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Blew new seal in rear shock?

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I just rebuilt my rear shock and hit a small jump maybe 3-4 feet and it all ready blew the rear seal?? I checked for nicks on the rod and felt smooth? Could it have been too much oil?

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Sharing which bike you are talking about will give us more info on the shock you have.

If it is not an emulsion shock meaning it has a reservoir then you cannot put too much fluid in unless you collapse the bladder or run the reservoir piston to low.

Did you use a bullet to protect the seal when sliding it on the shaft?

Is the seal in backwards?

 

 

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i put the seal in how it came out. the shock looks to be one off a 89 yz250 the seal said kyb 44mm i think. No didnt use bullet...not sure what that is.

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Likely a 16mm ID seal.

A seal bullet is a bullet shaped cover for the threads on the shock shaft. Keeps the threads and the sharp edge on the shock shaft from damaging the seal while installing it.

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on mine the threads are smaller and didnt even rub on seal. It didnt leak until I hit a small jump so just wandering what else could have caused it. anyone know where to get a seal cheap?

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Yes you are correct, many have smaller threaded area.

The seal still has to go over a sharp edge and needs to be protected there as well. Some shocks are very sharp at this juncture and may well damage the seal when sliding the seal head onto the shaft.

The fact that the shock started leaking after you hit a small jump is little indication of cause.

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If the seal is installed from the piston end of the rod, there's really no need for using a seal bullet.  The threads are 12mm, 4mm smaller than the 16mm shaft, and because the lips of the seal face upward, they trail over the threads and the top edge of the shaft, rather than leading and digging at the edge as they would if slipped on from the clevis end.  That and the fact that the seal has no hard plastic or metal shell makes it fairly difficult to damage during assembly.

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If the seal is installed from the piston end of the rod, there's really no need for using a seal bullet.  The threads are 12mm, 4mm smaller than the 16mm shaft, and because the lips of the seal face upward, they trail over the threads and the top edge of the shaft, rather than leading and digging at the edge as they would if slipped on from the clevis end.  That and the fact that the seal has no hard plastic or metal shell makes it fairly difficult to damage during assembly.

So if this is the case then what else could have caused it to blow? Im gonna do a thorough inspection when I replace it.

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The bushing in the seal head may be loose enough to cause trouble, but here again, the KYB seal is pretty tolerant of play in the shaft for a shock seal.  Dirt or a stray bit of metal debris in the seal pocket, possibly. 

 

Do you recall if the bladder was its original "tall dome" shape, or did the sides have 4 big "pleats" in it? 

 

If it was "pleated" or "puckered", did you fill it with 5 psi of air before filling the shock?

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Greyracer,

  I respect your opinion and you are definitely more experienced than I.

That being said I personally would not be comfortable without a bullet.

Without the bullet I would as a DIYer,

File the edge of the shock shaft to round the sharp edge. Granted some sharper than others and or

Assemble the seal head after the seal is on the shaft so I could ease the seal on the shaft by hand.

 

 

That being said you could be completely right as the shaft could have some damage or something else could be involved. 

Not being there at the time of assembly makes a great guessing game though.

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I put a new bladder on too. I did not put 5 psi in first though. Im gonna do a thorough clean when i reinstall and check everything again. Ill see what happens!!

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That being said I personally would not be comfortable without a bullet.

 

An alternative is to cover the end of the shaft with cellophane wrap and slip the seal on with a bit of Vaseline.  

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Rebuilt my shock today but noticed that there were quite a few nicks in the damping rod. So I think I'm just gonna get a used shock off eBay cause this one doesn't fit right any way.

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I think the problem is the oring that goes around the seal thingy cause it looks like its leaking from there and its not running down the shaft. Im gonna go to napa cause I heard they have tons of orings and see if that fixes it.

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If the shaft is pitted no o ring will work

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He's talking about the O-ring that seals the seal head to the shock body.

 

But, of course, you're right about a nicked shaft being a problem for the actual shaft seal.

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yes I have a shaft from another yamaha shock thats the same that im gonna try to switch over. The pits are only at bottom but it still leaks bad while just sitting there and it doesnt even get on the shaft

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