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KYB Shock lockup

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I've read in previous posts how Yam (KYB) shock bodies have been a problem causing shocks to lock up. I would think if that were the case, visual inspection would clearly show it. Other threads have blamed hydraulic lock and switching oil was the cure. Still locking up. The shock I'm working with is from a 2007 Yz450F, being used on a YZ 250. Have replaced the seal head at owners request on info he received via the grapevine these were the culprits. Changed from Maxima to HV1. Nothing appears to be out of compliance, no abnormal wear marks on piston ring, in shock body, seal bushing or shaft. The only thing I found from 1st tear down was the rebound needle was sticking so I polished that. Without visual evidence of malfunction I'm at a total loss. Not totally ready to give up yet though, so instead of just reading for answers, I'm asking.

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I've read in previous posts how Yam (KYB) shock bodies have been a problem causing shocks to lock up. I would think if that were the case, visual inspection would clearly show it. Other threads have blamed hydraulic lock and switching oil was the cure. Still locking up. The shock I'm working with is from a 2007 Yz450F, being used on a YZ 250. Have replaced the seal head at owners request on info he received via the grapevine these were the culprits. Changed from Maxima to HV1. Nothing appears to be out of compliance, no abnormal wear marks on piston ring, in shock body, seal bushing or shaft. The only thing I found from 1st tear down was the rebound needle was sticking so I polished that. Without visual evidence of malfunction I'm at a total loss. Not totally ready to give up yet though, so instead of just reading for answers, I'm asking.

In all of my years and all of my YZs, I have never heard of such a thing.

That said, if the rebound needle was jammed, somehow....it would keep the shock from moving. And in some cases when you put new fluid in, and don't charge the nitrogen, the shock will be locked.

But the nitrogen pressure nearly always pushes the needle back down and allows a passage around the piston.

So....it sounds more like a user error issue than a shock problem.

Just my two cents.

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Yes,

It's an epidemic Dave. You haven't heard? All of the shocks with check valves and rebound set at zero are exploding all over the country. :thumbsup:

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ive seen old kybs do this.

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That said, if the rebound needle was jammed, somehow....it would keep the shock from moving. And in some cases when you put new fluid in, and don't charge the nitrogen, the shock will be locked.

Not an instantaneous lockup. Shock was purchased placed on bike and ran over half a season then locked up. Ztore it down inspected and saw NO reason for this to happen. Nitrogen was still charged. reassembled w/ new sealhead. After several practices and a few races it did it again. Next teardown and fluid change. Shocked reported as wonderful for a few practices and races and then it locked up again.

[so....it sounds more like a user error issue than a shock problem./QUOTE]

First one I've ever had to do this, and did this one the same way I do all the rest. So...

I tried replacing everything individually when that was happening and never found the for sure cure untill I replaced the whole body. Went through probably 20-30 bodies in about 1 yrs time.

doc

I guess I could have come upon one of these. And Doc, if your viewing this, did you ever see any evidence in the bodies of tolerance issues?

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I just had the exact same problem. I have a 2009 yz 250. I got it brand new put about 30 hours on it and then the shock wouldnt work. I would ride for 10 mins the thing would heat up and lock up. Once it cooled down it would be fine after that. Then i would ride again and it would lock up. I was told this cant be the shock it has to be the linkage or something and then other people said no it has to be the shock. Well i sent it to factory connection and wrote a small letter to Ziggy. He wrote back and said let me know if this problem continues. Now after 2 days of riding it works fine no problems. He gave me a bag with all the parts he replaced and it works great now.

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i would expect it must be a piston band issue, as nothing else can alter much in a shock?

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Yes,

It's an epidemic Dave. You haven't heard? All of the shocks with check valves and rebound set at zero are exploding all over the country. :thumbsup:

Ah yes...another "I'm hiding behind my computer" unconstructive waste of time comment.

I thought you decided not to visit the forum because everyone was just too stupid for you?

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I just had the exact same problem. I have a 2009 yz 250. I got it brand new put about 30 hours on it and then the shock wouldnt work. I would ride for 10 mins the thing would heat up and lock up. Once it cooled down it would be fine after that. Then i would ride again and it would lock up. I was told this cant be the shock it has to be the linkage or something and then other people said no it has to be the shock. Well i sent it to factory connection and wrote a small letter to Ziggy. He wrote back and said let me know if this problem continues. Now after 2 days of riding it works fine no problems. He gave me a bag with all the parts he replaced and it works great now.

Ya know...these shocks are really simple and there are only few things that could cause the shock to lock up with enough force that it would present a problem like this.

Additionally, it's not like these are unique shocks. This design, and nearly all of the parts that make up these shocks, have been in service for a long time.

I just find it weird that all of sudden it's a problem, even more so when you consider how many of these units are out there.

I'd like to see this "bag of parts". :thumbsup:

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the ones i saw it on was old kxs, often they worked fine for years even, eric gorr actually measured the bore when heated and on that one found it closed up more than expected, so they worked the piston band to be a little looser i believe, on others i think people also changed the bodies.

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it will be the piston ring, behind it are two o-rings the air behind the ring, and between the o-rings heats up and expands the ring to sieze the unit. when it cools down it retracts. drill a hole in the ring like the kawasaki piston and problem solved.

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Not an instantaneous lockup. Shock was purchased placed on bike and ran over half a season then locked up. Ztore it down inspected and saw NO reason for this to happen. Nitrogen was still charged. reassembled w/ new sealhead. After several practices and a few races it did it again. Next teardown and fluid change. Shocked reported as wonderful for a few practices and races and then it locked up again.
[so....it sounds more like a user error issue than a shock problem./QUOTE]

First one I've ever had to do this, and did this one the same way I do all the rest. So...

I guess I could have come upon one of these. And Doc, if your viewing this, did you ever see any evidence in the bodies of tolerance issues?

Like mog said, I saw this problem on earlier ('97-'99) KX & YZ bodies and never did see any body or piston band damage. At that time I was told (whether right or wrong) that there had been a fire at the KYB factory causing a lot of bodies sent out before the bores(like Eric Gorr talked about) were properly finished.

At that time I tried everything including replacing pistons, piston bands, different brands of oil etc. The only thing that worked was replacing the bodies which like I said, over a period of a cpl yrs I ran into about 25-30 of them.

It supposedly only affected a cpl years worth of bodies back then, so don't see how it could be happening now but then again I guess anything can be possible.

I kinda like gavin lowes idea tho....:thumbsup:

doc

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I have heard this happen in kx models. Problem was the shock body. When the shock was hot it locked. Kawasaki importer gave new shock bodys to everyone who had this kind of bad shock.

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never did see any body or piston band damage

Since this shock was doing this prior to me opening it and your not observing damage either I do feel better, about my own sanity anyway. I agree GV's idea sounds good. Might be round three strategy. It's up to the owner.

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bet you havent seen it happen on kawasakis last 4-5 years (05 onwards) i have had 3-4 cusomers with yams with the problem, after this mod it didnt happen again.

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I have an 06 YZ450. I'm going through this right now. Shock is locked up. Wont go through its motion. I thought about binding linkage. I removed the lower linkage and swingarm would move through ist motion of up and down. I loosened up the spring of all its tension and shock is still locked up.

I did a ride about a month ago and had no problems. I just had parked the bike and was ready to take it out again. I taking off the shock and getting ready to get it serviced at a local suspension shop in HB. Just a little bizzare, never ran into this before.

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I realize it is not a KYB, but I had the same exact think happen to both an XR400 and an XR600 I had. The shock on the 600 would work fine when cold, but as soon as it got warm, it would nearly seize to the point of taking 5 seconds for it to rebound. The 400 was "tight" all the time.

People told me the same thing (linkage binding, swingarm pivot problem, etc.).

I was riding with Tim Morton who had had a lot of XR400s in his fleet, and while he said that it it not common, the piston will sometimes sieze in the Showa shock on the XR400 and 600 (nearly the same shock design).

So started the process of elimination. Cleaned and polished the rebound needle. Replaced the seal head/bushing. Still had problems.

Replaced the piston/valving stack with a Race Tech Gold Valve. Problem eliminated in both shocks.

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