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PostPosted: Fri Mar 07, 2014 12:01 pm 
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lurkin' kitty

Joined: Fri Mar 07, 2014 2:24 am
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Hi, first up, great forum - many thanks for all the explanations, diagrams and photos. I'm getting there with a complete rebuild of my front and rear shocks.

[Edit: I've got a Fox F100 RL fork - year 2007 (I believe - it's a second hand bike).]

I'm a bit stuck on the top assembly for the damper. I'm missing the shaft that rotates to adjust the rebound damping, and I can't even find a good diagram of the part to see its shape clearly.

All of the full rebuild videos and photos seem to ignore this - maybe there's nothing to check with this part?

As shown in the diagram I've got an (incorrect) replacement - from a FIT assembly, but it's the wrong diameter and I suspect completely the wrong shape too.

Attachment:
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Can anyone point me to the missing component - diagram or close up photo dismantled?

Also - I'm struggling to understand how this top end part would affect the rebound damping - any hints?!

Thanks a lot,
Martin


Last edited by murt88 on Fri Mar 07, 2014 10:32 pm, edited 2 times in total.

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PostPosted: Fri Mar 07, 2014 12:55 pm 
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bad kitty!
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This would be a matter for the resident Fox expert Marpili.


Magura :)

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PostPosted: Fri Mar 07, 2014 7:27 pm 
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big hucker
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Lol, I'm no expert. Thanks, though!

I'll search for a diagram when I get home from work. Curiously, how did the shaft go missing?

If I remember correctly, by turning the shaft it screws the shaft down/up and closes/opens a port near the bottom of the assembly. This changes the flow of fork oil to slow down or speed up the rebound.

Can you post up a full photo also? It looks like an RL damper, correct?

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PostPosted: Fri Mar 07, 2014 10:22 pm 
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lurkin' kitty

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Thanks Marpilli,

Yes, it's a RL fork (I've add that above now).

The shaft is missing because the adjuster was overtightened and broken by the previous owner of the bike (meaning the rebound damping was not adjustable any more), the fork was serviced (at which point the bike shop may have removed part of the broken shaft since I can't find any broken bits inside), and finally the red top-cap and remaining part of the shaft worked loose and are on a trail somewhere!

The forks (and rear shock) had various other broken components but I've been able to find parts or improvise, and even if costs a few bucks, I want to learn to do this stuff so I can service the other newer mountain bikes in my garage when the time comes.

A full image of the assembly partially dismantled:

Attachment:
full.jpg
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The lockout part (showing smooth internal surface) as well as the incorrect FIT part I got, showing a very different internal that is maybe press-fitted in.

Attachment:
wrong.jpg
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and the assembly put together without some bits to show the orifices and channels.

Attachment:
top2.jpg
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I'm hoping I can make or find a part once I know what I'm look for here! The FIT part seems to have the adjuster shaft fixed inside the lockout adjuster, whereas (looking at videos and your rebuild photos) it looks like my fork has the rebound damping adjuster shaft fixed inside the damping piston somehow?

Also, what's bugging me a bit is my novice understanding of the actual damping process means I don't get how these parts affect damping - maybe you can help me? I think I probably have something wrong in my basic understanding! Here's what I think (excuse incorrect terminology and I expect it's more complicated that I'm saying - just need a model I can cope with!):

Compression:

Attachment:
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- positive pressure in main chamber, negative in NC
- Fluid enters NC easily through check valve,
- Fluid also forced into X and then Y and then into the fork body, creating damping at each point
- lockout works by stopping X into Y
- Maybe some fluid moves out at base valve A shims but this would bypass the lockout to some extent so not sure - (or it's just a blowout valve?)

Rebound:

Attachment:
diagram.jpg
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- positive pressure in NC, negative pressure in main chamber
- fluid forced into main chamber from NC creating damping
- negative pressure in main chamber, but..
- Fluid enters at A easily through check valve? (which is why the fork needs to be pumped a few times when not used to charge X and Y through A)

Which leaves me wondering: If Y is a closed box to negative pressure and if fluid can enter through A easily anyway, how can anything in this top assembly or within the shaft affect rebound damping?

I'm sure it does (I just don't get it)!

[Edit: I now understand from later posts that the rebound adjuster connects to a rod that goes down the inside of the damping shaft and connects to a rotating part threaded into the bottom of the shaft. These combined adjust the size of a little port on the damping shaft that allows some fluid to escape the NC chamber into the shaft, bypassing the damping piston valve (shims). I was missing this rod.]

Many Thanks,
Martin


Last edited by murt88 on Sun Mar 09, 2014 9:53 pm, edited 1 time in total.

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PostPosted: Fri Mar 07, 2014 11:28 pm 
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big hucker
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We're about to head out to a friend's for dinner. But, I dug through my garage docs and found my previous service diagrams when I was troubleshooting an RLC (very similar).

The top section you've disassembled: 820-05-002-A 02-08 Base Valve RL (Vanilla or Float)

I couldn't find a diagram for it.

Diagram for the RLC which might help: https://googledrive.com/host/0Bxc99IsGY ... ection.htm

Diagram for the RL (100mm travel) damper cartridge: https://googledrive.com/host/0Bxc99IsGY ... s_list.pdf

Diagram of the rod: http://service.foxracingshox.com/consum ... 5_rev1.pdf

I actually have a spare Fox RLC damper in the garage (don't know what travel it supports) that I'll never use. If it would be helpful, I'd be happy to disassemble it and take photos. And, if you need any parts from it I'm sure we can work something out. ;)

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PostPosted: Fri Mar 07, 2014 11:29 pm 
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big hucker
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I'll read through the rest of your post when my wife and kids are not standing here over me (like they are right now) because we have to leave. :lol:

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PostPosted: Sat Mar 08, 2014 5:26 am 
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lurkin' kitty

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Thanks a lot Marpilli,

It never occurred to me that the adjuster might be connected to a rod that goes all the way to the bottom of the damper shaft (the bike shop threw away more stuff than I realised - several ball bearings, springs and a 200mm adjusting rod! (to be fair I wouldn't have understood at the time if they told me what they'd done anyway). However, I'd rather have a broken rod now..

Looking again, I see a little slot/port at the base of the piston shaft which connects to the NC chamber (see photo below). There's a moving part inside the bottom of the piston shaft (in the photo below it's out, I just realised I could rotate it out). When in place, the "adjuster rod" rotates it and it lifts up and down.

And so I'm guessing this adjustable port allows the fluid in the NC chamber to bypass the damping piston valve (shim washers etc) and exit straight into the damping shaft internal space during rebound.

Attachment:
adjuster.JPG
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In terms of understanding how it all works though, I'd appreciate it if you could have a quick look at what I've said above and in the first post if you get a chance (if the wife and kids give you a chance..!) and tell me if the basics are right?

One more question: the adjustable slot is covered by a small collar in my Fork (but the online images and diagrams don't have this collar it looks like..). It moves fairly easily (it has a cut from top to bottom) and I think when the fork is at full extension it probably gets pushed over the slot if it is not already there). Not sure why it is needed or if the compression action somehow moves it off the the slot - any ideas? I can only imagine it acts to stop or slow fluid leaving the NC. I will try the fork with and without it when I've got the rod sorted out. Do you have an idea how it works/what it does?

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BTW, thanks a lot for the offer of the parts - I live in Australia and postage from the US to here is fairly expensive so at this point I'll see if I can find a workaround (I have a few ideas about how I can make a replacement rod anyway, now I understand what it does).

Anyway, thanks again, much appreciated,
Martin


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PostPosted: Sat Mar 08, 2014 2:39 pm 
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big hucker
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I don't remember seeing a collar like that on my damper. If I can get through my list of chores for the day I'll grab the damper open it up and take some photos.

I am not a suspension expert by any stretch of the imagination. However, I'll share what little I do know and hope someone steps in and corrects me if I'm misguiding you. :)

I've not given much thought as to how the Fox damper works (specifically). My issue was that the rebound knob would just spin and not adjust the rebound rate. After looking at the diagrams I realized it had come unscrewed from the part that blocks the port. Once I had that back together, everything worked as I wanted and I moved on to other tasks. :)

I was once told that bicycle suspensions are basically smaller versions of motorcycle suspensions. All hydraulic dampers (that I know of) operate by varying the flow of oil through the mechanism.

A shim stack is the primary method of controlling the compression characteristics. Two good links that can explain shim stacks better than I ever will:

Rebound control is simply varying the rate of oil flow to change how quickly the fork returns to full extension.

Warning: Once you start searching and reading on this stuff the rest of your day will just disappear. ;)

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PostPosted: Sun Mar 09, 2014 9:16 pm 
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lurkin' kitty

Joined: Fri Mar 07, 2014 2:24 am
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Thanks for the reply again Marpilli.

My original issue was the same - spinning rebound knob, but In my case the rod was snapped. The bike shop (probably) removed the broken rod, but I think it was snapped on the section that meets the detent balls and so they threw away the detent balls, springs, and most of the rod. Which meant that the top section was being held in place by an o-ring and the adjuster at the bottom was spinning freely!!! It was never going to last longer than a ride or two which is what happened. And so I unnecessarily lost the top cap on the trail (and also the balls and springs).

I get all this now because of your diagrams and I feel justified spending the time and money to learn to service my own forks and shocks!

Thanks for the offer of photos. I think I get the instructions on the dimensions and rod diagram you posted - I think it's saying that the rod is milled to a square profile in the top section A and that the missing ball bearings and springs are detent balls that hold the square profile. I've started to make a replacement from some aluminium rod I found and it's looking good.

However, a photo of the rod close-up to confirm I'm interpreting the diagram correctly would be nice!

Also, any extra info or photos about that collar would be great. I'm assuming (for now) it was included with some versions of the fork and not others. I'd like to know what it does and how it works with respect to damping and compression for my curiosity as much as anything.

Thanks for the info about how damping works - that adds to what I know. So far I think my understanding of how this fork works is (more or less) right.
Several of my days have already disappeared so what's a few more, eh?!

Many thanks again,
Martin


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PostPosted: Sun Mar 09, 2014 10:32 pm 
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bad kitty!
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Magura wrote:
This would be a matter for the resident Fox expert Marpili.


Magura :)


QFT :D

Magura :)

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PostPosted: Mon Mar 10, 2014 12:03 am 
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lurkin' kitty

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:)


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PostPosted: Mon Mar 10, 2014 1:01 pm 
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big hucker
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Martin, I'll try to check on the collar and take photos of the rid tonight or tomorrow.

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PostPosted: Mon Mar 10, 2014 8:48 pm 
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lurkin' kitty

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No problem, thanks.


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PostPosted: Fri Mar 14, 2014 11:07 pm 
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big hucker
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I took a quick look last night and I didn't see a collar on mine. It is an RLC, though. Now that I have it opened I'll take a couple of photos tonight.

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PostPosted: Sat Mar 15, 2014 12:30 am 
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lurkin' kitty

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Great- thanks. I think I'll start with the collar in place the first time I reassemble.

I've done some trial runs making a new rod from a piece of plain aluminium rod and I think it should work well.

I don't think the rod takes a lot of direct force - the only bit I'm worried about is getting the tolerance right at the top of the rod where it seems like it's just a close fit and a single o-ring that contains the compression force of the fluid from escaping around the rod. If you can show me a few photos of each end of the rod in detail it will verify I'm not missing anything from the diagram :)

Thanks again
Martin


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PostPosted: Sat Mar 15, 2014 1:37 am 
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big hucker
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Just saw your message. Here's a quick pic of the entire assembly. (click to enlarge)

Image

I'll need to take a look at the diagram to see how it comes apart. Haven't stripped it down to that inner rod before. :)

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PostPosted: Sat Mar 15, 2014 2:20 am 
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big hucker
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** click on any image to enlarge **

I removed the detent set screw, spring, and ball from both sides.

Image


Then I removed a screw from the bottom.

Image

Image

Image Image


Out comes the damper rod.

Image

Image

Image


Gratuitous damper rod photos...

Image

Image

Image

Image

Image

Image

Image

Image

Image

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PostPosted: Sun Mar 16, 2014 11:16 am 
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lurkin' kitty

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This is great - thanks a lot for the photos.
Really appreciate the effort you've gone to.
I was more or less on track but it's good to see the details
- in particular the bit where the detent balls hold the rod were a bit hard to be sure of.
Will get on with making the final piece this week, and I will let you know how I go!
Many Thanks,
Martin


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PostPosted: Sun Mar 16, 2014 12:34 pm 
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big hucker
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I'm glad the photos help. And, I'm very impressed with your DIY damper rod project and I do hope you'll post up pics of the results when done. I'd also like to hear some detail on how you produced the part. Cool stuff, for sure. Good luck! :)

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PostPosted: Tue Apr 01, 2014 9:42 pm 
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lurkin' kitty

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My fork is reassembled with a new home-made damper adjusting rod so I thought I'd stick some photos up as promised.

The final result is rough around the edges but seems to be working okay. I can't really test it in anger as the rear RP2 shock is currently fully disassembled waiting for a Schrader value to arrive from ebay to charge the IFP chamber ;)

I don't have a lot of tools so this was all improvisation and lots of little mistakes!

I used a brass rod in the end (after doing some trials on aluminium) because I couldn't get the correct diameter in aluminium and hobby shops have a variety of brass rods cheap.

I struggled to get parts so I made little detent springs using this website and electric guitar wire. I used a cordless drill and I was surprised how easy this was: http://www.deansphotographica.com/machi ... ings2.html
I also made a replacement damping check washer from a steel olive oil can by clamping a piece of the steel between 2 pieces of wood, drilling a hole and then cutting with a scissors and tidying up with files and sandpaper. This wouldn't work for the shims but with the check washer I figured it will be fine.

I marked out the rod using the specs Marpilli provided (thanks again!).
Attachment:
IMG_1243.jpg
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I started by making an adjustable 'lathe' that allowed me to file the rod.
Attachment:
IMG_1244.jpg
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In general the rod design seems to not have many fine tolerances to it. The bits that I was most worried about was the fit of the top of the rod inside the lockout adjuster. This has a close fit and a single o-ring to resist the compression fluid pressure. So I started there and did that very cautiously. I figured if I had to start from scratch a few times with that so be it.

Used an o-ring from a rebuild kit I bought (I reckon this will be a bag of spares for all my forks).

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Making sure it fitted properly..

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Then filed out the narrow area.

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I couldn't think of a simpler design (suiting my limited tools) for the detent area. It needs to allow fluid through, have a detent pattern and also keep the rod strong (as wide a profile as possible). On the other hand I think the tolerances are low for it to work (i.e. even if it looks like rubbish it will work if it is roughly right!). I set up a small drill bit and screwed 2 pieces of wood together to hold the rod and allow me to mill (!) a rough groove in it by hand..

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When finished (but before tidying up with a little file) it looks like this:

Attachment:
IMG_1255.jpg
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All was going well until I got to the bottom end of the rod and I broke my little thread tapping tool leaving the tip in the rod. Having put a good bit of effort into the rod already, rather than start again, I cut the rod, and attached an aluminium trial piece I had made by cutting the 2 to match, drilling a hole and hammering a piece of hex key to hold the two prices together (and then filing and sanding).Really ugly looking but should work ok!

Attachment:
IMG_1259.jpg
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The main thing I struggled with was drilling small holes and tapping screw threads which I've never done before. I bought a cheap tap and die kit (probably my first mistake) and I think I need to be more precise with the drill bit sizes I used. However, on the plus side, brass and aluminium are much easier to shape than I expected, with a drill and some files.

The main thing I got from this is a good sense of how all the parts work inside the fork. I reckon if I built another rod now it wouldn't be such a frankenstein, but given it's hidden inside the fork who cares! I'll dismantle it after a few rides and see how it's all going in there.


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PostPosted: Tue Apr 01, 2014 11:36 pm 
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pussy
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Nicely done! I am quite sure your manufacturing tolerances and finish are better than the factory original. :)


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PostPosted: Wed Apr 02, 2014 12:48 am 
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lurkin' kitty

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:) not sure about that but so far there's no fluid squirting out the top so all good!


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PostPosted: Wed Apr 02, 2014 1:47 am 
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big hucker
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I am very impressed! And, thank you very much for taking the time to photograph and write up the process. Sometimes that's the bulk if the work. ;)

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PostPosted: Wed Apr 02, 2014 5:31 am 
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lurkin' kitty

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No problem, thanks again for all your help.
As I mentioned, I'm working on your RP2 Schrader valve mod project next - just waiting for the valve to arrive!


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PostPosted: Wed Apr 02, 2014 11:31 am 
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big hucker
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You'll like it. Mine is still holding up well. :)

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PostPosted: Wed Apr 20, 2016 3:41 pm 
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lurkin' kitty

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marpilli wrote:
I actually have a spare Fox RLC damper in the garage (don't know what travel it supports) that I'll never use. If it would be helpful, I'd be happy to disassemble it and take photos. And, if you need any parts from it I'm sure we can work something out. ;)


I realize this is a very old thread... And I'm restricted from sending private messages, but I was curious if by slim chance you may still have this damper assembly?


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PostPosted: Sat Apr 30, 2016 12:51 am 
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big hucker
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Mkap wrote:
marpilli wrote:
I actually have a spare Fox RLC damper in the garage (don't know what travel it supports) that I'll never use. If it would be helpful, I'd be happy to disassemble it and take photos. And, if you need any parts from it I'm sure we can work something out. ;)


I realize this is a very old thread... And I'm restricted from sending private messages, but I was curious if by slim chance you may still have this damper assembly?

My kids are older now and they tinker around in the garage at my workbench. The damper suffered an unfortunate accident in their hands. :cry:

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