Shock rebuild IFP height...now internal bypass teardown

moondog897

moondog897

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I'm in the middle of rebuilding my fox coilovers all 2.5 with 2.0 piggybacks. Fronts are ibp's but I haven't gotten that far yet. I've looked all over to find a spec for the ifp height but keep coming up empty. When I pulled the first one apart it was only 4 inches down from the top. I knew that wasn't enough but have no idea when the last time they were rebuilt was. I found a rebuild sheet for 2.0 shocks from Fox stating for an 11 inch res to install the ifp 8 inches. So for assembly I filled the res first and let it fill into the main body enough that when I installed the ifp it would push oil into the main body and not have any air in it. I installed the ifp to 8 inches and then topped off the body. Installed the shaft with piston and worked the air out. My big question was before I installed the bearing head into the body how far should I have the shaft/piston installed into the shock body. I left the shaft as close to full extension as I could and topped off the oil then installed the bearing and snap ring. My ifp did move a little but in the end with the shock fully extended the ifp wound up at 7.5 inches down. I charged and installed the shock but now I'm second guessing if I've got enough room for the ifp to travel as the shock compresses. Long story short I have two questions 1. Has anyone found an actual spec for the ifp on Fox 2.5 with 2.0 piggybacks? 2. How far in do you have the shock shaft installed before topping off the body with oil and installing the bearing? 

 
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I may be good with my height. When I pulled the second one down I measured the height and found it 7.5 inches down with the shock at full extension. Seems like I'm in the ballpark but would still like to hear if anyone has a more accurate spec for this and the shaft position when topping off the oil before final assembly.

 
If you think about it, if you had a shock with no reservoir and no air, the shock couldn’t move at all. You couldn’t move the ram in or out because hydronic fluid doesn’t compress.  All you need is for enough oil that when the shock fully extends, the IFP doesn’t hit the bottom of the reservoir.  Oil beyond that serves 2 purposes. 1) if some leaks out, you still have room before the IFP hits the bottom of the reservoir. 2) the more oil, the less space for nitrogen.  

Since the nitrogen adds to springiness of the shock, up I want the levels to be exactly the same and the more the less springy but you need at least enough nitrogen for the shock to fully compress before it slams the IFP into the top of the reservoir.  Also, If you have 100 grams of nitrogen in the reservoir and you lose 10 grams, that’s 10% but if you only have space for 25 grams nitrogen and you lose that same 10 grams, that’s a 40% loss.  

You want enough oil that the IFP never hits the bottom and not enough that can ever hit the top of the reservoir and the less nitrogen space, the heavier the spring action.

Mind you, I have rebuilt exactly 4 shocks in my life tine (well one leaked and I redid it so that makes 5) and I am prone to be completely full of Schiff.    

 
Another thing, since the IFP moves out as the ram goes in, you want the ram in the same position on each shock when you fill the fluid.  

Another thing I did before adding nitrogen was to push the ram all the way in and release the shredder valve to purge as much atmosphere as possible from the reservoir before filling with nitrogen  

I don’t know that that matters so much but I’m kinda retardid 

 
Five.five-six said:
Another thing, since the IFP moves out as the ram goes in, you want the ram in the same position on each shock when you fill the fluid.  

Another thing I did before adding nitrogen was to push the ram all the way in and release the shredder valve to purge as much atmosphere as possible from the reservoir before filling with nitrogen  

I don’t know that that matters so much but I’m kinda retardid 
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Right, that's what I had planned on. I also did the same thing as far as when I charged, I wanted as much of the air out of the res that I could so there was more room for nitrogen. I think I'd be fine with the way I'm doing it, I was just hoping to hear from someone with more experience with these.

 
moondog897 said:
Right, that's what I had planned on. I also did the same thing as far as when I charged, I wanted as much of the air out of the res that I could so there was more room for nitrogen. I think I'd be fine with the way I'm doing it, I was just hoping to hear from someone with more experience with these.
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Unfortunately you are only hearing from me…. Which is possibly less helpful than not hearing from anyone LOL

 
What gets confusing is some of the measurements I believe are with the Schrader valve in and some are not. on my Kings I've always bottomed it out left the Schrader valve out and as you push the shock body in it pushes oil in to the reservoir so you end up with a couple inches of oil

 
I should be good with how I set it up. On the second shock I set it exactly the same and left the res cap off. Fully extended the ifp was at 7.5" again and full compression it was at 4.5"

 
Ok I'm going in a different direction with this post now that I'm onto the fronts and hope I get some responses. My fronts are still fox 2.5 but they're internal bypasses. On both shocks I pulled the dust cap off and I can't budge either of the seal heads to remove the snap ring. I even made a sleeve to slide around the shock shaft to be able to just smack the top of the shaft with a dead blow and still no movement. I must be missing something. Anyone ever ran into this? I believe it's impossible to get the snap ring out without pushing the seal head in. Please help!

 
moondog897 said:
Ok I'm going in a different direction with this post now that I'm onto the fronts and hope I get some responses. My fronts are still fox 2.5 but they're internal bypasses. On both shocks I pulled the dust cap off and I can't budge either of the seal heads to remove the snap ring. I even made a sleeve to slide around the shock shaft to be able to just smack the top of the shaft with a dead blow and still no movement. I must be missing something. Anyone ever ran into this? I believe it's impossible to get the snap ring out without pushing the seal head in. Please help!
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Have you removed the Schroeder valves?   Shock order pressure would cause exactly what you are describing and if you do figure out how to get the snap rin out under pressure it could land you in the ER or the morgue.  

 
Try pushing the ram all the way in and release all the pressure, then pull the ram all the way out which will creat vacuume inside the shock and hopefully suck the seal heads in. 

 
I did take all the pressure off and removed one of the piggybacks to drain the oil. The shafts move freely in and out with no pressure. I talked to a couple local guys and it turns out the Fox internal bypasses are a major pain in the a$$ to get the snap ring out. The seal head sits right on top of 2 inch internal bypass tube so it can't be pushed in to remove the snap ring. Sounds like I just have to dig the snap ring out the hard way. 

 
moondog897 said:
I did take all the pressure off and removed one of the piggybacks to drain the oil. The shafts move freely in and out with no pressure. I talked to a couple local guys and it turns out the Fox internal bypasses are a major pain in the a$$ to get the snap ring out. The seal head sits right on top of 2 inch internal bypass tube so it can't be pushed in to remove the snap ring. Sounds like I just have to dig the snap ring out the hard way. 
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Perhaps get a large socket and tap tap tap with a dead blow?

 
Five.five-six said:
Perhaps get a large socket and tap tap tap with a dead blow?
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Unfortunately that doesn't work on this style. Believe me I tried, the bottom of the seal head sits on top of the bypass tube. It's impossible to push it in any further to remove the snap ring. Two different people have told me you just have to dig it out.

 
Five.five-six said:
That sucks 😞
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Well the first one wasn't as bad as what I thought it would be. I'm sure there are people on here than have done them but for anyone who hasn't the seal head does sit directly on top of the internal bypass tube so it's physically impossible to push it down to remove the snap ring. I peeled both ends of the snap ring up from the groove and then was able to get my pliers on to compress it just enough to remove. The second picture is of the internal bypass tube that the seal head sits on. After a lot of screwing around I think I'm finally heading in the right direction.

PXL_20210614_234349787.jpg

PXL_20210615_005324162.jpg

 
What stroke are these IBP? I'm have 10" stroke and I'm curious how many bleed or bypass ports they actually have.

 
Hey Moondog, I  am trying to decide whether to add bypass shock to my car or just get IBPs. I assume your car started with coilovers and then switched to IBPs. What are your thoughts?

 
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