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Reconditioning a used 2004-2011 DL650 shock

5405 Views 61 Replies 8 Participants Last post by  DesertBike
Original shock is off with Sasquatch for rebuild and upgrade. I was concerned it wouldn't be back in time for a riding class next month, so I bought this used shock off FleaBay:

I know some people who 3D print and I'm hoping to get one of them to make me a replacement preload adjuster knob, per this post:

Following this excellent post:

I am getting the preload adjuster working again. It was totally frozen when the shock arrived.

I've removed the knob (remains) and cap on the preload cylinder. Dry as could be and corroded inside:

which may explain the lack of turning.

So far I can't get the piston out. Have PB Blaster sitting in there to help loosen it for removal.

Then I'll see about the O-ring. Suspect it's dry and will fall apart upon removal.

Since I could not get the piston to move, I loosened the hose connection at the bottom of the cylinder. There was some oil in there, so at least it didn't all leak out.

For all I know, this shock was sitting in a junkyard for years. That might explain the rust.

Main part of the shock looks good, so if I can get the preload adjuster working again, it should be OK to use the shock.
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Preload piston is resisting my efforts. I think it's corroded in place, unfortunately.

I put PB Blaster in it and let it sit overnight. Perhaps the piston will be more cooperative this evening.

The central brass piece is reverse threaded, btw, counterclockwise to loosen. Didn't see that mentioned anywhere else.
Still stuck hard. What's the fix here? Bearing puller?

Something other than PB Blaster to break up the rust?
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Comment, the preload adjuster is pretty generic. Just that master cylinder and a slave that sits on top of the shock. Almost any similar master will work so if there's a bike wreckers nearby maybe shop there.
We don't have anything like that. I have to either make this one work, or order a replacement from somewhere. I looked, and the only used preload adjuster I could find even on eBay was near $100 with shipping from the UK.

That's almost as much as I paid for the shock, also I don't think it would be here in time.

Good news though. Sasquatch says my rebuilt shock should be done late this week or early next.

I'm still going to try to get this used shock working, eventually.
Probably what I'll try next. Heat gun to start with. More aggressive measures if that doesn't work.

A bearing puller isn't going to work. It would have to be a special purpose miniature type, and I would probably damage the cylinder body and brass piston insert in trying to use one.

PB Blaster isn't answering the mail this time.

Still waiting on the 3D printed knob.

Since I have the requisite modeling software I may customize the wording on the preload knob. Maybe swap High and Low for Fat and Skinny.
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I tried the heat gun on both "please/heatshrink" (low) and "no really, I insist" (high) settings.

I got the preload cylinder hot enough that it was hard to hold even with gloves on, but no dice as far as moving the piston. It's stuck HARD.

The remaining PB Blaster bubbled merrily, and this reminded me to wear my respirator if I try more heat. Vaporized PB Blaster is not on my list of "top 10 things I want in my lungs this week."

I might take another crack with the heat gun, by setting the cylinder body up in my bench vise so I don't have to hold it directly. It may need to "bake" a while to break the piston loose.

Aluminum (cylinder body) has a slightly higher thermal expansion coefficient than brass (pretty sure the piston is made of this) so that should work in my favor.

Of course, I don't want to distort the cylinder body by using too much heat. It's aluminum, so I have to be somewhat careful.

I'm not going to try a blowtorch. That would only end in tears (and a puddle of aluminum on my garage floor).

Any ideas on chemically breaking up the rust?

Another idea: What if I had a shank that matched the threading in the piston? I'll attempt to measure the threading. If it's a reasonably-common thread pattern, I might be able to use a bolt as a surrogate to "encourage" the piston to come out.

With the original hardware, it's hard to get much purchase on the piston when it's bottomed out in the cylinder body, as mine is. The threaded insert has a fairly slender neck, and comes down to an 8mm hex nut. Not much to get a grip on. I wouldn't want to put too much stress on the insert. It's brass. Not as strong as steel.
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More heat did nothing.

I guess chemistry is next, brute force after that.
Fill it with grease, wind it up. It'll either move or split the body.
It does seem as if brute force is all I'm left with.

I've shopped around but it looks as if chemical rust remover for this situation either does not exist, or would damage the aluminum cylinder body.

A third possibility is that I will only twist the "stem" off the central insert. That small (8mm) hex "nut" (it's not really a nut, just a machined set of flats) is the only way I have to turn it.
Yep, that's what happened. It felt like I might be making some progress in moving the piston, and then the 8mm hex sheared off the stem.

Good news though: I think it can be JB Weld-ed back on later, if I ever work out a way to get the piston to move. (spoiler alert: no JB Weld doesn't even come close to working here.)

With the preload adjuster working normally, there should not be all that much torque applied to the central stem.
Will a grease fitting fit in the hose attachment hole? You might be able to push it out with a grease gun or possibly compressed air.
Don't have an air compressor. If I had a hydraulic pump and the right fitting it might work to push out the piston.

Ditto for grease gun, don't have one or the needed fitting. Not sure a hand operated one would develop enough pressure to do anything. Some powered jobs seem to operate at high pressure though, plausible solution if I had access to one.

I can put the shock on as is and have no preload adjustment, or preload applied. It wouldn't be great, but should be rideable until I get my original shock back.
JB Weld did not work for getting the 8mm hex back on the central thingy. I may need to clean more extensively for it to cure properly.

If I can get the (spindle?) back out from the piston I may also be able to braze the 8mm nut back on.

Soldering could also work. In a normally functioning preload adjuster, there shouldn't be that much stress on the shaft, so should be strong enough.
This project is at an end. I have no way to get the piston free from the preload adjust cylinder without destroying either the piston, or cylinder. So it does not matter whether I can get the 8mm nut reattached or the spindle freed from the piston.

Cannot find any source anywhere for a replacement preload adjuster.

The preload adjuster is not strictly required to use the shock. It will be stuck at no preload but will still work.
Talked to some folks today, got a couple more ideas to break up the rust:

1) weak acid (lemon juice and vinegar solution).

2) electrolysis. Surprised no one suggested that already.
It isn't over until I can pull the piston loose by hand, but electrical rust removal seems to be working. Pics later.

My electrolyte water is getting dirty, and when I pulled the cylinder out of the water this morning, there was a bunch of loose rust in and around it. That rust could only have come from where the piston rusted to the cylinder wall.

This from less than an hour under power.

Few more hours in the spicy bath and I suspect I'll have a serviceable preload adjuster again.
Aluminum (cylinder body) has a slightly higher thermal expansion coefficient than brass (pretty sure the piston is made of this) so that should work in my favor.
Since you have a new shock coming, the best plan might be to just do the class with no preload.

Also, if the electroysis doesn't work you could put the whole thing in the oven and bake it at 300F, 400F? A thorough heat soak and the difference in thermal expansion might break it free.
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Baking is worth a try.

Neither piston nor spindle is brass as far as I can tell btw. Seems to be steel. Same principle applies anyway: its thermal expansion coefficient is much lower than that of aluminum.

Regarding the electrolysis: I'm using baking soda because I didn't have washing soda, which is similar and supposedly works a bit better.

Distilled water so that the minerals in tap water don't deposit on things/muck up the process.

Either is better than salt. Don't use salt unless you want to evolve chlorine gas, yikes!

Power supply is a wall wart I had left over from an external hard drive, which supplies up to 1.5A @ 12V. Great for testing LED strip lighting. Have it wired up with an inline fuse for extra fault-tolerance.
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