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Help me understand vintage Suspension Fork Operation

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Help me understand vintage Suspension Fork Operation

Old 03-23-23, 07:27 AM
  #1  
Saddle Tripper 
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Help me understand vintage Suspension Fork Operation

Good day. Pictures below show a NOS 1995 Quadra RockShox fork. It was still in original plastic wrap and box with sealed instructions and a couple doo-dads.

(I am putting together a vintage Mtn bike and I know there are better and newer forks today, but I want to complete this build before or if I change to a new fork)

the polymer (?) inserts are pliable, not cracked, and the original grease on them still soft.

however…….

When I push down on them (with the caps off) the fork compresses… but does not rebound unless I pull on them. I added some very light oil (per instructions) under the boot and they seem to pull out easier… but certainly not on their own.

questions: did these forks “work-in” or, is the stiffness and lack of spring back requiring a complete disassembly?

Or? If I re-install the black plastic caps … was the air seal so air tight and good that it was intended to provide what little shock absorption or, better said: resistance, action these had?

Did they or were they designed to have spring-back on their own as I am attempting?

wish I could better describe this… but I am looking for input on how these functioned - before I attempt a disassemble (if needed).

if the mountain bike forum is best for this - do redirect me. Thank you in advance. Tom




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Old 03-23-23, 08:17 AM
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The fork is supposed to spring back on its own. Otherwise, you'd have to dismount and pull it back after every bump.

In normal use, your weight would partly compress the fork, leaving most of the travel for bumps, but also having room to prevent topping out on the rebound.

From your description, I wonder if dried oil has become sticky, of perhaps the seals are adding friction.

Short of taking apart, you might try oiling and working it back and forth to see if it frees up.
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Old 03-23-23, 09:33 AM
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The boots were definitely sticky. Probably any lubricant in the forks themselves may have dried up as you suggest.

I used a light grade kerosene to remove the sticky and clean the boots. I added just a bit inside the fork itself ( lower section under the boots) as a gentle solvent - that may free up the spring/back. I did not want to use anything harsh that would affect the blemish free original paint.

I’ll work them back and forth - give it some time - and see if it works. There is no corrosion inside them. Squeaky clean and bright. I can rule-out rust at least. Thanks for the response!

update: the kerosene wasn’t strong enough to cut through the sticky coating from the old oil. Resorted to gasoline and engine assembly lube and made a thinned lube oil.

that did the trick. With a lot of push-pulling repeatedly they started to move freely. Now they rebound on their own. The gas will evaporate and leave the lube. It should work - the engine assembly lube is easy on rubber gaskets, parts, seals etc. yet gives a sticky long lasting lubrication.

tom

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Old 03-23-23, 05:45 PM
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I'm not a fork expert but I have a Specialized that is probably about the same age and it is hydraulic but the concept is the same. The one thing with shock forks is that the seals must stay lubricated or they deteriorate.

I was told long ago to hang my bike up by the front wheel so that the oil settled onto the seals. If just parked on the ground the oil runs out of the seals and puddles at the bottom of the shock tube and the seals "dry out". Not sure if all of that is true but that is what I was told. My fork is going on 25 to 30 years old and it still works fine....knock on wood...

You might try working it some more, and with more oil and see if you can get it to rebound. Maybe stand it upside down for a couple of days once you give it a good dose of oil. If it still sticks, and if you're not comfortable rebuilding it, there are a number of shops that specialize in just forks. It may be that the seals have deteriorated to the point that they have become sticky inside the shock tube.
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Old 03-23-23, 06:41 PM
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I may disassemble and soak the seals although they are now rebounding… they are definitely sticky yet.
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Old 03-23-23, 09:01 PM
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You have added a very effective SOLVENT into a fork that doesn't like SOLVENTS.
Kerosene is just a notch or two below Gasoline on the Petroleum list of sub-products.. Some just above Gasoline Cause Cancer and will eat paint right off of most surfaces. Toluene and Benzine quickly come to mind... Kerosene dries into a really sticky mess, eventually.. It may also dissolve your Nearly impossible to locate Polymer inserts into a disgusting Gluey goo.

The special Grease in your NOS forks from 30+ years ago has likely turned back into a far less luibricating product over the decades... It will need to be cleaned and replaced with Rock Shox Fork butter Grease, AKA: Rock Shox Judy Butter.

The Caps on most Rock shox act as a spacer and add pressure on the polymers... at least the last fork of that era tore apart was designed that way... those caps were adjustable so as to tune the fork's preload/sag.

Clean the fork internals... Change out the grease. Do Not Fill the fork with the grease! There are numerous Vids online showing the process in detail, and hundreds more not worth watching. ;-D Do Not Be tempted to use whatever axle goop you have in the Garage since Some of those will also Dissolve those Rare Polymers into gluey goo.Get the Rock Shox Fork Butter.
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Old 03-24-23, 12:01 AM
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I agree. Today’s plan is to disassemble, wipe and clean all of the fork internals. The use of the solvent was to loosen and unstick the dried up lubricant. As of last night it was not that not effective although I was able to get them to rebound . I ordered the grease last night.

thanks everyone for the information. Appreciate it.
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Old 03-24-23, 02:00 AM
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Disassembled, degreased and cleaned. Given the age of this fork, and due to sitting for so long it was best to do it and degrease. Using SRAM butter. Judy grease is no longer available. Seam owns Rock Shox now.
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