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Discussion Starter #1
I explain here how to replace the springs in the front fork of a Scrambler. The new springs are Wilbers made, and they are progressive springs.

The bike is installed firmly on the workshop table :


Here are the Wilbers springs, longer than OEM and progressive :


First, un-screw the axle nut, on left side :


Then un-screw the 4 screws that hold the axle within the fork foots :


Un-screw the 2 screws that hold the brake calliper, you can then remove it from the disk :


Un-screw the screw that holds the ABS sensor within the fork left foot :


The ABS sensor with its spacer :


You can then remove the axle nut, the axle and the wheel from the bike :


The wheel, with its axle, its spacer and its nut :


Inside the fork left foot, un-screw partially the screw that holds the ABS sensor cable :


The ABS sensor cable is free, we are quite ready to remove the legs :


Just grab the brake calliper, to protect the brake hose :


Un-screw the 4 screws that hold the mudguard on the fork legs :


The mudguard is released, we can then take the fork leg outside of the fork joints :


Un-screw only the screw in the upper joint, to be able to un-screw the fork cap :


Protect the fork cap with tape, because it is softer than the tool, un-screw slightly the cap :


Un-screw the 2 screws in the lower joint, holding the leg that may go down :


The leg is installed firmly on the workshop table :


While pushing down on the preload tube, you insert an opened washer, to maintain it down while you will unscrew the cap from the cartridge axle :


The cap is un-screwed, we can remove it entirely :


Here is the opened washer we used previously to unscrew the cap :


Both springs, side to side, the Wilbers is on right side, longer and progressive :


The left leg inside, without preload tube :


And here, I'm stuck, not understanding how to remove the spring...
 

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Discussion Starter #2
Hello

Waiting for the solution for the left leg, I just changed the right spring and removed, as adviced by Wilber, 20 cl of oil within each leg.
I've re-installed everything and checked the fork behaviour, statically in my garage. It already seems to be softer in compression, which is quite normal as some uncompressible oil has been replaced by an equivalent volume of compressible air.

Before modification, the fork values are :
- total length : 195 mm
- sag with bike weight only : 30 mm
- sag with bike and pilot (85 kg) : 50 mm
- maximum sag after riding, with strong braking phases : 135 mm

After modification :
- total length : 195 mm
- sag with bike weight only : 25 mm
- sag with bike and pilot (85 kg) : 50 mm
- maximum sag after riding, with strong braking phases : to be tested tomorrow
 

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Discussion Starter #6
Hello


About the air chamber, I first removed 2 cl of oil, after some calculations, but I was wrong.
In the second phase, using the 140 mm hose and syringe, I've removed some more oil (I don't know how much), but now, I'm sure the air chamber has got the right height.


This air chamber height (and so far volume) has an immediate effect on the behaviour of the fork in compression. The more air you have in the fork leg, the more compressible and soft is the fork.


The cheapiest way to change the fork behaviour may be : just increase the air chamber size by removing some oil.
 

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Discussion Starter #8
Hello

Before modification, the fork constants are :
- total length : 195 mm
- bike only sag : 30 mm
- bike + pilot (85 kg) sag : 50 mm
- maximum sag : 135 mm

After complete modification (2 progressive Wilbers springs + 140 mm air chamber) :
- total length : 195 mm
- bike only sag : 25 mm
- bike + pilot (85 kg) sag : 40 mm
- maximum sag : 145 mm

So, after modification, we have 20 mm more fork displacement : (135 - 50 = 85 mm) becomes (145 - 40 = 105 mm)
 

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Hello


About the air chamber, I first removed 2 cl of oil, after some calculations, but I was wrong.
In the second phase, using the 140 mm hose and syringe, I've removed some more oil (I don't know how much), but now, I'm sure the air chamber has got the right height.


This air chamber height (and so far volume) has an immediate effect on the behaviour of the fork in compression. The more air you have in the fork leg, the more compressible and soft is the fork.


The cheapiest way to change the fork behaviour may be : just increase the air chamber size by removing some oil.
Vince, I saw this excellent post and something bothered me but I couldn't put my finger on it. But now I realize your comment that the air chamber is only 120mm to start and you pulled out 20mm to make it 140mm. Doesn't the fork have 150mm of travel? How is this possible with 120mm of air space? Wouldn't it hydraulically bottom out at 120mm? I must be missing something.

Can you explain this? Shouldn't it have 150mm of air space? If so, I'll try it when I get a chance. -Thanks
 

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Discussion Starter #11
Hello
Vince, I saw this excellent post and something bothered me but I couldn't put my finger on it. But now I realize your comment that the air chamber is only 120mm to start and you pulled out 20mm to make it 140mm. Doesn't the fork have 150mm of travel? How is this possible with 120mm of air space? Wouldn't it hydraulically bottom out at 120mm? I must be missing something.
Can you explain this? Shouldn't it have 150mm of air space? If so, I'll try it when I get a chance. -Thanks
The air chamber height is measured when the spring and spacer are removed and the fork being entirely compressed. It means that in such conditions there's a 120 mm air column (or 140 mm after mod) remaining. So, when the fork is not compressed, even with the spring and spacer inside, you get a much taller air chamber, something like 140+195 mm.
 

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Vince, OK got it so it's not just a matter of pulling the caps and adjusting the fluid levels. Since it is basically a full disassembly, might as well buy the springs and tools to do it right like you did. Winter time project for me.
 

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Discussion Starter #13
Hello
Vince, OK got it so it's not just a matter of pulling the caps and adjusting the fluid levels.
It's certainly possible to remove some oil without dismounting the fork like I did, by just opening the caps and pumping the oil with a much longer and thinner hose. With a try & error procedure, you may find the right value to remove so that the fork becomes smoother in compression.


The left cap can be removed without dismounting anything, just unscrew the screw in the upper tee. The right cap certainly needs to remove the handlebar and the speedo unit support.


But, I'm afraid that my fork behaviour has also been enhanced by the Wilbers progressive springs, not only by the air chamber increase.
 

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Discussion Starter #14
Hello
But, I'm afraid that my fork behaviour has also been enhanced by the Wilbers progressive springs, not only by the air chamber increase.
I can confirm this : found in different place on the net that the difference between a progressive spring and a regular spring is that the first one requires less effort to compress the part where the coil are closer.


It explains why my fork has become softer on some shocks.
 

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Hi Scramblers just an update on the removal of the screw 5M worm screw that sits in the stub off the fork Leg.
I saw a video that said you had to use a 3 mm drill bit to drill out the 5M Worm Screw.
So I tried this new approach.
I took a 3 mm hex/allen nut and gently tapped it into the 5M worm screw.
Then I took my drill and with some very careful attempts it worked.

Have a look at this video.
 
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