[Asiaoildude]

OM says

427 cc right leg
298 cc left leg

IS this right? Legs look the same (although I guess left leg has brake system on it).

Fluid recommended is a 7.5 weight. I'm planning on changing to a 5 weight.

Does anyone know if there are any drain screws on the bottom of the legs? I can't see any so I'm assuming I'll have to suck the old oil out.

 

[Doc59]

Sorry to say but I think drain screws dissapeared back in the 80s.
Different oil quantities are because one fork does compression only and the other rebound only, can't remember which did which off the top of my head.
If you are going by quantity and not an oil level measurement then I think you would be better off pulling the fork legs off the bike and drain as much old oil out as you can, then refill with those quantities. If you suck the old oil out you will probably have some left in the bottom and end up with too much oil.

Let us know what difference the 5 weight makes when you do it.

 

[Asiaoildude]

Ok that makes sense and I figured it was going to be that hard.

 

[silverluxe]

One leg is compression and the other is rebound which is somewhat common with upside down forks. They definitely take different amounts of oil. Also you have to completely tear them down to get all of the oil out of them and then put in exactly those two amounts because there's no way to measure with a dip stick like old skool forks you may be use to.

I read through the tear down in the service manual and I think you may need a special tool or two in order to take them down far enough to drain them. It goes without saying that they have to come off of the bike though, unfortunately.

 

[Asiaoildude]

One leg is compression and the other is rebound which is somewhat common with upside down forks. They definitely take different amounts of oil. Also you have to completely tear them down to get all of the oil out of them and then put in exactly those two amounts because there's no way to measure with a dip stick like old skool forks you may be use to.

I read through the tear down in the service manual and I think you may need a special tool or two in order to take them down far enough to drain them. It goes without saying that they have to come off of the bike though, unfortunately.

Ah **** - surely not? if they're off - can't they be inverted and pumped to drain?

 

[Vincelp]

Hello

Ah **** - surely not? if they're off - can't they be inverted and pumped to drain?

I've maintained my Ducati ST2 quite a long time and, and I can say that, to drain it completely when you're renewing the oil, you have no other solution to completely remove the legs from the bike and put them upside-down.


If not, you will certainly leave some used oil in the damping cartridge, when there's one and if you put back the requested quantity of new oil, there will be to much oil, the air chamber will be smaller and the fork behaviour will change to a harder behaviour.


It also means that putting it upside-down is not enough, you must move the damping system to empty it entirely. In other case, it may keep some oil.


I'm going to install soon Wilbers spring instead of the OEM ones and I'll try to change the springs without emptying the fork legs. It should be possible because removing the spring doesn't require to remove the fork oil.

 

[Vincelp]

OM says
427 cc right leg
298 cc left leg
IS this right? Legs look the same (although I guess left leg has brake system on it).

The OM says that the left leg has got no spring nor damping system, which seems a little bit strange for me.


I've discussed by mail with people within Wilbers or Maxton and both of them told me that the too legs were different, the difference being only that the right leg has got a damping cartridge, when the left leg has'nt got one. None of them told me that the left leg had no spring... which would mean that it is empty and only acts in compression.

 

[Vincelp]

I found back one their answer and I can say that both legs have got a spring, the preload spacer length differs and the right leg has got a damping cartridge. All this explain why the oil volume is different.

 

[tonyjuliano]

In stock form, both legs have springs - but only one has a damping cartridge (the other just has a "dummy"). Only one leg controls damping, and it does an exceeding poor job at that.

 

[Ken Hall]

Tony is right. Both have spring and only one leg controls damping. The Dummy leg requires a special tool to take apart to change the oil. Unless you disassemble and clean the legs completely you will never get all the oil out of the forks. The quantity of oil added will be incorrect.

 

[ghug]

I just upgraded the rear shock to an Ohlins and need to do something with the fork. I'll upgrade cartridges and springs at some point in the future but I'm looking for an incremental improvement if it exists.

Does it stand to reason that if I remove oil with a syringe keeping track of the exact amount that I remove, then replace that amount using say 15-20w fork oil I could get a firmer ride. I'm a big guy and it's just way too squishy now. My other thought was just to add small amounts to what's in there now and keep exact track of those amounts.

I'd appreciate any help on this. Any other big guys try something like this out?

Thanks in advance!


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[Vincelp]

Hello

Does it stand to reason that if I remove oil with a syringe keeping track of the exact amount that I remove, then replace that amount using say 15-20w fork oil I could get a firmer ride. I'm a big guy and it's just way too squishy now. My other thought was just to add small amounts to what's in there now and keep exact track of those amounts.

You can do that, yes. You'll be able to do it only on the right leg, because the left leg has got an inner tube cover that won't allow a hose to go down and look for oil.
As the left leg hasn't got any damping system, changing the oil in it won't change anything on damping behaviour.


I wouldn't change the 7.5 oil directly for 15 or 20 oil. I would better try before with 10, generally speaking damping systems are very reactive to oil fluidity. Also consider to remove a little bit of oil height (about 2 cm), you'll get a softer fork on small shocks because of a larger compressible air chamber.

 

[ghug]

Thanks for the input Vincelp! I'll give this a try.


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