct for your weight, there should be no reason (other than for your peace of mind) to check "free sag" once you've set the "race sag".
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Post by AZRickD »

The only reason I mentioned free sag was that it was what stuck in my mind as I put in the rebuilt shock.

My race sag is currently (temporarily) set at 4.25" or 108mm (spec is 100mm).

Free sag is 1.25" or 31.8mm (spec is 30mm to 40mm) so I have plenty to play with.

I couldn't get the sag all the way set because my "shop buddy" (wife) wanted to drag the family to church tonite, so I lost my eye-baller before the job was done.

I should shave a bit off the race sag, I suppose, and with the KX forks being an inch longer, I'll have to do that to get the back end proportional with the higher front (if my shop buddy shows up).

BTW, shock spring is a 5.2. Fork springs are .43. I suit up at 225 pounds.

The MX-Tech spring calculator

http://www.mx-tech.com/index.php?id=spring_generator

says that for the KDX I need a 5.3 shock spring and .47 fork springs. With my .43 springs in there now, I couldn't imagine running .47 springs hence, I decided to go with a 5.2 shock spring. Since I plan on losing 20 pounds, (by next fall), MX-Tech says that 5.2 and .44s are suitable. I think it strikes a decent balance right now.

Rick
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Post by quailchaser »

Your on the right track. Just get your race sag set at 100mm. Don't worry doing the free sag check...since you have the right (darn close...anyway) spring, you know it'll be in the right range. :mrgreen:
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Post by AZRickD »

Given the KX fork mod, I might cheat and go to 95mm, if it "feels right."

Edit...

I've gotten the race sag down to 4-inches or 101mm. Free sag is roughly 1.25-inches or 28.5mm.

Not exactly to spec, but I don't have spec bike now, do I? :?

Here is what TeamGreen says about the optimal result:
Many times there is much confusion about the specifications above. Remember it this way, before check-ing your static sag, you must first set your race sag. If after setting the race sag the static sag is more than your range in the rear, the spring may be too stiff for your weight. In this case, the spring is not compressed enough to allow the suspension to extend far enough on its own. A spring that’s too firm does not allow the rear tire to hook up under acceleration and passes more of the bumps on to the rider. If the static sag is less than your range in the rear, the spring maybe too soft for your weight. In this case, the spring required so much preload to achieve the proper race sag that it makes the rear end too high or even top-out when the rider dismounts. As a result, the weight transfer is incorrect and the rear end tops-out under even light brak-ing and on downhill’s.
But this isn't a hard and fast rule. They also talk about adjusting the shock spring away from the optimal settings above to accomodate trail/track conditions:
Also, remember you may adjust your race sag within your specified range depending on track conditions and riding style. Less sag can improve turning ability at the cost of slightly reduced overall stability. More sag can improve overall stability but may reduce turning
performance slightly.
It will have to do, cuz I ain't fiddlin' with it anymore.

Rick
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Post by AZRickD »

Wanna see a video of me riding the KDX over whoops with a blown shock?

I submit these two videos from last weekend's Destry Abbott riding clinic.

The first one is of me riding a series of smallish whoops on the KDX which, I later found out by watching the video, had a blown rear shock (for about two months and finally rebuilt last week). Note the rear end hopping all over the place when I pass -- no shock damping to speak of. That was about as fast as I could go without the back end fish-tailing on me. I also developed some difficulty with hill climbing as (I thought) the front end would point all over the place. Turns out it wasn't the front end, it was the rear end bouncing all over the place. I thought I had lost the abliity to climb rocky hills all of a sudden.

http://good-times.webshots.com/video/30569...917060093498191

This next one is me on the 300XC. I was trying to match speeds with the KDX runs so I could compare the behavior of the rear end. After that, my runs on the KTM were much faster, of course, since it had a working rear end. I look forward to my first ride with a real shock this weekend.

http://good-times.webshots.com/video/30872...227060093498191

BTW, others (much better than I) were video taped making the same run, and faster too.
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Post by KDXer »

The KDX seems to ride in and out of the whoops where as the KTM seems to skip across the top. Could all be to do with the extra speed on the KTM but your shock sure looked soft. :mrgreen: Good to hear you got her all sorted. Should be a MUCH safer and smoother ride. Good deal !! :mrgreen:
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Post by AZRickD »

I was actually trying to keep the KTM as slow as the KDX for comparison purposes.

I went on a 35 mile ride over jeep, quad, and some 1Track. Lot's of whoops.

It was a joy to be on a bike that had the front and rear behaving the same way.

I couldn't find the nasty hill climb that was giving me trouble last time, but the small ones didn't show any tendency to wiggle.

End of thread.

Rick
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Post by AZRickD »

I did some rocky hills last week. No loose gravel but with odd, shallow ledges which were etched by ocassional water flow. It behaved nicely.

I also discovered that my problems in the whoops were also related to the bad shock. My front end is no longer searching because the rear end is no longer bouncing left and right.

Rick
I done KX-ed QuailChaser's KDX220R
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