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PostPosted: Thu Mar 14, 2019 11:08 pm 
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Location: Nottinghamshire
Got hold of a set of what appear to be either well looked after or hardly used Rockshox Judy SLs from 1997, to go on my '97 Greg Fuquay (to replace the '94 RS Mag21 SLs)... The Judy's seemed a bit quick on rebound and as such quite harsh on 'top out' - audible 'doink' if you compress hard and then lift the front wheel up quickly.

So I stripped them out, the damper unit sounded like it was full of air, so I'd totally drained this and replaced oil with 5wt shock oil, this took a long time as I had to fill small amounts at a time, cover over the fill hole, work it/tap lightly to achieve what is effectively a gravity bleed to get the air out. Sealed back up with the 3mm hex adjuster plunger bolt and the cartridge works through its travel with no slosh, smoothly and no sounds of air inside. Cleaned and rebuilt rest of the fork but to my disappointment it has only helped a little, even on slowest setting the fork is rebounding a little quick for my liking and furthermore adjusting this by 2x full rotations of the red damper adjuster has very little effect. I also still get a lot of 'top out' with the preloaders on near max, again I wonder if this is as result of the cartridge not working maybe as it should/wrong weight oil?

Never ridden these forks before so just don't know if its a characteristic? Can I run thicker oil, say 7.5wt or even 10wt in the damper cartridge to slow down the rebound?

BTW I'm 87kgs if this helps with ideas.

Cheers, Tom


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PostPosted: Fri Mar 15, 2019 1:27 pm 
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Are you aware of the fact, that you can adjust the rebound? With that tiny allen bolt that sits inside the dampening cartridge shaft.
I have 10wt to 15wt oil in my Judys, 5wt seems a bit too thin.

Edit: I just realized that you might have filled the whole cartridge "though" that said shaft that is covered by that allen bolt? The usual way would be to take the seal out, remove the old oil, fill new oil, then press the seal back in and just do the bleeding through that bore in the shaft.


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PostPosted: Fri Mar 15, 2019 3:42 pm 
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Thias wrote:
Are you aware of the fact, that you can adjust the rebound? With that tiny allen bolt that sits inside the dampening cartridge shaft.
I have 10wt to 15wt oil in my Judys, 5wt seems a bit too thin.

Edit: I just realized that you might have filled the whole cartridge "though" that said shaft that is covered by that allen bolt? The usual way would be to take the seal out, remove the old oil, fill new oil, then press the seal back in and just do the bleeding through that bore in the shaft.


Yes I'm aware of the damping adjustment, Instructions say no more than 2 full turns between max and min Damping but this seems to have very little impact.

With regards the cartridge itself, I didn't remove the seal I emptied the old oil via removing the 3mm allen screw plunger bolt and pouring/pumping the cartridge to get most of the oil out, kept doing this until nothing came out. I didn't dare remove the seal incase I can't or struggle to get hold of a replacement (if I damaged it). I then refilled bit by bit via the bore hole and worked the cartridge by hand with bore hole upwards at all times and with my finger over the hole to stop spillage and to get the air to rise to surface, kept doing this until it was full/no more air bubbling to top and the action of the cartridge was smooth through its entire stoke. I must say the consistency of the damping oil that came out visibly looked thicker than that I replaced it with, however that is no exact science but did at the time give me indication that the 5wt going back in maybe too thin?


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 Post subject: Re:
PostPosted: Sat Mar 16, 2019 6:09 am 
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Besides the adjust, the only acheivable variable is the weight of the oil. Bump up to 10 or 15wt.
*I say acheivable, because in theory you could maybe change out the springs lighter ones for some effect - if they were available, and that would likely result in a lot of brake dive.


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PostPosted: Sat Mar 16, 2019 9:12 am 
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I had exactly the same annoying clunk on my Judy’s when the top out
Over ruff hard ground it drove me nuts with the noise and also the vibration coming back up through the bar

No amount of adjustment to the damper worked - I even went back to using elastomers as I thought my stiff springs had to much of a return rate, more than the rebound cartridge could cope with.

The good news It is cureable I’ll be in touch once soon.


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PostPosted: Sat Mar 16, 2019 12:04 pm 
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Cheers guys, I assume that Spud is going to change out the oil for heavier? I did a 10mile ride on them yesterday, my forks appear stock with original elastomers in VGC and the added short springs. Whilst they are 'rideable', the dunk when bunny hopping or lifting the front wheel is horrible. Let me know how you get on Spud (assuming you're gonna up the weight of the oil in yours), I think I'll look to do the same but with 10wt oil and hoping I didn't wish for 15wt! Also be sure to remove any air from the cartridge as my thinking is air in it mostly effects the very end of the stroke (when fork is max extended) and thus giving zero damping at this point (the impact/dunk).


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 Post subject: Re:
PostPosted: Sat Mar 16, 2019 11:23 pm 
retrobike rider
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Oil increase of course. I have the same forks, but have no problems.
They are meant to be quite smooth, quite different to a MAG21.

The red adjuster are preload only, you set them so they sag about 20% of the travel when you ride on the bike normally.

What spring setup is in there?
Any colour marks?

It sound like you are trying to make a newer fork quit rigid.

The clunking though, there only plastic to click iirc.

You filled them up the normal method for this style of cartridge.

They should originally be an MCU/Spring setup.


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 Post subject: Re: Re:
PostPosted: Sun Mar 17, 2019 12:15 am 
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FluffyChicken wrote:
Oil increase of course. I have the same forks, but have no problems.
They are meant to be quite smooth, quite different to a MAG21.

The red adjuster are preload only, you set them so they sag about 20% of the travel when you ride on the bike normally.

What spring setup is in there?
Any colour marks?

It sound like you are trying to make a newer fork quit rigid.

The clunking though, there only plastic to click iirc.

You filled them up the normal method for this style of cartridge.

They should originally be an MCU/Spring setup.


http://www.retrobike.co.uk/gallery2/v/M ... y.pdf.html

The red knobs on the top of each leg control preload, I'm not on about that. What i'm talking about is REBOUND and control of the rebound, which is dialled in via a 3mm hex key on the base of one of the legs. I'm not trying to stiffen the fork up nor make it rigid either, compression is fine, i'm trying to stop it acting like a pogo stick and having harsh top-out. The forks have the still VGC MCU and very short springs. Correct me if i'm wrong ppl but there is no option to add more or less oil to the damping cartridge, you fill it, try and remove all air and thats it. The fork in action is indeed very smooth, just rebounds far far too quickly.

My Mag21SL is an air fork, very smooth and much less harsh top-out. Adjusting oil levels in my Mag21SL has a big effect on its compression curve but no such 'oil volume adjustment' with my JudySLs being a completely different type of fork.


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 Post subject: Re:
PostPosted: Sun Mar 17, 2019 2:37 pm 
retrobike rider
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It know the gallery well, I out it all there ;-)

I was referring to an earlier post where the top caps where adjusted up and down.
They adjust spring rate also which changes compression and rebound of the spring.

Nope, no other option with the damper, it goes from screwed all the way in to a few turns out, it just alters the port via a slider.
Eases the spring push against a plastic disc.

The Judy especially the 97 is a much more active for than the MAG21.

Have you checked the dummy side and checked the top out bumper (and that the shaft is the same length as the damper shaft.
Can't see why there would be a problem, given the excellent condition of them.


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