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PostPosted: Thu May 17, 2018 9:43 pm 
Dirt Disciple

Joined: Wed Apr 13, 2011 11:11 pm
Posts: 10
Location: Nottinghamshire
I'm trying to breathe some life into a 1992 Dynatech Quantum I've picked up. So I was amazed that upon re-inflating the forks they appeared to hold air! However very sticky and crap rebound. So I've flushed out the old oil, also had the wiper seals out, gave them all a good clean and smear of grease on upper seals and filled back up with 5wt Rockoil approx 35mm from the top on compression, pumped back up and seemed great (for a 25 year old fork).

However after a 10 mile ride, I've found that the rockoil is weeping up past the wiper seals (quite badly) and also have also lost a lot of air. Can anyone give me guidance as to whether this is normal (suspect not) and also any guides to replacing what I presume are lower seals in the legs that are probably shot and where I may source some in the UK?


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PostPosted: Fri May 18, 2018 8:29 am 
Retro Guru
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Joined: Tue Jun 25, 2013 10:47 am
Posts: 1118
Those forks shouldn't loose any oil at all. If they do, you need new main seals underneath the wipers. Are you sure, it is oil and not the grease you used for the wipers? (Just asking to be safe.) Those main seals then also leak air. But then the top caps may be doing so, too.

Here is the link to the manual. if you don't have that already: http://www.retrobike.co.uk/gallery2/d/4 ... ervice.pdf

All the work *can* be done without all those special tools. But it may be a bit dangerous.
The main "problem" is to separate the castings from the upper tubes. You can separate them by removing the circlip and then pulling. The main seal is a light press fit and is holding the tubes together. It should pop out by hand.But it won't after 30 Years. Heat from an hair dryer helps. And as a last resort - air pressure after removing the circlip. But be sure not to that tube into your face. Or anyone elses face... Be very, VERY careful with what you are doing with that pressurized fork. Those tubes can fly quite a distance if not held properly! Don't ask my how I know... :facepalm:


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PostPosted: Fri May 18, 2018 9:25 am 
Dirt Disciple

Joined: Wed Apr 13, 2011 11:11 pm
Posts: 10
Location: Nottinghamshire
Cheers for that! I've seen pullers etc online that you need to seperate them... never thought of presurising to remove them! 100% damping oil is its bright green and runny, the grease is golden. Photos were pre ride, after the ride its running down the back legs of the fork! Okay so i figure best way to split them might be whilst fork fitted in situ on bike, wiper seals pryed up, circlips out and then with one person stood over the bike, another holding the fork legs and then another pumping them up with their face away from the fork. Next million dollar question is where to source a reasonably priced seal kit?! Anyone??


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PostPosted: Fri May 18, 2018 10:07 am 
Retro Guru
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Joined: Tue Jun 25, 2013 10:47 am
Posts: 1118
You'll have to pull them one by one. So first remove the brake booster arch thingy. I removed the whole fork from the bike and clamped the steerer tube into my vise using soft Aluminium jaws to not mar it up. You could use some Aluminium sheet for that, too I guess. I also drained them beforehand or else its a mess. Then slid the casting in completely and pulled with full force using the momentum. A few pulls and on 3 of 5 forks the seals came out. ;)

The other two I had to use air pressure. But that was rather scary process. The second of those I made a jiig. I took a large cardbord box, put in a hole for my vise. Put the box over the vise and then clamped the fork into the vise. The box is to prevent the casting from flying across the room when the seal releases. Also put some rags between the cardboard and the pointy bit of the casting so it wouldn't pierce it. Then used my air compressor to inflate the fork while holding the needle in the valve.

Did I mention you better drain the fork before doing? And remove the circlip? :D

And be really really careful! That air pressure has quite some energy to release when the seal pops! Don't assume you can hold that casting with your hands when the pressure releases!


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 Post subject: Re:
PostPosted: Fri May 18, 2018 5:58 pm 
retrobike rider
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Joined: Fri Aug 08, 2008 2:36 pm
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Location: Yorkshire, England
I only had one never separate on me,but then I've not used my brute force method yet.. as it was easier to get a new fork


I always seperate with oil in them, hold the lower leg in a sink, or if you ahve the room in a work bench clamp. Rags and towels around the seals (remove wiper seal and circlip first of course). Then pump the forks up, you'll be over 100psi but do it bit by bit, giving the stanchion a twist and small tug as you go.
MAG20 are easier as they don't have the negative spring.

Keeping hold the dial area too (it is easier with two people, one holding one with pump).
And they'll pop, oil spurt goes into rags.
Don't do it without rags and don't just jam the air in while not really holding otherwise oil spurts all up the wall and to the roof ;-)

Never had a fork separate with just tugging even with no oil in ,so I just don't bother now.

Done quite a few.

I do have some seals I think but might not be the quickest way, but you'll not find wiper seals, just the oil.

Enduro also make seals too.

You can make air seals or I may have some I make too, mine are a bit stiffer so I prefer to fit them into the topcaps myself, they also don't look as pretty.


First take the brace off, check for cracks around the bolt holes, also check for cracks coming from the top of the lowers, around the seal area.

No point fixing a knackered leg.


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