Need some suspension help

[Thunderace]

I have a GP Suspension 25mm kit in my forks. The right fork leg is for rebound and the left is for compression. I am skilled enough to refresh the oil and change out some springs, but I'm having difficulty with the rebound leg.

I swapped the oil in the compression leg and installed a new spring. Everything went as planned and it's back on the bike. The rebound leg was disassembled and I installed new oil. The problem I am having is when I pump the cartridge rod up and down, I am not getting any resistance up or down. It's as if the oil is not getting inside the cartridge.

This is my first time dealing with separate functions from one fork to the other, so I'm not sure if this is normal.. Unfortunately, I did not check the functionality of the damper prior to emptying the old fluid.

Am I missing something? Is the rebound leg not supposed to have resistance? I'm just not sure if I have a bad cartridge.

 

[vinny337]

I wish I could help you Bro! that's the one thing I haven't touched yet.

 

[tdelegram]

Thermosman@gmail.com he'll answer any questions. If it ain't dirtbike I send it to him! In fact my 390 forks and shock are enroute back beefed up for me and will be tested at Barber.

 

[tad158]

When you put the oil in, before the spring, did you pump the damping rod? Now I don't have gp forks or something like that...but my forks have compression one and rebound in the other. When I rebuild them I have to pump the fork with the damping rod, then check the oil height. Many times after bleeding the cartridge like that I need to add more oil.

 

[Motofun352]

Shop manual is your friend. Spring out, fully compressed, air bubbles removed(ie pump, let set, repeat)...set oil level to the spec (the pro-motion tool makes this easy).

 

[Thunderace]

Removed fork cap, spring, spacer and damper rod
Turn fork upside down and empty fluid
Turn upright and pump damper, you can hear oil and air moving out of the damper
Fork upside down for over an hour, all oil extracted
Move damper rod up and down, action is smooth
Add 50cc of fork oil (total is about 300)
Begin to slowly move rod up and down
No resistance and no sound of it moving in and out of the cartridge
No change after 5 minutes of pumping
Add remainder of oil
No difference in resistance whatsoever
Let sit for several hours, no change
Let sit overnight, no change

It just doesn't make sense. I sent an email to GP Suspension as well. Tom, thanks for the idea of emailing Thermosman.

 

[tad158]

You need to put the needle spring and damping rod back in before you screw on the bleed rod tool. Then pump it.

 

[Thunderace]

Those two items don't effect oil going into or out of the cartridge. The other fork tube and all the other refreshes I have done in the past we done in the steps I listed above. I have never had a problem until yesterday.

 

[tad158]

This is how I do it....that is all....the other bit is that if the needle is not in there, there will be nothing to restrict the flow, and it should have almost no resistance, or basically the same as the compression stroke for that fork...dunno...The rebound leg is a bit more subtle on the damping, because when you pull the bleed rod out with the needle in place is when you feel resistance, when you push it down, it should go quickly....When you have a fork that has both rebound and compression, you are bleeding against both valve packs on each direction of the stroke....with this one, it is just the one direction, and with no needle they should be the same resistance, wide open. Once the needle goes in with all the other parts, and the fork cap on with the clicks set right, the damping is there.....at least that is how my rebound fork behaves.

 

[Thunderace]

I absolutely understand where you are coming from. It won't hurt anything to install everything, close it up and see if the fork functions like it should. I think I'm going to install everything tonight and see if the rebound adjuster works when it's all tightened up. I just didn't expect it to move up and down so easily. I'll let you know what I find out. Thanks for the help.

 

[Thunderace]

This is how I do it....that is all....the other bit is that if the needle is not in there, there will be nothing to restrict the flow, and it should have almost no resistance, or basically the same as the compression stroke for that fork...dunno...The rebound leg is a bit more subtle on the damping, because when you pull the bleed rod out with the needle in place is when you feel resistance, when you push it down, it should go quickly....When you have a fork that has both rebound and compression, you are bleeding against both valve packs on each direction of the stroke....with this one, it is just the one direction, and with no needle they should be the same resistance, wide open. Once the needle goes in with all the other parts, and the fork cap on with the clicks set right, the damping is there.....at least that is how my rebound fork behaves.

Thank you Brian for getting me out of my own head! I just reinstalled everything and at first it did not work. It was just a complete pogo stick. Then I put a towel on top of it and bounced up and down on it and something happened. When I compressed the fork 3/4 or so down the stroke, you could hear a "WHOOSH". You could hear the oil moving inside the cartridge. Then it began to restrict the upward movement like it should. I still need to get another spring in there, so it's going to come back apart, but at least I now know I don't have to get the cartridge serviced.

I owe you big time!

 

[tad158]

you owe me nothing....

oh and ps......

When do we get to see some pics of this beast!

 

[Thunderace]

I did get a reply back from GP Suspension this evening as well. Come to find out, the cartridges in my forks are prototypes, pre-production. They said that they have made some changes, but what I have are perfectly fine. They said sometimes on the rebound leg you have to hold your hand over the top of the open fork tube and pull down on the fork leg to create a vacuum inside. It helps pull the oil into the cartridge. By installing everything and leaning on it heavily, it forced the fluid into the cartridge.

I found out the other day that the brake pads on the bike are also prototypes from Ferodo. They were given to the previous owner to test and evaluate. He said they are amazing! I can't believe when I saw this bike on the net that I would be the one to own it. In my second email to the guy, I said "I am not a serious buyer, I am THE BUYER!" I feel blessed that I have to opportunity to own a work of art. Damn it's going to be a good year next year!

Pictures in the next thread! I've gotta make it look pretty first!

 

[tad158]

Awesome!....can't wait to see it....you should make a thread about the bike on the R1-Forum....

 

[Thunderace]

Awesome!....can't wait to see it....you should make a thread about the bike on the R1-Forum....

I never really had a bike worthy of a thread like that, but I bet the guys over there would drool over it! Like I said somewhere earlier, it's going to be a long winter, so I may just do that.

 

[gcally]

I have a GP Suspension 25mm kit in my forks. The right fork leg is for rebound and the left is for compression. I am skilled enough to refresh the oil and change out some springs, but I'm having difficulty with the rebound leg.

I swapped the oil in the compression leg and installed a new spring. Everything went as planned and it's back on the bike. The rebound leg was disassembled and I installed new oil. The problem I am having is when I pump the cartridge rod up and down, I am not getting any resistance up or down. It's as if the oil is not getting inside the cartridge.

This is my first time dealing with separate functions from one fork to the other, so I'm not sure if this is normal.. Unfortunately, I did not check the functionality of the damper prior to emptying the old fluid.

Am I missing something? Is the rebound leg not supposed to have resistance? I'm just not sure if I have a bad cartridge.

If you find that you need to try different springs let me know.
I have just about every weight Ohlin's springs laying around. I have .90, .95, 1.00, 1.05, and 1.10 springs.
The GP Suspension 25mm kit uses the same spring as the Ohlins 25/30 kits.

 

[Thunderace]

Sorry, it's too late, but thank you for the offer. I picked up some 1.10 fork springs and a 1.05 shock spring earlier this month. They are already installed and waiting for me to put them to use!