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The Complete Fox DHX 3/4/5 Service Thread

117K views 109 replies 51 participants last post by  ka81ua 
#1 ·
Hi all :thumbsup:

Here is the 4th Version of my Fox DHX 3/4/5 Service Guide

It shows you how to completely service (about 98%) your DHX, including the rebound and propedal assemblies. Servicing the rebound assembly will require careful use of a propane torch, so before commencing work on your shock, be sure you uderstand what you are doing by first reading the method in which to use the propane torch.

Make sure you download and read through the tutorial carefully before commencing work on your shock

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Shock Models Supported;
2005 - 2009 Fox DHX 3/4/5 Coils
2010 Fox DHX 3/4

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NOTE: CERTAIN DHX 5 THAT CAME STOCK ON SPECIALIZED SX TRAILS HAVE UNADJUSTABLE BOOST VALVES, MEANING THERE IS NO AIR VALVE FOR YOU TO ADJUST, INSTEAD THEY ARE FACTORY CHARGED WITH NITROGEN

DO NOT ATTEMPT TO SERVICE THESE SHOCKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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Download Links:
( I know the hosting sites arnt liked by many people, but sorry it will have to do for now :D )

Guide:
http://www.mediafire.com/?lotejczmzz0

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Enjoy boys and girls

Also if you use this guide please report your success, also CONSTRUCTIVE critisim is welcomed, oh, and do not ***** about how i used a shifting wrench, its all i had, use a spanner if you wish

Cheers!
 
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#87 · (Edited)
no air pressure

Hi guys,

First, want to thank Nick for a GREAT write up.

Then, my doubt. I have a Pushed DHX 5.0 that came in my used Ironhorse Sunday Team 2008 that I bought on ebay in 2010.

I don't know anything about the bike before me owning it. I know the shock was Pushed because it has the sticker.

Now, I understand that if the shock came OEM in a Sunday, it has a special tuning (or so says Dave Weagle), particular for the Sunday, that Fox did. I don't think this is the OEM shock, so I GUESS that is why the previous owner had it Pushed. Anyhow, whether it is the OEM or not, I suppose it was Pushed for the Sunday. Recently I spent a lot of time without riding (because I moved to another country and had snapped my Boxxer in half and bla bla bla) and after almost a year, I finnally got a chance to ride, boosted the shock up to my usual setup and went for a ride.
A week after, I noticed the bike had a little "play" in the shock area but all the links were fine so I thought it may be the airpressure and indeed there was no pressure at all.
So I have a leak. The next 3 days it has been losing like 30 psi overnight (consistently, 3 days in a row). I haven't tested (will do it this night afterwork) how much psi does my pump sucks in when connected, but from what I read it shouldn't be more than 15 or maybe 20.
I am pretty sure I may have ridden the bike without air pressure in the shock at the end of the day that time I rode, maybe, of this I am not sure. But I am sure I cycled the shock many times while on the bike because I was searching for this "play".

So all I find is that, if you ride it like that (without air pressure), you need to re bleed the shock and stuff. Is that really true? Because if oil cavitates (which is just a change of phase due to pressure) it should go back to the liquid phase after cooling down and the bike laying there for days. Now, if it sucked air in (is this possible as a consequence of no pressure?), that is a problem.

Let me know what you guys think. Another option is send it back to Push, but I really like doing this things and don't fear them at all. I also wouldn't like to spend the money Push charges for it, and even more important if I don't have to do any rebuild I rather just boost it up (maybe solve the shcradder valve leak by itself) and go just go ride.

Thanks in advance to you all and keep a good post like this up.
 
#88 ·
air leak

OK, so I tested two things:

1. The shock pump takes about 20 to 25 psi when I connect it. This number may seem a little high, but I am not surprised since I did these tests with the bottom out all the way in, so the volume in the boost chamber is smaller than with the bottom out completely open.

2. I sumerged the shock in water and indeed there is a very small air leak in the Schrader valve. The air does not seem to come out of the Schrader but from its outside diameter, suggesting that the leak is between the valve and the boost chamber body.

I still have the question about the re bleeding if the shock is cycled without air pressure.
 
#91 ·
I'm not able to unscrew the cap to get inside the shock body (step 4 in the manual) using an adjustable wrench. Its torqued very tightly. I tried torching it a bit but still haven't any success. Does anyone have a solution to this? Would getting a 25mm cone wrench help? It was pushed 4 years ago but hasn't had any maintenance since.

I don't really want to pay to have this rebuilt. Assuming i cant get the cap off, if I fill the piggyback with new oil, will it make it's way back into the body? Or am I stuck having to get it rebuilt now that there's no oil in the shock?
 
#94 ·
Thanks for the info.

Here's a tip to make it a bit easier to deal with rebuilding a shock. Put the shock body in a 31.8mm stem and put the stem in the vice. Works great. I managed to get the shaft cap off with this method using a dedicated 25 mm wrench. :thumbsup:

Now, hopefully I'll be able to do the oil change without screwing anything up.
 
#97 ·
I did! I opened the piggyback and got the shaft cap open using the method I posted above, dumped out all of the oil, and just filled it back up again based on the method described in the Nick's tutorial and using some Golden Spectro fork oil. Other than getting the shaft cap open, it was pretty straightforward. But I basically skipped steps 5-11, which means that I didn't replace any of the o-rings or take apart the rebound or propedal assembly. The shock seems to work fine though.

The only odd thing I noticed when taking apart the shock is that the IFP was set to 15/16" instead of 1.3", which is the default setting for my shock. I had my shock pushed 4 years ago so I thought that maybe that's why it's different. I called Push to confirm, but I guess the way they work on the suspension, the IFP may or may not move from its original position. I'm considering opening the piggyback again and moving the IFP to 1.3" to see how it feels.

Also, I don't know if the RC4 has the same internal parts as my shock, so I'm not sure if you'll run into issues if you decide to open up your shock.
 
#101 ·
Nick, your guide is amazing. Really well done—thanks.

I'm having a lot of trouble getting the rebound assembly out of the shaft. I've made the clamps (out of soft wood rather than hard wood) and heated as instructed. Heated more, clamped more, heated more, clamped more. No luck.

Is the hardwood likely to make a big difference? I know it's a bit of a tedious question, but I thought I'd ask before taking the circular saw to my table.

Failing that, any other ideas?

Cheers
 
#102 ·
Well, I got it sorted in the end. The hardwood did make a difference as it applies more pressure directly to the shaft rather than flexing.

For those about to try this themselves, here are a couple of tips for getting the rebound adjustment head and eyelet off the shaft:

- Use hardwood, as Nick says
- Heat the black anodised alloy rather than the shaft. You want to cause the outer threads to expand and crack the red loctite
- I've not done this myself, but a friend tells me that wrapping the shaft in paper wetted in IPA/isopropyl alc/brake & clutch increases the grip on the shaft. Might be worth a shot next time.
 
#104 ·
I used the guide to change the fluid in my '07 dhx 5.0 and the seal change went great but when it went back on I have TONS of rebound and it seems like a little more compression than I'd like. I just tore it down and loosened the shim stack bolt and it didn't change anything. I also took a measurement of the IFP when I first took it apart (18mm) but set it to the 38mm as per your manual. I'm having a hard time getting my shock pump keeping air in the reservoir but I don't see that effecting my compression AND rebound that greatly. Any ideas? When I took it off it was working but leaked and sounded like a sucking gash. I don't believe I messed up the shim stack but I did remove them to clean and inspect. Thanks for any help!
 
#109 ·
I know this is old but I just rebuilt an DHX Air 4.0 and 5.0 side by side and made the following observations.
  • 4.0 IFP at normal setting will result chamber volume similar to a 5.0 with boost valve in the middle position. (4.0 = same performance as 5.0 on middle setting)
  • 4.0 IFP 3mm shallower will result chamber volume similar to a 5.0 with boost valve in the smallest position.
  • 4.0 IFP may hit ProPedal valve if 5.0 depths are used. (cannot achieve volume similar to 5.0 in the largest position)
  • 5.0 boost chambers are about 6mm longer and 5.0 IFP depths are about 3mm deeper.
 
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