99 YZ400F Suspension Help

6 replies to this topic
  • rickybobby2189

Posted May 04, 2011 - 04:55 PM


Hey everyone first thanks for taking a look at my problem I have a 99 yz400f i bought back in febuary.When I got it the bike had sat most of its life and as soon as I got it and got to riding it the front forks started leaking as well as the weap hole and other minor stuff a that I have fixed(thanks to thumper talk) anyway to my problem...My rear shock seems very plush(Soft) even with the adjustment set all the way to Hard position. Its not leaking any fluids out and was wandering if this sounds like to you that the nitrogen has sat and leaked out.The biggest problem I have had out of this bike is leaks from rotted seals and I wonder if this would fall into the same list...Assuming my absorber is still good will the nitrogen container cause such a thing? If I could get by with just refilling would be great but I do always assume the worst. Anyone else ever had this problem who can shine some light? PS I do have a manual but have found nothing on this as far as help goes.Thanks once again any input is awesome.

  • grayracer513

Posted May 05, 2011 - 06:58 AM


I doubt you'll get much benefit out of simply recharging the nitrogen bladder. The likelihood is that the fluid is beat to death and full of air. Having the shock serviced (resealed and new fluid) is probably what's needed.

  • Michael Cahill

Posted May 05, 2011 - 07:17 AM


I may be in the same boat with the rear shock...

how much would a decent shock service cost?

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  • rickybobby2189

Posted May 05, 2011 - 06:03 PM


Can I not service the shock myself? I am not fond of paying the stealerships if I can keep from it.

  • grayracer513

Posted May 05, 2011 - 08:03 PM


Do you have access to high pressure nitrogen?

Shock servicing is not that tough if you're not changing the seal or revalving, but it's an A level job to change the seal because you either have to remove the clevis or disassemble the piston and valve assembly. There are minor safety hazards involved in opening the shock, also.

  • rickybobby2189

Posted May 06, 2011 - 05:19 PM


I do not have access to nitrogen.Is it not the same kind that goes into tires? And if it is can the people just put it in at a cetain PSI just like in a tire? I need more info on the rear shock rebuild.Is it harder than doing front forks? I didnt have much of a problem on them. I do have a little diy knowledge so hopefully I can get it taken care of myself

  • grayracer513

Posted May 06, 2011 - 06:55 PM


Most tire shops can't do it because their nitrogen setups don't run up to the 135-155 psi that the bladder requires. To do it right, you also need a special "no-loss" chuck that will not allow pressure to escape as it's disconnected. If there is an off-road shop or motorcycle shop in your neighborhood that has nitrogen for shocks, they can charge it.

The hang up for a lot of people is that the piston assembly is held on the shaft by a nut, and the end of the steel shock shaft threads are then peened over the nut. This peening must be removed adequately to unscrew the nut while removing a minimum of material from the shaft so that the nut will hold securely when it's replaced. And it should be replaced, also. You don't want to imagine what happens when this nut fails.

See the attached file for the rebuild method I use, from Dave Johnson at SMART Performance:

Attached Files

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