Leaky Fox RP3

[qvack_au]

Hit a bit of a snag rebuilding an old Cannondale today - the back shock wasn't holding air at all, so I did a basic air can service on it. Unfortunately after that it still wouldn't take any air, and checking it out a little more it's got a huge leak through the rebound / pro pedal knob.

My gut feeling is that it's stuffed, and since it's ~15 years old throwing money at a damper service seems like a bad idea. I can't find much at all on air leaks from rebound, it seems fairly common to have an oil leak but nothing much past that. There's nothing obviously wrong with the shock head, but there was a mention somewhere on the interwebs of a crack in the metal causing this to happen.

Any ideas? Unfortunately doesn't seem to be much around in used 190/45ish shocks right now so I'm a little stuck with the project at the moment

 

[link1896]

If the damper rod to top assemble O-Ring fails, aircan pressure can appear around the rebound adjust shaft. Much oil ejecting out around the adjuster or dry and just air?


Rebuild kits are 50ish on eBay, a Ford fuel rail schrader valve in the IFP fill port negates the need for a needle to charge the IFP pressure up.

 

[qvack_au]

If the damper rod to top assemble O-Ring fails, aircan pressure can appear around the rebound adjust shaft. Much oil ejecting out around the adjuster or dry and just air?


Rebuild kits are 50ish on eBay, a Ford fuel rail schrader valve in the IFP fill port negates the need for a needle to charge the IFP pressure up.

Cheers, thanks for the info. I'm just getting air out the top, there was a little grease but no oil with the rebound knob.

From the cutaway image it looks like the seal there is for the central shaft, which is linked to the nitrogen chamber, not the main one? The nitrogen still seems to be charged if that makes any difference.

It could be worth a shot if it's that cheap for a damper kit. Looks pretty complex to actually do it, I'm less worried about the nitrogen than the rest of it tbh as it looks like plenty of things that can go wrong. I'll keep digging to see if I can find a guide with pictures

 

[Flow-Rider]

I wasn't sure with your original post whether you meant the aircan of Ifp chamber.

There's only loctite sealing the shaft thread to eyelet housing from the air can pressure, if the aircan leaks out that much then the leak should stand out like daylight. Have you tried spraying watered down detergent around the shock or placing the shock in water to look for leaks?

 

[qvack_au]

Only leak is through the hole in the photo I posted - I can feel pressure build up when pumping up the air chamber after blocking it with my thumb.

There's no other leaks that I could see, I checked the valve thread first and the o-ring there looked fine. The rebound was the only part that bubbled, but to be fair if there was a small leak I wouldn't see it as it dumps everything within a few seconds. I had to use a floor pump to have a real shot at seeing bubbles...

 

[Flow-Rider]

Have you tried sealing the thread? Connect your foot pump to the shock and place the shock in a bucket of water and start pumping like mad, maybe a two-person job unless you have access to an air compressor. It could have a crack in it somewhere like you say too.

 

[qvack_au]

Have you tried sealing the thread? Connect your foot pump to the shock and place the shock in a bucket of water and start pumping like mad, maybe a two-person job unless you have access to an air compressor. It could have a crack in it somewhere like you say too.

Nope. I've got a compressor but my schraeder adapter is buggered. I'll pick one up tomorrow and give it a go, I've been meaning to do it for a while anyway as getting tubeless tires to bead by hand is great fun.

So to get that unthreaded do you need to break down the whole damper, or just clamp the shaft and unscrew the shock head? And if it's the second one I'm assuming there's nothing under pressure (don't need to bleed the N2 off first)?

 

[Flow-Rider]

It should unscrew now that you've removed the dials, but you'll need to release the gas and strip the shaft down to get dial assembly back in.
Have a look at this video and the last post on it.

 

[qvack_au]

Cheers, will have a crack at it tomorrow and see if I have any luck

 

[Flow-Rider]

There's a seal in there too like @link1896 said, I didn't see it in the exploded view drawing but it shows it on the later model shocks

 

[qvack_au]

So no luck at all unscrewing the head, even with a fair bit of force it wouldn't budge before the shaft moved in my vice.

I've checked by putting air in the damper hole and it's coming out of a different spot than I thought. It bleeds straight through to the other end of the shaft. Based on the cutaway and sketches I'm at a bit of a loss how it's leaking from here, but still seems to hold nitrogen?

 

[Flow-Rider]

It must only have a few PSI of air in the IFP chamber.

The last one I pulled apart was about 12 years ago, I recall that I released the gas and carefully heated up the end of the shaft to loosen the loctite. You've got to release the gas anyway because you'll never push the rod back enough to get cam in with 400psi pushing against it.

 

[qvack_au]

Well that probably says there's not 400 psi in there anyway, I can push it down with a screwdriver...

I'll order the damper kit and shelve this for a bit as it looks like they have to come from overseas. Curious to see exactly what is wrong after all of this anyway, but for now I'll see if I can pick up a replacement to get me up and running.

 

[wornoutwords]

I opened up the damper side on my rp23 in preparation of doing the schrader valve mod and it's bone dry. Refilled it, but even without any pressure in the ifp it was leaking out the propedal switch so my seals are definitely gone too

I got the following oring sizes out of the technical drawings i've seen
2.5x1mm
.154 x .050in
.362 x .103in
.989 x 0.070in

but the kits have close to a dozen different ones in them. Does anyone know what the other sizes are?
I went to my local oring guy but they have a $11 min order, and each of those is about 10-15cents so i'd rather get enough to do the damper and air can a few times over

 

[Flow-Rider]

I opened up the damper side on my rp23 in preparation of doing the schrader valve mod and it's bone dry. Refilled it, but even without any pressure in the ifp it was leaking out the propedal switch so my seals are definitely gone too

I got the following oring sizes out of the technical drawings i've seen
2.5x1mm
.154 x .050in
.362 x .103in
.989 x 0.070in

but the kits have close to a dozen different ones in them. Does anyone know what the other sizes are?
I went to my local oring guy but they have a $11 min order, and each of those is about 10-15cents so i'd rather get enough to do the damper and air can a few times over

You can't remove them and send them off to be matched at the o-ring shop?

 

[wornoutwords]

That's plan b I guess, they didn't have the 2.5mm in stock so I need to go in again anyway, although my preference is to do the total disassembly and reassembly in one sitting.

I've learnt the hard way not to leave half disassembled parts around the house. I have 2 boys, 8 & 4. And no matter where I hide it the little fuckers still somehow manage to find the forbidden treasure and somehow lose the tiniest screw

 

[Flow-Rider]

That's plan b I guess, they didn't have the 2.5mm in stock so I need to go in again anyway, although my preference is to do the total disassembly and reassembly in one sitting.

I've learnt the hard way not to leave half disassembled parts around the house. I have 2 boys, 8 & 4. And no matter where I hide it the little fuckers still somehow manage to find the forbidden treasure and somehow lose the tiniest screw

I know the feeling, I hide things so well that I even forget where they're hidden sometimes.

 

[wornoutwords]

It actually worked! the switch isn't floppy anymore and stays in place. I can barely cycle it with my hand in the propedal 1, and not at all in 3. The rebound makes a difference

this was what remained of that 2.5 x 1mm that's in the rebound rod thing @qvack_au i reckon this will be what's wrong with yours too.

All the other o rings looked ok, i just I replaced the ones that were easy to get to & didn't need any more deconstruction

Does anyone know what this is? it's about 5mm and it moves freely over shaft in the air can. Travel reducer?



Hilariously though i think this rp23 shock is a 190/45 instead of a 184/44 like i thought :O

here's a list of all the o rings in case anyone is curious (bought from cbc here in adel - https://conbear.com.au/)

3.68x1.78
7.59x2.62
2.5x1
25.12x1.78
26.7x1.78
41x1.78
17.04x3.53
7.5x1.5

 

[qvack_au]

It actually worked! the switch isn't floppy anymore and stays in place. I can barely cycle it with my hand in the propedal 1, and not at all in 3. The rebound makes a difference

this was what remained of that 2.5 x 1mm that's in the rebound rod thing @qvack_au i reckon this will be what's wrong with yours too.
View attachment 382608
All the other o rings looked ok, i just I replaced the ones that were easy to get to & didn't need any more deconstruction

Does anyone know what this is? it's about 5mm and it moves freely over shaft in the air can. Travel reducer?
View attachment 382609


Hilariously though i think this rp23 shock is a 190/45 instead of a 184/44 like i thought :O

here's a list of all the o rings in case anyone is curious (bought from cbc here in adel - https://conbear.com.au/)

3.68x1.78
7.59x2.62
2.5x1
25.12x1.78
26.7x1.78
41x1.78
17.04x3.53
7.5x1.5

Cheers thanks - haven't quite gotten around to it yet, but I'm pretty sure it must be leaking in two spots with that O ring looking pretty likely...