[jamesdc]

I have a few questions about fox dhx's. What oil is used and what weight? What is the depth for the piston in the resivor? Anyone have any suggestions on shim size and order and for what weight rider and what type of riding. Also what is the most efective way to bleed it; submerge? When I asked fox these questions the guy wouldn't tell me anything because they dont want anyone else servicing their shocks. Also who makes a better bottom out bumper, the stock one barely does anything


Thanks, James

 

[bullcrew]

I have a few questions about fox dhx's. What oil is used and what weight? What is the depth for the piston in the main chamber and the one in the resivor? Anyone have any suggestions on shim size and order and for what weight rider and what type of riding. Also what is the most efective way to bleed it; submerge? When I asked fox these questions the guy wouldn't tell me anything because they dont want anyone else servicing their shocks. Also who makes a better bottom out bumper, the stock one barely does anything


Thanks, James

OOOH AAAAH PUSH IT DaNAnaNA, OOOH AAAAH PUSH IT DaNAnaNA!

 

[-Danno-]

http://www.ridemonkey.com/forums/showthread.php?t=163201 has all you need to know.

 

[dhmike]

the only suggestion i have is to pay the 120 $ and send it into fox and let them dial your shock in.

 

[dhkid]

yea, there is a load of info in that thread. here are a few snips:

ifp depth depends on shock size,
oil weight is 10.

as for shims, cant help you there. just take your shock apart and measure them, i would go for same id and od shims, but thinner then the stock. that way you have more tuning options. make sure you keep the whole stack thickness the same, otherwise you will mess up the rebound.

as for a bottom out bumper, you can use one off a 5th element shock. those work well. otherwise your local mx shop should be able to help you out there.

 

[jamesdc]

yea, there is a load of info in that thread. here are a few snips:

ifp depth depends on shock size,
oil weight is 10.

as for shims, cant help you there. just take your shock apart and measure them, i would go for same id and od shims, but thinner then the stock. that way you have more tuning options. make sure you keep the whole stack thickness the same, otherwise you will mess up the rebound.

as for a bottom out bumper, you can use one off a 5th element shock. those work well. otherwise your local mx shop should be able to help you out there.

shock is 8.75 x 2.75

 

[-Danno-]

shock is 8.75 x 2.75

I know for the 2" stroke it's 28mm deep. You shock has a 19mm longer stroke so I'd think the right IFP depth should be ~33mm. 28+19*(shaft diameter/ifp diameter)^2. I'm guessing that the shaft diameter is half the ifp diameter. dhkid might know if that's a bit off.

 

[jamesdc]

while i have the shock apart can you remove or at least disable the propedal so it works like a roco

 

[dhmike]

sorry dhkid i'm not as smart as you .

 

[dhkid]

dhmike- i'll have you know that my dhx ended up getting pushed too. but its definitely good fun to mess around with shocks.

danno - honestly, i have no idea. i just work it out each time i take the shock apart. just take the volume of the shaft at bottom out/ifq cross sectional area. then add on the maximum depth of the chamber size adjuster, add on a few mm just to be safe.

33mm sounds about right. you can always measure the depth when you take it apart and put it back the same.


james - the easiest way to do that is to take out the check valve on the reservoir. its a spring and two large shims. you would have to unscrew the ifp chamber off the body to do that. will need a strap wrench.

that way the oil wont go though the boost valve. a better option is to use a stiffer spring in the boost valve, but i do not know where you can get them.

 

[Total Heckler]

OOOH AAAAH PUSH IT DaNAnaNA, OOOH AAAAH PUSH IT DaNAnaNA!

Classic.

(Banana doing the dance by the way)

 

[jamesdc]

As far as removing the propedal I took out the spring that operates the valve that regulates the propedal oil. I also removed the c clip inside the resivor so I can take out the piece that the spring pushes on the regulate the oil. I am planning on trying this out to see if it works, unless anyone thinks there is a problem with it.

 

[-Danno-]

As far as removing the propedal I took out the spring that operates the valve that regulates the propedal oil. I also removed the c clip inside the resivor so I can take out the piece that the spring pushes on the regulate the oil. I am planning on trying this out to see if it works, unless anyone thinks there is a problem with it.

I didn't pay attention to how the shims were arranged though. Do they go from largest to smallest or is there a particular order?

I didn't do anything but change the oil in mine, but I think that spring may reduce PP. I believe the way that shock works is that the PP knob is reverse threaded and when you turn it CCW it increases spring pressure. That spring pressure is used to add force to opening the control valve. Somewhat the same effect as reducing air pressure.

I know I read this somewhere, but it's been a while...

 

[dhkid]

james - bad idea. like danno said, the spring is holding the boost valve open (btw, the pro pedal and boost valve is the same thing. just that one effects the beginning of the travel, one later.) taking the spring out would only make the boost valve give out more damping. thats why i am saying the easiest way it to take out the check valve shims.

the small chamber inside the boost valve, where the spring is, its open to the atmosphere. so taking the boost valve out wont work, it would make your shock leak.

 

[bullcrew]

Classic.

(Banana doing the dance by the way)

lmao!

 

[MttyTee]

I was under the impression that Fox used 7.5 wt stock on all their stuff? I could be wrong. Even though the Roco doesn't have a Boost Valve it still has shims that meter oil displacement, (between the main body and resy). If you open up too much of a free bleed you may have to increase IFP pressure. If you don't have enough resistance you'll just be shuttling the oil into the resy and not through the main piston, which creates a vacuum (cavitation) behind the piston.

Or it might work fine???

 

[jamesdc]

I put the propedal back together and the last question I have is what weight oil, I've heard 5, 7, 7.5, 10, what is the right one?

 

[dhkid]

hey mtty tee, good to see you back again.

as far as i know, its all 10wt. even in the fox 40 cart. i heard (but not really confirmed) that the earlier dhx's used 7.5 wt and later changed to 10 wt.

edit: james, the dhx works fine on a range of oil weights, i have even tried 2.5wt but you basically just end up with a shock thats just a rebound damper. i know mojo use 20wt with a stock piston, although its reshimmed. 7.5 and 10 work nicely.

 

[jamesdc]

Thanks for the hep guys, I got it all reasembled and it works great, I set the IFP at about 34mm. The shock was fairly easy to bleed, i just bought 2 quarts of oil and fully submerged the shock in a plastic tub.

 

[jamesdc]

Well' the rebound went out again yesterday, It was working great until then. I've bled the shock twice today and there is no air and it has no dead play, the rebound knob just doesn't do anything. I set the rebound when I pulled it apart. I cant figure out why it wont work, anybody have any suggestions?

 

[Kanye West]

If you don't know how a shim stack works and what the order needs to be, and you don't know how to re-set the rebound needle properly, just give it to somebody who does before you cost yourself more money.

For ****s and giggles, but a bunch of small "spacer" shims, use 20w oil, and remove every other shim from the compression side starting with the second one up.

 

[jamesdc]

I did get the shims set right and I do know how to set the rebound needle. The shock worked great for a few days then crapped out on me again.

 

[Kanye West]

Apparently not. What else could go wrong to only affect the rebound?

 

[dhkid]

what do you mean by the rebound isn't working?

make sure you compress the shock a few times between rebound adjustments, especially if you go from full closed to full open. you can unscrew the rebound knob a bit too much that way, and the rebound needle wouldn't be able to move.

 

[MttyTee]

Check the air pressure. If you took the check shim/washer out then you have nothing but air pressure pushing against the oil until the Boost Valve starts to shut. With out enough resistance the oil won't open the compression shims and you'll be left with a big vacuum behind the piston.

 

[jamesdc]

The shock feels great, there is no air in it but the rebound adjustment doesn't work, no matter how I turn the knob it doesn't affect the rebound at all, its always on the fastest setting. When I get home I'll take pics of the shims and the rebound needle so you guys can see if they are set right. The first time I rebuilt the shock it worked perfect for a few days then it developed an air pocket. Sice then I have rebuilt it 3 times doing the exact same thing and trying differernt things and still no working rebound adjustment.

 

[Kanye West]

What exactly are you doing to set up the rebound needle? What is your bleed process?

 

[jamesdc]

for setting the rebound needle I back the adjuster to the fastest possible position then put the rebound needle in as far as it goes. When I bleed it I fully submerge all of the shock parts in oil and work the air out. Then I put the shock shaft shaft/ piston assembly in the shock body and srew on the end cap under the oil. Then I pull the shock shaft to full extension then I take the srew out of the center of the IFP and insert that into the resivor body and put it to 34mm depth then I put the screw in while it is still under the oil. I then take the shock out of the oil, drain the air chamber and tighten everything up and install the resivor cap and pump it up to 140

 

[Kanye West]

A good bleed takes about a half hour. If you get air behind the piston, you lose damping. Assemble/disassemble it about 4 times under oil, letting it sit between each one with the endcap open and facing upwards so the oil bubbles come out.

Get a torque wrench and get the piston nut to the right torque according to Fox. Tighten/untighten it as you work the rebound adjuster around to reset the needle. You'll feel it click in.

 

[jamesdc]

I bled the shock again just now and the rebound adjustment does work somewhat but its still way too fast. The shock rebounds at the right speed when the the spring is off so once the spring is on its REALLY fast. I'm starting to think the oil is too thin. What brand 10wt oil does fox use?
I know oil weight varies alot between brands even if they say they are the same weight. Right now I am using 10wt of this brand,

 

[JohnnyC]

I bled the shock again just now and the rebound adjustment does work somewhat but its still way too fast. The shock rebounds at the right speed when the the spring is off so once the spring is on its REALLY fast. I'm starting to think the oil is too thin. What brand 10wt oil does fox use?
I know oil weight varies alot between brands even if they say they are the same weight. Right now I am using 10wt of this brand,

Silkolene. Pj1 shouldn't be tooooo different though...


Did you add any shims or spacers to the compression stack?

 

[jamesdc]

Has anyone tried a heavier oil in a dhx. The rebound really lacks with the heavier springs that I have to run. I'm thinking about trying 12.5 or 15wt.


Also does anyone know how to fix the clunking problem that plauged some of the first dhx's. It seems like a problem with the piston since it happens right as the shock starts to compress.