Switching fork oils. Flush or drain and refill?

I am servicing the forks on my '07 WR450F. Basically new seals and an oil change. The bike is new to me and although it was very well looked after by the previous owner he can not tell me anything about the fork oil he last used. My problem is that I have read that it is bad to combine different brands of oils in a fork, or anything for that matter. So must I then completely disassemble my forks and thoroughly clean everything or can I simply drain as much as possible out of the fork including the dampening rod assembly and refill with the fresh oil?

Obviously i would prefer not to pull the dampening rod out if possible and i definitely dont want to open up the d/r.

I guess the best option would be to send the forks out for a rebuild, but whats the fun in that?

Also, does anyone know where there is an exploded view of the dampening rod and its guts?

Thanks in advance

just remove the cart complete and clean everything well, have a look to see if the big spring is loose on the base valve(well known fault on the wr base valves) then refill with oil, no point in just draining them, if you have them off the bike do the job right is what i say.

It definitely is best to do as mog suggests for the reasons he mentions and for the fact that it can be difficult to get all the oil out of the cartridge while it's installed. If you disassemble them from the fork, it's much easier to completely drain them.

If you use a solvent rinse, pump it out as you did the oil, then flush that by pumping in a couple of ounces of your new oil and pumping it back out.

If you aren't going to take it apart, then it depends a bit on the condition of the oil you find in the fork. If it's pretty clean, drain what you can, and flush the rest by circulating 6-7 ounces of new oil and dumping it. If it's dirty, you really should consider pulling it apart, but if you just can't, use some Dexron ATF and pump and dump until it looks clean, then drain as thoroughly as you can and chase it out with your new oil until you can't see red as you drain it. Avoid using solvents in this case, as it is too hard to be sure you get it all out.

Most oils are compatible with each other, but one or two are not, these will usually be labeled "do not mix".

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