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How to disassemble and fill up your rear preload adjuster (Pics)

62K views 58 replies 50 participants last post by  DesertBike 
#1 · (Edited by Moderator)
Last week I discovered that my preload adjuster was not working and after checking with the guys on the board I figured the oil was gone. This appears to be a very common problem, and can be attributed to slow leaks over time due to O-ring failure. If this is what has happened, you shock will look something like this, without no (or very little) preload active.



This is really pretty easy job to do once you figure out how the preload adjuster works. Here are the step-by-step instructions on how to disassemble, fill it up and reassemble. In my case I took the shock off the bike for a different reason, but you can do it by just dismounting the adjuster unit and working on it while the shock is in place.

1. Turn the adjuster as far counter clockwise as you can (decrease preload). This will save you a bit of effort later.

2. Take off the screw and the washer off the black plastic adjuster knob and remove the knob.



3. Now you see the hex nut which sits on the brass shaft, and there are two (some people have four) little balls underneath it.





4. Take out the balls and springs and do your best not to lose them. They are really tiny. Now comes the fun part of taking off the brass cylinder cover. This is the only part of this work where you may need a specialized tool. I went to a local hardware store and got this 10 dollar tool for removal of grinder discs. It worked perfectly. You may need to mount the adjuster back on the bike in order to crack the cylinder cover open. Mine came apart easily. Turn counterclockwise to open.



5. Here is what you should see when you open the cylinder. Note that one of my washers is stuck to the bottom side of the cylinder cover.



6. Now grab that brass shaft and wiggle the whole piston assembly out of the cylinder. You should end up with this



7. Note that the brass bolt with the hex top (the one you pulled on to get the thing out) screws in and out of the piston body. Inspect the O-ring on the piston - this is the most important part of the assembly. If it does not look healthy, replace it. You should probably replace it anyway. As you see, I had zero oil in the bottom of my cylinder. The oil should be at the bottom of the cylinder, so piston can press on it.

Fill up the cylinder up to the 45-degree point, ie right under the point where the vertical valley (the one cut into the cylinder wall) ends.



8. Now grab your little assembly consisting of the piston and the brass bolt thingy. Turn the bolt counterclockwise until it is screwed into the piston all the way. Then back it out a turn or two. This state of the assembly will represent minimal preload. Put the piston assembly into the cylinder body, making sure that the pin on the side of the piston fits in the sidewall valley (it wont fit otherwise). Press on the assembly a bit. O-ring should ensure the sealing and you should see no oil coming up from underneath the piston. This is what you should see



9. Now put the washer-bearing-washer on the brass bolt... you should see this



10. Put the brass cover on and turn it clockwise with your sexy tool (that sounds so wrong) until it is screwed on all the way. Obviously the assembly will resist a bit since you are putting pressure on the oil a bit. Et voila:



11. Now put back the little springs and the balls on top of them. Put back the metal nut, then plastic plack knob goes on it, and the washer and the little screw that keep it together. You are done!

12. Grab that plastic knob (yeah, sounds wrong again) and crank it clockwise as far as you can. As you are cranking it, the top part of the spring should start to move and you should see the sleeve starting to come out of the top part of the shock assembly, showing some lines. When you get to the far end of the preload (maximum, turning clockwise) you should see something like this... this is my case, yours might be a bit less if you put less oil than me.





If you are interested to learn about my artistic abilities and how this thing operates, here is a diagram and an attempt at the explanation:


 
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#3 ·
Now THAT is the best "How To" article I have seen in a long time!

Well Done!!!

B.L.
 
#7 ·
Thanks guys. I took pics along the way because I did not know what I was doing at first, and was sure I was going to mess up something. The diagram is also an attempt to explain things to myself and see if it makes sense.

I used fresh engine oil for my Wee, 15W50. It would probably be better to use some sort of hydraulic oil, but as someone said, the load is static and does not make much difference. Perhaps someone can comment on this.
 
#11 ·
Not brake fluid. We do not know if the hose and the seal at the top of the shock are resistant to the polyglycol ether brake fluid. Any petroleum oil will do, and probably the thinner the better. ATF would be good, or 5W-30 from your car's supply, or anything.

Great how-to-do!. I'd add a dab of grease to the threads and the roller thrust bearing.
 
#23 ·
Thanks, great write-up. I also wonder: do you not need to bleed the system? How is that done?
 
#26 · (Edited)
Again, great step by step

Thanks for taking the time to photograph and then upload your process...job well explained.

I jusst did my unit. Very easy to do and straight forward.

I used a plumbers wrench to break the threads on the threaded cap while the unit was still bolted to the bike, worked great, just becareful not to scratch the paint!


I cleaned it all up,(the remaining fluid that was inside was quite dirty) o-ring looked ok. Filled it up with 10w-30 and put it all back and gave it a test ride...so far, no leaks. I can't figure out what caused the failure...

BTW, the O-ring is 7/8"ID, 1/8" thick, making for a 1 1/8" OD

My first post! yoo-hoo....great forum guys
Cheers!
 
#27 ·
Very nice write up and thank you very much for taking time to document the process. I used it tonight and everything worked great except when I filled it to beginning of the cutout, I was unable to screw the cap back on. I found I needed to wick about 3mm of the fluid out of the cup to get the cap to screw back on. YMMV of course.

Dave...
 
#32 · (Edited)
Great write-up "Vlad"! The pictures and write-up made me brave enough to open up and potentially destroy my shock.

I will add a few thoughts to this thread.

I used 5-weight fork oil, which seems to work just fine.

As mentioned earlier, when adding fresh oil into the adjuster cup, there is a fine line between too little and too much. Too little and air will be caught between the fluid and the piston. Too much and the piston will not seal without leaking some fluid to the mechanical area above it, and the main piston at the spring will start to protrude, even with minimum preload dialed after re-assembly. As "Vlad" stated, a close approximation for fill-line is indeed just below the start of the 45-degree angle on the cylinder's inner sidewall. From there, add or remove small amounts of oil until you get it just right.

I considered replacing the 8-inch line that connects the remote adjuster to the larger master piston assembly, possibly a stainless line for more durability. After an exhaustive search on the web, I determined it could not be procured without an interactive request from a suspension supplier, which I never got around to. The thread fittings on both ends of the line are 8mm x 1.0, and banjo bolts could indeed be found on the web in this size, including eBay. However, I could not find an actual line with 8mm inner diameter banjo fittings, as everything available has larger 10mm diameter banjo fittings for brake lines.

I almost contacted Elka to see if they would sell me a line like the one shown on the shock below, but I never got around to it.


Here are a few more pictures I took for additional reference.

I found the right pin tool for only $4.29 at Harbor Freight










 
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