Fatty SL "clunk" noise while rebounding

Martinez

Martinez

Member
Tech question this time.

I own a Fatty SL HeadShok. First thing is that I can't find the exact model that I have in the catalogs. They all have a damping dial, when mine has only the ON/OFF option. Is it possible to have a fork "body" from one model and the insides of another model? Or maybe they made different forks for the European market? I'm clueless.

Anyway, let me get to the point.
When my shock rebounds, it makes a little clunk when it reaches it's top position. It's not as bad as it sounds, but a bit annoying. I pumped it with air to 150psi and it didn't help. The needle bearings and their track are all good and in position. The travel is also fine.
I've read somewhere that it may be because the oil level is low? When I lock the shock, there is still a little bit of travel, maybe a quarter of an inch.
Any idea how to adjust the rebound? Or maybe it's normal and I'm just overreacting?
 
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Brian

Brian

Administrator
Staff member
I have the same issue with a 2009 Fatty Ultra. I feel mine needs a rebuild. The clunk is very loud. You are not over reacting.
 
Martinez

Martinez

Member
Well, I guess I'll have to take a look inside then. Just need to make a castle tool. I will post a new thread with photos and stuff as soon as I get it done (assuming I won't fail miserably:D).
 
Martinez

Martinez

Member
I have a Fatty SL, but I can't find the exact same model in the catalogs. All Fatty SL's there have a damping dial, when mine has only the ON/OFF dial. The frame is from 1998, but the fork may be from a different period.

Anyway, I'm pretty sure mine is an air spring and oil damper combo. The job looks pretty straight forward as long as proper tools are used. Also, I'm not planning to mess with the needle bearings. Reinstalling them is the most difficult part of the job that requires voodoo and sorcery skills beyond my level of knowledge :D

As for the castle tool, I've seen a video with a guy undoing the screw with long 90 degrees needle nose pliers, but it's easy to mess things up with them, so I'll just make the tool from a piece of a steel pipe. Just need to find one that is thick enough so it won't bend.

Found the measurements:



I'll make one with a more simple handle than the above, but should work just as good.
 
Martinez

Martinez

Member
Well, I managed to get the oil damper out without the castle tool. Because of my impatience, I decided to try and undo the whole thing with a long enough 90 degree pin tool (the same I used to unscrew the top cap, just replaced the pins with longer ones for this operation). It unscrewed without any issues and with very little force. I DON'T RECOMMEND THIS METHOD! It worked for me, but it's easy to scratch the damper rod while doing this, so extra caution is a must.
If anyone decides to do this, I advise to put something between the rod and the tool to prevent damage. Piece of rubber hose or something similar, even wrapping the rod with a few layers of electrical tape will do.

Anyway, when i pulled the thing from the fork, there was a lot of oil everywhere. It was because the bottom cap of the oil damper was screwed only half way in and therefore wasn't sealed at all (not sure if I can put some Loctite on the thread to prevent it, as the cap is made from plastic and it screws into aluminium). There was even some oil inside the air cylinder (no clue how it got there). I think this is the reason the shock was rebounding so fast - no oil, so the air cylinder was doing all the work and there was nothing to slow it down.

I poured the remaining oil out and cleaned everything. Now I just need some new oil (maybe I'll get some tomorrow from a fellow biker) to put everything back together and see if there are any leaks. When I do, I'll make pictures and explain the whole process here.

On thing worth mentioning, is that the insides of my Headshok are unlike any of those I saw online. The one I have is much more simple.

Oh, one more thing. Because I had no intention of messing with bearings, I did everything without removing the fork from the bike. If you plan to service only the guts and leave bearings in peace, leave the fork on the bike, it will save you a lot of time.
 
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Brian

Brian

Administrator
Staff member
Very cool. Post pics if you can. And make sure you use the correct weight of oil. I should collect that info for a database.
 
Martinez

Martinez

Member
Got the oil, so I'll do the work in the evening. The guy only had a 10W viscosity, but it should work even better than the original since I'm a heavy rider ;) I've read people even put 20W inside, so there's a lot of possibilities for fine tuning.
 
Martinez

Martinez

Member
This manual is only for a specific type of Headshok, with ON/OFF option only! If your Headshok has a damping dial, some steps may be different. I have no knowledge of any other Headshoks than the one I have, so if yours is different - sorry, I can't help you. The manual also doesn't cover working with needle bearings and their tracks, so keep that in mind. All it really covers is removing the oil cartridge and air cylinder and changing oil in the cartridge.

You will need:

- allen key size 4 and 5
- shock pump
- pin tool
- castle tool (or longer pins for the pin tool)
- fork oil
- plastic bowl or something similar
- new seals if necessary
- paper towels
- a bit of patience ;)

So, here we go!

- Remove the front wheel.
- Remove air valve cap and release air pressure from the air cylinder. You'll find the valve on the bottom of the fork.

- Loosen up top stem screw a little bit (when it's too tight it will make unscrewing the top cap harder or impossible).
- Remove lockout dial screw and than the dial itself.
- Using the pin tool, remove top cap by turning it counter-clockwise.


- Next, using the castle tool (or in my case a pin tool with longer, homemade pins), unscrew the oil cartridge by turning it counter-clockwise. BE CAREFUL AND DON'T DAMAGE THE ROD WHILE DOING THIS! Put something between the tool and the rod to prevent damage. The rod is made from a very soft material and will scratch easily! I wrapped it with few layers of electrical tape.



- Pull the oil cartridge from the fork. The air cylinder sometimes comes out attached to the cartridge, but most of the times it will stay inside the fork. If it didn't come out, just push it from the bottom (where the valve is located) with your finger and pull it out. There will be a spring and a plastic shim an the air piston rod, remove them as well.


- The fork should be empty now.

- Remove the piston from the air cylinder (pressing the core of the air valve will help, if the piston is all the way down use a shock pump - few strokes and it will come out).
- Unscrew the bottom cap from the cartridge (mine was half way out, so i did it by hand, but you can use the pin tool to do it, just be careful and don't scratch the rod. Pour old oil out by moving the piston up and down a few times.
- You should end up with this:

- Check the insides of the air cylinder. Mine was full of oil. Clean it if necessary. Put a bit of oil on the air piston seals and put it back into the cylinder. Be careful and don't damage the seals while doing this. Press on the air valve while doing this to make it easier. Push the piston down the cylinder.
- Now for the oil cartridge. Do the following steps inside a plastic container to avoid spilling oil.
- Turn the cartridge upside down. Pull the rod so the piston inside the cartridge is all the way down (toward the top when in upright position).
- Fill it with oil. I used a 10W viscosity, but you can use different ones for different results. Default is 5W. High "W" means the fork will work slower, low "W" will make it faster. Pull the piston up and down a few times to get rid of air bubbles. Tap a few times on the cartridge with your finger to remove air bubbles from the walls. Top the oil up to the edge and leave the whole thing for a few minutes.


- Once all of the air is gone, thread the bottom cap back in. You will need to use the pin tool this time because of oil pressure making it hard to do by hand (when the cartridge is empty, it easily screws in by hand).

- Once the bottom cap is in its place, clean the cartridge from oil. Move the rod up and down a few times and check for any leaks. The cartridge should work quiet now.
- Reverse the process and put everything back inside the fork. Screw the cartridge back in it's place, as well as the top cap. Put the lockout dial back and secure it with the screw.
- Pump the air cylinder to desired pressure.

- Replace the front wheel.
- Have fun!


DID IT WORK?

Well... it's a lot better than before. The whole thing is now more quiet because there is no more air in the oil cartridge - no more squishy sounds when compressing or rebounding. The clunk is also gone and there is a much more pleasant tap when the fork rebounds. Could be more quiet if you ask me, but maybe I'm expecting too much. It is a 20 year old fork after all :p It still works fast, even with the 10W oil, I will try a higher viscosity next time. As for the lockout, this improved as well. There is hardly any play when engaged, but it doesn't hold when I lock the shock in a compressed state - it very slowly returns up. Maybe there is a seal inside the cartridge that needs replacing. Next time I'll order a complete set of seals and make a full service, including disassembly of the cartridge. I didn't replace any seals on this attempt.

If you have any questions feel free to ask, I may have missed something.
 
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Martinez

Martinez

Member
Ok, I had to redo the job. The lockout stopped working good after one day (no riding) and there were squishy sounds again when pushing the fork down. After pulling the guts once more everything looked normal (no oil leaks) but I could hear air inside the oil cartridge. I think the cartridges bottom cap seal was to blame, because it was worn a bit when I assembled it the first time and most likely some air got in thru it (at least that's my theory). I decided to open the cartridge this time - used 90 degree circlip pliers and unscrewed the top cap from the cylinder. It came out easily (by the look of the top cap I'm pretty sure someone opened it before without a proper tool, there's some scratches on it, nothing major though). The insides look like this (not my photo but those are identical to mine):



The seal that sits on the red piston looked good, but it wasn't big enough to cover the diametr of the cylinder, so I tried to find a replacement at a local hardware store. Found one that looked identical, but it turned out to be too big and I couldn't push the piston back into the cylinder with it on. I believe that it must be a specific one made for Cannondale, not a common size that you can buy anywhere. There was no other option than to cheat a little bit - I took some teflon tape and put one layer of it under the seal (between the seal and the red piston to be precise), so it pushed the seal a little bit out, increasing its diameter. After that it started to work as it should. I refilled the cylinder with oil again, paying even more attention to getting rid of all air bubbles and closed it with the bottom cap, which I equipped with a new seal (that one was a common one).

Note: when filling the cylinder with oil, it can't be topped all the way to the edge. Oil pressure is building inside as you screw the cap back in and makes it harder with every turn. You have to pour a bit of oil out, little by little, and find that sweet spot when you can screw the cap all the way in and don't leave any air inside.

Twenty four hours now passed and the lockout is rock solid! Not even a little bit of play and the fork is quiet as it should be. I will still look for a set of original seals, but it should be good for now. Now all I need to do is wait for the rain to stop, take the bike for a ride and see if it still works after that ;)
 
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MikeA

MikeA

Well-Known Member
This is an older post, but I thought I would add some notes for the next person looking here for info. This is a pre 2005 DL80 cartridge, the proper seal kit is still available, part #HD166. The piston ring is a standard -018 o-ring, but the replacement in the kit is a viton material. The piston ring does not fit tight in the cylinder, it's not supposed to. no teflon tape necessary. This is why on some models the fork will slowly drift down on lockout with steady down force. This is normal.

To replace all seals, the lockout shaft will have to be pressed out of the top hex. It comes apart like this DD60:

dd60.jpg


There is a bleed screw inside the lower shaft. Add oil, cycle the damper slowly till you don't hear air. top off so it's overfilled. Loosen the bleeder about 1 turn. tighten the cap, let oil spill over. When the cap begins to seal, the excess oil will purge out the bleeder. Tighten the cap and bleeder.

The end caps have u-cup seals that are directional. The lower cap needs to be installed to the shaft with the "bullet tool" in place to prevent damage.( part # HDTL168), it looks like this:

bullet.jpg


The light clunking still heard after purging the air from the damper may indicate the bearings need a reset. Linear bearings like Cannondale used in the telescope will migrate over time. This shortens the travel of the telescope and causes a light clunking. They actually recommend having a dealer perform a reset every 25 hours. The cartridge is removed and this tool is threaded in its place. With a few light slams downward till the marking on the tool lines up with the outer steerer, the bearings are knocked back into place.

reset tool.jpg
 
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Victor Haugen

Victor Haugen

Member
MikeA said:
This is an older post, but I thought I would add some notes for the next person looking here for info. This is a pre 2005 DL80 cartridge, the proper seal kit is still available, part #HD166. The piston ring is a standard -018 o-ring, but the replacement in the kit is a viton material. The piston ring does not fit tight in the cylinder, it's not supposed to. no teflon tape necessary. This is why on some models the fork will slowly drift down on lockout with steady down force. This is normal.

To replace all seals, the lockout shaft will have to be pressed out of the top hex. It comes apart like this DD60:

View attachment 5461

There is a bleed screw inside the lower shaft. Add oil, cycle the damper slowly till you don't hear air. top off so it's overfilled. Loosen the bleeder about 1 turn. tighten the cap, let oil spill over. When the cap begins to seal, the excess oil will purge out the bleeder. Tighten the cap and bleeder.

The end caps have u-cup seals that are directional. The lower cap needs to be installed to the shaft with the "bullet tool" in place to prevent damage.( part # HDTL168), it looks like this:

View attachment 5462

The light clunking still heard after purging the air from the damper may indicate the bearings need a reset. Linear bearings like Cannondale used in the telescope will migrate over time. This shortens the travel of the telescope and causes a light clunking. They actually recommend having a dealer perform a reset every 25 hours. The cartridge is removed and this tool is threaded in its place. With a few light slams downward till the marking on the tool lines up with the outer steerer, the bearings are knocked back into place.

View attachment 5463
Click to expand...

I also hear a "clunk" noise during the ride when the fork gets fully extended, and I think that it might also need a reset.
Will that tool fit into my Super Fatty DL80 fork from 2001 ?

Victor
 
MikeA

MikeA

Well-Known Member
Victor Haugen said:
I also hear a "clunk" noise during the ride when the fork gets fully extended, and I think that it might also need a reset.
Will that tool fit into my Super Fatty DL80 fork from 2001 ?

Victor
Click to expand...

Yes, it will fit your fork, it's part# KT016. It's expensive though. Any Cannondale dealer should be able to do the reset for you for fairly cheap though. The procedure can be done quickly with the fork still on the bike.
 
Victor Haugen

Victor Haugen

Member
MikeA said:
This is an older post, but I thought I would add some notes for the next person looking here for info. This is a pre 2005 DL80 cartridge, the proper seal kit is still available, part #HD166. The piston ring is a standard -018 o-ring, but the replacement in the kit is a viton material. The piston ring does not fit tight in the cylinder, it's not supposed to. no teflon tape necessary. This is why on some models the fork will slowly drift down on lockout with steady down force. This is normal.

To replace all seals, the lockout shaft will have to be pressed out of the top hex. It comes apart like this DD60:

View attachment 5461

There is a bleed screw inside the lower shaft. Add oil, cycle the damper slowly till you don't hear air. top off so it's overfilled. Loosen the bleeder about 1 turn. tighten the cap, let oil spill over. When the cap begins to seal, the excess oil will purge out the bleeder. Tighten the cap and bleeder.

The end caps have u-cup seals that are directional. The lower cap needs to be installed to the shaft with the "bullet tool" in place to prevent damage.( part # HDTL168), it looks like this:

View attachment 5462

The light clunking still heard after purging the air from the damper may indicate the bearings need a reset. Linear bearings like Cannondale used in the telescope will migrate over time. This shortens the travel of the telescope and causes a light clunking. They actually recommend having a dealer perform a reset every 25 hours. The cartridge is removed and this tool is threaded in its place. With a few light slams downward till the marking on the tool lines up with the outer steerer, the bearings are knocked back into place.

View attachment 5463
Click to expand...
Hi, regarding the bearing reset tool, I am still a bit confused on how to use it properly. How do you line up with the marking on the tool when there are no printed lines, but only text ? I have a DL80 Super Fatty fork, should I line up under or above the text 70/80 where the tool gets wider in diameter ? And what about the metal ring and the rubber ring that comes with the tool ?

Thanks for any replies

Best regards
Victor
 
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